the goal of defibrillation ( df ) testing is to verify the detection of ventricular tachyarrhythmias by implantable cardioverter - defibrillators ( icds ) , and to ascertain df efficacy .
all clinical trials , which demonstrated the benefit of icd therapy , have included some kind of df testing . according to the food and drug administration ,
the instructions for use of icds include the recommendation  with df testing at the time of implantation .
the absence of df testing may have medico - legal implications whether a device fails to terminate ventricular fibrillation ( vf ) during follow - up .
nevertheless , df testing has been deliberately omitted in the majority of patients enrolled in contemporary icd studies . despite the stochastic nature of df , ineffective shocks during vf induction result in system modifications in up to 5% of patients .
system modifications , such as repositioning of the electrode , reversal of polarity , use of a high - energy device , use of a dual instead of a single - coil electrode , or the implantation of an additional subcutaneous electrode , may be unnecessary or even harmful since many patients have a successful retesting with the original system configuration .
no single system modification in itself has ever been shown to improve outcome . with current devices and programming ,
an inadequate safety margin occurs infrequently , and the incidence of ventricular tachyarrhythmias requiring shocks is low at 46% per year . while df testing has never been shown to improve survival , it is associated with an increased , albeit small risk of major adverse events of 0.4% . by omitting routine df testing ,
the approach to icd implantation will likely change considerably , as the procedures will be shorter and performed without technical support and anaesthesia .
similar to the simple trial , we hypothesized that , with current high - energy icd devices , the omission of df testing during implantation will not result in an inferior shock efficacy during follow - up when compared with standard df testing .
as opposed to the simple trial , which used the composite outcome of arrhythmic death or failed appropriate shock , the primary end point of our study was the shock efficacy of all true ventricular tachycardia ( vt ) and vf episodes occurring in any patient during follow - up .
the nordic icd trial ( nct01282918 ) was a prospective , randomized , parallel group , multi - centre non - inferiority trial conducted at 48 centres in five european countries , and designed to investigate the effect of df testing at the time of icd implantation on first shock efficacy ( fse ) during follow - up .
briefly , patients with an indication for icd implantation according to the current european society of cardiology guidelines were included .
patients with hypertrophic or arrhythmogenic right ventricular cardiomyopathy were excluded because of special considerations necessary during icd implantation .
one thousand and seventy - seven patients were randomized ( 1 : 1 ) to first time icd implantation with or without df testing during the procedure .
patients were followed for at least 12 months through regular on - site visits , and remotely via home monitoring ( hm ; biotronik se & co. kg , berlin , germany ) .
all true ventricular tachyarrhythmias treated with an icd shock in any patient were included in the primary analysis .
the study was conducted in accordance with the declaration of helsinki , and country - specific regulatory requirements .
the protocol was approved by the institutional review board or ethics committee of each participating centre .
a standard df testing protocol was used by all participating centres , as described previously .
briefly , the initial shock for df was programmed to 15 j. if successful , df testing was terminated . if unsuccessful , a second shock programmed to 24 j was delivered , and had to be confirmed .
if unsuccessful , a system revision was recommended , and the df testing procedure was repeated .
the primary end point was the fse to terminate all true episodes of vt / vf during follow - up .
a blinded two - member clinical event committee reviewed the diagnostic information of the vt / vf treated with icd shocks .
safety end points included procedural serious adverse events , vt / vf conversion rate , and all - cause , cardiac , or arrhythmic mortality during follow - up .
all adverse events were reviewed and adjudicated by a data and safety monitoring board ( dsmb ) , consisting of three members .
all patient deaths were adjudicated by the dsmb according to a classification originally described by epstein et al .
the goal of the nordic icd trial was to demonstrate the non - inferiority of no df testing when compared with df testing with respect to the primary endpoint of fse .
this margin was chosen because the variation of fse in published trials was in the range of 8392% .
after a pre - specified blinded re - assessment , the sample size was increased to 1080 patients recruited over a period of 28 months , with a follow - up of at least 12 months .
the intention - to - treat ( itt ) population which included all randomized patients , the evaluated - for - safety population which included randomized patients who received an icd , and the per protocol ( pps ) population which included randomized patients who received an icd and did not have a major protocol violation .
however , for time - dependent outcomes , these patients were included up to the date of the protocol violation .
the primary analysis was performed in the per protocol episode data set ( p - pps ) , which included all sufficiently documented shocked episodes in pps patients .
baseline characteristics are presented group wise for the itt population as mean ( sd ) or frequency ( % ) . to compensate for the dependence structure induced by recurrent episodes with similar outcome in some of the patients , a random effects logit model with patients as a random factor and group as a fixed factor was used for calculation of a two - sided 95% confidence interval ( ci ) of the difference fsenodftest  fsedftest . to state non - inferiority , this ci had to lie completely above the pre - specified non - inferiority margin of 10% . without the use of a model that takes the correlation structure into account , the few patients with an extreme numbers of shocks would have dominated the results .
procedural and safety outcomes were compared with a student 's t test , or  test or fisher 's exact test , whichever was appropriate .
hazard rate reduction was assessed using a cox proportional hazards model . a two - tailed p - value < 0.05 was considered to be statistically significant .
data were analysed using sas ( version 9.4 ) and stata ( version 13.1 ) by an independent statistical institute ( department of medical biometry and epidemiology , university medical centre hamburg eppendorf , germany ) ( a.s . , k.w . ) .
the first draft of the manuscript was written by the first author , and revised by all co - authors .
the authors take full responsibility for the accuracy and completeness of the findings , as well as for the fidelity to the study protocol .
the nordic icd trial ( nct01282918 ) was a prospective , randomized , parallel group , multi - centre non - inferiority trial conducted at 48 centres in five european countries , and designed to investigate the effect of df testing at the time of icd implantation on first shock efficacy ( fse ) during follow - up .
briefly , patients with an indication for icd implantation according to the current european society of cardiology guidelines were included .
patients with hypertrophic or arrhythmogenic right ventricular cardiomyopathy were excluded because of special considerations necessary during icd implantation .
one thousand and seventy - seven patients were randomized ( 1 : 1 ) to first time icd implantation with or without df testing during the procedure .
patients were followed for at least 12 months through regular on - site visits , and remotely via home monitoring ( hm ; biotronik se & co. kg , berlin , germany ) .
all true ventricular tachyarrhythmias treated with an icd shock in any patient were included in the primary analysis .
the study was conducted in accordance with the declaration of helsinki , and country - specific regulatory requirements .
the protocol was approved by the institutional review board or ethics committee of each participating centre .
a standard df testing protocol was used by all participating centres , as described previously .
briefly , the initial shock for df was programmed to 15 j. if successful , df testing was terminated . if unsuccessful , a second shock programmed to 24 j was delivered , and had to be confirmed .
if the shocks were successful twice , df testing was terminated . if unsuccessful , a system revision was recommended , and the df testing procedure was repeated .
the primary end point was the fse to terminate all true episodes of vt / vf during follow - up .
a blinded two - member clinical event committee reviewed the diagnostic information of the vt / vf treated with icd shocks .
safety end points included procedural serious adverse events , vt / vf conversion rate , and all - cause , cardiac , or arrhythmic mortality during follow - up .
all adverse events were reviewed and adjudicated by a data and safety monitoring board ( dsmb ) , consisting of three members .
all patient deaths were adjudicated by the dsmb according to a classification originally described by epstein et al .
the goal of the nordic icd trial was to demonstrate the non - inferiority of no df testing when compared with df testing with respect to the primary endpoint of fse .
this margin was chosen because the variation of fse in published trials was in the range of 8392% .
after a pre - specified blinded re - assessment , the sample size was increased to 1080 patients recruited over a period of 28 months , with a follow - up of at least 12 months .
the intention - to - treat ( itt ) population which included all randomized patients , the evaluated - for - safety population which included randomized patients who received an icd , and the per protocol ( pps ) population which included randomized patients who received an icd and did not have a major protocol violation .
however , for time - dependent outcomes , these patients were included up to the date of the protocol violation .
the primary analysis was performed in the per protocol episode data set ( p - pps ) , which included all sufficiently documented shocked episodes in pps patients .
baseline characteristics are presented group wise for the itt population as mean ( sd ) or frequency ( % ) . to compensate for the dependence structure induced by recurrent episodes with similar outcome in some of the patients , a random effects logit model with patients as a random factor and group as a fixed factor was used for calculation of a two - sided 95% confidence interval ( ci ) of the difference fsenodftest  fsedftest . to state non - inferiority , this ci had to lie completely above the pre - specified non - inferiority margin of 10% . without the use of a model that takes the correlation structure into account , the few patients with an extreme numbers of shocks would have dominated the results .
procedural and safety outcomes were compared with a student 's t test , or  test or fisher 's exact test , whichever was appropriate .
mortality was analysed in the itt population using the kaplan  meier approach and the log - rank test .
hazard rate reduction was assessed using a cox proportional hazards model . a two - tailed p - value < 0.05 was considered to be statistically significant .
data were analysed using sas ( version 9.4 ) and stata ( version 13.1 ) by an independent statistical institute ( department of medical biometry and epidemiology , university medical centre hamburg eppendorf , germany ) ( a.s . , k.w . ) .
the first draft of the manuscript was written by the first author , and revised by all co - authors .
the authors take full responsibility for the accuracy and completeness of the findings , as well as for the fidelity to the study protocol .
the baseline clinical characteristics and cardiovascular medications of the 1077 patients comprising the intention - to - treat population ( without df = 537 and with df = 540 ) are presented in table 1 .
seven hundred and one patients ( 65.1% ) had an ischaemic cardiomyopathy and 873 ( 81.8% ) received the icd for primary prevention of sudden cardiac death .
ten patients ( six in the df group and four in the without df group ) did not receive an icd , leaving 1067 patients for the safety evaluation ( figure 1 ) .
both groups were well matched for baseline demographics and clinical characteristics , as well as for the use of dual ( 51.6% ) and a single coil ( 48.4% ) electrode ( table 2 ) . 

table 1baseline demographic and clinical characteristics of subjects by treatment group ( intention to treat)characteristictotal ( n = 1077)without df test ( n = 537)with df test ( n = 540)age ( year)64.8 ( 10.9)64.7 ( 11.2)64.9 ( 10.6)male sex , n ( % ) 873 ( 81.1)430 ( 80.1)443 ( 82.0)ischaemic disease , n ( % ) 701 ( 65.1)341 ( 63.5)360 ( 66.7)hypertension , n / total n ( % ) 509/700 ( 72.7)249/349 ( 71.3)260/351 ( 74.1)diabetes mellitus , n ( % ) 368 ( 34.2)183 ( 34.1)185 ( 34.3)renal insufficiency , n ( % ) 303 ( 28.1)144 ( 26.8)159 ( 29.4)nyha class , n ( % )  i59 ( 5.5)31 ( 5.8)28 ( 5.2 )  ii464 ( 43.1)226 ( 42.1)238 ( 44.1 )  iii487 ( 45.2)254 ( 47.3)233 ( 43.1 )  iv14 ( 1.3)5 ( 0.9)9 ( 1.7 )  unknown53 ( 4.9)21 ( 3.9)32 ( 5.9)nyha class , n ( % )  ii523 ( 48.6)257 ( 47.9)266 ( 49.3 )  iii501 ( 46.5)259 ( 48.2)242 ( 44.8 )  unknown53 ( 4.9)21 ( 3.9)32 ( 5.9)estimated bmi ( n = 1054)28.2 ( 4.9)28.1 ( 4.8)28.2 ( 5.1)lvef , n ( % )  < 20%101 ( 9.4)53 ( 9.9)48 ( 8.9 )  2030%566 ( 52.6)278 ( 51.8)288 ( 53.3 )  > 30%404 ( 37.5)204 ( 38.0)200 ( 37.0 )  not done6 ( 0.6)2 ( 0.4)4 ( 0.7)af at enrolment , n ( % ) 85 ( 7.9)45 ( 8.4)40 ( 7.4)indication for implantation , n / total n ( % )  primary prevention873/1067 ( 81.8)434/531 ( 81.7)439/536 ( 81.9 )  secondary prevention194/1067 ( 18.2)97/531 ( 18.3)97/536 ( 18.1)hospital stay ( days ) ( n = 1066)4.0 ( 4.0)4.0 ( 3.6)4.0 ( 3.8)medication , n ( % )  ace inhibitors / at receptor blockers , n ( % ) 986 ( 91.6)501 ( 93.3)485 ( 89.8 )  -blockers , n ( % ) 1007 ( 93.5)500 ( 93.1)507 ( 93.9 )  ca antagonists , n ( % ) 140 ( 13.0)74 ( 13.8)66 ( 12.2 )  spironolactones , n ( % ) 618 ( 57.4)302 ( 56.2)316 ( 58.5 )  ( other ) diuretics , n ( % ) 794 ( 73.7)395 ( 73.6)399 ( 73.9 )  nitrates , n ( % ) 75 ( 7.0)38 ( 7.1)37 ( 6.9 )  digitalis , n ( % ) 105 ( 9.7)54 ( 10.1)51 ( 9.4 )  lipid - lowering agents , n ( % ) 763 ( 70.8)377 ( 70.2)386 ( 71.5 )  amiodarone , n ( % ) 116 ( 10.8)61 ( 11.4)55 ( 10.2 )  dronedarone , n ( % ) 5 ( 0.5)4 ( 0.7)1 ( 0.2 )  sotalol , n ( % ) 9 ( 0.8)5 ( 0.9)4 ( 0.7 )  ( other ) anti - arrhythmics , n ( % ) 22 ( 2.0)9 ( 1.7)13 ( 2.4 )  platelet aggregation inhibitor , n ( % ) 753 ( 69.9)370 ( 68.9)383 ( 70.9 )  anti - coagulants , n ( % ) 350 ( 32.5)183 ( 34.1)167 ( 30.9 )  other cardiovascular medication , n ( % ) 255 ( 23.7)121 ( 22.5)134 ( 24.8)values are means  sd .
there were no significant differences at p < 0.05 between groups , except for ace inhibitors p = 0.039 .
t - test for metric variables , -test for categorical , or fisher 's exact test ( f ) if  is not appropriate.ace inhibitors , angiotensin converting enzyme inhibitors ; af , atrial fibrillation ; at receptor blockers , angiotensin receptor blockers ; bmi , body mass index ; df , defibrillation ; nyha , new york heart association ; itt , intention - to - treat ; lvef , left ventricular ejection fraction . 

table 2procedural characteristics according to treatment group ( successful primary implantable cardioverter - defibrillator implantation ; evaluated - for - safety)characteristictotal ( n = 1067)without df test ( n = 533)with df test ( n = 534)p - valueimplanted lead type , n ( % )  single coil516 ( 48.36)262 ( 49.16)254 ( 47.57)0.603  dual coil551 ( 51.64)271 ( 50.84)280 ( 52.43)type , n ( % )  single chamber icd466 ( 43.67)236 ( 44.28)230 ( 43.07)0.648  dual chamber icd245 ( 22.96)116 ( 21.76)129 ( 24.16 )  crt - d356 ( 33.36)181 ( 33.96)175 ( 32.77)left position , n ( % ) 1058 ( 99.16)527 ( 98.87)531 ( 99.44)0.341 ( f)vegm signal amplitude ( mv ) ( n = 1057)12.42 ( 5.30)12.72 ( 5.37)12.12 ( 5.21)0.065pacing threshold ( v ) at pulse duration of 0.4 ms ( n = 527)0.51 ( 0.20)0.49 ( 0.17)0.53 ( 0.22)0.040pacing threshold ( v ) at pulse duration of 0.5 ms ( n = 533)0.45 ( 0.23)0.45 ( 0.27)0.44 ( 0.17)0.613patients received df test , n ( % ) 527 ( 49.39)7 ( 1.31)520 ( 97.38)delivered icd shocks per patient0.71 ( 1.16)0.01 ( 0.11)1.41 ( 1.31)<0.001df energy at final position ( j ) ( n = 526)16.74 ( 4.47)16.67 ( 4.38)patients with intra - procedural system revisions and icd re - programming , n / total n ( % ) 25/527 ( 4.74)25/520 ( 4.81)patients with electrode repositionings , n / total n ( % ) 8/527 ( 1.52)8/520 ( 1.54)patients with changes of shock polarity , n / total n ( % ) 20/527 ( 3.80)20/520 ( 3.85)patients with modification of lead system ( shock pathway ) ,
n / total n ( % ) 5/527 ( 0.95)5/520 ( 0.96)patients with other revisions / re - programming , n / total n ( % ) 7/527 ( 1.33)7/520 ( 1.35)procedure duration ( min ) ( n = 1060)64.54 ( 39.88)63.11 ( 40.84)65.97 ( 38.88)0.243fluoroscopy exposure duration ( min ) ( n = 1056)8.02 ( 11.43)8.00 ( 11.44)8.05 ( 11.43)0.943crt - d , cardiac - resynchronization therapy with defibrillator ; df , defibrillation ; efs , evaluated for safety ; vegm , ventricular electrogram ; icd , implantable cardioverter-defibrillator.one patient was not inducible . 

itt , full analysis set ( all patients as randomized ) ; efs , evaluated for safety set ( all patients randomized , who had a successful primary icd implantation ) ; pps , per protocol set ( all patients randomized , who are compliant with the study protocol ) ; p - pps , all randomized patients at least one day at risk before protocol deviation ( includes all sufficiently documented shocked episodes until time point of protocol deviation ) .
baseline demographic and clinical characteristics of subjects by treatment group ( intention to treat ) values are means  sd .
there were no significant differences at p < 0.05 between groups , except for ace inhibitors p = 0.039 .
t - test for metric variables , -test for categorical , or fisher 's exact test ( f ) if  is not appropriate . ace inhibitors , angiotensin converting enzyme inhibitors ; af , atrial fibrillation ; at receptor blockers , angiotensin receptor blockers ; bmi , body mass index ; df , defibrillation ; nyha , new york heart association ; itt , intention - to - treat ; lvef , left ventricular ejection fraction .
procedural characteristics according to treatment group ( successful primary implantable cardioverter - defibrillator implantation ; evaluated - for - safety ) crt - d , cardiac - resynchronization therapy with defibrillator ; df , defibrillation ; efs , evaluated for safety ; vegm , ventricular electrogram ; icd , implantable cardioverter - defibrillator .
itt , full analysis set ( all patients as randomized ) ; efs , evaluated for safety set ( all patients randomized , who had a successful primary icd implantation ) ; pps , per protocol set ( all patients randomized , who are compliant with the study protocol ) ; p - pps , all randomized patients at least one day at risk before protocol deviation ( includes all sufficiently documented shocked episodes until time point of protocol deviation ) . of the 534 patients randomized to the df arm with a successful first icd implantation ( figure 1 ) , testing was performed in 97.4% . in one patient , vt / vf was not inducible .
four hundred and ninety - four of 519 inducible patients ( 95.2% ) passed the test without any system reconfiguration , and 440 patients ( 84.8% ) had their vt / vf terminated with a 15 j shock . in 25 patients ,
the initial df test was not successful , and system reconfigurations were performed once in 20 and more than once in 5 ( table 2 ) .
all patients subsequently passed the test successfully , but still with a higher energy level at the final position ( 22.2  7.4 j vs. 16.4  4.0 j , p < 0.001 ) and with significantly more shocks ( 5.7  3.0 vs. 1.2  0.7 , p < 0.001 ) than the 494 patients who passed the test immediately .
in addition , the duration of the procedure ( 90.2  56.2 min vs. 63.5  36.1 min , p < 0.001 ) and fluoroscopy exposure ( 11.6  14.2 min vs. 7.5  10.7 min , p = 0.064 ) was increased . during a median follow - up of 22.7 and 22.9 months , respectively , 211 true vt / vf episodes with at least one appropriate shock occurred in 8.6% of the per protocol patients with df testing , while 218 true vt / vf episodes occurred in 8.8% of patients without df testing ( table 3 , figure 1 ) .
all true vt / vf episodes were terminated with any appropriate icd shock in the without df test group , whereas 96.7% of all vt / vf were terminated in the group with df test .
thus , the conversion efficacy was 100.0% without df testing and 96.7% with df testing .
the model - based shock efficacy was 97.1% without df testing and 94.1% with df testing .
the difference in fse was 3.0% ( ci 3.0% , 9.0% ) in favour of the without df test group , and remained above the pre - defined 10% margin for the primary end point ( pnon - inferiority < 0.001 , table 3 , figure 2 ) . 

table 3primary analysis  shock efficacy ( per protocol episode data set)totalwithout df testwith df testall patients with at least one delivered appropriate shock for a true vt / vf episode , n / total n ( % ) 91/1046 ( 8.7)46/523 ( 8.8)45/523 ( 8.6)all true vt / vf episodes with at least one delivered appropriate icd shock ( vt / vf ) , n429218211delivered appropriate shocks per true vt / vf episode ( mean ( sd))1.18 ( 0.69)1.09 ( 0.37)1.28 ( 0.90)true vt / vf episodes terminated with first appropriate icd shock , n / total n ( % ) 384/429 ( 89.5)204/218 ( 93.6)180/211 ( 85.3)true vt / vf episodes terminated with any appropriate icd shock , n / total n ( % ) 422/429 ( 98.4)218/218 ( 100.0)204/211 ( 96.7)true vt / vf episodes not terminated with any appropriate icd shock , n / total n ( % ) 7/429 ( 1.6)0/218 ( 0.0)7/211 ( 3.3)conversion efficacy [ proportion ( 95% ci)]0.98 ( 0.97;0.99)1.00 ( 0.98;1.00)0.97 ( 0.93;0.99)first shock efficacy model based [ proportion ( 95% ci)]0.96 ( 0.89;0.98)0.97 ( 0.91;0.99)0.94 ( 0.83;0.98))difference between the groups ( without df testing vs. with df testing ) : 0.03 ( 0.03;0.09).df , defibrillation ; icd , implantable cardioverter - defibrillator ; p - pps , per protocol episode data set ; vt / vf , ventricular tachycardia / ventricular fibrillation . 

primary analysis  shock efficacy ( per protocol episode data set ) difference between the groups ( without df testing vs. with df testing ) : 0.03 ( 0.03;0.09 ) .
df , defibrillation ; icd , implantable cardioverter - defibrillator ; p - pps , per protocol episode data set ; vt / vf , ventricular tachycardia / ventricular fibrillation .
a total of 201 serious adverse events related to the study procedure occurred in 168 patients ( 15.7% ) , of which 89 events occurred in 74 patients without df testing and 112 events occurred in 94 patients with df testing within 30 days of follow - up ( p = 0.095 ) .
the only significant difference in single serious adverse events was intra - operative hypotension , which manifested more often in patient with df testing ( 1.7% ) than those without df testing ( 0.0% ) ( p = 0.004 ) .
lead - related complications occurred in 15 patients without df testing ( 2.8% ) compared with 24 events in 21 patients with df testing ( 3.9% ) ( p = 0.311 ) .
one sudden death occurred in each study group within 30 days of follow - up , and the mean length of hospitalization was 4.0 days in both study groups ( table 1 ) .
the proportion of patients with inappropriate shocks during follow - up was low at 3.7% , and similar between groups .
forty - four and 52 patients without and with df testing died , respectively ( p = 0.377 , table 4 ) . differences with respect to non - cardiac and cardiac mortality were not statistically significant .
six deaths ( 5 with df and 1 without df testing ) were adjudicated arrhythmic and due to repetitive ventricular tachyarrhythmias / vt clusters ( p = 0.100 , table 4 ) . 

table 4mortality ( intention - to - treat)outcomeeventsincidencelog rank95% ciwithout df test ( n = 537)with df test ( n = 540)without df testwith df testp - valuehrlowerupperall - cause mortality44 ( 8.2%)52 ( 9.6%)0.0440.0530.3770.8350.5591.248non - cardiac mortality24 ( 4.5%)23 ( 4.3%)0.0240.0230.9071.0350.5841.833unknown ( primary organ cause)6 ( 1.1%)10 ( 1.9%)0.0060.010.3060.5930.2161.632cardiac mortality14 ( 2.6%)19 ( 3.5%)0.0140.0190.3500.7210.3611.438arrhythmic mortality1 ( 0.2%)5 ( 0.9%)0.0010.0050.1000.1980.0231.694non - arrhythmic mortality13 ( 2.4%)13 ( 2.4%)0.0130.0130.9480.9750.4522.103unknown cardiac mortality0 ( 0.0%)1 ( 0.2%)00.001df , defibrillation ; hr , hazard ratio ; itt , intention to treat.incidence referring to person - years without df test ( 1001.5 ) and with df test ( 985.9 ) . mortality ( intention - to - treat ) df , defibrillation ; hr , hazard ratio ; itt , intention to treat . incidence referring to person - years without df test ( 1001.5 ) and with df test ( 985.9 ) .
the baseline clinical characteristics and cardiovascular medications of the 1077 patients comprising the intention - to - treat population ( without df = 537 and with df = 540 ) are presented in table 1 .
seven hundred and one patients ( 65.1% ) had an ischaemic cardiomyopathy and 873 ( 81.8% ) received the icd for primary prevention of sudden cardiac death .
ten patients ( six in the df group and four in the without df group ) did not receive an icd , leaving 1067 patients for the safety evaluation ( figure 1 ) .
both groups were well matched for baseline demographics and clinical characteristics , as well as for the use of dual ( 51.6% ) and a single coil ( 48.4% ) electrode ( table 2 ) . 

table 1baseline demographic and clinical characteristics of subjects by treatment group ( intention to treat)characteristictotal ( n = 1077)without df test ( n = 537)with df test ( n = 540)age ( year)64.8 ( 10.9)64.7 ( 11.2)64.9 ( 10.6)male sex , n ( % ) 873 ( 81.1)430 ( 80.1)443 ( 82.0)ischaemic disease , n ( % ) 701 ( 65.1)341 ( 63.5)360 ( 66.7)hypertension , n / total n ( % ) 509/700 ( 72.7)249/349 ( 71.3)260/351 ( 74.1)diabetes mellitus , n ( % ) 368 ( 34.2)183 ( 34.1)185 ( 34.3)renal insufficiency , n ( % ) 303 ( 28.1)144 ( 26.8)159 ( 29.4)nyha class , n ( % )  i59 ( 5.5)31 ( 5.8)28 ( 5.2 )  ii464 ( 43.1)226 ( 42.1)238 ( 44.1 )  iii487 ( 45.2)254 ( 47.3)233 ( 43.1 )  iv14 ( 1.3)5 ( 0.9)9 ( 1.7 )  unknown53 ( 4.9)21 ( 3.9)32 ( 5.9)nyha class , n ( % )  ii523 ( 48.6)257 ( 47.9)266 ( 49.3 )  iii501 ( 46.5)259 ( 48.2)242 ( 44.8 )  unknown53 ( 4.9)21 ( 3.9)32 ( 5.9)estimated bmi ( n = 1054)28.2 ( 4.9)28.1 ( 4.8)28.2 ( 5.1)lvef , n ( % )  < 20%101 ( 9.4)53 ( 9.9)48 ( 8.9 )  2030%566 ( 52.6)278 ( 51.8)288 ( 53.3 )  > 30%404 ( 37.5)204 ( 38.0)200 ( 37.0 )  not done6 ( 0.6)2 ( 0.4)4 ( 0.7)af at enrolment , n ( % ) 85 ( 7.9)45 ( 8.4)40 ( 7.4)indication for implantation , n / total n ( % )  primary prevention873/1067 ( 81.8)434/531 ( 81.7)439/536 ( 81.9 )  secondary prevention194/1067 ( 18.2)97/531 ( 18.3)97/536 ( 18.1)hospital stay ( days ) ( n = 1066)4.0 ( 4.0)4.0 ( 3.6)4.0 ( 3.8)medication , n ( % )  ace inhibitors / at receptor blockers , n ( % ) 986 ( 91.6)501 ( 93.3)485 ( 89.8 )  -blockers , n ( % ) 1007 ( 93.5)500 ( 93.1)507 ( 93.9 )  ca antagonists , n ( % ) 140 ( 13.0)74 ( 13.8)66 ( 12.2 )  spironolactones , n ( % ) 618 ( 57.4)302 ( 56.2)316 ( 58.5 )  ( other ) diuretics , n ( % ) 794 ( 73.7)395 ( 73.6)399 ( 73.9 )  nitrates , n ( % ) 75 ( 7.0)38 ( 7.1)37 ( 6.9 )  digitalis , n ( % ) 105 ( 9.7)54 ( 10.1)51 ( 9.4 )  lipid - lowering agents , n ( % ) 763 ( 70.8)377 ( 70.2)386 ( 71.5 )  amiodarone , n ( % ) 116 ( 10.8)61 ( 11.4)55 ( 10.2 )  dronedarone , n ( % ) 5 ( 0.5)4 ( 0.7)1 ( 0.2 )  sotalol , n ( % ) 9 ( 0.8)5 ( 0.9)4 ( 0.7 )  ( other ) anti - arrhythmics , n ( % ) 22 ( 2.0)9 ( 1.7)13 ( 2.4 )  platelet aggregation inhibitor , n ( % ) 753 ( 69.9)370 ( 68.9)383 ( 70.9 )  anti - coagulants , n ( % ) 350 ( 32.5)183 ( 34.1)167 ( 30.9 )  other cardiovascular medication , n ( % ) 255 ( 23.7)121 ( 22.5)134 ( 24.8)values are means  sd .
there were no significant differences at p < 0.05 between groups , except for ace inhibitors p = 0.039 .
t - test for metric variables , -test for categorical , or fisher 's exact test ( f ) if  is not appropriate.ace inhibitors , angiotensin converting enzyme inhibitors ; af , atrial fibrillation ; at receptor blockers , angiotensin receptor blockers ; bmi , body mass index ; df , defibrillation ; nyha , new york heart association ; itt , intention - to - treat ; lvef , left ventricular ejection fraction . 

table 2procedural characteristics according to treatment group ( successful primary implantable cardioverter - defibrillator implantation ; evaluated - for - safety)characteristictotal ( n = 1067)without df test ( n = 533)with df test ( n = 534)p - valueimplanted lead type , n ( % )  single coil516 ( 48.36)262 ( 49.16)254 ( 47.57)0.603  dual coil551 ( 51.64)271 ( 50.84)280 ( 52.43)type , n ( % )  single chamber icd466 ( 43.67)236 ( 44.28)230 ( 43.07)0.648  dual chamber icd245 ( 22.96)116 ( 21.76)129 ( 24.16 )  crt - d356 ( 33.36)181 ( 33.96)175 ( 32.77)left position , n ( % ) 1058 ( 99.16)527 ( 98.87)531 ( 99.44)0.341 ( f)vegm signal amplitude ( mv ) ( n = 1057)12.42 ( 5.30)12.72 ( 5.37)12.12 ( 5.21)0.065pacing threshold ( v ) at pulse duration of 0.4 ms ( n = 527)0.51 ( 0.20)0.49 ( 0.17)0.53 ( 0.22)0.040pacing threshold ( v ) at pulse duration of 0.5 ms ( n = 533)0.45 ( 0.23)0.45 ( 0.27)0.44 ( 0.17)0.613patients received df test , n ( % ) 527 ( 49.39)7 ( 1.31)520 ( 97.38)delivered icd shocks per patient0.71 ( 1.16)0.01 ( 0.11)1.41 ( 1.31)<0.001df energy at final position ( j ) ( n = 526)16.74 ( 4.47)16.67 ( 4.38)patients with intra - procedural system revisions and icd re - programming , n / total n ( % ) 25/527 ( 4.74)25/520 ( 4.81)patients with electrode repositionings , n / total n ( % ) 8/527 ( 1.52)8/520 ( 1.54)patients with changes of shock polarity , n / total n ( % ) 20/527 ( 3.80)20/520 ( 3.85)patients with modification of lead system ( shock pathway ) ,
n / total n ( % ) 5/527 ( 0.95)5/520 ( 0.96)patients with other revisions / re - programming , n / total n ( % ) 7/527 ( 1.33)7/520 ( 1.35)procedure duration ( min ) ( n = 1060)64.54 ( 39.88)63.11 ( 40.84)65.97 ( 38.88)0.243fluoroscopy exposure duration ( min ) ( n = 1056)8.02 ( 11.43)8.00 ( 11.44)8.05 ( 11.43)0.943crt - d , cardiac - resynchronization therapy with defibrillator ; df , defibrillation ; efs , evaluated for safety ; vegm , ventricular electrogram ; icd , implantable cardioverter-defibrillator.one patient was not inducible . 

itt , full analysis set ( all patients as randomized ) ; efs , evaluated for safety set ( all patients randomized , who had a successful primary icd implantation ) ; pps , per protocol set ( all patients randomized , who are compliant with the study protocol ) ; p - pps , all randomized patients at least one day at risk before protocol deviation ( includes all sufficiently documented shocked episodes until time point of protocol deviation ) .
baseline demographic and clinical characteristics of subjects by treatment group ( intention to treat ) values are means  sd .
there were no significant differences at p < 0.05 between groups , except for ace inhibitors p = 0.039 .
t - test for metric variables , -test for categorical , or fisher 's exact test ( f ) if  is not appropriate . ace inhibitors , angiotensin converting enzyme inhibitors ; af , atrial fibrillation ; at receptor blockers , angiotensin receptor blockers ; bmi , body mass index ; df , defibrillation ; nyha , new york heart association ; itt , intention - to - treat ; lvef , left ventricular ejection fraction .
procedural characteristics according to treatment group ( successful primary implantable cardioverter - defibrillator implantation ; evaluated - for - safety ) crt - d , cardiac - resynchronization therapy with defibrillator ; df , defibrillation ; efs , evaluated for safety ; vegm , ventricular electrogram ; icd , implantable cardioverter - defibrillator .
itt , full analysis set ( all patients as randomized ) ; efs , evaluated for safety set ( all patients randomized , who had a successful primary icd implantation ) ; pps , per protocol set ( all patients randomized , who are compliant with the study protocol ) ; p - pps , all randomized patients at least one day at risk before protocol deviation ( includes all sufficiently documented shocked episodes until time point of protocol deviation ) .
of the 534 patients randomized to the df arm with a successful first icd implantation ( figure 1 ) , testing was performed in 97.4% . in one patient , vt / vf was not inducible .
four hundred and ninety - four of 519 inducible patients ( 95.2% ) passed the test without any system reconfiguration , and 440 patients ( 84.8% ) had their vt / vf terminated with a 15 j shock . in 25 patients ,
the initial df test was not successful , and system reconfigurations were performed once in 20 and more than once in 5 ( table 2 ) .
all patients subsequently passed the test successfully , but still with a higher energy level at the final position ( 22.2  7.4 j vs. 16.4  4.0 j , p < 0.001 ) and with significantly more shocks ( 5.7  3.0 vs. 1.2  0.7 , p < 0.001 ) than the 494 patients who passed the test immediately .
in addition , the duration of the procedure ( 90.2  56.2 min vs. 63.5  36.1 min , p < 0.001 ) and fluoroscopy exposure ( 11.6  14.2 min vs. 7.5  10.7 min , p = 0.064 ) was increased .
during a median follow - up of 22.7 and 22.9 months , respectively , 211 true vt / vf episodes with at least one appropriate shock occurred in 8.6% of the per protocol patients with df testing , while 218 true vt / vf episodes occurred in 8.8% of patients without df testing ( table 3 , figure 1 ) .
all true vt / vf episodes were terminated with any appropriate icd shock in the without df test group , whereas 96.7% of all vt / vf were terminated in the group with df test .
thus , the conversion efficacy was 100.0% without df testing and 96.7% with df testing .
the model - based shock efficacy was 97.1% without df testing and 94.1% with df testing .
the difference in fse was 3.0% ( ci 3.0% , 9.0% ) in favour of the without df test group , and remained above the pre - defined 10% margin for the primary end point ( pnon - inferiority < 0.001 , table 3 , figure 2 ) . 

table 3primary analysis  shock efficacy ( per protocol episode data set)totalwithout df testwith df testall patients with at least one delivered appropriate shock for a true vt / vf episode , n / total n ( % ) 91/1046 ( 8.7)46/523 ( 8.8)45/523 ( 8.6)all true vt / vf episodes with at least one delivered appropriate icd shock ( vt / vf ) , n429218211delivered appropriate shocks per true vt / vf episode ( mean ( sd))1.18 ( 0.69)1.09 ( 0.37)1.28 ( 0.90)true vt / vf episodes terminated with first appropriate icd shock , n / total n ( % ) 384/429 ( 89.5)204/218 ( 93.6)180/211 ( 85.3)true vt / vf episodes terminated with any appropriate icd shock , n / total n ( % ) 422/429 ( 98.4)218/218 ( 100.0)204/211 ( 96.7)true vt / vf episodes not terminated with any appropriate icd shock , n / total n ( % ) 7/429 ( 1.6)0/218 ( 0.0)7/211 ( 3.3)conversion efficacy [ proportion ( 95% ci)]0.98 ( 0.97;0.99)1.00 ( 0.98;1.00)0.97 ( 0.93;0.99)first shock efficacy model based [ proportion ( 95% ci)]0.96 ( 0.89;0.98)0.97 ( 0.91;0.99)0.94 ( 0.83;0.98))difference between the groups ( without df testing vs. with df testing ) : 0.03 ( 0.03;0.09).df , defibrillation ; icd , implantable cardioverter - defibrillator ; p - pps , per protocol episode data set ; vt / vf , ventricular tachycardia / ventricular fibrillation . 
 figure 2primary outcome in the per protocol population
. primary analysis  shock efficacy ( per protocol episode data set ) difference between the groups ( without df testing vs. with df testing ) : 0.03 ( 0.03;0.09 ) .
df , defibrillation ; icd , implantable cardioverter - defibrillator ; p - pps , per protocol episode data set ; vt / vf , ventricular tachycardia / ventricular fibrillation .
a total of 201 serious adverse events related to the study procedure occurred in 168 patients ( 15.7% ) , of which 89 events occurred in 74 patients without df testing and 112 events occurred in 94 patients with df testing within 30 days of follow - up ( p = 0.095 ) .
the only significant difference in single serious adverse events was intra - operative hypotension , which manifested more often in patient with df testing ( 1.7% ) than those without df testing ( 0.0% ) ( p = 0.004 ) .
lead - related complications occurred in 15 patients without df testing ( 2.8% ) compared with 24 events in 21 patients with df testing ( 3.9% ) ( p = 0.311 ) .
one sudden death occurred in each study group within 30 days of follow - up , and the mean length of hospitalization was 4.0 days in both study groups ( table 1 ) .
the proportion of patients with inappropriate shocks during follow - up was low at 3.7% , and similar between groups .
forty - four and 52 patients without and with df testing died , respectively ( p = 0.377 , table 4 ) . differences with respect to non - cardiac and cardiac mortality were not statistically significant .
six deaths ( 5 with df and 1 without df testing ) were adjudicated arrhythmic and due to repetitive ventricular tachyarrhythmias / vt clusters ( p = 0.100 , table 4 ) . 

table 4mortality ( intention - to - treat)outcomeeventsincidencelog rank95% ciwithout df test ( n = 537)with df test ( n = 540)without df testwith df testp - valuehrlowerupperall - cause mortality44 ( 8.2%)52 ( 9.6%)0.0440.0530.3770.8350.5591.248non - cardiac mortality24 ( 4.5%)23 ( 4.3%)0.0240.0230.9071.0350.5841.833unknown ( primary organ cause)6 ( 1.1%)10 ( 1.9%)0.0060.010.3060.5930.2161.632cardiac mortality14 ( 2.6%)19 ( 3.5%)0.0140.0190.3500.7210.3611.438arrhythmic mortality1 ( 0.2%)5 ( 0.9%)0.0010.0050.1000.1980.0231.694non - arrhythmic mortality13 ( 2.4%)13 ( 2.4%)0.0130.0130.9480.9750.4522.103unknown cardiac mortality0 ( 0.0%)1 ( 0.2%)00.001df , defibrillation ; hr , hazard ratio ; itt , intention to treat.incidence referring to person - years without df test ( 1001.5 ) and with df test ( 985.9 ) . mortality ( intention - to - treat ) df , defibrillation ; hr , hazard ratio ; itt , intention to treat . incidence referring to person - years without df test ( 1001.5 ) and with df test ( 985.9 ) .
defibrillation testing during icd implantation has been a matter of debate for the last two decades . to the best of our knowledge ,
the nordic icd trial is the first prospective randomized trial , which investigated the effect of df testing on the actual fse during follow - up as the single primary end point .
this is in contrast with the recently published simple trial , which used the composite outcome of arrhythmic death or failed appropriate shock to terminate a spontaneous episode of vt / vf to determine the non - inferiority of the no testing approach .
nordic icd also provides detailed information about intra - operative df testing outcome . in 9196% of icd implants ,
system modifications were reported in 2.212.0% of patients . with the high - energy devices used in the nordic icd study , only 4.8% of all inducible patients had an inadequate safety margin , which required one or two system reconfigurations in 3.8 and 1.0% , respectively .
this is in agreement with the results of the sudden cardiac death in heart failure trial ( scd - heft ) , in which 97.8% of patients had a df threshold 20 j. following the system revisions , all patients passed the test successfully , but with a significantly higher energy level than for those who did not require revision ( 22.2 j vs. 16.4 j , p < 0.001 ) .
this is in agreement with a canadian survey in which an insufficient safety margin with the initial system configuration could be improved in only 56% of patients .
while the device revisions provided no benefit to our patients during follow - up , they significantly increased the total procedure time by 30 min and the fluoroscopy exposure by 40% .
the mean number of shocks needed to find an acceptable safety margin was also increased more than four - fold .
however , in a trial with variable use of devices , the shock efficacy is similar to that observed in the nordic icd trial .
the observed lower rate of arrhythmic death for patients without df testing ( 0.2 vs. 0.9% ) corresponds to the sudden cardiac death rate reported in another trial ( 0.9 and 1.2% in patients without and with df testing ) during a similar follow - up period . because the simple trial did not use a specific model for multiple shock events in the same patient ,
the shock efficacy can only be compared at the level of raw shock efficacy . in the nordic icd and the simple trials ,
a higher raw shock efficacy was observed in the group without df vs. with df testing ( nordic icd : 93.6 vs. 85.3% and simple : 92.0 vs. 88.5% ) . on the other hand
, the higher first shock energy we used ( 40 j vs. 31 j in simple ) was not associated with a higher fse irrespective of testing .
the high level of fse is consistent with the relatively low mean df energy ( 16.7 j ) during testing , with > 95% of the inducible patients undergoing successful testing without any system reconfiguration .
a 15.7% serious adverse events rate ( 17.6% with testing and 13.9% without testing , p = 0.095 ) was found within 30 days following successful icd implantation .
this is much higher than what has been described in recent reports , in which the complication rates ranged between 2.3 and 2.7% in patients with and without an adequate safety margins during df testing or compared with the simple trial results regarding adverse events included in the pre - defined as the primary safety outcome ( 5.6% without df testing vs. 6.5% with df testing ) .
it is noteworthy that the nordic icd trial not only collected data on protocol - specified complications but also on all procedure- and patient - related adverse events which might explain our higher event rate .
the 30-day procedure - related mortality rate was 0.2% , and consisted of two sudden deaths which is in the range of recent reports .
the stroke rate was 0.8% for patients without and 0.2% for patients with df testing ( p = 0.217 ) , which is in agreement with the 0.4% rate reported in the credit registry .
the two types of adverse events that were increased in patients with df testing were intra - operative hypotension ( 1.7% vs. 0.0% , p = 0.004 ) and lead - related complications ( 3.9 vs. 2.8% , p = 0.311 ) . a recent article summarized implant - related complications that were directly or indirectly related to the df testing procedure .
the rate of haemodynamic complications was 1% , and lead dislodgement was listed as the most frequent single complication with rates between 1 and 6% .
both the nordic icd and simple trials showed a trend towards lower procedural complication rates in patients without df testing despite the different definitions and methods used for analysing these events ( nordic icd : 13.9 vs.17.6% , p = 0.095 , simple : 5.6 vs. 6.5% , p = 0.33 ) .
the rates of all - cause , cardiac , and non - cardiac mortality were similar between patients with and without df testing , which is in agreement with most non - randomized trials reported . in accordance with the simple trial , no statistical difference in all - cause mortality between patients with and without df testing
however , the annual mortality rates of nordic icd were lower when compared with other large randomized icd trials , and also lower than those of the simple trial .
the nordic icd trial supports the hypothesis that if 40 j devices are used , df testing does not improve df efficacy during follow - up .
it suggests that df testing or the various measures to improve df efficacy lengthen the procedure , and may even be harmful .
the nordic icd trial is one of two large prospective randomized trials , which do not support the routine use of df testing during left - sided first time icd implantation .
this work was supported by biotronik se & co. kg ( berlin , germany ) . funding to pay
reports receiving grants and personal fees form medtronic , st jude medical , biosense , biotronik , and boston scientific during the conduct of the study , and grants and personal fees from biosense and biotronik outside of the submitted work .
reports receiving grants , personal fees , and non - financial support from biotronik during the conduct of the study , and personal fees and non - financial support from boehringer ingelheim outside the submitted work .
reports personal fees from biotronik during the conduct of the study , and grants from st jude medical and personal fees from boston scientific outside the submitted work .
 aimsthis trial was designed to test the hypothesis that shock efficacy during follow - up is not impaired in patients implanted without defibrillation ( df ) testing during first implantable cardioverter - defibrillator ( icd ) implantation.methods and resultsbetween february 2011 and july 2013 , 1077 patients were randomly assigned ( 1 : 1 ) to first time icd implantation with ( n = 540 ) or without ( n = 537 ) df testing . 
 the intra - operative df testing was standardized across all participating centres , and all icd shocks were programmed to 40 j irrespective of df test results . 
 the primary end point was the average first shock efficacy ( fse ) for all true ventricular tachycardia and fibrillation ( vt / vf ) episodes during follow - up . 
 the secondary end points included procedural data , serious adverse events , and mortality . during a median follow - up of 22.8 months 
 , the model - based fse was found to be non - inferior in patients with an icd implanted without a df test , with a difference in fse of 3.0% in favour of the no df test [ confidence interval ( ci ) 3.0 to 9.0% , pnon - inferiority < 0.001 for the pre - defined non - inferiority margin of 10% ) . a total of 112 procedure - related serious adverse events occurred within 30 days in 94 patients ( 17.6% ) tested compared with 89 events in 74 patients ( 13.9% ) not tested ( p = 0.095).conclusiondefibrillation efficacy during follow - up is not inferior in patients with a 40 j icd implanted without df testing . 
 defibrillation testing during first time icd implantation should no longer be recommended for routine left - sided icd implantation . 
Introduction
Methods
Trial design and oversight
Intra-operative testing
End points
Statistical analysis
Results
Study population
Intra-operative testing
Shock efficacy
Serious adverse events
Mortality
Discussion
Conclusion
Supplementary material
Funding