Cardiac conduction system regeneration prevents arrhythmias after myocardial infarction

Arrhythmias are a hallmark of myocardial infarction (MI) and increase patient mortality. The cardiac conduction system is implicated in arrhythmias, but how it is altered following MI is poorly understood. We demonstrate complete conduction system restoration during neonatal mouse heart regeneration, versus pathological remodelling at non-regenerative stages. Tissue-cleared whole-organ imaging identified disorganised bundling of conduction fibres after MI, global His/Purkinje disruption and regional loss of connexin-40. Single-cell RNA-sequencing revealed that Purkinje cells undergo specific molecular changes to regenerate the network, versus sustained aberrant electrical alterations during fibrotic repair. This manifested functionally as transition from normal rhythm to pathological conduction delay beyond the regenerative window. Modelling the non-regenerative phenotype in the infarcted human heart implicated these changes as causative for bundle branch block and ventricular dyssynchrony, as observed in patients. These findings elucidate the mechanisms underpinning conduction system regeneration versus repair and reveal the consequences of MI-induced damage for clinical arrhythmogenesis.