Adequacy of pacing rate during exercise in rate responsive ventricular pacing

Our objective was to determine the adequate pacing rate during exercise in ventricular pacing by measuring exercise capacity, cardiac output, and sinus node activity. Eighteen patients with complete AV block and an implanted pacemaker underwent cardiopulmonary exercise tests under three randomized pacing rates: fixed rate pacing (VVI) at 60 beats/min and ventricular rate-responsive pacing (VVIR) programmed to attain a heart rate of about 110 beats/min or 130 beats/min (VVIR 110 and VVIR 130, respectively) at the end of exercise. Compared with VVI and VVIR 130, VVIR 110 was associated with an increased peak oxygen uptake (VVIR 110: 20.3 +/- 4.5 VVI: 16.9 +/- 3.1; P < 0.01; and VVIR 130: 19.0 +/- 4.1 mL/min per kg, respectively; P < 0.05 and a higher oxygen uptake at anaerobic threshold (15.3 +/- 2.7, 12.7 +/- 1.9; P < 0.01, and 14.6 +/- 2.6 mL/min per kg; P < 0.05). The atrial rate during exercise expressed as a percentage of the expected maximal heart rate was lower in VVIR 110 than in VVI or VVIR 130 (VVIR 110: 75.9% +/- 14.6% vs VVI: 90.6% +/- 12.8%; P < 0.01; VVIR 110 vs 130: 89.1% +/- 23.1% P < 0.05). There was no significant in cardiac output at peak exercise between VVIR 110 and VVIR 130. We conclude that a pacing rate for submaximal exercise of 110 beats/min may be preferable to that of 130 beats/min in respect to exercise capacity and sympathetic nerve activity.