Stable Angina and Myocardial Infarction

Stable angina is a predictable episode of chest discomfort caused when the heart muscle temporarily receives less oxygen than it needs, usually during exertion. Acute myocardial infarction, commonly called a heart attack, involves death of heart muscle cells because of prolonged inadequate blood supply. The central distinction is temporary, reversible oxygen deprivation versus irreversible tissue injury.

What happens in the coronary arteries

The coronary arteries supply oxygenated blood to the heart muscle. Atherosclerosis, the accumulation of plaques within arterial walls, commonly underlies both conditions.

• In stable angina, a relatively fixed coronary narrowing limits the increase in blood supply needed during exertion or emotional stress; the resulting ischaemia does not cause heart muscle cell death.
• Acute myocardial infarction commonly follows plaque rupture or erosion with formation of a blood clot, which abruptly reduces coronary blood flow.
• Not every infarction results from a newly formed coronary clot; a severe imbalance between oxygen supply and demand can also cause myocardial infarction.

Symptoms and diagnostic distinction

Symptoms can overlap, so chest discomfort alone cannot reliably distinguish the two conditions. Assessment may require an electrocardiogram (ECG) and blood tests for cardiac troponin, a marker of heart muscle injury.

• Stable angina usually follows a consistent pattern, lasts a few minutes, and improves with rest or prescribed nitrate medication.
• Infarction often causes prolonged pressure or discomfort that may occur at rest, sometimes with sweating, breathlessness, nausea, or pain spreading to the arm or jaw.
• An infarction can occur without typical chest pain, particularly in people with diabetes and older adults.
• Myocardial infarction is diagnosed using a rise or fall in troponin, with an elevated value, together with evidence of acute myocardial ischaemia; an elevated troponin alone does not establish infarction.
• A normal initial ECG does not exclude myocardial infarction, and repeat ECGs or troponin measurements may be needed.

Why urgency and treatment differ

Acute myocardial infarction is a medical emergency, whereas stable angina generally permits planned evaluation and long-term management.

• Stable angina management includes risk-factor control and medicines; coronary angioplasty with stenting or bypass surgery is considered according to symptoms, coronary anatomy, and clinical risk.
• Acute infarction requires urgent assessment and treatment, including restoration of coronary blood flow when indicated, to limit muscle damage.
• New, worsening, or rest-related chest discomfort should not be assumed to be stable angina and requires urgent assessment.