Transient post-reperfusion left bundle branch block and accelerated idioventricular rhythm with paradoxical QRS narrowing.

Accelerated idioventricular rhythm (AIVR) commonly follows coronary reperfusion and has been called a "reperfusion arrhythmia". Transient left bundle branch block (LBBB) is only rarely seen after interventional reperfusion and is usually considered a procedural complication. We report herein electrocardiograms (ECGs) in a case of acute lateral myocardial infarction which demonstrate both post-perfusion AIVR and a simultaneous transient LBBB with fusion complexes causing paradoxical QRS narrowing.