Choosing the stimulation rate in patients with intermittent bradycardia and a single lead pacemaker.

In order to assess the prevalence of intermittent bradycardia in a pacemaker population, we retrospectively evaluated the occurrence of intrinsic heart activity in 229 patients with ventricular pacing. Spontaneous heart activity was recorded in 60% of the patients. However, the stimulation rate had been decreased in only 40% of the patients in order to allow for longer periods of intrinsic heart activity. In the second part of the study we prospectively assessed differences in pacemaker utilization in 19 patients with intermittent bradycardia and single lead pacemakers. All patients were observed over four periods of 14 days, with the following pacing modes: 70 beats/min, 50 beats/min, hysteresis sensing 50 beats/min, and pacing 70 beats/min; and search hysteresis sensing 50 beats/min and pacing 70 beats/min. Search hysteresis pacing is a new feature that theoretically allows for a shorter time of pacing than that of hysteresis pacing. A reduction in the stimulation rate from 70 beats/min to 50 beats/min resulted in a 60% reduction in pacemaker utilization (P < 0.05). Search hysteresis decreased pacemaker utilization by 33% (P < 0.05). There was no statistical difference between conventional hysteresis and fixed rate pacing at 70 beats/min. Most patients found fixed rate pacing preferable to hysteresis pacing. In order to minimize battery consumption and to avoid unfavorable hemodynamics in patients with ventricular pacing, the stimulation mode and rate should be optimized in patients with intermittent bradycardia to allow for longer periods of intrinsic heart activity.