Myocardial stunning is the temporary loss of contractile function of heart muscle cells following a brief period of severe ischaemia (reduced blood flow), despite the restoration of normal blood supply. The affected heart muscle is still alive (it has not undergone irreversible necrosis), but it takes hours to days to recover its normal function after blood flow is restored. The key feature distinguishing stunning from infarction is reversibility: if blood supply is maintained, the stunned muscle gradually recovers.
The classic scenario for myocardial stunning is a heart attack treated promptly by emergency PCI. When the blocked artery is reopened within a few hours, heart muscle cells that were ischaemic but not yet dead are saved from infarction. However, they may show abnormal wall motion and reduced contractility for days or weeks after the procedure, producing a temporarily lower ejection fraction that improves as the stunned myocardium recovers.
Myocardial stunning also occurs after cardiac arrest itself, independently of any coronary artery blockage. The global ischaemia of cardiac arrest, followed by reperfusion when circulation is restored, causes widespread stunning of the entire heart muscle. This post-arrest myocardial dysfunction is a recognised component of post-cardiac arrest syndrome and typically contributes to the need for vasopressor support in the early intensive care period. It begins to resolve within 24 to 48 hours in most survivors, with ejection fraction recovering over subsequent days to weeks.
It is important for patients and families to know that a low ejection fraction measured very early after cardiac arrest or PCI may not reflect long-term cardiac function. Repeat assessment, typically by echocardiography, is usually recommended 6 to 12 weeks after the event to determine the true baseline ejection fraction, which informs decisions about ICD implantation.
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