[Diameter of coronary arteries before and after bypass grafting (author's transl)].

Patients with patent coronary bypass grafts showed the followings: 1. a decrease in prestenotic coronary diameter due to a reduction in flow. 2. An increase of the poststenotic segment of the bypassed vessel due to an increase in flow via the venous graft. 3. An increase of the bypassed stenosis, mainly due to a general decrease of vessel diameter proximal to the stenosis. 4. No change in diameter in non bypassed arteries. The postoperative changes in diameter were not dependent on the time elapsed since surgery and were independent from the severity of coronary sclerosis and the number of risk factors. A correlation was found between the amount of the diameter changes and the amount of reduction in exercise induced ST-segment depression. The decrease in coronary diameter proximal to the stenosis is not due to progression of coronary sclerosis but to a functional change. A narrow poststenotic vessel does not constitute a contraindication for bypass grafting because its true diameter is flow dependent and cannot be judged with certainty from the preoperative angiogram.