RESUMEN
BACKGROUND AND AIM OF THE STUDY: With the failure of animal trials to detect thrombosis in the Medtronic Parallel valve, interest has returned to finding a suitable in-vitro method for preclinical valve assessment. A technique has been developed that uses renneted milk to detect clotting around heart valves. The study aim was to determine whether the milk test could discern differences in clotting between the Parallel valve and the clinically successful St. Jude Medical (SJM) valve. METHODS: The Parallel valve and the SJM valve were tested in the aortic position of a rigid model heart chamber at 2 l/min, 70 bpm pulsatile flow. Initially, the valves were run for 30 min to obtain data for localized clotting. Subsequently, the valves were run for only 5 min to obtain data for the initial stages of clotting, including clot origin. RESULTS: Both valves clotted around their hinge regions in the 30-min tests, and this compared well with documented thrombogenic sites in vivo. The extent of clotting was similar, but clot adherence to the hinge pockets was greater on the Parallel valve than on the SJM valve. After the 5-min runs, no clot was visible on the SJM valve, but clot was consistently found in the hinge recesses of the Parallel valve, adjacent to the pivot. CONCLUSION: A renneted milk test can discern differences between the clotting potentials of different heart valves. The Parallel valve clotted earlier than the SJM valve, indicating that it was more thrombogenic. Early-stage clotting was seen to occur around the pivot in the hinge pockets. The milk test has potential for contributing to in-vitro preclinical assessment techniques.
Asunto(s)
Prótesis Valvulares Cardíacas , Trombosis/etiología , Válvula Aórtica/cirugía , Remoción de Dispositivos , Enfermedades de las Válvulas Cardíacas/cirugía , Implantación de Prótesis de Válvulas Cardíacas , Humanos , Válvula Mitral/cirugía , Modelos Cardiovasculares , Complicaciones Posoperatorias/etiología , Diseño de Prótesis , Falla de Prótesis , Flujo Pulsátil , Factores de TiempoRESUMEN
BACKGROUND AND AIM OF THE STUDY: An in-vitro technique has been developed to assess the flow-induced thrombosis of artificial heart valves, using renneted milk as a blood analog. Previous studies have demonstrated similarities between the clotting of blood and milk on both microscopic and macroscopic scales. The study aim was to further validate the milk test by comparing the locations of milk clot to those of thrombus formation on a wide selection of mechanical heart valves. METHODS: Nine different valves were tested in the aortic position of a model heart chamber in the Edinburgh milk rig. These included caged-ball valves (Starr-Edwards silastic ball with bare struts and metal ball with cloth-covered struts), tilting-disc valves (Björk-Shiley Standard, Björk-Shiley Monostrut, Medtronic-Hall, and Ultracor), and bileaflet valves (St. Jude Medical, Edwards-Duromedics, and CarboMedics). Renneted milk was pumped through the valves for 30 min at 2 l/min, 70 bpm pulsatile flow. After each run, valves were photographed for comparison with documented sites of thrombosis. RESULTS: All valves developed milk clot in specific, reproducible locations when run in the aortic position. Milk clot was found on the struts of caged-ball valves and tilting-disc valves, and around the hinge mechanism of the bileaflet valves. This compared favorably to documented cases of thrombosis in vivo. CONCLUSION: Renneted milk may be used to model flow-induced thrombus formation and to predict the thrombogenic sites of mechanical heart valves. Whilst it is not suggested that milk mimics the entire blood coagulation cascade, these results indicate that such behavior may not be necessary for predicting fluid mechanically induced clotting.