Quantitative morphometric analysis of the pulmonary arteries in two patients with D-transposition of the great arteries and persistence of the fetal circulation

Quantitative morphometric studies were performed on the pulmonary arteries of two newborns who died at 1 and 3 days of age with both transposition of the great arteries and persistence of the fetal circulation. Similar studies were performed on two normal control subjects (age 2 and 6 days), one newborn infant (age 1 day) with secondary persistence of the fetal circulation, and one newborn infant (age 2 days) with isolated D-transposition of the great arteries. Morphometric data, summarized herein, showed greatest mean percent wall thickness in the patients with persistent fetal circulation either alone or with D-transposition of the great arteries, as compared to those without it. When wall thickness was related to external diameter of the vessel, the greatest difference in thickness was observed in the smallest vessels (<150 μ in diameter). Extension of smooth muscle peripherally and to the smallest vessels (<50 μ) was similarly most marked in those infants with persistence of the fetal circulation, either secondary or with D-transposition of the great arteries. Alevolar/artery ratio determinations were similar among the six subjects. These comparative data indicate that cyanotic congenital heart disease and persistence of the fetal circulation may coexist but at the same time be unrelated in a single patient. Furthermore when such coexistence is unrecognized, pharmacologic manipulation of the ductus arteriosus may be hazardous. Speculation: Increased pulmonary arterial muscle similar to that seen in our two patients has been associated with the abnoral hemodynamics found in infants with hypoplastic left heart syndrome, aortic stenosis, and coarctation of the aorta. In contrast to these conditions we speculate that the increased muscle in the pulmonary arteries observed in our two patients was independent of D-transposition anatomy and its associated pathophysiology. Both adult and neonatal rats exposed to either environmental hypoxia or, in a latter case, maternal hypoxia develop increased muscle in the pulmonary arteries. These experimental models may be analogous to the two infants presented herein. In short, we strongly suspect that intrauterine hypoxia occurred in our two patients and may have been the stimulus producing the observed increase in muscle in their peripheral pulmonary arteries and resulting in, postnatally, persistence of the fetal circulation.