Optimized temporary biventricular pacing acutely improves intraoperative cardiac output after weaning from cardiopulmonary bypass: A substudy of a randomized clinical trial

Objective: Permanent biventricular pacing benefits patients with heart failure and interventricular conduction delay, but the importance of pacing with and without optimization in patients at risk of low cardiac output after cardiac surgery is unknown. We hypothesized that pacing parameters independently affect cardiac output. Accordingly, we analyzed aortic flow measured with an electromagnetic flowmeter in patients at risk of low cardiac output during an ongoing randomized clinical trial of biventricular pacing (n = 11) versus standard of care (n = 9). Methods: A substudy was conducted in all 20 patients in both groups with stable pacing after coronary artery bypass grafting, valve surgery, or both. Ejection fraction averaged 33% ± 15%, and QRS duration was 116 ± 19 ms. Effects were measured within 1 hour of the conclusion of cardiopulmonary bypass. Atrioventricular delay (7 settings) and interventricular delay (9 settings) were optimized in random sequence. Results: Optimization of atrioventricular delay (171 ± 8 ms) at an interventricular delay of 0 ms increased flow by 14% versus the worst setting (111 ± 11 ms, P < .001) and 7% versus nominal atrioventricular delay (120 ms, P < .001). Interventricular delay optimization increased flow 10% versus the worst setting (P < .001) and 5% versus nominal interventricular delay (0 ms, P < .001). Optimized pacing increased cardiac output 13% versus atrial pacing at matched heart rate (5.5 ± 0.5 vs 4.9 ± 0.6 L/min, P = .003) and 10% versus sinus rhythm (5.0 ± 0.6 L/min, P = .019). Conclusions: Temporary biventricular pacing increases intraoperative cardiac output in patients with left ventricular dysfunction undergoing cardiac surgery. Atrioventricular and interventricular delay optimization maximizes this benefit.