Pacemaker-Mediated Tachycardia Triggered by Phrenic Nerve Stimulation During Cryoballoon Ablation of Atrial Fibrillation: A Case Report

Pacemaker-mediated tachycardia (PMT) - also known as endless loop tachycardia - is a well-known phenomenon in dual-chamber pacemakers programmed in atrial tracking modes, such as DDD or VDD. The initiating triggers of PMT are also well recognized and most frequently include ventricular premature beats (VPBs) or loss of atrial capture. In this report, we describe a case where an unusual trigger - such as a stimulus delivered in the superior vena cava (SVC) for testing phrenic nerve capture - initiated PMT.