Hibernating myocardium is a condition in which an area of heart muscle has chronically reduced blood flow due to significant narrowing of the supplying coronary artery, but has adapted by downregulating its metabolic and contractile activity rather than dying. The muscle cells are alive (viable) but functioning poorly or not at all, appearing weakened or non-contracting on imaging. Crucially, if blood flow is restored by coronary revascularisation (PCI or CABG), the hibernating muscle can recover its contractile function over weeks to months.
Hibernating myocardium is distinguished from myocardial stunning (temporary dysfunction after a brief episode of ischaemia, recovering within hours to days after blood flow is restored) and from myocardial scar (infarcted tissue that is permanently non-functional and will not recover with revascularisation). In practice, all three may coexist in the same patient following myocardial infarction.
Identifying viable hibernating myocardium is clinically important in patients with severely impaired left ventricular function: if the dysfunction is due to hibernation rather than scar, revascularisation may substantially improve ejection fraction and heart failure symptoms. Viability imaging can be performed by cardiac MRI (absence of late gadolinium enhancement scar and preserved wall thickness), PET scanning (detecting metabolic activity with FDG tracer), or dobutamine stress echocardiography (testing for contractile reserve).
For cardiac arrest survivors with impaired left ventricular function and ischaemic heart disease, the presence of hibernating myocardium is an important consideration in planning revascularisation. A low ejection fraction due partly to hibernation may improve significantly after successful PCI or CABG, potentially affecting ICD implantation decisions.
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