Inferior, posterior and lateral wall myocardial infarction
ST segment elevation and T wave inversion are present in II, III and aVF, the inferior leads. The ST segment is coved and T waves are inverted in V5 and V6, the lateral leads. Minimal ST segment depression is seen in lead I and aVL, which can be taken as reciprocal to the ST segment elevation in inferior leads. There are tall R waves in V1 and V2 with R/S ratio more than 1, and ST segment depression with upright T waves. These feature are suggestive of posterior wall infarction, being the inverse of Q wave, ST elevation and T wave inversion which would have been recorded in a posterior lead. Together with the changes in inferior and lateral leads, the full diagnosis is inferior, posterior and lateral wall infarction. This combination can occur in occlusion of a dominant left circumflex coronary artery which supplies the inferior, posterior and lateral walls of the left ventricle. A distal occlusion of a dominant right coronary artery can also cause this pattern. A more proximal occlusion of right coronary artery would produce right ventricular infarction and null out the ST segment depression in anterior leads seen in true posterior wall infarction. The term true posterior wall infarction is sometimes used as inferior wall infarction was called posterior wall infarction earlier.