Comparison of low rate dual chamber pacing to activity responsive rate variable ventricular pacing

A study was undertaken to evaluate exercise performance in 18 dual chamber pacemaker patients believed to be chronotropically incompetent. All patients were paced in a DDD AV synchronous mode at 80 beats per minute (beats/min) as well as an externally triggered, activity responsive VVIR mode. Patients underwent two single blind, randomized symptom-limited treadmill tests (Sheffield protocol). Four of the 18 patients achieved intrinsic rates greater than 100 beats/min and were deleted from the primary study. It was noted that all four of these patients performed best with intrinsic rate response and AV synchrony. Thirteen of the remaining 14 patients demonstrated improved exercise tolerance in the VVIR mode. Average exercise time in the VVIR mode (7:25 +/- 3:12 min) was significantly greater (P less than 0.05) than the DDD mode (6:01 +/- 2:27 min). Work performed was significantly greater (P less than 0.05) in the VVIR mode (4.77 +/- 1.97 METS) than in the DDD mode (3.78 +/- 0.77 METS). Maximum heart rates were 83.86 +/- 5.11 beats/min in DDD mode versus 116.00 +/- 10.56 beats/min in VVIR mode. The results demonstrated that improved exercise tolerance can be achieved with single chamber rate variable pacing compared to DDD pacing in patients with chronotropic incompetence. However, potential symptoms associated with loss of AV synchrony should be ruled out.