Structural study of pulmonary circulation and of heart in total anomalous pulmonary venous return in early infancy.

Quantitative morphometric techniques have been applied to the injected and inflated lung and to the heart in 9 infants with total anomalous pulmonary venous return dying with obstruction to pulmonary venous return. In 5 (mean age at death 55 days) pge 20 days) to an infradiaphragmatic site. Structural changes were present in the pulmonary circulation in all patients, even in the youngest, an 8-day-old child. In both types of total anomalous pulmonary venous return increased arterial muscularity was severe, as shown by increase in wall thickness and by extension of muscle into smaller and more peripheral arteries than normal; these changes tended to increase with age. Where the pulmonary venous blood drained to a supradiaphragmatic site, the severity of arterial medial hypertrophy correlated inversely with the magnitude of the pulmonary: systemic flow ratio, increasing as the pulmonary blood flow fell. Vein wall thickness was increased and in all but the youngest child the veins were 'arterialised'. At the lung periphery the arteries and alveoli appeared to have multiplied normally. Arterial size varied according to whether pulmonary venous blood drained above or below the diaphragm; the diameter of pre- and intra-acinar arteries was increased only in cases where the pulmonary venous return drained to a supradiaphragmatic site, being normal when it drained to an infradiaphragmatic site. In the heart the left ventricle was of normal size in all but one case. Dilation and severe hypertrophy of the right ventricle and septum were present only in cases of drainage to a supradiaphragmatic site. In the older patients with the latter anomaly dilation of the pulmonary arteries and right ventricle suggested that a large left-to-right shunt had preceded the onset of obstruction to pulmonary venous return and that the more severe right ventricular and septal hypertrophy in these cases might be the result of a longer duration of pulmonary hypertension. In contrast, in total anomalous pulmonary venous return to an infradiaphragmatic site it appears that obstruction to pulmonary venous return develops soon after birth and prevents a large increase in pulmonary blood flow, and thus neither the pulmonary arteries nor the right ventricle become dilated. In infants with total anomalous pulmonary venous return and obstruction to pulmonary venous return, it is striking how rapidly the pulmonary circulation develops new muscle.