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 microns was measured. The number of arterioles was calculated per mm2; a distinction was made between vessels between 20 and 100 microns and those smaller than 20 microns. 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.