In 1987, catheter ablation of ventricular tachycardia was a newly emerging field. The primary therapy for drug refractory ventricular tachycardia was surgical ablation, which was successful in controlling this arrhythmia in 80% to 90% of selected patients, but yielded an operative mortality of 5% to 15% (Cox, 1989). Over the subsequent two decades, significant developments in ablation and mapping technology contributed to improved outcomes: catheter ablation, first, using direct-current energy and radiofrequency current, later. The initial acute success rates using radiofrequency current were on average 75%, with a recurrence rate of 21% over a follow-up time average of 21 months (Gu¨rsoy, 1993; Stevenson, 1993; Gonska, 1994; Kim, 1994; Wilber, 1995; Stevenson, 1998). The limitation of catheter ablation at this time was 2-fold. First, only conventional radiofrequency current (non-irrigated) was available; secondly, only patients with hemodynamically tolerated and

catheter ablation of ventricular tachycardias.

**3. Catheter ablation**

stable ventricular tachycardia could be treated, for which an ECG of the spontaneous ventricular tachycardia had been obtained and mapping could be performed during such event (Bogun, 2006; de Chillou, 2002).

#### **3.1 Electroanatomic systems and substrate mapping**

The introduction of the electroanatomic mapping system allowed creation of ventricular geometry and displayed low-voltage areas of scar or infarction (Marchlinski, 2000). Mapping during stable sinus or paced rhythm to identify targets for ventricular tachycardia, the so-called substrate mapping (Reddy, 2003; Volkmer, 2006), allows performing catheter ablation in patients with unstable, hemodynamically nontolerated ventricular tachycardia, in patients with multiple ventricular tachycardias, or in patients without inducible ventricular tachycardia (Figure 1).

Fig. 1. A and B show the substrate respectively, in the posterior and inferior view in a patient with ischemic dilated cardiomiopathy. In substrate mapping the scar region (grey area) was defined as areas with bipolar local electrogram ≤0.5 mV and the normal myocardium (purple area) was defined as areas with a bipolar local electrogram ≥1.5 mV. The white dots represent the ablation lesions.

Today, most patients with recurrent ventricular tachycardia have an ICD that promptly terminates ventricular tachycardia, so its hemodynamic impact and ECG morphology are often unknown. Thus, substrate mapping is often the only method to perform catheter ablation in patients with an ICD (Kuck, 2009). By selecting catheter ablation for an individual patient, risks and benefits that are determined by patient characteristics, as well

Prevention of Sudden Death – Implantable Cardioverter

**3.1.2 Catheter ablation in nonischemic patients**

in these studies reached 8-18%.

beneficial.

**3.1.3 Prophylactic catheter ablation**

Defibrillator and/or Ventricular Radiofrequency Ablation 91

of catheter ablation of ventricular tachycardia with respect to ventricular tachycardia recurrence, the periprocedural mortality should also be considered in these patients. Indeed, the effectiveness of catheter ablation in ICD patients must be balanced with the safety profile of this interventional procedure. The reported procedure-related mortality ranges from 0% to 3.5%. In addition, major complications including stroke, myocardial infarction, tamponade, valve injury, and atrio-ventricular block occurred in 8-10% of the patients. In the Euro-VT study, the rate of major complications was only 1.6% and the 1-year mortality

Data on catheter ablation in ICD patients with nonischemic ventricular tachycardia from large multicenter trials are lacking. The anatomic substrate is different in patients with nonischemic ventricular tachycardia, since more extensive scar is often present in the epicardium and not in the endocardium, compared with the majority of patients with a previous myocardial infarct. In both groups, epicardial ablation has been successfully applied after failure of endocardial ablation. In general, acute success rates of catheter ablation are similar to ischemic ventricular tachycardia patients, but recurrence rates seem to be higher (Soejima, 2004; Delacretaz, 2000; Nazarian, 2005; Verma, 2005; Dalal, 2007). Moreover, catheter ablation has been shown to eliminate electrical storm in patients with and without underlying heart disease by either inhibiting the trigger factors for ventricular tachycardia/ventricular fibrillation, namely ventricular premature beats, or by modifying the substrate for ventricular tachycardia/ventricular fibrillation. Catheter ablation significantly reduces the number of ICD interventions in patients with electrical storm (Della Bella, 2004). In a recent single-center study, 95 patients with electrical storm, leading to a mean number of 14 ICD shocks per patient per day, underwent catheter ablation. Seventy-two patients had underlying coronary artery disease, 10 patients had dilated cardiomyopathy, and 13 patients had right ventricular disease. After catheter ablation, electrical storm was acutely suppressed in all patients and did not recur during follow-up of 22 months in patients in whom either no ventricular tachycardia could be induced or clinical ventricular tachycardia became noninducible. Furthermore, death from any cause could significantly be reduced in both groups compared with patients in whom the clinical ventricular tachycardia remained inducible and electrical storm recurred. Both cardiac death as well as sudden cardiac death was significantly higher in patients with electrical storm recurrences (50% versus 0%). This observation indicates that a successful ventricular tachycardia ablation procedure may be associated with a reduction of total mortality in subgroups of patients. The procedure typically is prompted by frequent defibrillator therapies despite multiple combinations of antiarrhythmic drugs. Use of catheter ablation earlier during the clinical course of ventricular tachycardia, soon after its onset, may be

The role of prophylactic radiofrequency catheter ablation of arrhythmogenic substrate in patients with a previous myocardial infarction in preventing ICD therapy was evaluated in the Substrate Mapping and Ablation in Sinus Rhythm to Halt Ventricular Tachycardia (SMASH-VT) trial and in the Catheter ablation of stable ventricular tachycardia before defibrillator implantation in patients with coronary heart disease (VTACH) trial (Reddy,

as the availability of appropriate facilities with technical expertise should be considered. In the past, catheter ablation of ventricular tachycardia has often been considered a procedure of last resort; now, a recent consensus document has suggested that catheter ablation should generally be considered early in the treatment of patients with recurrent ventricular tachycardia, recognizing that ventricular tachycardia was based mostly upon uncontrolled cohort studies and single-center reports. In the setting of high-risk patients with ICDs, catheter ablation of ventricular tachycardia has been proven to decrease the number of shocks.

#### **3.1.1 Catheter ablation in ischemic patients**

In most studies, catheter ablation has been performed in patients with ischemic heart disease after multiple ICD interventions, including patients with incessant ventricular tachycardia. In almost all of these studies, patients were included after failure of 1 or multiple antiarrhythmic drugs. The second largest prospective multicenter trials conducted in the United States using irrigated radiofrequency current included more than 350 patients with structural heart disease, predominantly coronary artery disease (Calkins, 2000; Stevenson, 2008). Both studies differ with respect to patient inclusion and to electrophysiological end-points, but the results were similar. In the cooled radiofrequency current trial, the acute success rate was 71% when the end-point was the elimination of all mappable ventricular tachycardias and 41% when the end-point was the elimination of ventricular tachycardia of any kind. In the thermocool trial, the acute success rate was 49% when elimination of all inducible ventricular tachycardia was used as the end-point. The Kaplan–Meier recurrence rate of sustained ventricular arrhythmia was 56% during 1 year of follow-up. The thermocool trial limited the follow-up time to 6 months for the efficacy endpoint. Independence from ventricular tachycardia was 53%. In the thermocool trial, the frequency of ventricular tachycardia was reduced by ≥75% in 67% of patients. An increase in the number of ventricular tachycardia episodes was observed in 20% of patients. Patients with ventricular tachycardia recurrences were older, had more heart failure, more atrial fibrillation, multiple myocardial infarction sites, and more inducible ventricular tachycardias; they received more radiofrequency lesions, and more often, had a ventricular tachycardia inducible after ablation compared with patients without ventricular tachycardia recurrences. In the cooled radiofrequency current study, a ≥75% reduction in the ventricular tachycardia frequency in the two months after ablation compared to the two months before ablation was observed in 99 of 122 patients (81%), of whom 115 had an ICD. Only the absence of an inducible ventricular tachycardia, recognized as the clinical ventricular tachycardia, was a predictor of clinical success. Another European multicenter study (Euro-VT study) performed catheter ablation using external irrigation in 63 patients with recurrent scar-related ventricular tachycardia (Tanner, 2009). Catheter ablation was acutely successful in 51 patients (81%). During a mean follow-up of 12 ± 3 months, 31 patients (49%, 19 of 51 initially successfully ablated patients and 12 of 12 unsuccessfully ablated patients) experienced ventricular tachycardia recurrence. However, even among the patients with recurrence, the number of ICD therapies was significantly reduced in 79% of the cases. One limitation of catheter ablation studies in ICD patients must be addressed. In almost all studies, antiarrhythmic drugs were not systematically withdrawn after ablation. Therefore, any beneficial effect of catheter ablation in these studies may be influenced by drug therapy, even when most patients were drug failures before ventricular tachycardia ablation. While the above-mentioned and previously conducted studies clearly showed the beneficial effect

90 – Prediction, Prevention and Management of Cardiovascular Arrhythmic Events

as the availability of appropriate facilities with technical expertise should be considered. In the past, catheter ablation of ventricular tachycardia has often been considered a procedure of last resort; now, a recent consensus document has suggested that catheter ablation should generally be considered early in the treatment of patients with recurrent ventricular tachycardia, recognizing that ventricular tachycardia was based mostly upon uncontrolled cohort studies and single-center reports. In the setting of high-risk patients with ICDs, catheter ablation of ventricular tachycardia has been proven to decrease the number of

In most studies, catheter ablation has been performed in patients with ischemic heart disease after multiple ICD interventions, including patients with incessant ventricular tachycardia. In almost all of these studies, patients were included after failure of 1 or multiple antiarrhythmic drugs. The second largest prospective multicenter trials conducted in the United States using irrigated radiofrequency current included more than 350 patients with structural heart disease, predominantly coronary artery disease (Calkins, 2000; Stevenson, 2008). Both studies differ with respect to patient inclusion and to electrophysiological end-points, but the results were similar. In the cooled radiofrequency current trial, the acute success rate was 71% when the end-point was the elimination of all mappable ventricular tachycardias and 41% when the end-point was the elimination of ventricular tachycardia of any kind. In the thermocool trial, the acute success rate was 49% when elimination of all inducible ventricular tachycardia was used as the end-point. The Kaplan–Meier recurrence rate of sustained ventricular arrhythmia was 56% during 1 year of follow-up. The thermocool trial limited the follow-up time to 6 months for the efficacy endpoint. Independence from ventricular tachycardia was 53%. In the thermocool trial, the frequency of ventricular tachycardia was reduced by ≥75% in 67% of patients. An increase in the number of ventricular tachycardia episodes was observed in 20% of patients. Patients with ventricular tachycardia recurrences were older, had more heart failure, more atrial fibrillation, multiple myocardial infarction sites, and more inducible ventricular tachycardias; they received more radiofrequency lesions, and more often, had a ventricular tachycardia inducible after ablation compared with patients without ventricular tachycardia recurrences. In the cooled radiofrequency current study, a ≥75% reduction in the ventricular tachycardia frequency in the two months after ablation compared to the two months before ablation was observed in 99 of 122 patients (81%), of whom 115 had an ICD. Only the absence of an inducible ventricular tachycardia, recognized as the clinical ventricular tachycardia, was a predictor of clinical success. Another European multicenter study (Euro-VT study) performed catheter ablation using external irrigation in 63 patients with recurrent scar-related ventricular tachycardia (Tanner, 2009). Catheter ablation was acutely successful in 51 patients (81%). During a mean follow-up of 12 ± 3 months, 31 patients (49%, 19 of 51 initially successfully ablated patients and 12 of 12 unsuccessfully ablated patients) experienced ventricular tachycardia recurrence. However, even among the patients with recurrence, the number of ICD therapies was significantly reduced in 79% of the cases. One limitation of catheter ablation studies in ICD patients must be addressed. In almost all studies, antiarrhythmic drugs were not systematically withdrawn after ablation. Therefore, any beneficial effect of catheter ablation in these studies may be influenced by drug therapy, even when most patients were drug failures before ventricular tachycardia ablation. While the above-mentioned and previously conducted studies clearly showed the beneficial effect

shocks.

**3.1.1 Catheter ablation in ischemic patients**

of catheter ablation of ventricular tachycardia with respect to ventricular tachycardia recurrence, the periprocedural mortality should also be considered in these patients. Indeed, the effectiveness of catheter ablation in ICD patients must be balanced with the safety profile of this interventional procedure. The reported procedure-related mortality ranges from 0% to 3.5%. In addition, major complications including stroke, myocardial infarction, tamponade, valve injury, and atrio-ventricular block occurred in 8-10% of the patients. In the Euro-VT study, the rate of major complications was only 1.6% and the 1-year mortality in these studies reached 8-18%.

#### **3.1.2 Catheter ablation in nonischemic patients**

Data on catheter ablation in ICD patients with nonischemic ventricular tachycardia from large multicenter trials are lacking. The anatomic substrate is different in patients with nonischemic ventricular tachycardia, since more extensive scar is often present in the epicardium and not in the endocardium, compared with the majority of patients with a previous myocardial infarct. In both groups, epicardial ablation has been successfully applied after failure of endocardial ablation. In general, acute success rates of catheter ablation are similar to ischemic ventricular tachycardia patients, but recurrence rates seem to be higher (Soejima, 2004; Delacretaz, 2000; Nazarian, 2005; Verma, 2005; Dalal, 2007). Moreover, catheter ablation has been shown to eliminate electrical storm in patients with and without underlying heart disease by either inhibiting the trigger factors for ventricular tachycardia/ventricular fibrillation, namely ventricular premature beats, or by modifying the substrate for ventricular tachycardia/ventricular fibrillation. Catheter ablation significantly reduces the number of ICD interventions in patients with electrical storm (Della Bella, 2004). In a recent single-center study, 95 patients with electrical storm, leading to a mean number of 14 ICD shocks per patient per day, underwent catheter ablation. Seventy-two patients had underlying coronary artery disease, 10 patients had dilated cardiomyopathy, and 13 patients had right ventricular disease. After catheter ablation, electrical storm was acutely suppressed in all patients and did not recur during follow-up of 22 months in patients in whom either no ventricular tachycardia could be induced or clinical ventricular tachycardia became noninducible. Furthermore, death from any cause could significantly be reduced in both groups compared with patients in whom the clinical ventricular tachycardia remained inducible and electrical storm recurred. Both cardiac death as well as sudden cardiac death was significantly higher in patients with electrical storm recurrences (50% versus 0%). This observation indicates that a successful ventricular tachycardia ablation procedure may be associated with a reduction of total mortality in subgroups of patients. The procedure typically is prompted by frequent defibrillator therapies despite multiple combinations of antiarrhythmic drugs. Use of catheter ablation earlier during the clinical course of ventricular tachycardia, soon after its onset, may be beneficial.

#### **3.1.3 Prophylactic catheter ablation**

The role of prophylactic radiofrequency catheter ablation of arrhythmogenic substrate in patients with a previous myocardial infarction in preventing ICD therapy was evaluated in the Substrate Mapping and Ablation in Sinus Rhythm to Halt Ventricular Tachycardia (SMASH-VT) trial and in the Catheter ablation of stable ventricular tachycardia before defibrillator implantation in patients with coronary heart disease (VTACH) trial (Reddy,

Prevention of Sudden Death – Implantable Cardioverter

**3.2 Open questions in VT catheter ablation 3.2.1 The role of antiarrhythmic therapy**

ablation than with drug therapy. (Epstein, 1998 ).

(Carbucicchio, 2008).

**3.2.2 The role of ventricular function**

Defibrillator and/or Ventricular Radiofrequency Ablation 93

effectiveness of catheter ablation in reducing ventricular tachycardia events, but does not give clinical guidance on the relative role of catheter ablation in comparison to antiarrhythmic drug therapy. The complication rate becomes even more important if an interventional procedure is performed prophylactically. In both trials, the incidence of ablation related death was 0% and of major complications 4.7% and 3.8%, respectively. The event rate in the control group of the VTACH trial was roughly twice as that observed in

Many important questions remain. Should ablation be preferred over antiarrhythmic drugs? The largest prospective, randomized trial evaluating several drug regimen in patients with an ICD for secondary prevention showed that the combination of beta-blockers and amiodarone had the greatest effect, with a reduction of ICD shocks by 73% compared to the control group (beta-blocker alone) and of 57% compared to the sotalol group, with an incidence of ICD shocks in the control group of approximately 30% after 1 year (Connolly, SJ et al. 2006). In a previous trial, sotalol reduced the risk of death from any cause or the delivery of a first shock for any reason by 48%. Furthermore, sotalol reduced the probability of the delivery of an appropriate first ICD shock or a first shock of any reason (Pacifico, 1999). Sotalol also prevented the occurrence of shocks in response to supraventricular arrhythmias, a frequent cause of inappropriate defibrillator therapy. Despite these beneficial effects, drug efficacy depends on patient compliance. In particular, if a lifetime therapy is required and is associated with side effects, this may lead to a discontinuation of drugs therapy. Furthermore, antiarrhythmic drugs such as amiodarone may increase the defibrillation threshold (Hohnloser, 2006). Even if this may not play a significant role in the majority of patients with modern devices, it can be harmful in the individual patient. In a randomized clinical trial comparing cooled radiofrequency catheter ablation of ventricular tachycardia and drugs therapy, arrhythmic recurrences was significantly lower with cooled

Regarding catheter ablation procedural outcomes, multiple small series, single center of catheter ablation for ventricular tachycardia have reported freedom from recurrent ventricular tachycardia in 50-80% of patients over follow-up, which ranges from 6 to 18 months. Long-term results are sparse, and completeness of reported follow-ups is sometimes suboptimal. Patients remained on antiarrhythmic drugs (amiodarone 94% and sotalol 5%) postprocedure and those with persistently inducible clinical ventricular tachycardia had shorter time to death, and shorter time to ventricular tachycardia recurrence and were the only patients with recurrence of ventricular tachycardia storm

In our experience, among the 66 patients referred to our clinic for radiofrequency catheter ablation of recurrent post infarction ventricular tachycardias, only 19 (29%) showed recurrences during a mean follow-up of 26 ± 12 months. This finding "per se" highlights the role of radiofrequency catheter ablation in the overall clinical management of recurrent post infarction ventricular tachycardias in patients with ICD. In addition, our findings stressed the role of poor left ventricular function as an independent predictor of recurrent ventricular tachycardia. Among patients with ejection fraction < 35%, 11 out of 25 (44%) still continued

SMASH-VT, but the relative reduction in events was similar, at 35–40%.

2007; Kuck, 2010). SMASH-VT was a prospective randomized three-center trial of catheter ablation versus no intervention for patients with implantation of a secondary prophylactic ICD within the prior 6 months or who had received recent appropriate ICD therapy. Catheter ablation resulted in reduced appropriate ICD therapy from 33 to 12% (hazard ratio 0.35). Secondary end-points included a reduction in ventricular tachycardia storm, but no effect on total mortality occurred. Although this landmark study demonstrated proof of the principle that catheter ablation can have a favorable effect, limitations such as the lack of adjudicator blinding, stratification and standard ICD programming make the results more difficult to interpret. Most importantly, the role of antiarrhythmic drugs was not addressed by this study design, limiting direct applicability of the results to clinical practice (El-Damaty, & Sapp, 2011). VTACH trial was similar in design to that of SMASH-VT. One hundred and ten patients presenting with ventricular tachycardia and prior myocardial infarction were randomly allocated to catheter ablation or no intervention, followed by ICD implantation. Antiarrhythmic drug use was discouraged, and not significantly different between groups. Patients were stratified by center and ejection fraction (cut-off 30%); a blinded committee adjudicated outcomes and ICD programming was standardized. The VTACH trial showed that catheter ablation, performed before ICD implantation in patients after the first episode of a hemodynamically stable ventricular tachycardia, significantly prolonged the median time to first ventricular tachycardia/ventricular fibrillation from 5.9 months to 18.6 months. The benefit was more pronounced in patients with left ventricular ejection fraction > 30% (Figure 2).

Modified from Kuck et al., Lancet, 2010

Fig. 2. Survival free from ventricular tachycardia (VT) or ventricular fibrillation (VF) in patients with left-ventricular ejection fraction (LVEF) less or equal than 30% and leftventricular ejection fraction greater than 30%.

Furthermore, catheter ablation reduced the overall incidence of appropriate ICD interventions by 28% and the incidence of ICD shocks by 43%. Even more importantly, catheter ablation reduced the median number of appropriate ICD interventions per patient and year of follow-up by 93%. In addition, catheter ablation significantly reduced the rate of hospitalizations for cardiac reasons. This well designed trial provides further support for the

92 – Prediction, Prevention and Management of Cardiovascular Arrhythmic Events

2007; Kuck, 2010). SMASH-VT was a prospective randomized three-center trial of catheter ablation versus no intervention for patients with implantation of a secondary prophylactic ICD within the prior 6 months or who had received recent appropriate ICD therapy. Catheter ablation resulted in reduced appropriate ICD therapy from 33 to 12% (hazard ratio 0.35). Secondary end-points included a reduction in ventricular tachycardia storm, but no effect on total mortality occurred. Although this landmark study demonstrated proof of the principle that catheter ablation can have a favorable effect, limitations such as the lack of adjudicator blinding, stratification and standard ICD programming make the results more difficult to interpret. Most importantly, the role of antiarrhythmic drugs was not addressed by this study design, limiting direct applicability of the results to clinical practice (El-Damaty, & Sapp, 2011). VTACH trial was similar in design to that of SMASH-VT. One hundred and ten patients presenting with ventricular tachycardia and prior myocardial infarction were randomly allocated to catheter ablation or no intervention, followed by ICD implantation. Antiarrhythmic drug use was discouraged, and not significantly different between groups. Patients were stratified by center and ejection fraction (cut-off 30%); a blinded committee adjudicated outcomes and ICD programming was standardized. The VTACH trial showed that catheter ablation, performed before ICD implantation in patients after the first episode of a hemodynamically stable ventricular tachycardia, significantly prolonged the median time to first ventricular tachycardia/ventricular fibrillation from 5.9 months to 18.6 months. The benefit was more pronounced in patients with left ventricular

Fig. 2. Survival free from ventricular tachycardia (VT) or ventricular fibrillation (VF) in patients with left-ventricular ejection fraction (LVEF) less or equal than 30% and left-

Furthermore, catheter ablation reduced the overall incidence of appropriate ICD interventions by 28% and the incidence of ICD shocks by 43%. Even more importantly, catheter ablation reduced the median number of appropriate ICD interventions per patient and year of follow-up by 93%. In addition, catheter ablation significantly reduced the rate of hospitalizations for cardiac reasons. This well designed trial provides further support for the

Modified from Kuck et al., Lancet, 2010

ejection fraction > 30% (Figure 2).

ventricular ejection fraction greater than 30%.

effectiveness of catheter ablation in reducing ventricular tachycardia events, but does not give clinical guidance on the relative role of catheter ablation in comparison to antiarrhythmic drug therapy. The complication rate becomes even more important if an interventional procedure is performed prophylactically. In both trials, the incidence of ablation related death was 0% and of major complications 4.7% and 3.8%, respectively. The event rate in the control group of the VTACH trial was roughly twice as that observed in SMASH-VT, but the relative reduction in events was similar, at 35–40%.

#### **3.2 Open questions in VT catheter ablation 3.2.1 The role of antiarrhythmic therapy**

Many important questions remain. Should ablation be preferred over antiarrhythmic drugs? The largest prospective, randomized trial evaluating several drug regimen in patients with an ICD for secondary prevention showed that the combination of beta-blockers and amiodarone had the greatest effect, with a reduction of ICD shocks by 73% compared to the control group (beta-blocker alone) and of 57% compared to the sotalol group, with an incidence of ICD shocks in the control group of approximately 30% after 1 year (Connolly, SJ et al. 2006). In a previous trial, sotalol reduced the risk of death from any cause or the delivery of a first shock for any reason by 48%. Furthermore, sotalol reduced the probability of the delivery of an appropriate first ICD shock or a first shock of any reason (Pacifico, 1999). Sotalol also prevented the occurrence of shocks in response to supraventricular arrhythmias, a frequent cause of inappropriate defibrillator therapy. Despite these beneficial effects, drug efficacy depends on patient compliance. In particular, if a lifetime therapy is required and is associated with side effects, this may lead to a discontinuation of drugs therapy. Furthermore, antiarrhythmic drugs such as amiodarone may increase the defibrillation threshold (Hohnloser, 2006). Even if this may not play a significant role in the majority of patients with modern devices, it can be harmful in the individual patient. In a randomized clinical trial comparing cooled radiofrequency catheter ablation of ventricular tachycardia and drugs therapy, arrhythmic recurrences was significantly lower with cooled ablation than with drug therapy. (Epstein, 1998 ).

Regarding catheter ablation procedural outcomes, multiple small series, single center of catheter ablation for ventricular tachycardia have reported freedom from recurrent ventricular tachycardia in 50-80% of patients over follow-up, which ranges from 6 to 18 months. Long-term results are sparse, and completeness of reported follow-ups is sometimes suboptimal. Patients remained on antiarrhythmic drugs (amiodarone 94% and sotalol 5%) postprocedure and those with persistently inducible clinical ventricular tachycardia had shorter time to death, and shorter time to ventricular tachycardia recurrence and were the only patients with recurrence of ventricular tachycardia storm (Carbucicchio, 2008).

#### **3.2.2 The role of ventricular function**

In our experience, among the 66 patients referred to our clinic for radiofrequency catheter ablation of recurrent post infarction ventricular tachycardias, only 19 (29%) showed recurrences during a mean follow-up of 26 ± 12 months. This finding "per se" highlights the role of radiofrequency catheter ablation in the overall clinical management of recurrent post infarction ventricular tachycardias in patients with ICD. In addition, our findings stressed the role of poor left ventricular function as an independent predictor of recurrent ventricular tachycardia. Among patients with ejection fraction < 35%, 11 out of 25 (44%) still continued

Prevention of Sudden Death – Implantable Cardioverter

choice might be radiofrequency catheter ablation.

**4. Conclusions**

Defibrillator and/or Ventricular Radiofrequency Ablation 95

tachycardias in patients with previous myocardial infarction: a) for patients with ejection fraction ≤35%, ICD still remains the first choice (class 1A). However, radiofrequency catheter ablation is indicated to reduce ICD shocks (class 1C) (Zipes, 2006), b) for patients with ejection fraction >35% and <50%, the first choice might be radiofrequency catheter ablation and any effort should be made to successfully ablate the VT, repeating the procedure if needed. The implantation of ICD might be limited to those patients in whom the ventricular tachycardia is not successfully ablated. c) For patients with EF ≥50%, the first

In conclusion, the published studies have shown the important role of catheter ablation in patients with structural heart disease and ICD implantation who experienced appropriate ICD therapy due to recurrent ventricular tachycardias. Successful catheter ablation in these patients prevents or reduces the number of ventricular tachycardia recurrences as well as the rate of ICD shocks, improving the quality of life and probably long-term mortality. Finally, the question whether ablation can replace ICD in patients with structural heart disease is presented. The results of recently published studies are promising for further expansion of ventricular tachycardia ablation indication, but several points merit additional consideration. Catheter ablation of ventricular tachycardia is still an extremely complex procedure and the reported results reflect the outcome of such ablations from highly experienced and high-volume centers and, therefore, cannot be extrapolated to all electrophysiology departments without additional simplification and standardization of the ablation procedures and strategies. In spite of being able to achieve acute complete success in the majority of patients who underwent catheter ablation of ventricular tachycardia, accurate long-term prediction of outcome based on current risk predictors is difficult. Therefore, we cannot currently replace ICD with catheter ablation, although in selected patients, with hemodynamically stable and/or slow ventricular tachycardia and preserved or mildly reduced left ventricular function (for which data from randomized studies are lacking), catheter ablation might be considered an alternative to ICD. In addition, even upon developing more effective ablation strategies and finding good predictors of long-term outcome after a single center ablation procedure, the substrate of arrhythmia in patients with structural heart disease is dynamic. Due to this inherently dynamic characteristics of the arrhythmic substrate, cardioverter defibrillator implantation, cannot be replaced in the long-term, with catheter ablation of ventricular tachycardia. It is in fact necessary to stratify the risk repetitively and regularly, in order to perform repeated ablation procedures, if necessary. Thus, before widespread recommendation of catheter ablation of ventricular tachycardia becomes evident, especially prophylactic ablation, standardizing the ablation procedure and strategies, endpoints, and the follow-up should be performed. Further studies are necessary to clarify the role of catheter ablation of ventricular tachycardia on long-term mortality of patients with structural heart disease (Arya, 2009). ICD remains a life-saving device for patients with sustained ventricular tachycardia late after myocardial infarction; but in selected patients, especially in patients with ejection fraction > 30%, who are receiving an ICD for stable ventricular tachycardia, arrhythmic substrate ablation can be considered early. Evidence of a positive effect on survival, subsequent hospital admissions, or quality of life is needed before catheter ablation can be recommended for routine use. We believe that today's trial is further evidence to support early use of catheter ablation, as a

to have ventricular tachycardia recurrences, independently of whether the ventricular tachycardia responsible for ICD therapies was inducible at the end of the procedure or not. Most clinical trials (Moss, 2004; Moss, 1996; Buxton, 1999; Bardy, 2005) testing the efficacy of antiarrhythmic versus ICD therapy have used the ejection fraction as the marker for advanced disease, with the qualifying criteria in the range of 30–40% or less. Interestingly, in the AVID trial (Domanski, 1999) a subgroup analysis suggested that there was no benefit of ICD therapy over amiodarone for patients with ejection fraction between 36% and 40%, being all the benefit accrued to those patients with ejection fraction 35% or less. This observation raises the critical question we addressed in conceiving this study, about predictors of ventricular tachycardia recurrences, and consequently about therapeutic options, for patients with ejection fraction greater than 35%. Our findings show that, among patients with ejection fraction >35% and <50%, no recurrent ventricular tachycardia was further detected in the patients in whom the ventricular tachycardia responsible for ICD therapies was not inducible at the end of the procedure (100% specificity). Whereas ventricular tachycardia recurrences continued only in the patients, in whom the clinical ventricular tachycardia was inducible (100% sensitivity) (Colella, 2009). Actually, inducibility of the clinical ventricular tachycardia, more than being a predictor of ventricular tachycardia recurrences, is simply the consequence of radiofrequency catheter ablation failure (Della Bella, 2002), i.e. of the fact that the clinical ventricular tachycardia has not been successfully ablated. Accordingly, at least in patients with ejection fraction >35% and <50%, the procedure should be repeated until an acutely successful ablation of the clinical ventricular tachycardia is achieved. For these patients, indeed, radiofrequency catheter ablation might be considered a reasonable alternative to ICD as the first choice. Finally, our findings show that in all the 24 patients with ejection fraction >50% no recurrent ventricular tachycardia was any longer detected during the follow-up. Based upon our findings, a simple algorithm (Figure 3) is proposed for the management of recurrent ventricular

Fig. 3. Algorithm for the management of recurrent Ventricular Tachycardias in patients with previous Myocardial Infarction.

tachycardias in patients with previous myocardial infarction: a) for patients with ejection fraction ≤35%, ICD still remains the first choice (class 1A). However, radiofrequency catheter ablation is indicated to reduce ICD shocks (class 1C) (Zipes, 2006), b) for patients with ejection fraction >35% and <50%, the first choice might be radiofrequency catheter ablation and any effort should be made to successfully ablate the VT, repeating the procedure if needed. The implantation of ICD might be limited to those patients in whom the ventricular tachycardia is not successfully ablated. c) For patients with EF ≥50%, the first choice might be radiofrequency catheter ablation.

#### **4. Conclusions**

Cardiac Defibrillation

94 – Prediction, Prevention and Management of Cardiovascular Arrhythmic Events

to have ventricular tachycardia recurrences, independently of whether the ventricular tachycardia responsible for ICD therapies was inducible at the end of the procedure or not. Most clinical trials (Moss, 2004; Moss, 1996; Buxton, 1999; Bardy, 2005) testing the efficacy of antiarrhythmic versus ICD therapy have used the ejection fraction as the marker for advanced disease, with the qualifying criteria in the range of 30–40% or less. Interestingly, in the AVID trial (Domanski, 1999) a subgroup analysis suggested that there was no benefit of ICD therapy over amiodarone for patients with ejection fraction between 36% and 40%, being all the benefit accrued to those patients with ejection fraction 35% or less. This observation raises the critical question we addressed in conceiving this study, about predictors of ventricular tachycardia recurrences, and consequently about therapeutic options, for patients with ejection fraction greater than 35%. Our findings show that, among patients with ejection fraction >35% and <50%, no recurrent ventricular tachycardia was further detected in the patients in whom the ventricular tachycardia responsible for ICD therapies was not inducible at the end of the procedure (100% specificity). Whereas ventricular tachycardia recurrences continued only in the patients, in whom the clinical ventricular tachycardia was inducible (100% sensitivity) (Colella, 2009). Actually, inducibility of the clinical ventricular tachycardia, more than being a predictor of ventricular tachycardia recurrences, is simply the consequence of radiofrequency catheter ablation failure (Della Bella, 2002), i.e. of the fact that the clinical ventricular tachycardia has not been successfully ablated. Accordingly, at least in patients with ejection fraction >35% and <50%, the procedure should be repeated until an acutely successful ablation of the clinical ventricular tachycardia is achieved. For these patients, indeed, radiofrequency catheter ablation might be considered a reasonable alternative to ICD as the first choice. Finally, our findings show that in all the 24 patients with ejection fraction >50% no recurrent ventricular tachycardia was any longer detected during the follow-up. Based upon our findings, a simple algorithm (Figure 3) is proposed for the management of recurrent ventricular

Fig. 3. Algorithm for the management of recurrent Ventricular Tachycardias in patients with

previous Myocardial Infarction.

In conclusion, the published studies have shown the important role of catheter ablation in patients with structural heart disease and ICD implantation who experienced appropriate ICD therapy due to recurrent ventricular tachycardias. Successful catheter ablation in these patients prevents or reduces the number of ventricular tachycardia recurrences as well as the rate of ICD shocks, improving the quality of life and probably long-term mortality.

Finally, the question whether ablation can replace ICD in patients with structural heart disease is presented. The results of recently published studies are promising for further expansion of ventricular tachycardia ablation indication, but several points merit additional consideration. Catheter ablation of ventricular tachycardia is still an extremely complex procedure and the reported results reflect the outcome of such ablations from highly experienced and high-volume centers and, therefore, cannot be extrapolated to all electrophysiology departments without additional simplification and standardization of the ablation procedures and strategies. In spite of being able to achieve acute complete success in the majority of patients who underwent catheter ablation of ventricular tachycardia, accurate long-term prediction of outcome based on current risk predictors is difficult. Therefore, we cannot currently replace ICD with catheter ablation, although in selected patients, with hemodynamically stable and/or slow ventricular tachycardia and preserved or mildly reduced left ventricular function (for which data from randomized studies are lacking), catheter ablation might be considered an alternative to ICD. In addition, even upon developing more effective ablation strategies and finding good predictors of long-term outcome after a single center ablation procedure, the substrate of arrhythmia in patients with structural heart disease is dynamic. Due to this inherently dynamic characteristics of the arrhythmic substrate, cardioverter defibrillator implantation, cannot be replaced in the long-term, with catheter ablation of ventricular tachycardia. It is in fact necessary to stratify the risk repetitively and regularly, in order to perform repeated ablation procedures, if necessary. Thus, before widespread recommendation of catheter ablation of ventricular tachycardia becomes evident, especially prophylactic ablation, standardizing the ablation procedure and strategies, endpoints, and the follow-up should be performed. Further studies are necessary to clarify the role of catheter ablation of ventricular tachycardia on long-term mortality of patients with structural heart disease (Arya, 2009). ICD remains a life-saving device for patients with sustained ventricular tachycardia late after myocardial infarction; but in selected patients, especially in patients with ejection fraction > 30%, who are receiving an ICD for stable ventricular tachycardia, arrhythmic substrate ablation can be considered early. Evidence of a positive effect on survival, subsequent hospital admissions, or quality of life is needed before catheter ablation can be recommended for routine use. We believe that today's trial is further evidence to support early use of catheter ablation, as a

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**7**

**Just in Time Support to Aide**

Frank A. Drews and Paul M. Picciano

*University of Utah / Aptima Corp.*

*United States of America*

**Cardio-Pulmonary Resuscitation**

Cardiovascular disease is the leading cause of death in the United States with over 696,000 cases recorded by the Center for Disease Control (CDC) in 2002 (National Center for Health Statistics, 2002). In particular, Sudden Cardiac Arrest (SCA) claims 300,000 to 400,000 American lives annually (AHA, 2005, Huikuri, Castellanos & Myerburd, 2001, Zipes & Wellens, 1998). Ventricular fibrillation is believed to be the insidious perpetrator associated with the majority of these heart maladies (AHA, 2005, Cummins & Hazinski, 2000). Unfortunately, most victims that experience SCA have only a small chance of survival (Stiell, Nichol, Wells, De Maio, Nesbitt, Blackburn, & Spaite, 2003; Zipes & Wellens, 1998). Increasing the probability of survival of SCA victims requires skilled and knowledgeable responders. Usually the task falls to EMTs, firefighters, police officers, or other highly trained responders. Unfortunately, these experts are not always available on site which means that critical time is lost by moving responders to the victim. An alternative approach to provide rapid access to responders is to develop and provide supportive technology that guides a novice through the procedure of resuscitating the victim by presenting information and feedback at the time when it is needed. However, such approach needs methodologically and conceptually to be rooted in cognitive psychology and human factors since these fields can direct work that aims at the robust improvement of human performance of novices. The successful application of this approach has the potential to improve usability of medical devices for non-experts, beyond the design of defibrillators. Below we will outline the elements that need to be included in the development of a system that allows an untrained responder to deal with a SCA by providing elementary cardiopulmonary resuscitation (CPR). This approach is based on the idea of Just-in-Time Support (JITS). First, we will outline the tradition into which such JITS falls conceptually. Then, we will describe the differences between current architectures of Intelligent Tutorial Systems (ITS) and the constraints under which a true JITS has to operate. In the following section we provide a conceptual framework that allows analysis of human performance in the context of complex procedural tasks. Next, we will describe a JITS developed for the purpose of evaluating the feasibility and effectiveness of this approach, and report the results of an experimental study that evaluated a JITS. Finally, we will discuss the findings in the context of future developments of defibrillators and other systems that require guidance of novice users when using these advanced medical technologies in emergency

**1. Introduction**

situations.

### **Just in Time Support to Aide Cardio-Pulmonary Resuscitation**

Frank A. Drews and Paul M. Picciano *University of Utah / Aptima Corp. United States of America*

#### **1. Introduction**

Cardiac Defibrillation

104 – Prediction, Prevention and Management of Cardiovascular Arrhythmic Events

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metabolite desethylamiodarone on the ventricular defibrillation threshold. *JACC*,

for management of patients with ventricular arrhythmias and the prevention of sudden cardiac death: a report of the American college of cardiology/American heart association task force and the European society of cardiology committee for practice guidelines (Writing committee to develop guidelines for management of patients with ventricular arrhythmias and the prevention of sudden cardiac death): developed in collaboration with the European heart rhythm association and the

> Cardiovascular disease is the leading cause of death in the United States with over 696,000 cases recorded by the Center for Disease Control (CDC) in 2002 (National Center for Health Statistics, 2002). In particular, Sudden Cardiac Arrest (SCA) claims 300,000 to 400,000 American lives annually (AHA, 2005, Huikuri, Castellanos & Myerburd, 2001, Zipes & Wellens, 1998). Ventricular fibrillation is believed to be the insidious perpetrator associated with the majority of these heart maladies (AHA, 2005, Cummins & Hazinski, 2000). Unfortunately, most victims that experience SCA have only a small chance of survival (Stiell, Nichol, Wells, De Maio, Nesbitt, Blackburn, & Spaite, 2003; Zipes & Wellens, 1998). Increasing the probability of survival of SCA victims requires skilled and knowledgeable responders. Usually the task falls to EMTs, firefighters, police officers, or other highly trained responders. Unfortunately, these experts are not always available on site which means that critical time is lost by moving responders to the victim. An alternative approach to provide rapid access to responders is to develop and provide supportive technology that guides a novice through the procedure of resuscitating the victim by presenting information and feedback at the time when it is needed. However, such approach needs methodologically and conceptually to be rooted in cognitive psychology and human factors since these fields can direct work that aims at the robust improvement of human

> improve usability of medical devices for non-experts, beyond the design of defibrillators. Below we will outline the elements that need to be included in the development of a system that allows an untrained responder to deal with a SCA by providing elementary cardiopulmonary resuscitation (CPR). This approach is based on the idea of Just-in-Time Support (JITS). First, we will outline the tradition into which such JITS falls conceptually. Then, we will describe the differences between current architectures of Intelligent Tutorial Systems (ITS) and the constraints under which a true JITS has to operate. In the following section we provide a conceptual framework that allows analysis of human performance in the context of complex procedural tasks. Next, we will describe a JITS developed for the purpose of evaluating the feasibility and effectiveness of this approach, and report the results of an experimental study that evaluated a JITS. Finally, we will discuss the findings in the context of future developments of defibrillators and other systems that require guidance of novice users when using these advanced medical technologies in emergency situations.

> performance of novices. The successful application of this approach has the potential to

Just in Time Support to Aide Cardio-Pulmonary Resuscitation 107

but offers nothing to guide learning and performance (Linn, 1990). However, the tutor

*Tutor Model*. The tutor model is essential in a ITS since it incorporates the didactic ideas of the designer. Without a tutoring model (e.g., instructional module, or pedagogical agent) an ITS would be limited to the administration and scoring of tests lacking the ability to impart knowledge or understanding to the user. Structurally, the instructional module interacts with the expert model and the student model to formulate relevant information to the user. It evaluates the student model in terms of the expert model and decides what information to present, how to display the information, and when to do so. The tutor model is the visible module for the user. Through the interface, the pedagogical agent serves as the teacher,

The above description of the ITS architecture illustrates some of strength of the approach that guides the development of an ITS. However, there are also limitations that are associated with the development and use of such system. These limitations become particularly salient when the goal is to design a system that does not provide knowledge, but that can be used as a just-in-time support system. Certainly, both systems have similarities– e.g., both are primarily aimed at novices, are computer based, and leverage best practices of expert systems and user-interface principles. However, for the current purpose it is also critical to understand the differences between these systems. The differences can be described with regard to the goals, the time available for performance, the intended cognitive processing strategies and the system input. A brief summary of these issues is

*Objectives*. The disparate objectives of each system are yoked to the temporal constraints associated with their use. With the ITS, the extended time horizon enables the goals of learning, long-term retention and fosters accuracy in the speed-accuracy trade-off. This situation can be contrasted with the JITS that is not focused on learning, since retention is inconsequential and potentially counter-productive in situations where a JITS is being used. The objective is to allow the user to perform the task to a satisfactory degree in the limited time available. Due to the temporal constraints, it is more important to sufficiently complete all requisite steps in the given, limited time rather than to strive for flawless performance on

**Paradigm Objectives Time Available Processing Strategies System Input**

Deep/elaborative Adaptive, transferable Declarative

Shallow /perceptual

Mimicking Procedural Passive collection Requires user input to computer

Active collection Monitors user actions

Long time horizon Self paced Low time pressure

Short time horizon

Externally paced Significant time pressure

Table 1. Differences between Just-in-Time Support (JITS) and Intelligent Tutoring Systems

provided in Table 1, and will be discussed in detail in the next sections.

some tasks while failing to complete others.

Long term retention

Learning Accuracy over speed

Short term performance Complete task Speed over accuracy

(ITS) on critical dimensions.

**Intelligent Tutoring Systems**

**Just-in-Time Support**

model serves this purpose.

consultant, assistant, or coach.

**1.1.2 Limitations of ITS**

### **1.1 Intelligent Tutorial Systems (ITS)**

**1.1.1 Description of ITS**

Intelligent Tutoring Systems (ITS) have been developed over the last decades. Early systems focused on supporting students in acquiring knowledge, thus these systems were similar to flash cards but were also capable of analyzing a student's responses (Uhr, 1969). The next generation systems were more sophisticated because they moved from a scripted hierarchical structure of knowledge towards systems that were able to deal with potentially all requests that a student would submit to the system. For example SCHOLAR (Carbonell, 1970) tutored students in South American geography and was designed to deal with a variety of questions that might be asked by a student learner. The next important step in the development of ITS was embodied in the work of Collins (1977). Earlier that decade Craik & Lockhart (1972) demonstrated that deeper, more elaborate processing improved learning and retention. In application of this line of reasoning, Collins (1977) implemented a Socratic method of exploration for his system. What was remarkable about this approach was that it allowed the student to "discover" knowledge, empowering the student to acquire knowledge from experience and individual cases, through self-directed exploration of the knowledge base. Despite the wide range of ITS there are a number of basic elements that all of these systems have in common. These elements will be outlined next.

Many ITS projects share a basic architecture consisting of the same components. Perhaps the most basic components as described by Burns and Capps (1988) are the "Expert Model", the "Student Model" and the "Tutor". These modules are essential to the development of the JITS framework and will be discussed in depth.

*Expert Model.* The expert model is designed to encapsulate all available knowledge for a particular domain. Domains for which ITS's have been developed included arithmetic – BUGGY (Brown & Burton, 1978), programming language - LISPIT (Anderson, 1988), and electronic troubleshooting – SOPHIE (Brown, Burton, and deKleer, 1982). Clearly, it is a challenge to develop an expert model for an ITS and the difficulty is a function of how well defined a domain is. For example, when dealing with technical procedures like maintaining an aircraft, the problem space is well understood, i.e., the steps involved in performing a procedure are clearly structured and the means to perform the task are well defined. Clearly less well understood domains provide a significantly higher challenge for the designer of the expert model, and with Anderson (1988) one has to emphasize that, ". . . a great deal of effort needs to be expended to discover and codify the domain knowledge" (p.22). The information contained in the expert model is usually assembled by experts in specific fields and serves as the standard to which the student's actions and knowledge is compared.

*Student Model.* The student (or user) model is the system's representation of a specific learner's abilities and knowledge concerning the domain under consideration. Because of the dynamic nature of learning, a single or a static student model is not sufficient in an ITS. This is because overall the student acquires knowledge during the use of the system and progesses towards the development of expertise, but this track is not linear and perturbations of the user's proficiency across and even within a training session need to be accommodated. A critical function of ITS is to properly diagnose the user and identify when and what type of assistance is needed. If students perform below their normal baselines, the system must respond according. For the system to accurately gauge a student, it must go beyond a simple comparison to the expert model. One issue of current diagnostic functions implemented in ITS's is that they evaluate response accuracy by comparison with the knowledge base (Linn, 1990; Marshall, 1990). This allows for the categorization of a student, but offers nothing to guide learning and performance (Linn, 1990). However, the tutor model serves this purpose.

*Tutor Model*. The tutor model is essential in a ITS since it incorporates the didactic ideas of the designer. Without a tutoring model (e.g., instructional module, or pedagogical agent) an ITS would be limited to the administration and scoring of tests lacking the ability to impart knowledge or understanding to the user. Structurally, the instructional module interacts with the expert model and the student model to formulate relevant information to the user. It evaluates the student model in terms of the expert model and decides what information to present, how to display the information, and when to do so. The tutor model is the visible module for the user. Through the interface, the pedagogical agent serves as the teacher, consultant, assistant, or coach.

#### **1.1.2 Limitations of ITS**

Cardiac Defibrillation

106 – Prediction, Prevention and Management of Cardiovascular Arrhythmic Events

Intelligent Tutoring Systems (ITS) have been developed over the last decades. Early systems focused on supporting students in acquiring knowledge, thus these systems were similar to flash cards but were also capable of analyzing a student's responses (Uhr, 1969). The next generation systems were more sophisticated because they moved from a scripted hierarchical structure of knowledge towards systems that were able to deal with potentially all requests that a student would submit to the system. For example SCHOLAR (Carbonell, 1970) tutored students in South American geography and was designed to deal with a variety of questions that might be asked by a student learner. The next important step in the development of ITS was embodied in the work of Collins (1977). Earlier that decade Craik & Lockhart (1972) demonstrated that deeper, more elaborate processing improved learning and retention. In application of this line of reasoning, Collins (1977) implemented a Socratic method of exploration for his system. What was remarkable about this approach was that it allowed the student to "discover" knowledge, empowering the student to acquire knowledge from experience and individual cases, through self-directed exploration of the knowledge base. Despite the wide range of ITS there are a number of basic elements that all

Many ITS projects share a basic architecture consisting of the same components. Perhaps the most basic components as described by Burns and Capps (1988) are the "Expert Model", the "Student Model" and the "Tutor". These modules are essential to the development of the

*Expert Model.* The expert model is designed to encapsulate all available knowledge for a particular domain. Domains for which ITS's have been developed included arithmetic – BUGGY (Brown & Burton, 1978), programming language - LISPIT (Anderson, 1988), and electronic troubleshooting – SOPHIE (Brown, Burton, and deKleer, 1982). Clearly, it is a challenge to develop an expert model for an ITS and the difficulty is a function of how well defined a domain is. For example, when dealing with technical procedures like maintaining an aircraft, the problem space is well understood, i.e., the steps involved in performing a procedure are clearly structured and the means to perform the task are well defined. Clearly less well understood domains provide a significantly higher challenge for the designer of the expert model, and with Anderson (1988) one has to emphasize that, ". . . a great deal of effort needs to be expended to discover and codify the domain knowledge" (p.22). The information contained in the expert model is usually assembled by experts in specific fields and serves as the standard to which the student's actions and knowledge is compared. *Student Model.* The student (or user) model is the system's representation of a specific learner's abilities and knowledge concerning the domain under consideration. Because of the dynamic nature of learning, a single or a static student model is not sufficient in an ITS. This is because overall the student acquires knowledge during the use of the system and progesses towards the development of expertise, but this track is not linear and perturbations of the user's proficiency across and even within a training session need to be accommodated. A critical function of ITS is to properly diagnose the user and identify when and what type of assistance is needed. If students perform below their normal baselines, the system must respond according. For the system to accurately gauge a student, it must go beyond a simple comparison to the expert model. One issue of current diagnostic functions implemented in ITS's is that they evaluate response accuracy by comparison with the knowledge base (Linn, 1990; Marshall, 1990). This allows for the categorization of a student,

of these systems have in common. These elements will be outlined next.

JITS framework and will be discussed in depth.

**1.1 Intelligent Tutorial Systems (ITS)**

**1.1.1 Description of ITS**

The above description of the ITS architecture illustrates some of strength of the approach that guides the development of an ITS. However, there are also limitations that are associated with the development and use of such system. These limitations become particularly salient when the goal is to design a system that does not provide knowledge, but that can be used as a just-in-time support system. Certainly, both systems have similarities– e.g., both are primarily aimed at novices, are computer based, and leverage best practices of expert systems and user-interface principles. However, for the current purpose it is also critical to understand the differences between these systems. The differences can be described with regard to the goals, the time available for performance, the intended cognitive processing strategies and the system input. A brief summary of these issues is provided in Table 1, and will be discussed in detail in the next sections.

*Objectives*. The disparate objectives of each system are yoked to the temporal constraints associated with their use. With the ITS, the extended time horizon enables the goals of learning, long-term retention and fosters accuracy in the speed-accuracy trade-off. This situation can be contrasted with the JITS that is not focused on learning, since retention is inconsequential and potentially counter-productive in situations where a JITS is being used. The objective is to allow the user to perform the task to a satisfactory degree in the limited time available. Due to the temporal constraints, it is more important to sufficiently complete all requisite steps in the given, limited time rather than to strive for flawless performance on some tasks while failing to complete others.

Table 1. Differences between Just-in-Time Support (JITS) and Intelligent Tutoring Systems (ITS) on critical dimensions.

Just in Time Support to Aide Cardio-Pulmonary Resuscitation 109

detect and interpret a change in system state. The s*ubjectively available time* is a measure that assesses the time pressure that is subjectively perceived by an operator. The *number of simultaneous goals* reflects the number of objectives the user can maintain concurrently and their relevance to the overall goal. The *availability of plans* is an expression of the controller's access to heuristics, plans, procedures or something rule-like to guide actions that are performed to accomplish the overall goal. The *event horizon* is composed of the extent to which previous information on the control task is being utilized in a given decision, plus the "prediction length", which is an extrapolation of the future state of the system. Finally, the *mode of execution* is a reflection of the overall way how an operator performs the control task. Two modes are possible, a "subsumed" (ballistic or feed forward) mode where actions are executed automatically. This mode requires assumptions and predictions with regard to the dynamics of the controlled system. The second mode is a "feedback" mode in which data of the tasks' state and progress guide future actions because a constant assessment of

The control continuum that describes the level of control of an operator is anchored by an absence of control at one end of the continuum, and highlights several milestones as control progresses to a very high-level of control at the other end of the continuum. Hollnagel identified four characteristic regions of control. From the level of least control to level of greatest control the regions are labeled: *scrambled, opportunistic, tactical,* and *strategic* levels of control*.* A more detailed description of these levels with regard to the dimensions outlined

The level of *scrambled* control resides on the lowest end of the continuum, and is an expression of a lack of control of the operator. The user performs the next action at random and the choice of action is unpredictable, resulting in a trial and error approach with limited determination of the outcome. Here, this approach results in user actions being incongruous with the situation. Clearly, a user operating in a scrambled control mode has no knowledge about the process and lacks any heuristics, rules or procedures that would allow performing the task. Consequentially, the user experiences a great deal of stress due to high cognitive workload, time pressure, and a futile understanding of the system and/or the current

The *opportunistic* level of control is the next region on the continuum of control. What is important at this level is the fact that the operator expresses some ability to move the system toward the overall goal state. Similar to the scrambled mode of control, the operator still perceives significant time pressure, but it is possible for the user to plan the next action that is being performed. In addition, actions are no longer characterized by chance. Overall these changes are a reflection of the fact that control now becomes a cognitive problem, i.e., control is based on the user's ability to recognize and act on salient cues in the environment and that are provided by the system. Thus, the operator moved from a subsumed mode of execution to a feedback based mode, with feedback being accessible and interpretable and

A the level of *tactical* control a noticeable change in perceived time pressure occurs which allows for short range planning. The user experiences an expansion of the event horizon that is involved in planning, in both directions (previous states and predicted states). Performance now is based on previously acquired rules or procedures and the operator is now in a position where it is possible to anticipate needs associated with the control task

performance changes the guidance that is provided.

**1.2.1 Control modes**

above will be provided next.

environmental conditions.

the environment being somewhat familiar.

*Time available.* A student using an ITS to acquire some knowledge will not experience time pressure. The user determines the start time, duration, and sets the pace of the interaction with the system. This more relaxed situation can be contrasted with the context in which a JITS is being used. Here, the task will be subject to considerable time pressure due to the task criticality (a non-critical task could tolerate awaiting the arrival of an expert), making the task externally, and not internally paced. The JITS user operates under a limited time envelope in which to perform the task.

*Processing strategies*. A significant discrepancy between systems is also evident in the targeted cognitive processes involved in performance. The aim of an ITS is to target a deeper level of processing (Craik & Lockhart, 1972) which allows long term retention. Thus, intelligent tutoring systems utilize declarative knowledge permitting extensive mental associations and abstractions. This more elaborative processing strategy serves not only long-term retention, but also pliant, adaptive application with the development of domain expertise. In contrast a JITS targets a shallower, perceptual level of information processing. As a consequence, mimicking-type strategies, though inferior to elaborative processing for memory, are efficient for accomplishing procedural tasks without any previous practice in the task.

*System input*. The final difference concerns the input mechanisms that are implemented in each system. Traditional ITS requires a direct manipulation by the user (i.e., type, point and click, etc.). The system itself is designed to be passive whereas a JITS is specifically designed to actively collect data from the environment in which the task is performed. Equipped with an array of sensors the JITS system identifies changes of state and updates its models based on those changes. This process is implemented in such way that it is transparent to the operator (sensors are integrated with the tools used), and overall drives updated cues and feedback that guide performance to meet standards that suffice. Feedback and plan adaptability consequentially rely upon the external data the system is able to collect and integrate. The operator is permitted to act in a goal directed manner on the world (essential for performing a task), and is not required to provide additional information necessary to update the system's representation of the environment and the task progress.

Clearly, there are significant differences between the traditional ITS approach and the JITS design. One of the additional differences relates to the challenge of assessing performance of a human operator. To do this, a control theoretical perspective as proposed in the COCOM model can be useful. In the next sections we will describe this framework.

#### **1.2 COCOM as conceptual framework**

Erik Hollnagel (1993) developed the Contextual Control Model (COCOM) that describes a continuum of human control and can serve JITS development in both design and evaluation of operator performance. The model provides designers with a tool to identify parameters and determine control characteristics of an operator, which not only enables prediction of control conditions, but also establishes means to manipulate control states. Additionally, the model provides an effective assessment tool to evaluate performance hypotheses.

Before the nominal control modes can be described it is important to explain the parameters that characterize a given state of control of an operator. Based on Holnagel's model it is possible to distinguish several dimensions that help characterize the level at which a person is performing a control task. *Determination of outcome* is a reflection of an operator's ability to detect and interpret a change in system state. The s*ubjectively available time* is a measure that assesses the time pressure that is subjectively perceived by an operator. The *number of simultaneous goals* reflects the number of objectives the user can maintain concurrently and their relevance to the overall goal. The *availability of plans* is an expression of the controller's access to heuristics, plans, procedures or something rule-like to guide actions that are performed to accomplish the overall goal. The *event horizon* is composed of the extent to which previous information on the control task is being utilized in a given decision, plus the "prediction length", which is an extrapolation of the future state of the system. Finally, the *mode of execution* is a reflection of the overall way how an operator performs the control task. Two modes are possible, a "subsumed" (ballistic or feed forward) mode where actions are executed automatically. This mode requires assumptions and predictions with regard to the dynamics of the controlled system. The second mode is a "feedback" mode in which data of the tasks' state and progress guide future actions because a constant assessment of performance changes the guidance that is provided.

#### **1.2.1 Control modes**

Cardiac Defibrillation

108 – Prediction, Prevention and Management of Cardiovascular Arrhythmic Events

*Time available.* A student using an ITS to acquire some knowledge will not experience time pressure. The user determines the start time, duration, and sets the pace of the interaction with the system. This more relaxed situation can be contrasted with the context in which a JITS is being used. Here, the task will be subject to considerable time pressure due to the task criticality (a non-critical task could tolerate awaiting the arrival of an expert), making the task externally, and not internally paced. The JITS user operates under a limited time

*Processing strategies*. A significant discrepancy between systems is also evident in the targeted cognitive processes involved in performance. The aim of an ITS is to target a deeper level of processing (Craik & Lockhart, 1972) which allows long term retention. Thus, intelligent tutoring systems utilize declarative knowledge permitting extensive mental associations and abstractions. This more elaborative processing strategy serves not only long-term retention, but also pliant, adaptive application with the development of domain expertise. In contrast a JITS targets a shallower, perceptual level of information processing. As a consequence, mimicking-type strategies, though inferior to elaborative processing for memory, are efficient for accomplishing procedural tasks without any previous practice in

*System input*. The final difference concerns the input mechanisms that are implemented in each system. Traditional ITS requires a direct manipulation by the user (i.e., type, point and click, etc.). The system itself is designed to be passive whereas a JITS is specifically designed to actively collect data from the environment in which the task is performed. Equipped with an array of sensors the JITS system identifies changes of state and updates its models based on those changes. This process is implemented in such way that it is transparent to the operator (sensors are integrated with the tools used), and overall drives updated cues and feedback that guide performance to meet standards that suffice. Feedback and plan adaptability consequentially rely upon the external data the system is able to collect and integrate. The operator is permitted to act in a goal directed manner on the world (essential for performing a task), and is not required to provide additional information necessary to update the system's representation of the environment and the

Clearly, there are significant differences between the traditional ITS approach and the JITS design. One of the additional differences relates to the challenge of assessing performance of a human operator. To do this, a control theoretical perspective as proposed in the COCOM

Erik Hollnagel (1993) developed the Contextual Control Model (COCOM) that describes a continuum of human control and can serve JITS development in both design and evaluation of operator performance. The model provides designers with a tool to identify parameters and determine control characteristics of an operator, which not only enables prediction of control conditions, but also establishes means to manipulate control states. Additionally, the model provides an effective assessment tool to evaluate performance

Before the nominal control modes can be described it is important to explain the parameters that characterize a given state of control of an operator. Based on Holnagel's model it is possible to distinguish several dimensions that help characterize the level at which a person is performing a control task. *Determination of outcome* is a reflection of an operator's ability to

model can be useful. In the next sections we will describe this framework.

envelope in which to perform the task.

the task.

task progress.

hypotheses.

**1.2 COCOM as conceptual framework**

The control continuum that describes the level of control of an operator is anchored by an absence of control at one end of the continuum, and highlights several milestones as control progresses to a very high-level of control at the other end of the continuum. Hollnagel identified four characteristic regions of control. From the level of least control to level of greatest control the regions are labeled: *scrambled, opportunistic, tactical,* and *strategic* levels of control*.* A more detailed description of these levels with regard to the dimensions outlined above will be provided next.

The level of *scrambled* control resides on the lowest end of the continuum, and is an expression of a lack of control of the operator. The user performs the next action at random and the choice of action is unpredictable, resulting in a trial and error approach with limited determination of the outcome. Here, this approach results in user actions being incongruous with the situation. Clearly, a user operating in a scrambled control mode has no knowledge about the process and lacks any heuristics, rules or procedures that would allow performing the task. Consequentially, the user experiences a great deal of stress due to high cognitive workload, time pressure, and a futile understanding of the system and/or the current environmental conditions.

The *opportunistic* level of control is the next region on the continuum of control. What is important at this level is the fact that the operator expresses some ability to move the system toward the overall goal state. Similar to the scrambled mode of control, the operator still perceives significant time pressure, but it is possible for the user to plan the next action that is being performed. In addition, actions are no longer characterized by chance. Overall these changes are a reflection of the fact that control now becomes a cognitive problem, i.e., control is based on the user's ability to recognize and act on salient cues in the environment and that are provided by the system. Thus, the operator moved from a subsumed mode of execution to a feedback based mode, with feedback being accessible and interpretable and the environment being somewhat familiar.

A the level of *tactical* control a noticeable change in perceived time pressure occurs which allows for short range planning. The user experiences an expansion of the event horizon that is involved in planning, in both directions (previous states and predicted states). Performance now is based on previously acquired rules or procedures and the operator is now in a position where it is possible to anticipate needs associated with the control task

Just in Time Support to Aide Cardio-Pulmonary Resuscitation 111

transitions that skip a level. For example, an operator in a tactical control mode may encounter a completely novel crisis. During such encounter the subjectively available time may diminish and no heuristics for employment are available. Clearly, a scrambled condition has resulted. Hollnagel (1993) insists that there is a constraint in moving to and from strategic control with strategic control only being reached from the tactical region and

Knowing the characteristics of each control mode, allows identifying the region in which an operator is performing. Knowledge of the task, tools, and context permits a developer of a system to articulate mode control predictions which provide a workspace that can be manipulated in an effort to improve an operator's level of control. For example, one implementation is to make accessible a plan to a user where the person did not have any previously. In addition, it is possible to rectify the absence of salient features by providing guidance. Finally, clear feedback can be presented to promote interpretation that can guide

Lastly, the application of COCOM as a model of human performance provides some guidance for the development of assessment tools of human performance in the context of complex tasks, i.e., the assessment of performance using a JITS system. Thus, Hollnagel's model provides valuable characteristics to describe the task and desired performance which

After the above description and analysis of the COCOM model it is now possible to identify several important design recommendations. These recommendations guided the implementation of the Just-in-Time System to provide CPR expertise. Below each of these

Provide a plan of action to the user that is adaptable to dynamic conditions and needs

Provide easily interpretable feedback to help the user correct actions and update system

Clearly any direction provided to a user of a JITS needs to include the visual and auditory modality to provide instructions and feedback. Visual displays can inform a novice on how to proceed when performing individual steps of the task. This implies that a dynamic visual

A substantial amount of research has been conducted to identify what characterizes expert behavior and expert performance (e.g., Chi, Glaser, & Farr, 1988,). Glaser and Chi (1988) established seven general attributes representative of experts. These attributes are presented

also only be able to degrade to the tactical level.

can allow prediction of performance in a given situation.

**1.2.3 Design considerations based on COCOM**

Provide salient, action-directing cues to the user

demonstrate sequential actions in a procedural task

illustrate a task which is difficult to describe verbally

**1.3 Additional design considerations**

Work within time constraints that are derived from the task.

obtain attention focused on specific tasks or presentation displays

represent invisible system functions or behaviors in a transparent fashion.

action.

principles is outlined.

display has to

**1.3.1 Expertise**

in table 3.

state continuously

that are in the near future. The meanings of the outcomes of actions are more completely understood, and two or three goals the operator pursues may be active at once, with a plan, rule, or procedure supporting each of the goals. Feedback is an important input and being utilized for comparison with higher level goals.

Finally, the *strategic* level of control is a state of high stability and planning that is well beyond the immediate context of the control task. Performance at this level is effective and robust with the event horizon being further extended in both directions. The operator has the opportunity to contemplate the highest level goals and performs at both modes of execution (i.e., feedback and feed forward control). Finally, performing at the strategic level of performance requires substantial motivation to do so. The user must embrace the high cognitive load associated with this level of performance that is a result of extended planning, reasoning, and observation to attain a strategic mode of control. Because of this high cognitive demand, strategic control often cannot be maintained for long periods. A summary of the different modes of control and their association with the different COCOM parameters is displayed in Table 2.

Table 2. Summary of COCOM parameters and control states (adapted from Hollnagel, 1993).

One important aspect with regard to the different modes of control is related to how an operator can switch between these modes. Below we will discuss the process of transitioning between modes.

#### **1.2.2 Mode transitions**

The transition between control modes is also of importance, and can be discussed in terms of changes in the parameters outlined above. Since those characteristics describe a state of control, it is appropriate to speak about an operator moving along the control continuum as result of a change in one or more of those parameters.

The most direct transition is a simple step to an adjacent level of control. This shift may be either an increase or a reduction of control performance. However, it is possible to have

prediction

Plans and contingencies available for

Extensive planning & use of historic data

subsumed

driven

all

110 – Prediction, Prevention and Management of Cardiovascular Arrhythmic Events

that are in the near future. The meanings of the outcomes of actions are more completely understood, and two or three goals the operator pursues may be active at once, with a plan, rule, or procedure supporting each of the goals. Feedback is an important input and being

Finally, the *strategic* level of control is a state of high stability and planning that is well beyond the immediate context of the control task. Performance at this level is effective and robust with the event horizon being further extended in both directions. The operator has the opportunity to contemplate the highest level goals and performs at both modes of execution (i.e., feedback and feed forward control). Finally, performing at the strategic level of performance requires substantial motivation to do so. The user must embrace the high cognitive load associated with this level of performance that is a result of extended planning, reasoning, and observation to attain a strategic mode of control. Because of this high cognitive demand, strategic control often cannot be maintained for long periods. A summary of the different modes of control and their association with the different COCOM

Parameters Scrambled Opportunistic Tactical Strategic

**Goals** 0-1 1 2-3 2-many

Some history,

little planning

employed Minimal Most goals supported by

**Execution** Subsumed Feedback Feedback Feedback +

**Action Selection** Random Cue driven Plan driven Prediction

Table 2. Summary of COCOM parameters and control states (adapted from Hollnagel, 1993). One important aspect with regard to the different modes of control is related to how an operator can switch between these modes. Below we will discuss the process of

The transition between control modes is also of importance, and can be discussed in terms of changes in the parameters outlined above. Since those characteristics describe a state of control, it is appropriate to speak about an operator moving along the control continuum as

The most direct transition is a simple step to an adjacent level of control. This shift may be either an increase or a reduction of control performance. However, it is possible to have

plans

data

**Outcomes** Obscured Limited Context dependent Elaborate +

Severe Light-Moderate None

Planning (based on current situation), use of previous

utilized for comparison with higher level goals.

parameters is displayed in Table 2.

**Pressure** Severe Significant –

None

only

result of a change in one or more of those parameters.

**Determination of**

**Subjective Time**

**Simultaneous**

**Availability of**

**Event horizon** Present

transitioning between modes.

**1.2.2 Mode transitions**

**Plans**

**Mode of**

transitions that skip a level. For example, an operator in a tactical control mode may encounter a completely novel crisis. During such encounter the subjectively available time may diminish and no heuristics for employment are available. Clearly, a scrambled condition has resulted. Hollnagel (1993) insists that there is a constraint in moving to and from strategic control with strategic control only being reached from the tactical region and also only be able to degrade to the tactical level.

Knowing the characteristics of each control mode, allows identifying the region in which an operator is performing. Knowledge of the task, tools, and context permits a developer of a system to articulate mode control predictions which provide a workspace that can be manipulated in an effort to improve an operator's level of control. For example, one implementation is to make accessible a plan to a user where the person did not have any previously. In addition, it is possible to rectify the absence of salient features by providing guidance. Finally, clear feedback can be presented to promote interpretation that can guide action.

Lastly, the application of COCOM as a model of human performance provides some guidance for the development of assessment tools of human performance in the context of complex tasks, i.e., the assessment of performance using a JITS system. Thus, Hollnagel's model provides valuable characteristics to describe the task and desired performance which can allow prediction of performance in a given situation.

#### **1.2.3 Design considerations based on COCOM**

After the above description and analysis of the COCOM model it is now possible to identify several important design recommendations. These recommendations guided the implementation of the Just-in-Time System to provide CPR expertise. Below each of these principles is outlined.

Clearly any direction provided to a user of a JITS needs to include the visual and auditory modality to provide instructions and feedback. Visual displays can inform a novice on how to proceed when performing individual steps of the task. This implies that a dynamic visual display has to

#### **1.3 Additional design considerations**

#### **1.3.1 Expertise**

A substantial amount of research has been conducted to identify what characterizes expert behavior and expert performance (e.g., Chi, Glaser, & Farr, 1988,). Glaser and Chi (1988) established seven general attributes representative of experts. These attributes are presented in table 3.

Just in Time Support to Aide Cardio-Pulmonary Resuscitation 113

also is important to not attempt to transform novices into experts when developing JITS systems since acquisition of expertise exceeds available time. Often, tasks may consist of a single trial, which is clearly not sufficient to establish expertise. However, by abandoning the effort to create an expert and embracing the task of mimicking one, several advantages arise. For example, a shallow level of information processing can be targeted. Certainly such level of processing is inferior for retention, but it reduces the demand on the novice's limited cognitive resources and leverages more primitive processes such as perception-action mechanisms. To summarize the following design principles with regard to expertise need to

Minimize cognitive burdens (memory, search, attention capture) as much as possible.

Feedback can be defined as information that is provided to an operator that is relevant in the context of assessing performance or outcomes. In order to provide closed-loop control, feedback must be communicated directly to a user, and if provided correctly it has the

Numerous reviews and meta-analyses demonstrated the effectiveness of accurate feedback in a variety of tasks (Azevedo & Bernard, 1995, Kluger & DeNisi, 1996, Salmoni, Schmidt, & Walker,1984). Reliable feedback enhances learning and performance. In support of immediate task facilitation, Goodman (1998) concluded that frequent and immediate feedback to study participants improved performance during practice. Similarly, Young & Lee (2001) found that more feedback in the "acquisition phase" facilitated task performance (but not retention). In JITS supported tasks, "practice" occurs simultaneously with the "test". Therefore, frequent and immediate feedback will likely generate desired effects for JITS systems. An additional benefit of feedback is that it increases motivation. Participants often invest more effort, show more interest in the task, and persist longer than those who do not receive feedback. Interestingly, Salmoni, Schmidt, & Walker (1984) found these

Based on the above, a number of recommendations for optimal delivery of feedback in a

Since most of the tasks supported by JITS entail spatial arrangements, information needs to be presented visually to the user. Technology-intense domains typically require visual

ii. Excess precision (based on user knowledge) will likely be ignored

i. User must be able to relate feedback to relevant activity ii. User must be ready to attend to feedback information Feedback may serve as motivation in completing the task

guide the development of a JITS:

Keep information visible

**1.3.3 Feedback**

JITS can be provided:

**1.3.4 Visual displays**

System should assume monitoring role

potential to enhance operator control.

 Break information down into comprehensible chunks Use concrete (as opposed to abstract) representations

effects persisted for some time even after removing feedback.

Customize feedback pursuant to operator knowledge

i. Conflicting information can confuse the user

Feedback provided must be reliable

Feedback timing is critical

Ensure the pace of information delivery is apt for user population

Table 3. Expert characteristics (Glaser & Chi, 1988).

#### **1.3.2 Expert-novice differences**

Johnson (1988) observed that novices do not have extensive domain knowledge, and cannot encode information well (e.g. they lack an adequate representation and experience pattern matching difficulties) nor process new information quickly. Miller & Perlis (1997) also discussed novices' inferior knowledge base and structure, adherence to superficial cues, and utilization of small, fragmented information units. Not only did novices utilize more superficial knowledge, but the knowledge base lacked cross referencing and the organization that experts are able to impose.

In developing a system for non-experts it is of critical importance to understand the limitations of novices. This can lead to an implementation of guidance that truly supports performance but does not exceed novices' abilities. Below are the design recommendations pertinent to each expert characteristic described in Table 3.

The emphasis in employing these design recommendation is that it is imperative to provide information congruent with the operator's knowledge. For the development of an effective system it is important to design systems that are suited for the user's level of expertise. It also is important to not attempt to transform novices into experts when developing JITS systems since acquisition of expertise exceeds available time. Often, tasks may consist of a single trial, which is clearly not sufficient to establish expertise. However, by abandoning the effort to create an expert and embracing the task of mimicking one, several advantages arise. For example, a shallow level of information processing can be targeted. Certainly such level of processing is inferior for retention, but it reduces the demand on the novice's limited cognitive resources and leverages more primitive processes such as perception-action mechanisms. To summarize the following design principles with regard to expertise need to guide the development of a JITS:

#### **1.3.3 Feedback**

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112 – Prediction, Prevention and Management of Cardiovascular Arrhythmic Events

4. Experts have superior short- and long-term memory in their domains.

6. Experts are able to spend great deal of time analyzing a problem qualitatively.

Johnson (1988) observed that novices do not have extensive domain knowledge, and cannot encode information well (e.g. they lack an adequate representation and experience pattern matching difficulties) nor process new information quickly. Miller & Perlis (1997) also discussed novices' inferior knowledge base and structure, adherence to superficial cues, and utilization of small, fragmented information units. Not only did novices utilize more superficial knowledge, but the knowledge base lacked cross referencing and the

In developing a system for non-experts it is of critical importance to understand the limitations of novices. This can lead to an implementation of guidance that truly supports performance but does not exceed novices' abilities. Below are the design recommendations

 Novices do not excel in the given domain, they need help. Thus, there is a need for JITS. Novices need to parse information into simpler, more digestible chunks. Critical parameters and combinations must be salient. The system helps the user to construct

 The pace at which information is delivered to novices should be slowed. Information about sequential steps may also need altering. Repetitions in displaying this information may be necessary. The pedagogical model should monitor and control the

 The system should relieve burdens to short term and long term memory of novices by holding the information and making it visible, accessible, and congruent with the

 Novices do not understand abstract concepts of the domain. Cues and feedback must utilize concrete representations. Designers cannot assume knowledge on the part of the user. Metaphors, higher level concepts, and domain knowledge are likely to be lost on a

 Novices will not have time or ability to analyze the situation on a deeper level. A context-aware system will be responsible for identifying the proper course of action. Novices will likely be far too stressed to have any resources available to deal with the challenges required in building situation comprehension. Smart algorithms and sensors take over this job in conjunction with the situation assessment the system monitors operator performance in order to optimize cues and feedback to assist the user optimally. The emphasis in employing these design recommendation is that it is imperative to provide information congruent with the operator's knowledge. For the development of an effective system it is important to design systems that are suited for the user's level of expertise. It

1. Experts excel in their own domain.

2. Experts perceive large meaningful patterns. 3. Experts solve problems quickly with little error.

5. Experts represent problems more abstractly.

7. Experts have strong self-monitoring skills. Table 3. Expert characteristics (Glaser & Chi, 1988).

**1.3.2 Expert-novice differences**

organization that experts are able to impose.

patterns in small increments.

current subtask.

novice.

pertinent to each expert characteristic described in Table 3.

pace and sequence pursuant to operator needs.

Feedback can be defined as information that is provided to an operator that is relevant in the context of assessing performance or outcomes. In order to provide closed-loop control, feedback must be communicated directly to a user, and if provided correctly it has the potential to enhance operator control.