Impacts of ventricular rate regularization pacing at right ventricular apical vs. septal sites on left ventricular function and exercise capacity in patients with permanent atrial fibrillation.

Aims: The deleterious effects of right ventricular apex (RVA) pacing may offset the potential benefit of ventricular rate (VR) regularization during atrial fibrillation (AF). Recent studies suggested that right ventricular septal (RVS) pacing may prevent the potential deleterious effects of RVA pacing and enhance the VR regularization (VRR) with ventricular pacing due to closer proximity of the pacing site to the retrograde atrioventricular conduction.

Methods And Results: We randomized 24 patients with permanent AF and symptomatic bradycardia to undergo RVA (n = 12) or RVS (n = 12) pacing. A VRR algorithm was programmed for all patients at 6-month after implantation. All patients underwent 6 min hall walk (6MHW) to assess exercise capacity at 6, 12, and 24 months, and radionuclide ventriculography to determine left ventricular ejection fraction (LVEF) at 6 and 24 months. Baseline characteristics were comparable in both groups except pacing QRS duration was significantly shorter during RVS pacing than RVA pacing (132 +/- 4 vs. 151 +/- 6 ms, P = 0.012). In both groups, VRR significantly increased the percentage of ventricular pacing and reduced VR variability (P < 0.05) without increasing mean VR (P > 0.05). At 6 months, 6MHW and LVEF were comparable in patients with RVA and RVS pacing (P > 0.05). At 24 months, patients with RVA pacing had significant decreases in LVEF and 6MHW after VRR pacing (P < 0.05), whereas RVS pacing with VRR preserved LVEF and improved 6MHW (P < 0.05).

Conclusion: In patients with permanent AF, VRR pacing at RVS, but not at RVA, preserves LVEF and provides incremental benefit for exercise capacity.