Delayed Trans-Septal Activation Results in Comparable Hemodynamic Effect of Left Ventricular and Biventricular Endocardial Pacing

Abstract

Background— We sought to compare left ventricular (LV epi ) and biventricular epicardial pacing (BIV epi ) with LV (LV endo ) and BIV endocardial pacing (BIV endo ) in patients with chronic heart failure with an emphasis on the underlying electrophysiological mechanisms and hemodynamic effects. Methods and Results— Ten patients with chronically implanted cardiac resynchronization devices underwent temporary LV endo and BIV endo pacing with an LV endocardial roving catheter. A pressure wire and noncontact mapping array were placed to the LV cavity to measure LVdP/dt max and perform electroanatomical mapping. At the optimal endocardial position, the acute hemodynamic response (AHR) was superior to epicardial stimulation, the AHR to BIV endo pacing and LV endo pacing being comparable (21±15% versus 22±17%; P =NS). During intrinsic conduction, QRS duration was 185±30 ms, endocardial LV total activation time 92±27 ms, and trans-septal activation time 60±21 ms. With LV endo pacing, QRS duration (187±29 ms; P =NS) and endocardial LV total activation time (91±23 ms; P =NS) were comparable with intrinsic conduction. There was no significant difference in endocardial LV total activation time between LV endo and BIV endo pacing (91±23 versus 85±15 ms; P =NS). Assessment of isochronal maps identified slow trans-septal conduction with both LV endo and BIV endo pacing resulting in activation of almost the entire LV endocardium prior to septal breakout, thereby limiting any possible fusion with either pacing mode. Conclusions— The equivalent AHR to LV endo and BIV endo pacing may be explained by prolonged trans-septal conduction limiting fusion of electrical wavefronts. The optimal AHR was associated with predominantly LV pre-excitation and depolarization. Our results suggest that LV pacing alone may offer a viable endocardial stimulation strategy to achieve cardiac resynchronization.