From the Guidelines
Acute coronary syndrome on ECG is characterized by ST-segment changes, T-wave inversions, and sometimes Q waves, with ST-elevation myocardial infarction (STEMI) showing ST-segment elevation of at least 1 mm in two or more contiguous leads, and non-ST elevation ACS (NSTEMI and unstable angina) showing ST-segment depression, T-wave inversions, or a normal ECG. The ECG changes in acute coronary syndrome can vary depending on the specific type of ACS, with STEMI typically showing persistent ST-segment elevation (>20 min) and non-ST elevation ACS showing transient or no ST-segment elevation 1. The location of the coronary artery occlusion can also be inferred from the ECG changes, with anterior leads (V1-V4) indicating left anterior descending artery lesions, inferior leads (II, III, aVF) indicating right coronary artery occlusions, and lateral leads (I, aVL, V5-V6) indicating circumflex artery involvement. Other ECG findings can include hyperacute T waves, reciprocal ST depression, and new left bundle branch block, which can mask STEMI.
Some key ECG findings in acute coronary syndrome include:
- ST-segment elevation of at least 1 mm in two or more contiguous leads in STEMI
- ST-segment depression, T-wave inversions, or a normal ECG in non-ST elevation ACS
- Hyperacute T waves in early STEMI
- Reciprocal ST depression in leads opposite to the area of infarction
- New left bundle branch block, which can mask STEMI These ECG changes occur because myocardial ischemia alters the normal electrical activity of the heart, with ST elevation representing transmural injury and ST depression indicating subendocardial ischemia, as noted in the 2020 ESC guidelines for the management of acute coronary syndromes 1.
From the Research
Acute Coronary Syndrome on ECG
The electrocardiogram (ECG) is a crucial diagnostic tool for acute coronary syndromes (ACS), which include ST-segment elevation myocardial infarction (STEMI), non-STEMI (NSTEMI), and unstable angina. Key ECG findings in ACS include:
- ST-segment elevation in STEMI 2, 3, 4
- ST-segment depression in NSTEMI 2, 3, 5, 4
- T-wave inversions in NSTEMI 2, 3, 5
- Q waves in myocardial infarction 5
ECG Patterns in ACS
ECG patterns in ACS can vary, and some patients may have normal or non-specific ECG findings. However, certain patterns are associated with specific types of ACS:
- STEMI: ST-segment elevation 2, 3, 4
- NSTEMI: ST-segment depression, T-wave inversions, or normal ECG 2, 3, 5
- Unstable angina: ST-segment depression, T-wave inversions, or normal ECG 3, 6
Diagnostic and Therapeutic Implications
ECG findings in ACS have important implications for diagnosis and treatment:
- STEMI: immediate reperfusion therapy with primary percutaneous coronary intervention (PCI) or fibrinolytic therapy 2, 3, 4
- NSTEMI: high-sensitivity troponin measurements and prompt invasive coronary angiography and revascularization 2, 5
- Unstable angina: coronary angiography and revascularization, as well as medical therapy with antiplatelet agents, anticoagulants, and statins 2, 5, 6