the effect of cardiac resynchronisation therapy ( crt ) in patients with heart failure without left bundle branch block ( lbbb ) is disputable . we present a case of a patient with rate - dependent lbbb .
a 55-year - old woman with dilated cardiomyopathy , a left ventricular ( lv ) ejection fraction of 32% ( bloodpool radionuclide scintigraphy ) and new york heart association class iii despite optimal pharmacological therapy was referred for crt device implantation .
a 24-h electrocardiogram registration showed complete lbbb that disappeared at slower heart rates between 70 and 80  bpm ( fig .  1 ) .
since lbbb was present for the vast majority of the time , the patient was accepted for crt implantation according to current guidelines .
echocardiography during narrow qrs showed a dilated left ventricle without visual signs of dyssynchrony , normal interventricular mechanical delay ( 18  ms ) and no lv intraventricular dyssynchrony ( septal to lateral strain delay 53  ms ) or atrioventricular ( av ) dyssynchrony . 

112-lead surface electrocardiogram during normal ventricular conduction and during left bundle branch block . a narrow qrs ( 90  ms ) , heart rate 67  bpm .
b wide qrs ( 160  ms ) with complete lbbb , heart rate 73  bpm 12-lead surface electrocardiogram during normal ventricular conduction and during left bundle branch block . a narrow qrs ( 90  ms ) , heart rate 67  bpm .
b wide qrs ( 160  ms ) with complete lbbb , heart rate 73  bpm the patient gave written informed consent for a study that was approved by the institutional ethics committee and complies with the declaration of helsinki . during implantation ,
paul , mn , usa ) was placed in the left ventricle to optimise the av delay by measurement of the maximum rate of lv pressure rise ( dp / dtmax ) .
the leads were implanted transvenously in the right ventricular outflow tract , right atrial appendage , and in a coronary sinus tributary on the midposterolateral lv free wall .
pacing leads , pressure recording , and 12-lead surface electrocardiogram were connected to an external pacing and data acquisition computer ( flexstim ii , boston scientific corp . , st.paul , mn , usa ) . the custom - made stimulation protocol consisted of cycles of six beats of atrio - biventricular pacing separated by periods of 14 beats of atrial pacing ( aai , baseline ) .
this cycle was repeated with biventricular pacing without atrial pacing ( vdd ) , separated by periods of no pacing ( sinus rhythm , baseline ) .
each cycle with one of four av delays ( 20% , 40% , 60% , and 80% of intrinsic av conduction time ) was repeated four times in random order .
the optimal av delay was defined by the highest relative increase in dp / dtmax compared with baseline .
complete lbbb was present during aai pacing at 85  bpm ( qrs 160  ms , interventricular delay 130  ms on intracardiac electrograms ) . during sinus rhythm ( 75  bpm )
there was no lbbb ( qrs 90  ms , interventricular delay 60  ms ) .
lbbb caused a sudden decline in average baseline dp / dtmax from 820    75 to 662    52  mmhg / s ( p  <  0.001 , paired t test ; fig . 
optimised crt did not change dp / dtmax compared with baseline ; crt with short av delay worsened dp / dtmax ( fig . 
2acute haemodynamic response to cardiac resynchronisation therapy ( crt ) during left bundle branch block ( lbbb ) and normal ventricular activation .
a absolute lv dp / dtmax values at baseline ( no crt ) and during crt with four different av delays .
b relative increase in lv dp / dtmax during crt compared with baseline without crt . mean    standard error are shown .
squares narrow qrs , diamond lbbb , avi intrinsic atrioventricular interval , av delay atrioventricular delay acute haemodynamic response to cardiac resynchronisation therapy ( crt ) during left bundle branch block ( lbbb ) and normal ventricular activation
. a absolute lv dp / dtmax values at baseline ( no crt ) and during crt with four different av delays .
b relative increase in lv dp / dtmax during crt compared with baseline without crt . mean    standard error are shown .
squares narrow qrs , diamond lbbb , avi intrinsic atrioventricular interval , av delay atrioventricular delay
lv dp / dtmax is a measure of systolic function that can reflect acute haemodynamic improvement achieved by crt [ 35 ] . in this case ,
acute decrease in haemodynamic function by induction of lbbb was previously shown in a preclinical model .
systematic human research about the effect of crt during both conditions within the same patient is difficult since data before onset of lbbb are often lacking . in the absence of lbbb , biventricular pacing
, crt also failed to improve quality of life and functional and echocardiographic parameters in heart failure patients with qrs < 130  ms and mechanical dyssynchrony . in this case ,
crt with a short av delay worsened dp / dtmax , which can be explained by impaired diastolic filling : advanced ventricular contraction causes premature mitral valve closure and thereby premature ending of atrial contraction ( a wave truncation ) . during lbbb ,
biventricular pacing increased dp / dtmax by 20% ; it was thereby almost restored to the baseline level during normal ventricular conduction .
crt is only effective during lbbb , and may have an adverse effect during normal intrinsic ventricular depolarisation . a rate - adaptive av delay that is long at slow heart rates and shortens quickly when the heart rate increases to around 75  bpm would promote predominantly intrinsic depolarisation during narrow qrs , and predominantly biventricular pacing during lbbb .
however , most currently available crt - d devices do not have this programming option . since the heart rate was above the critical value during the majority of the time , one could argue that the crt - d can be programmed according to usual practice in patients with permanent lbbb .
the presence of a rate - dependent lbbb demonstrated important basic crt principles : 
 induction of lbbb had a pronounced negative effect on cardiac function as reflected by an acute decrease in lv dp / dtmax;during lbbb , biventricular pacing almost completely restored lv dp / dtmax to baseline level during intrinsic normal ventricular conduction;biventricular pacing had no beneficial effect on lv dp / dtmax during normal ventricular conduction .
induction of lbbb had a pronounced negative effect on cardiac function as reflected by an acute decrease in lv dp / dtmax ; during lbbb , biventricular pacing almost completely restored lv dp / dtmax to baseline level during intrinsic normal ventricular conduction ; biventricular pacing had no beneficial effect on lv dp / dtmax during normal ventricular conduction .
 a 55-year - old woman with dilated cardiomyopathy and rate - dependent left bundle branch block had a cardiac resynchronisation therapy ( crt ) device implanted . during implantation 
 , the maximum rate of left ventricular pressure rise ( dp / dtmax ) was measured invasively . 
 this case presents a description of the acute negative effect of a left bundle branch block on dp / dtmax , and the different effect of crt on left ventricular haemodynamic function in the presence and absence of a left bundle branch block . 
Case Report
Discussion
Conclusions