A rate-responsive pacemaker controlled by right ventricular blood temperature.

To demonstrate the capabilities of a rate-responsive pacemaker controlled by right ventricular blood temperature, a prototype pacemaker was developed and tested in dogs with complete atrioventricular (AV) block. Using a previously obtained data base of right ventricular blood temperature recorded both during rest and during treadmill exercise from dogs with either induced AV block or normal AV conduction, a control algorithm which identified periods of exercise was developed. This algorithm was implemented in a microprocessor-based, rate-responsive pacemaker which generates two pacing rates: a basal rate (86 bpm) during rest and a higher rate (113 bpm) during moderate exercise. With repeated trials of submaximal treadmill exercise (2.25, 3.0, 5.0 mph, 16% grade) the pacemaker correctly detected the onset and cessation of exercise with latencies ranging from 35 to 124 seconds. Pacemaker rate increase latency decreased as the exercise level was increased. Pacemaker response latency was not affected by the choice of resting or exercise pacing rate. These preliminary data indicate that right ventricular blood temperature can provide a reliable index to control pacemaker rate. An implantable temperature-controlled pacemaker using this algorithm is presently under long-term evaluation in dogs performing untethered exercise.