[Hemodynamic benefits of AV interval adjustment and heart rate increase during exercise in dual-chamber pacing as determined by Doppler].

In order to determine the relative significance of ventricular rate increase and AV delay on exercise cardiac output, we have studied 10 patients (8 male and 2 female, 16-59 years) with complete chronic heart block treated with AV sequential pacing. Cardiac output variations (delta CO) were estimated by pulsed Doppler comparisons of the aortic flow velocity in the supine position, at rest and during bicycle exercise. The following pacing programs were tested: DDD with AV intervals of 50, 100 and 150 ms (DDD50 o DDDD100, DDD150), VVI at 70 ppm (VVI70), and VVI at the maximal available rate in this pacing mode-113 or 130 ppm depending on the PM type (VVIM). Exercise measurements in DDD mode were taken when that rate was reached. The delta CO was calculated as a percent change of the product flow velocity integral x heart rate, from that obtained with VVI70 mode at rest. At rest, the delta CO obtained with DDD pacing was 20.4 +/- 14.7% and the optimal AV delay was 50 ms in 1 patient, 100 ms in 3 patients and 150 ms in six. During exercise, the delta CO was higher in DDD and VVIM modes (82.0 +/- 30.8% and 56.2 +/- 37.6%, respectively; p less than 0.01) than in VVI70 mode (20.4 +/- 10.4%; p less than 0.005), the greatest delta CO was reached at DDD mode in 8 out of 10 patients (p less than 0.03). The optimal AV delays were 50 ms in 5 patients, 100 ms in 4 patients and 150 ms in one. Thus, DDD pacing with the optimal AV delay seems to obtain greater haemodynamic benefits during exercise than does rate-responsive pacing; the optimal exercise AV delay varies from patient to patient and is usually less than 150 ms.