Fusion of electrical wave fronts in cardiac resynchronization therapy predicts response: an acute pressure-volume loop study

Abstract

Purpose: In cardiac resynchronisation therapy (CRT), the contribution of right ventricular (RV) stimulation to overall pump function remains controversial. Recent research suggests that in patients with left bundle branch block, eligible for CRT, optimal hemodynamic benefit can be obtained by fusion of the intrinsic (right bundle branch (RBB)) wave front and the invoked wave front of left ventricular (LV) pacing. RV stimulation would only be necessary in patients with long intrinsic AV-delays since in such cases fusion with the intrinsic RBB wave front would compromise optimal AV-delay. To evaluate this hypothesis, we conducted acute hemodynamic measurements in CRT patients with varying AV-delays during LV only and biventricular (Biv) pacing. Methods: Patients eligible to CRT were included. Prior to CRT implantation, patients underwent a temporary pacing procedure. Temporary leads were placed in the right atrium, RV and at the posterolateral wall, and a conductance catheter was used to acquire left ventricular pressure and volume data. Stroke work (SW) and dP/dtmax were used to assess acute hemodynamic response during RV, LV and Biv pacing. Pacing was performed with a fixed AV-delay of 100ms. Analyses were done for the total study population, as well as for a normal AV-delay and first degree AV-block group. Results: Fifty-seven patients were included (37 (65%) males, age 67±10 years, LVEF 22±13%, QRS 154±21ms, ischemic cardiomyopathy 35 (61%) patients, AV-delay 189±34ms, 18 (32%) first degree AV-block). A positive correlation was observed between AV-delay and SW response to LV only pacing (R2 = 0.08, p = 0.032). No correlation was found during Biv pacing nor in dP/dtmax response. No significant differences were found in SW and dP/dtmax response between LV only and biv pacing in the normal AV-delay group (mean 170±18ms) (ΔSW 35±45% vs 31±50%, p=0.415; Δ dP/dtmax 8±18% vs 12±25%, p=0.258, respectively) and the first degree AV-block group (mean 230±23ms) (ΔSW 45±43% vs 30±46%, p=0.124; Δ dP/dtmax 7±14% vs 5±27%, p=0.652, respectively). Conclusion: The present study revealed that a longer AV-delay was positively correlated with SW response during LV, possibly due to AV optimisation. No differences in acute hemodynamic response were found between both pacing modalities in the normal and first degree AV-block group, suggesting that wave front fusion either by biventricular pacing or by fusion of LV pacing and intrinsic conduction is of minor importance.