Does left anterior descending coronary artery acute occlusion proximal to the first septal perforator counteract ST elevation in leads V5 and V6?

The mechanisms of the so-called extensive anterior acute myocardial infarction including ST-segment elevation in leads V1 (ST↑V1) through V6 (ST↑V6) are not clear. This report is focused on the electrocardiographic (ECG) changes in 2 cases with anterior AMI. In case 1, the ECG showed complete right bundle-branch block, left anterior fascicular block, and ST↑V2 through ST↑V6 on admission, but 5 minutes later, after the disappearance of complete right bundle-branch block and left anterior fascicular block, a striking ST depression in V6 (ST↓V6) and ST↑V1 occurred. In case 2, the ECG showed ST↑V1 through ST↑V6. The physiopathologic mechanisms of these ECG findings are discussed.