Anatomy. The absence of pulmonary valve leaflets creates to and fro flow across the pulmonary outflow throughout uterine life. (Most also have an absence of the ductus arteriosus.) This leads to volume loading of the RV and massive dilation of the main and branch PAs. The capacitance of the proximal PAs allows massive pulmonary regurgitation during diastole. Dilation of the primary and secondary branch pulmonary arteries creates bronchial compression, leading to bronchomalacia.
Physiology. The clinical course of TOF/APV depends primarily on the severity of PA dilation and bronchomalacia. In the most extreme cases, difficulty with ventilation and respiratory failure are present just after birth and are refractory to conventional ventilation. HFJV and prone positioning are sometimes helpful. However, when this is requisite, neonatal repair is mandatory and may be curative. When disease is less severe, newborns may be asymptomatic and surgery deferred for several months. In these cases, close monitoring for adequate growth and for recurrent respiratory infections is important.
Repair. Currently, repair for TOF/APV includes resection of the dilated main and branch PAs and replacement of these with homograft tissue. The distal branch PAs undergo reduction plasty and are anastomosed to the homograft. Bronchomalacia may be addressed by posterior pexy of the membranous trachea to the level of the carina, which stents open the mainstem bronchi. Distal bronchomalacia may persist.
Postoperative management. (1) The RV was volume-loaded preoperatively and may exhibit echocardiographic dysfunction due to the acute change in loading conditions. Maintaining RV preload by avoiding venodilation and replacing lost volume is important. (2) Junctional rhythm may occur and should be considered if a change in clinical status occurs. (3) Bronchomalacia may be significant causing expiratory obstruction and respiratory insufficiency. Some patients experience the prolonged need for mechanical ventilation, though with adequate PAplasty and bronchopexy the need for chronic ventilation is less common.