skip to main content

Endless Loop Tachycardia — EECC MCQ

Instant feedback + full explanation. One question, done properly.

ModerateArrhythmia & ElectrophysiologyEndless Loop TachycardiaEECC

A 68-year-old man with a dual-chamber pacemaker for SSS develops a new regular tachycardia at the upper tracking rate of 130 bpm. His device interrogation shows atrial sensing with ventricular pacing at 130 bpm. What pacemaker-mediated tachycardia (PMT) is this?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: A — Endless loop tachycardia (ELT) — a re-entrant circuit using the pacemaker as the antegrade limb (sensing the P wave, pacing the ventricle) and retrograde VA conduction as the retrograde limb; broken by extending the PVARP (post-ventricular atrial refractory period)

Endless loop tachycardia (ELT) is a PMT unique to dual-chamber pacemakers: (1) mechanism: a retrograde P wave (conducted back to the atrium via the AV node or accessory pathway after a ventricular paced beat or PVC) is sensed by the atrial lead → triggers a ventricular paced beat → which conducts retrogradely to the atrium → sensed again → creates a continuous loop at or near the upper tracking rate; (2) ECG appearance: regular tachycardia at/near the programmed upper rate limit with ventricular paced complexes; (3) treatment: (a) magnet application (switches to asynchronous mode, breaking the loop); (b) programming: extend the PVARP (post-ventricular atrial refractory period) so retrograde P waves fall within the refractory period and are not sensed; (c) automatic PMT termination algorithms (most modern devices have these); (d) reduce VA conduction (beta-blocker); (e) ablate if retrograde pathway is an accessory pathway.

Reference: ESC (2021): Pacing Guidelines