Ischemia in the Territory of the First Major Septal Perforator Branch Anomalously Originating From the First Diagonal Branch Leads to a Transient Leftward Shift of the QRS Axis in the Frontal Plane

rigination of the first major septal perforator branch from a site other than the left anterior descending coronary artery (LAD) is a relatively rare and benign congenital variation. 1 Coronary angiography reveals anomalous vessels originating directly from the aorta and from the proximal portion of the right coronary artery as collateral circulation to the LAD, particularly in patients with proximal LAD disease.2,3 Anomalous vessels also arise from the proximal circumflex coronary artery, diagonal branch, or obtuse marginal branch.4 A transient leftward QRS axis shift on the electrocardiogram (ECG) during anginal attacks is a specific predictor of proximal LAD disease.5–8 Conduction disturbance caused by ischemia of the anterior fascicle of the left bundle branch, which is supplied by the first major septal perforator branch of the LAD, 9 is thought to be one reason for the axis shift. Here, we describe a patient with a non-Q wave myocardial infarction whose coronary arteriogram documented severe luminal narrowing in the first major septal perforator branch arising anomalously from the first diagonal branch. Exercise ECG showed a transient leftward QRS axis shift.