When the Pacemaker Goes Rogue: Pacemaker-Induced Tachycardia, Syncope, and Car Crash.

A 78-year-old male with a history of ischemic heart disease with prior myocardial infarction, severe left ventricular systolic dysfunction, and a device-related implantable cardioverter defibrillator (DR ICD) was admitted following a road traffic accident due to a sudden loss of control of the vehicle following a syncope. Initial investigations ruled out acute coronary syndrome and did not point to neurological causes. Device interrogation revealed the presence of pacemaker-mediated tachycardia (PMT), but since the episode trigger had been programmed off, it was not possible to determine when they occurred, how long they lasted, or their rate. However, atrial threshold testing promptly provoked a PMT. The induced PMT led to a tachycardia of 130 bpm, causing severe symptomatic hypotension with a mean blood pressure falling below 50 mmHg. This could be easily reproduced several times. Given the patient's severe left ventricular systolic dysfunction and the absence of any overt alternative explanation, the PMT likely triggered the syncope preceding the car accident. Management focused on reprogramming the DR ICD. The most critical adaptation was a mode switch from DDD to DDIR to prevent atrial tracking, effectively terminating PMT episodes. A prolongation of the postventricular atrial refractory period (PVARP) was not possible due to the very slow VA conduction. The follow-up revealed no other episodes of PMT and the patient no longer experiences episodes of presyncope or syncope. This report highlights the potential for PMTs to induce severe hemodynamic instability and syncope, underscoring the importance of meticulous device evaluation.