Can You Have a STEMI with Only ST Segment Depression?
No, by definition you cannot have a STEMI with only ST segment depression—STEMI requires ST segment elevation in at least 2 contiguous leads. However, there are two critical exceptions where isolated ST depression represents a STEMI-equivalent requiring immediate reperfusion therapy.
Definition of STEMI
STEMI is defined by new ST elevation at the J point in at least 2 contiguous leads of ≥2 mm (0.2 mV) in men or ≥1.5 mm (0.15 mV) in women in leads V2-V3, and/or ≥1 mm (0.1 mV) in other contiguous chest or limb leads 1. Patients presenting with ST segment depression alone are classified as having either unstable angina or NSTEMI, not STEMI 1.
STEMI-Equivalent Exceptions with ST Depression
1. True Posterior MI (Posterobasal Infarction)
ST depression in ≥2 precordial leads (V1-V4) that is maximal in V3-V6, without ST elevation in other leads, indicates transmural posterior injury and qualifies as a STEMI-equivalent 1. This pattern represents:
- Acute occlusion of the posterior descending artery or left circumflex artery 1
- The ST depression is actually a "mirror image" of ST elevation occurring in the posterior wall
- These patients qualify for immediate reperfusion therapy (fibrinolysis or primary PCI) 1
- Posterior chest leads (V7-V9) showing ST elevation confirm the diagnosis 1
2. Multilead ST Depression with ST Elevation in aVR
Multilead ST depression with coexistent ST elevation in lead aVR has been described in patients with left main or proximal left anterior descending artery occlusion 1. However, recent evidence challenges this as a reliable STEMI-equivalent:
- A 2019 study found that among patients with STE-aVR and multilead ST depression, only 10% had an acutely occluded coronary artery, and none had left main or LAD occlusions 2
- Despite low rates of acute occlusion, this pattern carries 31% in-hospital mortality versus 6.2% in typical STEMI 2
- Urgent (rather than emergent) catheterization is recommended, not routine STEMI activation 2
Clinical Classification
Patients with ST depression alone (excluding the above exceptions) are classified as:
- NSTEMI if cardiac biomarkers (troponin T or I, CK-MB) exceed the upper limit of normal with clinical presentation consistent with ischemia 1
- Unstable angina if biomarkers remain normal 1
- These patients should not receive fibrinolytic therapy, which is contraindicated 1
Prognostic Significance of ST Depression
While not meeting STEMI criteria, ST depression carries important prognostic information:
- ST depression ≥0.5 mm (0.05 mV) indicates higher risk than isolated T-wave changes or normal ECG 1
- Greater magnitude and number of leads with ST depression correlate with worse outcomes 1
- Patients with ST depression benefit from early invasive strategy and antiplatelet therapy 1
Key Clinical Pitfalls
- Always obtain posterior leads (V7-V9) in patients with isolated anterior ST depression to identify posterior STEMI 1
- Do not activate STEMI protocols for STE-aVR with multilead ST depression without confirming acute occlusion 2
- Compare with prior ECGs when available, as baseline abnormalities (LVH, LBBB, paced rhythm) can obscure interpretation 1
- Transient ST changes during symptomatic episodes that resolve when asymptomatic strongly suggest acute ischemia and high-risk disease 1