Segmental study of the terminal coronary vessels in coarctation of the aorta: a natural model for study of the effect of coronary hypertension on human coronary circulation.

An electron microscopic study of the coronary terminal circulation (starting with the small coronary arteries) was carried out on small pieces of myocardium operatively resected from the left ventricle on 11 patients with coarctation of the aorta. The patients were 4 to 20 years of age. Structural modifications were found in the small coronary arteries and arterioles. Two patterns of morphologic alterations were noted in these small resistance vessels. In the first pattern, seen in most of the children, the components of the arterial wall were still distinguishable, and well represented portions of smooth muscle layers were visualized together with muscle cells showing signs of degeneration and more or less widespread collagenous islets. The second pattern, seen in young adults, was characterized by a total collagenous transformation of the arterial wall. In contrast, the smaller microvessels (precapillary sphincter, metarterioles and capillaries) appeared free of pathologic change. It is postulated that the precapillary sphincters play a special protecting and regulating role in the coronary microcirculation in such cases with elevated coronary pressure. It is suggested that surgery should be performed at an early age to prevent further development of structural changes in the microvessels. The microcirculatory damage may contribute to the increased surgical mortality in patients with coarctation of the aorta operated on at a later age. These findings should trigger further research on the small coronary vessels in systemic hypertension.