Abnormal electrocardiographic activity revealed by isolated rat heart preparations at various times after experimental myocardial infarction.

Experimental myocardial infarction has been induced in rats by isoprenaline pretreatment and progress of the lesions has been observed histologically at intervals over a period of 6 weeks. This revealed transition from extensive ischaemic degeneration to apparently complete recovery of much of the affected muscle, leaving lesser areas of necrotic cells to become replaced by dissecting collagen-fibre scars. Isolated perfused preparations of affected and normal hearts were used to give electrocardiogram records. Oscilloscope photographs were measured. Ischaemia was associated, typically, with enlarged Q waves and decreased R and S waves, plus evidence of bundle branch block. These abnormalities abated as lesions resolved, leaving residual Q enlargement and arrhythmias, consistent with persistent scarring.