Activity-sensing, rate-responsive pacing: improvement in myocardial performance with exercise.

A sensor that detects body activity by low frequency sonic impulses has been incorporated in a pacemaker so that body activity may be translated to an increased pacing rate in response to exercise. The pacemaker is designed for patients who may benefit from an increased cardiac output mediated by an increased heart rate during exercise. Following permanent pacemaker implantation, six patients (mean age 69 years) entered a single blind, randomized, crossover trial for comparison of activity-sensing, rate-responsive pacing (A) to fixed rate demand pacing (D). Ventricular function was assessed by gated radionuclide ventriculography at rest and at exercise, while exercise capacity was assessed by treadmill performance, along with measurements of oxygen consumption and carbon dioxide production. Total treadmill duration and maximum oxygen consumption were similar in the two pacing modes (A = 284 +/- 244 s, 13.4 +/- 3.4 ml O2/min/kg; D = 256 +/- 250 s, 11.7 +/- 3.7 ml O2/min/kg). Anaerobic threshold, however, was significantly improved (A = 266 +/- 199 s, (p less than .05), 13.0 +/- 2.2 ml O2/min/kg (p less than .01); D = 231 +/- 208 s, 10.8 +/- 2.3 ml O2/min/kg).(ABSTRACT TRUNCATED AT 250 WORDS)