Classification of Myocardial Infarction Types

Universal Definition and Overall Classification

The American College of Cardiology defines myocardial infarction (MI) as five distinct types based on underlying pathophysiology and clinical circumstances, according to the Third Universal Definition of MI. 1, 2

Type 1 MI is caused by atherosclerotic plaque rupture, ulceration, fissuring, erosion, or dissection that produces an intraluminal thrombus, leading to reduced myocardial blood flow or distal platelet emboli. 1, 2
Although most patients have severe coronary artery disease (CAD), 5‑20 % may show non‑obstructive or no CAD on angiography, a proportion that is higher in women. 3, 4
This type represents the classic “heart attack” resulting from acute coronary thrombosis. 1

Type 2 MI occurs when a condition other than CAD creates a myocardial oxygen supply‑demand mismatch. 1, 2
Frequently precipitating conditions include:
- Coronary artery spasm [4]
- Coronary endothelial dysfunction [4]
- Coronary embolism [3]
- Hypotension or severe hypertension (with or without left‑ventricular hypertrophy) [5]

Type 3 MI is diagnosed when a patient experiences cardiac death with symptoms suggestive of myocardial ischemia and presumed new ischemic ECG changes or new left‑bundle‑branch block, but death occurs before cardiac biomarkers can be obtained or rise. 1, 3
This category acknowledges that some patients die before blood samples can be drawn or before biomarkers become elevated. 4

Defined by a troponin rise > 5 × the 99th‑percentile upper reference limit (URL) in patients with normal baseline troponin values. 5, 2
If baseline troponin is already elevated (≤ 99th‑percentile URL) but stable or falling, a ≥ 20 % rise is required. 5
At least one additional criterion must be met (any of the following):
- Symptoms suggestive of myocardial ischemia [2]
- New ischemic ECG changes or new left‑bundle‑branch block [4]
- Angiographic evidence of a procedural complication (loss of patency, slow/no‑flow, embolization) [4]
- Imaging demonstration of new loss of viable myocardium or new regional wall‑motion abnormality [2]

Detected by coronary angiography or autopsy in the setting of myocardial ischemia with a rise and/or fall of cardiac biomarkers, with at least one value above the 99th‑percentile URL. 2, 4

Defined by cardiac biomarker elevation > 10 × the 99th‑percentile URL in patients with normal baseline troponin values. 2, 3, 4
Requires at least one additional criterion (any of the following):
- New pathological Q waves or new left‑bundle‑branch block [3]
- Angiographically documented new graft or native coronary artery occlusion [3]
- Imaging evidence of new loss of viable myocardium or new regional wall‑motion abnormality [4]

The American College of Cardiology also classifies MI by ECG presentation to guide immediate treatment decisions. 1
ST‑Elevation MI (STEMI): Patients with chest discomfort or ischemic symptoms who develop ST‑segment elevation in two contiguous leads. 1
Non‑ST‑Elevation MI (NSTEMI): Patients presenting without ST‑segment elevation. 1