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Ventricular pacing at or near the upper rate limit of the pacemaker is evident on electrocardiography (ECG). The presence of a paced rhythm exactly at the upper rate limit with atrial sensing and exact A-V association warrants evaluation for pacemaker-mediated tachycardia (PMT).
A Holter monitor or event recorder also shows ventricular pacing at or near the upper rate limit and the initiation of the episodes. In the differential diagnosis of PMT, sinus and tracked atrial tachyarrhythmias must be considered. Monitoring of episodes, their initiation, and termination will help arrive at a diagnosis.
Telemetered intracardiac electrograms obtained through the pacemaker programmer generally indicate the diagnosis.
Media Gallery
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Pacemaker-Mediated Tachycardia. Telemetered ECG tracing with surface lead II (top) and intracardiac electrograms (atrial electrogram [center] and ventricular electrogram [lower]) and marker channel (bottom) showing pacemaker-mediated tachycardia (PMT). The intracardiac markers indicate that the retrograde P waves, labeled AS for atrial-sensed event, occur 280 milliseconds after the ventricular-paced beats, labeled VP.
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Pacemaker-Mediated Tachycardia. Telemetered ECG tracing showing atrioventricular (AV)–paced rhythm at 60/min after termination of the pacemaker-mediated tachycardia (PMT). The tracing, from top to bottom, shows lead II, atrial electrogram, ventricular electrogram, and marker channels. The intracardiac markers indicate the rhythm is atrial paced (AP) and ventricular paced (VP). Note that the VP beats are ventricular pseudofusion beats.
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Pacemaker-Mediated Tachycardia. This is a typical example of PMT with ventricular pacing at maximum tracking rate (VP-MT) and then termination of the tachycardia as the atrial sensing (AS) is in the postventricular atrial refractory period (PVARP). This is due to PVARP extension, which is a feature of this particular pacemaker. The solid line indicates where PMT is detected and this is the point at which PVARP extension occurs. As this electrogram was detected, but not sensed to be acted upon, the ventricular tracking stopped and the tachycardia terminated. In some cases, pacemakers have a program to lengthen the PVARP after PMT detection to potentially stop the tachycardia. Alternatively, prevention of one ventricular paced beat can also stop the tachycardia. Some pacemakers use this algorithm.
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