This ECG was obtained from a patient who suffered an obstruction of the circumflex coronary artery. Unfortunately, he was in the approximately 15-18% of the population in whom the circumflex artery is dominant. That means that it connects with the posterior descending artery, perfusing not only the lateral wall of the left ventricle, but also the posterior and inferior walls. In this case, the obstruction is in the midportion of the artery, and the high lateral wall is spared. The large number of leads with ST elevation indicate the large amount of myocardium affected. Leads II, III, and aVF have ST elevation, as do Leads V3 through V6. Lead aVL has reciprocal ST depression. The T waves in the affected leads are "hyperacute", or taller than normal. This is usually an early change in acute M.I., and disappears after the onset of ST elevation.
It is not always easy to determine from the ECG that the circumflex artery is the culprit artery, rather than the right coronary artery, which perfuses the inferior wall in the majority of people. Some clues are: Lead III has ST elevation equal to that of Lead II, the low lateral wall (V5 and V6) are affected, and aVL has reciprocal depression but Lead I does not.
This is a very large M.I., due to the dominance of the circumflex artery. The patient did not survive, in spite of aggressive treatment.