HIGHER SYMPATHETIC-NERVE ACTIVITY DURING VENTRICULAR (VVI) THAN DURING DUAL-CHAMBER (DDD) PACING

Objectives. We determined the short-term effects of single-chamber ven tricular pacing and dual-chamber atrioventricular (AV) pacing on direc tly measured sympathetic nerve activity. Background. Dual-chamber AV c ardiac pacing results in greater cardiac output and lower systemic vas cular resistance than does single-chamber ventricular pacing, However, it is unclear whether these hemodynamic advantages result in less sym pathetic nervous system outflow. Methods. In 13 patients with a dual-c hamber pacemaker, we recorded the electrocardiogram, noninvasive arter ial pressure (Finapres), respiration and muscle sympathetic nerve acti vity (microneurography during 3 min of underlying basal heart rate and 3 min of ventricular and AV pacing at rates of 60 and 100 beats/min. Results, Arterial pressure was lowest and muscle sympathetic nerve act ivity was highest at the underlying basal heart rate. Arterial pressur e increased with cardiac pacing and was greater with AV than with vent ricular pacing (change in mean blood pressure +/- SE: 10 +/- 3 vs, 2 /- 2 mm Hg at 60 beats/min; 21 +/- 5 vs. 14 +/- 2 mm Hg at 100 beats/m in; p < 0.05), Sympathetic nerve activity decreased with cardiac pacin g and the decline was greater with AV than with ventricular pacing (60 beats/min -40 +/- 11% vs. -17 +/- 7%; 100 beats/min -60 +/- 9% vs, -4 8 +/- 10%; p < 0.05). Although most patients showed a strong inverse r elation between arterial pressure and muscle sympathetic nerve activit y, three patients with severe left ventricular dysfunction (ejection f raction less than or equal to 30%) showed no relation between arterial pressure and sympathetic activity, Conclusions. Short-term AV pacing results in lower sympathetic nerve activity and higher arterial pressu re than does ventricular pacing, indicating that cardiac pacing mode m ay influence sympathetic outflow simply through arterial baroreflex me chanisms, We speculate that the greater incidence of adverse outcomes in patients treated with single-chamber ventricular rather than dual-c hamber pacing may be due in part to increased sympathetic nervous outf low. (C) 1996 by the American College of Cardiology