A First Septal Perforator Arising Directly from the Left Main Coronary Artery

An anomalous origin of the first septal perforator artery is uncommon, and an origin directly from the left main coronary artery (LMCA) is exceptional. We report the case of a 61-year-old man with type 2 diabetes mellitus and hypertension, admitted for a non-ST-elevation acute coronary syndrome. Coronary angiography revealed two tandem stenoses involving the ostial and proximal left anterior descending artery (LAD). Incidentally, the first septal perforator arose directly from the LMCA, proximal to the LAD–circumflex bifurcation, rather than from the proximal LAD. The patient underwent percutaneous treatment of the proximal LAD, with preservation of the anomalous septal branch at the end of the procedure. He was discharged on optimal medical therapy and remained asymptomatic. Recognising this variant is clinically relevant. Because this branch supplies the anterior interventricular septum and the proximal conduction system, it may be jailed during left main or bifurcation revascularisation, influencing the choice of technique and the need for branch protection. An aberrant origin may also lead to cannulation of the wrong vessel during alcohol septal ablation for hypertrophic obstructive cardiomyopathy. Finally, an apparently absent proximal septal branch on the LAD should prompt a search for an ectopic origin.