Sympathetic nervous system response to dynamic exercise in complete AV block patients treated with AV synchronous pacing with fixed AV delay or with auto-AV delay.

To investigate the sympathetic nervous system (SNS) responses and circulatory responses to exercise in eight patients (five male and three female) with complete atrioventricular block (CAVB) treated with atrioventricular (AV) synchronous pacing, a symptom-limited, multistaged treadmill stress test was performed, and plasma norepinephrine (NE) and circulatory parameters were measured at rest, at peak exercise, and in the recovery period. The eight patients were tested using the fixed AV interval (150 or 156 msec). Their exercise tolerance was generally poor. In all measured points, plasma NE levels were significantly higher in the eight study patients than those in the 12 normal subjects (eight male and four female). Systolic blood pressure (SBP) of CAVB patients elevated significantly after exercise compared to that at peak exercise. Heart rate (HR) responses of CAVB patients were characterized by their poor increase at peak exercise. These results suggest that some latent cardiac dysfunction continues in the CAVB patients however satisfactorily the AV synchronous pacing might perform. AV synchronous pacing with three different kinds of auto-atrioventricular delay (auto-AVD) was applied to three of the eight patients. In each AVD mode, a treadmill stress test was performed repeatedly according to the same protocol. Plasma NE concentrations under the condition with fixed AVD at peak exercise increased compared to those under the other two conditions with auto-AVD. These findings suggest that AV synchronous pacing with auto-AVD was better than that with fixed AVD during exercise. Plasma NE response to exercise seems to be a useful indicator for evaluating the condition of patients treated with DDD pacemakers and their adaptation for cardiac function.