A 13-year-old girl was admitted to our hospital with a history of syncope after exercise. Neither left ventricular (LV) function nor hypertrophy was detected by transthoracic echocardiography. However, 24-h Holter electrocardiogram demonstrated ST segment depression with increasing heartbeat. Exercise ²⁰¹Tl myocardial scintigram also demonstrated ischemia of the anterior LV wall. Multi-slice coronary computed tomography (CT) demonstrated hypoplasia of the left main coronary artery. The syncope on exertion was ascribed to myocardial ischemia due to hypoplasia of the left main coronary artery. We performed off-pump coronary artery bypass graft (CABG) (left internal thoracic artery-left descending artery). The postoperative course was uneventful and postoperative stress ²⁰¹Tl myocardial scintigram demonstrated the absence of myocardial ischemia. Coronary CT demonstrated good graft patency. To date, there has not been any recurrence of syncope on exertion. We herein report a successful off-pump CABG for a patient with syncope due to hypoplasia of the left main coronary artery. Syncope on exertion due to hypoplasia of the left main coronary artery is very rare. However, certain forms of congenital coronary anomalies are associated with adverse cardiac events, including sudden cardiac death. The diagnosis, therefore, can be important and CABG is indicated, especially when there is repetitive syncope due to myocardial ischemia.

The patient was a 68-year-old man. In January 2017, he underwent aortic valve replacement (Carpentier-Edwards Perimount Magna, 25 mm, Edwards Lifescience Corporation, Irvine, USA) for aortic stenosis and coronary bypass surgery with two saphenous vein grafts (SVG-#7 and SVG-4PD) for asymptomatic myocardial ischemia. He was treated as an outpatient by a local physician for at least a week during November 2017, with a principal complaint of mild fever, but no other significant symptoms. Transthoracic echocardiography suggested prosthetic valve endocarditis, so he was referred to the author's hospital. The day after admission, he had symptoms of thoracic discomfort, and emergency cardiac catheter examination showed a lesion thought to be due to a thrombus in the left main coronary trunk ; so, thrombus aspiration was carried out. However, no improvement in blood flow was achieved, so balloon angioplasty was carried out, with the aim of improving blood flow in the left circumflex artery, where coronary artery bypass grafting had not been performed. Improvement in blood flow was achieved, and a culture was carried out using the aspirated thrombus. Streptococcus pasteurianus was detected in the culture.