The coronary arterioles in newborns, infants and children. A morphometric study of normal hearts and hearts with aortic atresia and complete transposition

The state of development of the intramyocardial coronary arterioles in normal hearts and hearts with congenital malformations is unknown, although these vessels play an important role in regulating myocardial blood flow. To remedy the situation, we studied 64 normal hearts (ranging in age from 23 weeks gestational age to 75 years), 13 hearts with complete transposition (5 with intact ventricular septum and 8 with a defect) and 11 hearts with classical aortic atresia. The medial thickness of arterioles with an external diameter from 20 to 100 μm was measured. The number of arterioles was calculated per mm2; a distinction was made between vessels between 20 and 100 μm and those smaller than 20 μm. The results show that the arteriolar vascular bed is not yet full grown at term. Within the first year of life the medial smooth muscle mass increases, most likely due to growth and peripheral extension onto the smaller branches. In the hearts of patients with aortic atresia who lived for a week or less, the arteriolar media appeared to lag behind that in normal hearts. In those patients who survived into the second post-natal week, however, the arteriolar bed was almost as anticipated for normal. The normal values obtained in the latter group could be due to intrinsic differences, rather than expressing actual and rapid growth. A decrease in both medial thickness and the number of arterioles was observed in hearts with complete transposition, affecting all heart compartments without a distinction between cases with and without a ventricular septal defect. This suggests either that the arteriolar bed lags behind the anticipated developmental state (despite the adjustment in muscle mass between the right and left ventricle) or that generalized dilatation of the vascular bed may give the impression that the medial thickness and number of arterioles is decreased. The functional consequences of these findings need further investigation. © 1986.