A Computational Fluid Dynamic Analysis of Various Heart Valves and Aortic Conduits, on Coronary Filling
Introduction: Aortic heart valve replacement/reconstruction may involve alterations of the geometry of the anatomic valve and surrounding tissue (often to the extent of complete excision). Several different types of valves and aortic prosthesis conduits are at the surgeon’s disposal to aid in repair, but what are the benefits of each? We sought to create models to investigate the benefits of these different options on the fluid dynamics into the coronary arteries, and hence the flow to the myocardial tissue. Procedure: Valve geometries of tri-leaflet (to represent normal anatomic and bio-prosthetic configuration), bi-leaflet (St. Jude), and single disc (Bjork-Shiley), were compared with a sinus and non-sinus conduit. The coronary arteries were placed at 17mm, based on 30 cadaver measurements (measured from the sinus leaflet junction straight up to the center of the coronary opening). As 85% of resting coronary filling occurs during diastole, the valves were placed in a closed position; a falling backpressure was placed at the aorta, and an outlet pressure at the coronary arteries of 5mmHg to represent coronary backpressure. Simulations were run at one millisecond time steps, for the total 215 milliseconds of the diastolic cycle. Analysis Results & Discussion: Fluid flow patterns and stresses were determined in the models. Mass flow rates where determined from each of the two coronary outlets. Maximum velocity and wall shear were calculated. The data from these models showed little variation in the fluid dynamics, as they relate to coronary filling, of the different valve geometries. There was however significant differences in the sinus and non-sinus geometries, ex. Wall shear for the non-sinus model was almost double that of the sinus model for the trileaflet valve configuration. Conclusion: Computational fluid dynamics can assist in determining the advantages and disadvantages to clinical decisions. The geometries of the prosthesis involved in heart valve surgery, specifically the devices surrounding the chosen valve, can have a significant effect on the overall flow regime into the coronaries, and hence have an impact on the functioning of the myocardial tissue as a whole. Further research with these models is anticipated with the release of ANSYS 8.0 & CFX 5.7, at which time their ability to handle fluid/solid interactions will be used to study the entire cycle of coronary filling.
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