Hydrodynamic performance of the Medtronic Freestyle Aortic Root Bioprosthesis

The Freestyle Aortic Root Bioprosthesis is comprised of a porcine aortic root preserved in buffered 0.2% glutaraldehyde solution. It is fixed at a pressure sufficient to distend the aortic wall, but the leaflets are fixed with no transvalvular gradient. The bioprosthesis is treated with alpha-amino-oleic acid (AOA) to reduce the potential for leaflet calcification. In order to conduct in-vitro performance studies, a simulated aorta test chamber was developed. The test chamber material formulation can be altered to produce a wide range of desired compliances, while maintaining repeatable dimensional specifications. The test chamber design also allows for performance testing simulating a variety of implant techniques. Both Freestyle and the stented control valves (Hancock Standard Model 242) were mounted within the simulated aortas for these studies. Steady state and pulsatile flow pressure drop studies demonstrated a significantly lower gradient across the Freestyle valve when compared to stented Hancock Standard controls. In addition, the smaller size (19,21,23 mm) Freestyle valves had superior EOA's compared to the Standard St. Jude bileaflet mechanical and Hancock modified orifice (MO) porcine valve designs. The regurgitant volumes were equivalent to the control (Hancock Standard model 242) valves when compared to the Freestyle valves with equivalent flow areas. Additional studies were conducted in order to determine the effects of sizing and configuration on hydrodynamic performance. These studies were performed in four configurations: total root, inclusion, partially scalloped (two sinuses) and fully scalloped valve. These studies demonstrated that both pressure drop and regurgitation are significantly affected by valve sizing and implant technique. Accelerated wear studies were performed on three of each size and six of the largest Freestyle valves. Stented Hancock Standard valves and non-AOA treated Freestyle valves were used as controls. Hydrodynamic performance tests were conducted at intervals throughout the study. No evidence was found to indicate a difference in wear or hydrodynamic performance between the AOA treated and untreated Freestyle valves.