Natural resistance to atherosclerosis exhibited by the first centimeter of left and right coronary arteries.

A combined gross and histologic study carried out on 270 selected male subjects with the common type of distribution of the coronary arteries revealed a natural resistance to intimal thickening and plaque development exhibited by the left main coronary artery and by the first centimeter of the right coronary artery. The importance of this natural resistance in children, adolescents, young and mature adults up to 55 years old was demonstrated by means of a comparative investigation, involving the degree of intimal thickness, the media thickness versus intima thickness ratio and the per cent of subjects with atherosclerotic plaques. These parameters were examined in 6 selected samples: (a) at 5 mm distal to the aortic origin of the left main coronary artery, compared with those detected at 10 mm and 20 mm distal to the point of origin of the anterior descending artery; (b) at 5 mm from the aortic origin of the right coronary artery, compared with those recorded at 20 mm and 30 mm from the same point of origin. The differences between the above-mentioned samples appeared statistically significant in all age groups investigated. The first atherosclerotic lesions developed about three decades later in the left main coronary artery than in the proximal segment of the anterior descending artery. In the age group 51-55 years old, only 13.3% of subjects showed atherosclerotic plaques in the left main coronary artery, compared to 77.6% in the proximal segment of the anterior descending artery. Also only 6.6% of subjects 51-55 years old showed atherosclerotic plaques at 5 mm distal to the aortic origin of the right coronary artery, compared to 50.0% at 30 mm.