Exercise hemodynamic benefits of rate adaptive ventricular pacing

To investigate the exercise hemodynamic benefits of activity-sensing rate adaptive ventricular pacing (VVIR) over fixed rate pacing (VVI) mode.

Activity sensing rate adaptive pacemaker was implanted in 19 patients (13 males and 6 females, mean age 54.8 years) with bradycardia. All patients underwent symptom-limited upright bicycle exercise in VVIR and VVI pacing modes in random order after implantation. With electrocardiogram monitor and M-mode echocardiography, heart rate, stroke volume and cardiac output were measured at rest and at each stage of exercise.

All patients were pacemaker dependent, without any spontaneous heart rhythm throughout this study. In the activity sensing ventricular pacing mode, all patients achieved a significant increase in exercise duration compared to fixed rate ventricular pacing mode (mean +/- s, 437 +/- 45 vs 323 +/- 23sec; P < 0.01), with a mean maximum pacing rate of 113 +/- 23ppm. Although the cardiac output was significantly improved in both pacing modes (10.2 +/- 1.4L/min with VVIR and 7.5 +/- 1.1L/min with VVI), the maximum exercise cardiac output in VVIR was increased over VVI by 46% (P < 0.05). Additionally, the stroke volume was significantly increased by 50% or more at rest in VVI mode, but was relatively maintained in VVIR mode (P > 0.05).

Rate adaptive ventricular pacing can significantly improve the exercise capacity and cardiac output in patients with bradycardia. The increment of exercise cardiac output in VVIR mode is mainly dependent upon the pacing rate during exercise.