Acute Coronary Syndromes, Heart Failure, and Cardiogenic Shock

1. Where the Chest Pain Sits on the Spectrum

A coronary artery narrows with plaque, and the muscle downstream gets less blood than it needs. That's ischemia. So the whole family of conditions you're about to learn is just different amounts of that same problem.

Stable angina happens at a fixed frequency. A predictable amount of exertion brings it on. Rest or medication relieves it promptly, and the pattern doesn't change.
Unstable angina is new onset, or it's happening at rest, or the established pattern has changed — more frequent, more severe, less responsive to nitroglycerin. You treat it the same as an infarct in the field.
Prinzmetal's angina is different from both. The artery spasms instead of staying narrowed by plaque, so a patient with normal arteries can still get transient ST elevation. It's often at rest, and it often shows up in a younger patient.
NSTEMI is an actual infarction, but it doesn't elevate the ST segment. The 12-lead might show depression, T-wave inversion, or nothing at all.

So the label depends on the pattern of pain and what the 12-lead does — not on how bad the pain feels to the patient.

Three things the Instructional Guidelines want you to carry out of this section. ACS is not a self-limiting disease. The chest pain can dissipate while the ischemia and the injury keep going. And a single anginal episode can be the precursor to a full infarction. So a patient whose pain goes away — even after nitroglycerin — has not necessarily had the event resolve. That never downgrades your transport decision.

Here's the fact that trips people up on the exam: a normal or non-diagnostic 12-lead does not rule out ACS. Roughly half of infarcts never elevate the ST segment. The tracing rules a STEMI in. It does not rule ACS out — only serial troponins at the hospital do that. So you repeat the 12-lead whenever symptoms change, because the pattern can still develop.