Necrosis is the premature death of cells or tissue caused by external injury, disease, or loss of blood supply. Unlike apoptosis (programmed cell death), necrosis is an uncontrolled process triggered by a harmful external event and typically causes inflammation as the immune system responds to the dying tissue.
In cardiac medicine, necrosis most commonly refers to myocardial necrosis (the death of heart muscle cells) caused by prolonged interruption of blood supply during a heart attack (myocardial infarction). When a coronary artery is blocked, the affected area of heart muscle first becomes ischaemic (deprived of oxygen). If blood flow is not restored within 20 to 40 minutes, cells begin to die irreversibly. The extent of myocardial necrosis determines how much heart function is lost; it is reflected by the rise in troponin in the blood.
Dead myocardial tissue cannot regenerate to functioning muscle. Instead, it is replaced by fibrous scar tissue over the following weeks. This scar tissue does not contract, which permanently reduces the heart’s pumping efficiency. Areas of scar tissue are also electrically abnormal and can act as substrates for ventricular tachycardia and ventricular fibrillation, increasing the long-term risk of sudden cardiac arrest.
In cardiac arrest survivors, the degree of myocardial necrosis (reflected by ejection fraction on echocardiography) informs decisions about ICD implantation, medication, and rehabilitation. Brain tissue can also undergo necrosis after cardiac arrest if hypoxic brain injury is severe and sustained.
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