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Pacemaker-mediated Tachycardia — EECC MCQ

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HardArrhythmia & ElectrophysiologyPacemaker-mediated TachycardiaEECC

A 65-year-old man with a dual-chamber pacemaker set to DDD mode presents with palpitations. Telemetry shows a regular tachycardia at 120 bpm with paced ventricular complexes. The atrial channel shows retrograde P waves following each ventricular paced beat, which are then tracked by the pacemaker. What is this arrhythmia?

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Correct answer: E — Pacemaker-mediated tachycardia (PMT) — an endless loop tachycardia

Pacemaker-mediated tachycardia (PMT), also known as endless-loop tachycardia, is a re-entrant circuit unique to dual-chamber pacemakers in DDD mode. The circuit involves: (1) a ventricular paced beat conducts retrogradely to the atrium via the AV node or accessory pathway; (2) the atrial channel senses the retrograde P wave; (3) after the programmed AV delay, the pacemaker delivers a ventricular paced beat, completing the loop. The rate is limited by the upper tracking rate. Management includes applying a magnet (interrupts sensing), programming a PVARP (post-ventricular atrial refractory period) longer than the retrograde VA conduction time, or activating the PMT termination algorithm.

Reference: ESC (2021): Guidelines on Cardiac Pacing and CRT