Allograft reconstruction of the right ventricular outflow tract: Techniques and results

Abstract

A variety of valved and non-valved conduits have been used to establish right ventricle to pulmonary artery continuity in pediatric patients with complex congenital anomalies of the right ventricular outflow tract. Ross and Somerville originally described right ventricular outflow tract reconstruction with an extra-cardiac valved aortic allograft in 1966 (15). As early as 1968, aortic allograft calcification and degeneration were reported and attributed to then current methods of allograft collection, processing and storage (6). The disappointing results with the use of aortic allografts led to a search for more promising options for right ventricular outflow tract reconstruction. Mechanical valve prostheses were implanted in older children who were at a stage of physical development that would allow implantation of the relatively large valves. However, the inherent risk factors associated with thromboembolism and anticoagulation led most cardiac surgeons to avoid the use of a mechanical valve in the right ventricular outflow tract of pediatric patients. Favorable results with porcine valved bioprostheses implanted in adults led to their use in children in the early 1970’s. Unfortunately, it was not long before multiple problems presented themselves. Early valvar calcification and degeneration, conduit rigidity, and formation of intimai peel quickly curtailed enthusiasm for the use of porcine bioprostheses in the pediatric population (1, 10). As the popularity of porcine bioprostheses for pediatric use declined, interest in aortic valve allografts resurfaced. New methods of preservation and storage including antibiotic sterilization and cryopreservation resulted in increased cell viability and implied increased allograft durability (2, 4). In spite of less toxic preservation and storage methods, aortic valve allograft calcification continued to plague certain subsets of patients; younger children and patients with pulmonary hypertension (14, 16). The calcification problem along with the limited availability of aortic allografts prompted the use of pulmonary allografts for right ventricular outflow tract reconstruction in the mid 1980s. Pulmonary valve allografts with comparable viability demonstrated several potential advantages over aortic allografts (13). Pulmonary allograft anatomy and physiology accurately simulate the native right ventricular outflow tract, branch pulmonary arteries are available for distal reconstruction, and pulmonary allograft conduit calcium content is less than that of aortic conduits. Results with pulmonary allografts have been consistently superior to aortic allografts for reconstituting the right ventricle to pulmonary artery connection (3). However, recent follow-up of infants who received pulmonary allografts for right ventricular outflow tract reconstruction reveals that there is still room for improvement. Allograft calcification and degeneration that require reoperation are persistent problems for 16% of the infant population within ten years after implantation (9).