Mechanics of cryopreserved aortic and pulmonary homografts

Background and aim of the study: The surgical placement of pulmonary valve grafts into the aortic position (the Ross procedure) has been performed for three decades. Cryopreserved pulmonary valves have had mixed clinical resu lts, however. The objectives of this study were to compare the mechanics of cryopreserved human aortic and pulmonary valve cusps and roots to determin e if the pulmonary root can withstand the greater pressures of the aortic p osition. Methods: Six aortic and six pulmonary valve roots were obtained from the Ox ford Valve Bank. They were harvested during cardiac transplantation from he arts explanted for dilated cardiomyopathy (mean patient age 68 years). The whole roots were initially stored frozen at -186 degrees C, then shipped pa cked on dry ice. After complete thawing, the roots were pressurized whole; test strips were then cut from the valve cusps, roots and sinuses and teste d for stress/strain, stress relaxation, and ultimate failure strength. Results: The pulmonary roots were more distensible (30% versus 20% strain t o lock-up) and less compliant when loaded to aortic pressures. The pulmonar y valve cusp and root tissue also showed greater extensibility and greater stiffness (lower compliance) when subjected to the same loads. Conclusion: We conclude that mechanical differences between aortic and pulm onary valve tissues are minimal. The pulmonary root should withstand the fo rces imposed on it when placed in the aortic position. However, if implante d whole, the pulmonary root will distend about 30% more than the aortic roo t when subjected to aortic pressures. These geometric changes may affect va lve function in the long term and should be appreciated when implanting a p ulmonary valve graft.