Ischaemia

Ischaemia is a reduction in blood flow to an organ or tissue that is sufficient to impair its function or cause damage. It results from obstruction or narrowing of the artery supplying that tissue, whether from atherosclerotic plaque, a clot, a spasm, or external compression. The reduced blood flow deprives cells of the oxygen and glucose they need for normal metabolism. If ischaemia is severe or prolonged, it progresses to infarction (cell death).

Myocardial ischaemia, affecting the heart muscle, is the most clinically significant form for the SCA UK audience. It occurs when coronary artery disease narrows one or more coronary arteries sufficiently to limit blood supply to part of the heart muscle. Stable ischaemia causes chest pain (angina) on exertion, when the heart’s oxygen demand exceeds the restricted supply. Unstable ischaemia, in which a plaque ruptures and triggers a clot, can cause a heart attack (myocardial infarction) even at rest. Severe acute myocardial ischaemia is a major cause of ventricular fibrillation and sudden cardiac arrest.

Cerebral ischaemia, affecting the brain, occurs in stroke (if a clot blocks a cerebral artery) and during cardiac arrest itself, when the cessation of blood flow deprives the entire brain of oxygen. After successful resuscitation, the reperfusion of ischaemic brain tissue triggers secondary injury through oxidative stress, inflammation and excitotoxicity. Targeted temperature management in the intensive care unit is designed in part to limit this reperfusion injury.

Ischaemia can also affect the kidneys (renal ischaemia, contributing to acute kidney injury after cardiac arrest), the bowel (mesenteric ischaemia, a rare but serious complication of low cardiac output), and the limbs (peripheral arterial disease, presenting as pain on walking or, in severe cases, rest pain or tissue loss). Management of ischaemia in all organs centres on restoring blood flow as rapidly as possible, controlling risk factors and, where appropriate, revascularisation through angioplasty or surgery.