Determining the Cause
a. EKG: ST Segment Elevation
Differential Diagnosis
Myocardial Infarction
| Next Pivotal Assessment | Findings |
|---|---|
| Coronary Angiography | Coronary Occlusion |
[Coronary angiography may be indicated even before troponin results are available if the electrocardiogram (ECG) shows certain high-risk changes consistent with ST-elevation myocardial infarction (STEMI) or life-threatening ischemia.]
ECG shows ST-elevation MI (STEMI):
ST elevation ≥1 mm in ≥2 contiguous leads
New or presumed new left bundle branch block (LBBB)
Posterior MI (ST depression in V1–V3 with tall R waves)
Patient is in cardiogenic shock, ongoing chest pain, or has ventricular arrhythmias.
Very high clinical suspicion of MI even without biomarker confirmation:
e.g., classic crushing chest pain, diaphoresis, hypotension, and high-risk history
STEMI is a clinical diagnosis based on ECG, not troponin.
Waiting for troponin delays life-saving reperfusion, which must be done within 90 minutes ("door-to-balloon time").
Troponins confirm diagnosis later but are not needed to initiate emergent PCI in STEMI.
| Scenario | Angiography Timing |
|---|---|
| STEMI on ECG | Immediate (don’t wait for troponin) |
| NSTEMI or unstable angina | After troponin and risk stratification |
| No ischemic ECG changes | Wait for troponin and clinical evaluation |
Would you like a decision algorithm for STEMI vs NSTEMI management?
To definitely establish a diagnosis of myocardial infarction (MI the Fourth Universal Definition of MI (2018) is used. The diagnosis requires both clinical and biochemical evidence of myocardial injury with evidence of acute myocardial ischemia.
To definitely diagnose MI, the following must be met:
Rise and/or fall of cardiac troponin (cTn) with at least one value above the 99th percentile upper reference limit (URL)
(Most sensitive and specific marker)
At least one of the following:
Symptoms of ischemia (e.g., chest pain, pressure, shortness of breath)
ECG changes consistent with ischemia:
New ST-segment/T-wave changes or new left bundle branch block (LBBB)
ST elevation or depression
Development of pathological Q waves
Imaging evidence of new loss of viable myocardium or new regional wall motion abnormality
Identification of coronary thrombus by angiography or autopsy
| Requirement | Description |
|---|---|
| Troponin | Rise/fall with value above 99th percentile |
| + 1 of | Symptoms, ECG changes, imaging, or angiographic evidence of thrombus |
Type 1: Spontaneous MI due to atherosclerotic plaque rupture/thrombosis
Type 2: Secondary to ischemia from increased demand or decreased supply (e.g., anemia, hypotension)
Type 3: Sudden cardiac death before biomarkers are available
Type 4 & 5: MI related to PCI or CABG procedures
High-sensitivity troponin I or T (hs-cTn)
12-lead ECG
Echocardiogram
Coronary angiography (if needed)
Would you like a checklist or diagnostic pathway/flowchart?