23-03: Acute Inferior Myocardial Infarction

ECG Findings

• ST-segment elevation in inferior leads (II, III, aVF)

• Q-wave formation in the inferior leads (II, III, aVF)

• Reciprocal ST-segment depressions in the anterior leads (V₁-V₃) and high lateral leads (I, aVL)

Pearls

1. The right coronary artery supplies blood to the right ventricle, the sinoatrial (SA) node, the inferior portions of the left ventricle, and usually the posterior portion of the left ventricle and the atrioventricular (AV) node.

2. The left circumflex supplies blood to the lateral ventricle but also frequently supplies blood to the inferior portions of the left ventricle.

3. Infarctions involving the SA node may produce sinus dysrhythmias including tachycardias, bradycardias, and sinus arrest.

4. Infarctions involving the AV node may produce AV blocks.

5. In the presence of acute inferior injury, a right-sided ECG should be obtained to look for right ventricular involvement.

6. Since the right coronary artery so often supplies the posterior left ventricle, look for evidence of a posterior infarction (as present in the example) and consider obtaining an ECG with posterior leads.

7. Reciprocal ST-depression is very common in cases of inferior STEMI involving right coronary artery occlusion. In fact, ST depression in aVL may precede the development of ST elevation in the inferior leads. Inferior STEMI due to left circumflex occlusion often lacks reciprocal ST depression in aVL.