From the Guidelines
STEMI equivalents include new left bundle branch block (LBBB), hyperacute T-wave changes, true posterior MI, and multilead ST depression with coexistent ST-elevation in lead aVR, which require immediate reperfusion therapy to reduce morbidity and mortality. These equivalents are critical to recognize as they indicate coronary occlusion and necessitate urgent intervention, similar to classic STEMI 1. The pathophysiology behind these patterns involves acute occlusion of the coronary artery by the “plaque + superimposed thrombus complex”, leading to myocardial cell necrosis and infarction.
Some key STEMI equivalents to consider include:
- New left bundle branch block (LBBB) with appropriate clinical context
- Hyperacute T-wave changes, characterized by tall, symmetric T-waves preceding ST elevation
- True posterior MI, indicated by ST depression in V1-V3 with tall R waves
- Multilead ST depression with coexistent ST-elevation in lead aVR, suggesting left main or triple vessel disease These patterns should trigger the same urgent response as classic STEMI, including immediate cardiology consultation, antiplatelet therapy (aspirin 162-325mg), and preparation for emergent coronary angiography 1. Recognition of these patterns is critical because delays in reperfusion therapy significantly increase morbidity and mortality.
The use of aspirin as first-line therapy for AMI is supported by evidence showing a 23% relative risk reduction in 5-week vascular mortality with aspirin therapy administered within the first 24 hours after acute STEMI 1. Therefore, aspirin should be administered as soon as possible, with a loading dose of 162-325mg, followed by a daily dose of 81mg to minimize bleeding risk.
From the Research
STEMI Equivalents
The following are considered equivalents of ST-Elevation Myocardial Infarction (STEMI):
- Wellens syndrome 2, 3
- De Winter T waves 2, 3
- aVR ST elevation 2, 3
- Left bundle-branch block (LBBB) with a Sgarbossa score of ≥3 4
- Hyperacute T-waves 3
- Subtle ST-segment elevations 3
- ST-segment elevation in leads aVR/V1 with concomitant ST-segment depression in ≥8 other leads 3
- High R-peak with positive T-waves combined with horizontal ST-segment depression in leads V1/V2 3
Incidence of STEMI Equivalents
The incidence of STEMI equivalents varies, with a study finding that 4.4% of patients with prehospital ECGs available met the criteria for STEMI equivalency 2. Another study found that 4.7% of patients without prehospital ECGs available had initial hospital ECGs that met the STEMI equivalent criteria 2.
Diagnosis and Triage
The Sgarbossa electrocardiography criteria are a validated tool to aid in the diagnosis of STEMI in the presence of LBBB 4. A diagnosis and triage algorithm incorporating the Sgarbossa criteria can quickly and accurately identify patients with acute coronary artery occlusion 4. Prehospital clinicians should be educated on the recognition of STEMI equivalents to improve patient outcomes 2.