Acute dissection of the internal mammary artery: a fatal complication of coronary artery bypass grafting. A case of acute traumatic dissection of the right internal mammary artery is presented in a patient who had both IMAs grafted for recurrent angina 10 years after initial vein coronary revascularisation. The event was mistaken for spasm, but because of severe circulatory collapse no time was available to treat the patient appropriately. The purpose of this report is to facilitate the early recognition and avoidance of this potentially fatal complication. 