176-71: Insights into electrical delay between right and left ventricular leads in cardiac resynchronization therapy patients: effect of right ventricular pacing vs. normal sinus rhythm

Purpose: The nature and significance of electrical delay between right (RV) and left ventricular (LV) pacing leads are poorly understood. We evaluated differences in RV-LV electrical delay and LV activation pattern along a quadripolar LV lead during RV pacing (RVP) and normal sinus rhythm (NSR). Methods: Electrical delays between the RV and all 4 poles of the LV lead (D1, M2, M3, and P4, distal to proximal) were measured during RVP and NSR in 234 pts (73% male, 46% ischemic, QRS 155 ms, 68 ± 12 yrs) receiving a CRT implant with a quadripolar lead. The activation pattern was defined by the order of earliest to latest LV electrode activation, either sequential distal-to-proximal, or sequential proximal-to-distal, or non-sequential. Results: The average RV-LV electrical delay was significantly longer during RVP than NSR (each p ≤ 0.001, Fig A). The latest activating electrode was frequently D1 or P4 during both RVP (D1: 27%, P4: 51%) and NSR (D1: 30%, P4: 40%) (Fig B), while the earliest activating electrode was most frequently D1 for both RVP (61%) and NSR (56%) (Fig C). A non-sequential activation pattern was observed in 100/234 (43%) patients during RVP and 112/234 (48%) during NSR (Fig D). A difference in activation pattern between RVP and NSR was observed in 190/234 (81%) patients. RVP produced greater electrical delay between the latest and earliest activating LV electrodes than NSR (27 ± 21 vs. 21 ± 13 ms, p \u3c0.001). Conclusion: Activation pattern along a quadripolar LV lead was frequently different between RV pacing and normal sinus rhythm, with RV pacing producing greater delay between early and late sites. These results may have important implications for using conduction delays to optimize CRT programming with a quadripolar LV lead