Abstract 19550: Vectorcardiography Predicts the Optimal Hemodynamic Effect of Cardiac Resynchronization Therapy in Canine LBBB Hearts
Introduction: In cardiac resynchronization therapy (CRT) optimization of timing of left ventricular (LV) stimulation is often cumbersome. Previous studies in animals and patients showed that the optimal hemodynamic effect of CRT coincides with minimal electrical asynchrony as well as with mechanical interventricular asynchrony halfway between that during left bundle branch block (LBBB) and LV-pacing (LVP) at short atrioventricular delay (AVD). We hypothesized that the QRS vector amplitude reflects electrical interventricular asynchrony and can be used for optimization of timing of LV stimulation during CRT.
Methods: In 6 canine LBBB hearts the LV was paced at 7 sites per dog over a wide range of AVDs. Surface ECGs were recorded from the limb leads and the QRS vector amplitude was calculated in the frontal plane. Mechanical interventricular asynchrony was determined from the time delay between upslopes of LV and right ventricular pressure curves and LV pump function was assessed as LV dP/dtmax.
Results: As compared to LBBB, stepwise shortening of the AVD during LVP first decreased the QRS vector amplitude and subsequently increased it in the opposite direction (figure, panel A). For all pacing sites combined, a strong correlation was found between the QRS vector amplitude and mechanical interventricular asynchrony (r=0.92±0.10). The QRS vector amplitude halfway between LBBB and LVP at short AVD accurately predicted the AVD at which actual peak LV dP/dtmax was achieved (−3±27ms). The value of LV dP/dtmax achieved at the vectorcardiography (VCG)-predicted best AVD was -3.6±4.9% of the observed peak LV dP/dtmax (figure, panel B).
Conclusions: In canine LBBB hearts the QRS vector amplitude reflects electrical interventricular asynchrony and its halfway value accurately predicts the optimal hemodynamic effect. Therefore, VCG could provide a reliable and simple new tool for individual optimization of timing of LV stimulation in CRT.
- © 2010 by American Heart Association, Inc.