Date of Award
Master of Science in Biomedical Engineering - (M.S.)
Biomedical Engineering Committee
David S. Kristol
Background - The stent, Delrin® support frame, for porcine heart valves has been blamed for reduced durability of these valves due to the additional stress caused by the relative stiffness of the stent. There is a tendency among surgeons to do away with the stent in the aortic position and use porcine stentless valves which are sewn directly in the aortic position after removing diseased valve. These stentless valves are extremely difficult to test and no appropriate holder has been designed for this purpose. New approach for in vitro testing of these valves has been developed at Sheihigh, Inc., Millburn NJ. The stentless valves are sewn in real porcine heart; the aortic root is dissected out and the aortic root is connected to a holder then inserted in the Pulse Duplicator System.
This aortic root is kept fresh with antiseptic solutions but not fixed with glutaraldehyde since it can become stiffer than the natural aorta.
Method - In vitro hemodynamics, blood flow performance, of porcine bioprostheses were tested under physiological conditions using the pulse duplicator system. The system is comprised of a test chamber in which the porcine bioprosthesis is inserted, a pressure transducer, a flow probe, an amplifier pair, and real time software to analyze the fluid dynamics of stented and unstented porcine bioprostheses.
Thirteen Shethigh Porcine valves were tested in the Pulse Duplicator System for this study which include 7 - 25mm valve, 4 stented and 3 stentless, and 6 - 23mm valves, 3 stented and 3 stentless.
Results - Preliminary results from testing three of each stented and stentless 23mm valves at a rate of approximately 90 Beats Per Minute (BPM) showed an average of a 6% increase in the Effective Orifice Area (EOA) of the Stentless bioprosthesis over the standard Stented bioprosthesis. The EOA ranged from a high of 2.41cm2 for the 25mm stentless to a low of 21 8cm2 for the 25mm stented bioprosthesis. The mean EOA for the stented bioprostheses was 1.94cm2 and 2.06cm2 for the stentless bioprostheses.
Conclusion - The series of tests which were performed using aortic roots and sizers to size the aortic root to implant the valve into the proper size root revealed that sizing the root is critical when trying to achieve a maximum Effective Orifice Area. Sizing of the stented valve implanted is not as critical due to the stent providing a predefined area for the valve, but then there is no means for the valve to distend at high flow rates. The stentless bioprosthesis is superior to the standard bioprosthesis in the sense there is no stress on the valve comparable to the stented bioprosthesis. At high flow rates the EOA of the stentless valve is not limited to the inside diameter of the valve because it is allowed to distend outward at times of high flow rates. Using stentless valves is of importance at times of high flow rates in order to eliminate the stenosis, the abnormal narrowing of the orifice, opening, in a heart valve, which is produced in stented valves.
Parker, Sean, "In situ aortic root in vitro testing of the stented and stenless porcine aortic heart valves" (1999). Theses. 871.