Abstract 3248: Left Ventricular Endocardial Asynchrony in Left Bundle Branch Block is Similar Between Simultaneous Biventricular Pacing and Single Site Left Ventricular Pacing
Introduction: Cardiac Resynchronization Therapy is generally considered to act through decreasing the electrical asynchrony by fusion of the activation wavefronts migrating from the left ventricular (LV) and right ventricular (RV) pacing electrodes. For the investigation of this idea, we used extensive mapping during left bundle branch block (LBBB), LV pacing (LVP) and biventricular pacing (BiVP).
Methods: In 6 anaesthetized dogs, LBBB was induced. Pacing was performed from 6 epicardial LV sites (ensuring full LV capture) all or not simultaneous with RV apex. Endocardial and epicardial activation were measured using LV non-contact mapping (EnSite®) and 108 epicardial (LV+RV) contact electrodes, respectively, enabling estimation of total activation time (TAT). The LV endocardial activation was quantified by the length and angle of the 2D activation delay vector (ADV) in the LV short axis. LV pump function was assessed as LV dP/dTmax.
Results: For all 36 measurements LVP increased TAT (108±16ms* vs. 93 ±6ms, *=p<0.05 vs. LBBB) whereas BiVP decreased it (86±9ms*#, #=p<0.05 vs. LVP). ADV-length was decreased by both LVP and BiVP (10±5ms (p=0.40) and 8±4ms*#) vs. LBBB (12±7ms). The angle of the ADV was not significantly different between LVP and BiVP (difference=30±31 degrees, p=0.44). The figure⇓ shows typical examples of LV short axis electical activation and vectors. LVP and BiVP increased LV dP/dTmax. by 12±8%* and 16±8%*# versus LBBB.
Conclusion: In these normal canine hearts the beneficial effect of BiVP on pump function seems to originate primarily from LV preexcitation. The activation wavefront from the RV lead creates only limited fusion with the wavefront from the LV lead.