How Can Right Ventricular Function Be Optimized During Cardiac Resynchronization Therapy?
Sites and sequence for Cardiac Resynchronization Therapy (CRT) which yield optimal cardiac functions, and effects on right ventricular (RV) function, are unknown. This study was determined the pacing site(s) and interventricular delay(s) that produce maximal RV function in normal dogs. The right atrium (RA) was paced at 120 bpm in 6 healthy dogs to measure the effects with a physiologic activation sequence. For single-site pacing (SSP), 1 of 2 RV sites (apex and base) or 1 of 5 left ventricular (LV) sites (anterior and posterior base, anterior and posterior mid free-wall, and apex) were paced. For multi-site pacing (MSP), LV pacing was initiated by stimulating either 1 of 5 pacing sites or all 5 pacing sites simultaneously. RV function was assessed by dRVP/dtmax, and the shortest QRS duration, and compared to values during RA pacing alone. Values of dRVP/dtmax and QRS duration were compared (repeated measures ANOVA). With SSP, maximal dRVP/dtmax occurred with pacing the RV base alone (22% greater than RA pacing, but not statistically significant), and least with pacing LV apex alone (-34%, compare to RV base alone). With MSP, RV function was optimal with the longest interventricular delay (32 ms), and when pacing the RV base with any of the LV sites. QRS durations for all pacing sites were significantly longer compared to RA pacing. Conclusions: Optimizing LV contraction hinders RV contraction. RV function is optimized with increasing interventricular asynchrony. CRT can be optimized to improve RV function.