A 75 year old man was admitted because of stable angina pectoris without any history of myocardial infarction. His risk profile consisted of arterial hypertension and hypercholesterolaemia. At the time he was being treated with 100 mg aspirin, 100 mg metoprolol, 20 mg pravastatin, and 40 mg isosorbide mononitrate daily. ECG showed sinus rhythm, no Q waves, and slight T wave inversions at lead aVL and I. A bicycle stress test resulted in horizontal ST segment depression of 2 mm at 75 W. Coronary angiography was performed and revealed coronary artery disease with complete occlusion of the proximal part of the left coronary artery. The left anterior descending and left circumflex (LCX) branch of the left coronary artery were filled by collateral vessels originating from a large right coronary artery. An additional severe stenosis was found in the proximal part of the LCX. The left ventriculogram did not show any wall motion abnormalities with an ejection fraction of 68%. Immediate coronary bypass grafting was performed without any complication.

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According to the literature total occlusion of the left main coronary artery usually causes a large infarction of the anterior wall leading to cardiogenic shock or sudden cardiac death. Sporadically left main occlusion may occur as a severe complication of percutaneous transluminal balloon angioplasty requiring urgent bypass surgery. This case shows that slow occlusion of the left main coronary artery may develop without myocardial infarction because of excellent collateral blood flow.