Undesirable cardiac arrhythmias associated with rate hysteresis pacemakers.

The introduction of the ventricular inhibited pulse generator with the feature of rate hysteresis has been associated with a variety of rhythm disturbances, some causing serious concern. This pulse generator has two different pacing rates: (1) the automatic rate, which is the interval between two successive paced beats (usually 860 msec or 70/min), and (2) the hysteresis interval, which results in a 1,000 msec delay between a sensed cardiac contraction and the next pacemaker discharge. The hysteresis interval after a sensed signal may result in long pauses that may predispose to the development of serious cardiac arrhythmias. Two examples of this type of complication were recently observed. One patient had bigeminal rhythm with mechanically ineffective cardiac contractions and an effective cardiac rate of 35/min; he experienced dyspnea and weakness during these prolonged episodes. Another patient had repeated episodes of ventricular fibrillation. The cardiac arrhythmias were not controlled by antiarrhythmic agents, and both patients required replacement of the pulse generator. The proposed advantages of pulse generator hysteresis are (1) prolongation of battery life, and (2) maintenance of effective atrial transport; these advantages may be outweighed by undesirable cardiac arrhythmias that may be associated with this mode of pacemaker function. Rate hysteresis cardiac pacemakers should be reserved for patients having predominantly sinus rhythm without ventricular irritability. In patients with frequent ectopic ventricular activity, atrial fibrillation or high degree atrioventricular block, the rate hysteresis pacemaker offers no advantage over the conventional demand pacemaker. For patients with frequent ectopic ventricular activity not easily controlled by antiarrhythmic agents, consideration should be given to the use of a permanent demand pacemaker with external rate control, which may provide greater flexibility in arrhythmia management.