Coronary Atherosclerosis

Atherosclerosis is the gradual build-up of fatty plaques within the walls of arteries. When it affects the coronary arteries, which supply the heart muscle, it produces a major form of coronary artery disease. Myocardial ischemia occurs when these arteries cannot deliver enough oxygen-rich blood to meet the heart muscle's needs.

How a coronary plaque develops

Atherosclerosis is a disease of the arterial wall, not simply fat collecting inside a pipe. It involves lipid accumulation, inflammation and the formation of fibrous tissue.

• Low-density lipoprotein (LDL) cholesterol can accumulate within the artery's inner lining and undergo changes that promote inflammation.
• Immune cells called macrophages take up lipids and become foam cells, contributing to early fatty lesions.
• Over time, a plaque develops with a lipid-rich core and a fibrous cap. Plaque growth can narrow the arterial lumen, while the affected artery becomes less able to dilate normally.

How narrowing produces myocardial ischemia

The central problem is an oxygen supply-demand mismatch. A narrowed coronary artery may supply sufficient blood at rest but cannot increase flow adequately when the heart works harder.

• During exertion or emotional stress, the heart's oxygen requirement rises. Restricted blood flow can then cause ischemia, often producing angina, a sensation of chest discomfort or pressure.
• Reduced oxygen delivery impairs aerobic energy production and can temporarily weaken the heart muscle's contraction.
• Brief ischemia can be reversible when blood supply improves or demand falls. Ischemia does not itself necessarily mean that heart muscle has died.

How plaque disruption causes an acute coronary event

A plaque can cause sudden harm even if it had not previously produced severe narrowing. Plaque rupture or erosion can trigger clot formation at its surface.

• Platelets and the coagulation system form a thrombus, which can abruptly reduce or block coronary blood flow.
• An acute reduction in blood supply may cause unstable angina; if ischemia is sufficiently severe and prolonged, heart muscle cells die, producing a myocardial infarction, or heart attack.
• Thus, coronary atherosclerosis causes disease through both gradual limitation of blood flow and sudden plaque-related thrombosis.