From the Guidelines
Inferior wall MI is characterized by ST-segment elevation in leads II, III, and aVF, with reciprocal ST-segment depression in leads I and aVL, and possible ST-segment depression in V1-V3 if right ventricular involvement is present, as recommended by the 2017 ESC guidelines for the management of acute myocardial infarction in patients presenting with ST-segment elevation 1. The ECG changes associated with an inferior wall myocardial infarction (MI) are crucial for timely diagnosis and treatment. Key changes to look for include:
- ST-segment elevation of ≥1 mm in leads II, III, and aVF
- Reciprocal ST-segment depression in leads I and aVL
- Possible ST-segment depression in V1-V3 (if right ventricular involvement)
- Q waves may develop in II, III, and aVF over time These changes occur because the inferior wall of the left ventricle is supplied by the right coronary artery in most people, as noted in the AHA/ACCF/HRS recommendations for the standardization and interpretation of the electrocardiogram 1. When this artery is occluded, it causes ischemia and injury to the inferior myocardium, leading to the characteristic ECG changes. It's essential to record right precordial leads (V3R and V4R) to identify concomitant right ventricular (RV) infarction, as recommended by the 2017 ESC guidelines 1. Prompt recognition of these ECG changes is crucial for timely diagnosis and treatment of inferior wall MI, which typically involves immediate reperfusion therapy (e.g., primary percutaneous coronary intervention or thrombolysis) and standard acute coronary syndrome management.
From the Research
ECG Changes in Inferior Wall Myocardial Infarction
The ECG changes associated with an inferior wall myocardial infarction (MI) include:
- ST segment elevation in leads II, III, and aVF 2, 3, 4
- ST segment elevation in leads V1-V3, with the magnitude of ST segment elevation being maximal in lead V1 and decreasing gradually from lead V1 to V3 and from lead V1 to V3R-V5R 2
- P-wave parameters, such as P-wave duration (PWD) and P-wave dispersion (PWDisp), can help in the diagnosis of atrial infarction in patients with inferior STEMI 5
- PR-segment displacement can also be observed in patients with atrial infarction 5
Diagnostic Criteria
The diagnostic criteria for basal inferior-septal wall AMI can be formulated as follows:
- ST segment elevation ≥ 2 mm in lead V1 in the clinical setting of inferior wall AMI 2
- The magnitude of ST segment elevation is the tallest in lead V1 and decreases gradually from lead V1 to V3 and from lead V1 to V3R-V5R 2
Culprit Artery Identification
Several methods and algorithms using 12-lead ECG have been developed to localize the lesion in inferior wall STEMI, including: