Tachycardia-termination algorithm: a valuable feature for interruption of pacemaker-mediated tachycardia.

A 45-year-old man who had been implanted with a VVI pacemaker for sinus arrest complained of syncope, dizziness and throbbing in the neck. His pacemaker function was normal, but during ventricular pacing, retrograde V-A conduction was observed. This pacer was replaced by a DVI unit which caused periodic abdominal muscular contractions. We replaced this unit with an Intermedics Cosmos DDD-M pacemaker. This type of pacemaker in a patient with V-A conduction may cause pacemaker-mediated tachycardia (PMT). However, the Cosmos has a tachycardia-termination algorithm which detects continued pacing at the ventricular tracking rate, allows it to proceed for 15 consecutive pace events, and inhibits the 16th ventricular output pulse, thus breaking the reentry loop. The Cosmos pacer has a number of features to prevent initiation of PMT, and is also able to terminate the tachycardia when it occurs because of the tachycardia-termination algorithm. This feature is valuable in DDD-M pacemakers implanted in patients with V-A conduction. Whether this algorithm will be effective in all cases remains to be determined.