Growth and development of the pulmonary vascular bed in patients with tetralogy of Fallot with or without pulmonary atresia.

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Abstract
In a consecutive autopsy series of 17 patients with tetralogy of Fallot (TOF), including 5 patients with associated pulmonary atresia (TOF + PA), radiopaque material was injected into the pulmonary and collateral arteries and the lungs were examined using quantitative techniques to assess pulmonary vascular and alveolar structure and growth. Three types of systemic collateral arteries (SCA) were distinguished by their origin, each showing a characteristic type of anastomosis with a pulmonary artery: bronchial artery collaterals arise from bronchial arteries (so judged by origin and distribution) and anastomose with pulmonary arteries inside the lung. Direct aortic collaterals arise from the descending aorta, enter the lung at the hilum and supply a lobe, or at least a segment. Inside the lung, structure and distribution are those of a pulmonary artery; outside the lung, those of a systemic artery. These vessels sometimes anastomose inside the lung with pulmonary arteries from neighboring segments of lobes. Indirect aortic collaterals arise from major branches of the aorta other than bronchial arteries (e.g., internal mammary, subclavian) and usually anastomose with the central pulmonary arteries outside the lung. All 3 types of SCA were found in TOF + PA, but only bronchial artery collaterals were found in TOF. SCA narrowed at the site of anastomosis with a pulmonary artery; this apparently protected the peripheral intraacinar arteries from high flow and pressure and prevented changes of excessive muscularity and intimal hyperplasia. In most patients, the intraacinar arteries were smaller than normal; in patients who had large, surgically created shunts of long duration they were fewer in number, of greater muscularity and with severe occlusive changes of intimal hyperplasia. The number of alveoli was reduced in almost all patients, but because alveolar size was increased, only a few patients had a small lung volume. Early surgical correction of TOF may prevent the impairment in alveolar and vascular growth described here. In TOF + PA patients, selective arteriography of all large aortic collaterals should be performed preoperatively to determine their intrapulmonary distribution and relationship with central pulmonary arteries. This will help in selecting the surgical procedure and identify collaterals that can be safely ligated.