Comparative evaluation of rate modulated dual chamber and VVIR pacing.

While dual chamber pacing is considered superior to VVI pacing at rest, there is a continuing debate as to the relative benefit of AV synchrony versus rate increase with exercise. To evaluate this question and to correlate different methods of evaluation, 14 patients with DDDR pacemakers were studied using serial treadmill exercise test with a CAEP protocol. Patients were exercised in DDD, DDDR, and VVIR modes. Echo-Doppler cardiac outputs were determined and pulmonary gas exchange was measured during exercise. There was a significant improvement in cardiac output with exercise in the DDDR versus VVIR modes, and in DDDR versus DDD modes in patients with chronotropic incompetence. There were small increases in exercise duration in DDDR versus VVIR modes, and small but consistent increases in VO2 at all levels of exercise, though not statistically significant. In this group of patients, DDDR pacing was superior to VVIR pacing, and superior to DDD pacing when chronotropic incompetence was present.