Optimized biventricular pacing in atrioventricular block after cardiac surgery.

BACKGROUND: Temporary pacing is required after open-heart surgery for treatment of heart block. Atrioventricular delay and ventricular pacing site might be manipulated to increase cardiac output. We hypothesized that by optimizing both atrioventricular delay and ventricular pacing site a 10% improvement in cardiac output would be observed compared with a standard pacing protocol.
METHODS: Seven patients in first or third degree heart block after valve replacement surgery had temporary wires sewn to the right atrium, right ventricle, and left ventricle. Cardiac output was measured by integrating flow velocity from an ultrasonic aortic flow probe. After optimization of atrioventricular delays during atrial synchronous right ventricular pacing, the effects of ventricular pacing site were tested at the optimum atrioventricular delay for 10-second intervals.
RESULTS: Biventricular pacing was beneficial in all patients with a mean increase of 22% in cardiac index over right ventricular pacing (1.95 L/min/m2 +/- 0.27 standard error of the mean (SEM) to 2.38 L/min/m2 +/- 0.27 SEM, p = 0.0012) and 14% over left ventricular pacing (2.08 L/min/m2 +/- 0.22 SEM to 2.38 L/min/m2 +/- 0.27 SEM, p = 0.0133). Comparing optimized with standard pacing for 30-second intervals yielded a mean increase of 10% in cardiac index over three respiratory cycles (2.87 L/min/m2 +/- 0.33 SEM to 2.60 L/min/m2 +/- 0.37 SEM, p = 0.009) and 17% at the corresponding end-expiratory beats (2.76 L/min/m2 +/- 0.33 SEM to 2.36 L/min/m2 +/- 0.36 SEM, p = 0.011).
CONCLUSIONS: Biventricular pacing at optimum atrioventricular delay improves cardiac output in patients with postoperative heart block by at least 10% compared with standard pacing.