Transient focal septal block.

A 65-year-old woman with an acute myocardial infarction, as judged by serial enzyme changes, developed transitory Q waves in leads V2 to V4 and leads 2, 3, and aVF during an attack of pain in the chest. These Q waves were not present 12 hours later. It is suggested that these changes represent a focal block in the septal fibers of the left bundle-branch system. This defect could underlie the transient right precordial Q waves seen in myocardial infarction or ischemia, as well as the fixed Q waves of many patients without septal infarction at autopsy.