Why Temporary Pacing in Acute Inferior Myocardial Infarction or No-Reflow Becomes a Trigger-Not a Remedy-For Ventricular Fibrillation: Undersensing, "R-On-T", Catheter Trauma and the Ischaemic Substrate.

Temporary pacing during acute inferior MI or no-reflow can trigger ventricular fibrillation rather than prevent it. Four mechanisms are highlighted: (1) acute ischemia lowers VF threshold and creates repolarization heterogeneity; (2) fragmented electrograms cause undersensing and asynchronous spikes; (3) bradycardia-related long RR cycles position spikes on the T-wave ("R-on-T"); and (4) catheter micro-displacement induces mechanical extrasystoles. We propose a bedside decision framework-three questions before pacing-and a prevention bundle focused on urgent ischemia reversal, continuous electrogram surveillance, and early electrode removal. Bradycardia in this setting is often transient, but the electrophysiological vulnerability is not. Treating ischemia first and avoiding unnecessary pacing are paramount to prevent iatrogenic arrhythmia.