Effects on the timing of left ventricular pressure rise when pacing the right ventricular free wall in cardiac resynchronization therapy

FUNDING ACKNOWLEDGEMENTS: Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Norwegian Research Council. BACKGROUND/INTRODUCTION: The timing of left ventricular pressure rise (Td) is associated with dispersion of regional work distribution and prolongs with dyssynchrony and dyssynergistic contractions. Synergistic contractions shorten Td and result from effective biventricular pacing (BIVP). Attempts have been made to optimize right ventricular (RV) lead position with septal lead placement away from the apex. In this study we attempted to study the effects from RV free wall (RVfw) compared to septal/ apical RV (RVsept) lead positioning on Td. PURPOSE: RVfw pacing results in activation of RVfw before LV activation with a delay that may hamper the myocardial synergy resulting from biventricular pacing. This effect has not yet been demonstrated and may play an important role to understand non-response to CRT. METHODS: 9 mongrel dogs were included in the study and handled according to ethics committee approved protocol/GLP. Pacing electrodes were placed epicardial on the left atrial appendage, the RVfw and LV, and endocardial in the septum. Pressure was measured with a Micro-tip pressure sensor (Millar Inc.) in the LV. BIVP was performed from LV combined with RVsept or RVfw. Td was measured from 10 consecutive beats. Mixed models were utilized for the repeated measurements. RESULTS: The average Td with BiVP-RVfw, BIVP-RVsept and LV pacing only was 116ms (95% CI: 110, 122), 114ms (95% CI: 108, 120), and 118ms (95% CI: 112, 124) respectively (p<0.001). BiVP with RVsept shortened Td by 4.1 ms (95% confidence interval (CI): -5.3, -2.9, p<0.001), whereas BiVP with RVfw pacing location shorten Td by 1.8 ms (95% CI: -2.8, -0.8, p<0.001), compared to LVP. The SD from 10 beats was on average 0.8ms (range 0-1.6ms). CONCLUSION(S): Myocardial Synergy with shortening of Td compared to LV only pacing was demonstrated with BIVP regardless of RV position. The synergistic effect from BIVP is more pronounced with BIVP-RVsept than from BIVP-RVfw. RV lead position may play an important role in cardiac resynchronization therapy that can be revealed when measuring the time-course of LV pressure rise.