ADEQUACY OF PACING RATE DURING EXERCISE IN RATE-RESPONSIVE VENTRICULAR PACING

Our objective was to determine the adequate pacing rate during exercis e in ventricular pacing by measuring exercise capacity, cardiac output , and sinus node activity. Eighteen patients with complete AV block an d an implanted pacemaker underwent cardiopulmonary exercise tests unde r three randomized pacing rates: fixed rate pacing (VVI) at 60 beats/m in and ventricular rate-responsive pacing (VVIR) programmed to attain a heart rate of about 110 beats/min or 130 beats/min (VVIR 110 and VVI R 130, respectively) at the end of exercise. Compared with VVI and VVI R 130, VVIR 110 was associated with an increased peak oxygen uptake (V VIR 110: 20.3 +/- 4.5 vs 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, a nd 14.6 +/- 2.6 mL/min per kg; P < 0.05). The atrial rate during exerc ise expressed as a percentage of the expected maximal heart rate was l ower 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 VVIR 130: 89.1% +/- 23.2% ; P < 0.05). There was no significant difference 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 th at of 130 beats/min in respect to exercise capacity and sympathetic ne rve activity.