High value of right ventricular to left ventricular interlead electrical delay during right ventricular pacing predict favorable response in patients with cardiac resynchronization therapy

Introduction: Anatomical and electrical separation of left ventricular (LV) and right ventricular (RV) electrodes is significant for successful cardiac resynchronization therapy (CRT). During bi-ventricular pacing, the electrical activation was composed by RV and LV pacing wavefronts. So the region with latest activation during intrinsic rhythm might not correspond to the optimal pacing site during CRT. Hypothesis: We assess the hypothesis that interlead electrical delay measurements during RV and LV pacing besides intrinsic rhythm could predict favorable response to CRT. Methods and results: We evaluated 51 heart failure patients (age 64±13 years, LV ejection fraction 28±12%, QRS duration 155±37ms) who had successfully implanted CRT. The LV-RV interlead electrical delay (IED) during intrinsic rhythm, RV pacing (RV pacing-LV sensing: RVp-LVs) and LV pacing (LV pacing-RV sensing: LVp-RVs) were measured intraoperatively by utilizing intracardiac electrograms. After CRT implantation, 33 (65%) patients responded to CRT. The responders showed a significantly higher value of RVp-LVs compared with non-responders (166±42 vs. 141±36ms, respectively, p=0.04) and the absolute value of the difference between RVp-LVs and LVp-RVs was lower in responders than in non-responders (16±19 vs. 28±22ms, respectively, p=0.04). The IED during intrinsic rhythm (71±53 vs. 40±44ms, p=0.07) and LVp-RVs (170±47 vs. 146±35, p=0.06) showed higher tendency in responders, however they couldn't predict responders. Moreover, among narrow QRS patients (n=21; median QRS duration 118ms, 95 to 140ms), RVp-LVs was significantly higher in responders than in non-responders (159±32 vs. 121±32ms, p=0.01). Same as the entire cohort, the IED during intrinsic rhythm couldn't predict responders (59±24 vs. 35±36ms, p=0.11). At multivariate analysis, RVp-LVs was the only independent predictor of reverse remodeling in narrow QRS subgroup (p=0.03). Conclusion: Interlead electrical delay during intrinsic rhythm couldn't predict LV reverse remodeling after CRT. However high value of RVp-LVs measured intraoperatively was associated with favorable response irrespective of QRS width, which implies an optimal LV lead position during CRT implantation.