Mechanical cardiac valve prostheses: wear characteristics and magnitudes in three bileaflet valves.

Three different bileaflet mechanical heart valves were evaluated for wear and durability characterization. The designs of the three mechanical heart valves encompass both geometrical and material interface differences. The St. Jude Medical mechanical heart valve is partially characterized by a flat-on-flat leaflet-to-orifice closing stop interface with the orifice constructed of a graphite substrate with pyrolytic carbon coating. The CarboMedicsTM mechanical heart valve is partially characterized by a flat-on-cylindrical leaflet-to-orifice closing stop interface and the orifice is constructed of solid pyrolytic carbon. The Sorin Biomedica BicarbonTM mechanical heart valve is characterized by a flat-on-flat leaflet-to-orifice closing stop interface with the leaflets constructed of pyrolytic carbon and the orifice constructed of a titanium alloy. In vitro mechanical wear analysis was performed in accordance with current FDA and ISO guidelines for accelerated life and durability testing. Comparisons revealed that the St. Jude Medical mechanical heart valve had the lowest magnitude of wear, but both the St. Jude Medical and CarboMedics mechanical heart valves proved to be very wear resistant. The Sorin Biomedica Bicarbon mechanical heart valve showed an extremely high wear rate and magnitude. The overall mechanism for material removal and wear must be fully determined to assess the long term efficacy of the mechanical heart valve.

An interlaboratory comparison of the FDA protocol for the evaluation of cavitation potential of mechanical heart valves.

Five laboratories carried out measurements of cavitation threshold for a common set of six mechanical prosthetic heart valves, two each from three different manufacturers. This study was intended to evaluate to what extent FDA's current guidance for cavitation testing would lead to consistent results in a variety of laboratory settings and to seek areas for improvement in the recommended test protocol. The inter-laboratory study protocol specified: (1) characterization of the test fluid by oxygen content and electrical conductivity, (2) location and frequency response of pressure sensors, (3) determination of ventricular and atrial pressures (P) and loading rates (dP/dt) averaged over the time period of valve closure and over the time periods of 1 ms, 5 ms, and 20 ms prior to video visualization. The protocol did not specify: (1) the fluid pumping equipment to be used to generate cavitation, (2) the pump or fluid parameters adjusted to raise or lower the loading rate, (3) the equipment, technique, or sensitivity used to visualize cavitation, and (4) a specific definition of the threshold for cavitation. Results from the five laboratories are reported. Significant differences in results were observed in dP/dt and in the pressure difference across the valves during closure at cavitation threshold. Specific differences in test systems included a wide range of ventricular compliance and single valved versus double valved test systems. Three single valve systems with compliant ventricles produced results in reasonable agreement with one another. Further similarity in test equipment should be specified to assure adequate interlaboratory reliability for cavitation testing. Areas needing better specification include the design of the valve mount, the design of the cavitation generators, and qualitative criteria for detection of threshold cavitation.