unstable angina

If stable angina is a warning light that comes on only when you push the engine, unstable angina is that light flashing while the car idles. The chest pain now appears at rest or with trivial effort, or has suddenly become more frequent, more severe or longer-lasting than before.

It sits at the milder end of the acute coronary syndrome spectrum. The underlying problem is usually a plaque that has become unstable — cracked or partially clotted — narrowing the artery further or intermittently, so blood flow is threatened even without extra demand. Crucially, the artery is not yet blocked enough, or for long enough, to kill muscle.

That last point is what separates unstable angina from a heart attack: by definition, cardiac troponin does not rise, meaning there is no detectable muscle death. The ECG may be normal or show ischemic changes. Even so, unstable angina is treated as an emergency, because the same unstable plaque can progress to a full infarction at any moment.

With more sensitive troponin assays now in use, many cases once labelled unstable angina are reclassified as NSTEMI; true troponin-negative unstable angina has become less commonly diagnosed.