Cardiovascular

Unstable Angina

Unstable angina is acute coronary ischaemia that causes rest or crescendo pain but stops short of killing myocytes, so troponin never rises and falls diagnostically.

Definition

Unstable angina is acute myocardial ischaemia with no acute myocardial injury. The clinical picture is rest pain, new severe angina, or previously stable angina now more frequent, longer or more easily provoked. High-sensitivity troponin shows no rise and fall with a value above the 99th-percentile upper reference limit. Both halves are required.

First principles

Ischaemia without necrosis is the entire distinction

Coronary flow falls far enough to starve myocardium but recovers before myocytes die. The ECG can show the ischaemia; the blood cannot, because nothing has leaked out of dying cells. NICE CG95 recommendation 1.2.6.1 defines myocardial infarction as a rise and/or fall in troponin with at least one value above the 99th-percentile upper reference limit, plus evidence of ischaemia. Unstable angina meets the second half and not the first.

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