Structural integrity assessment of heart valve prostheses: a damage tolerance analysis of the CarboMedics Prosthetic Heart Valve.

The design of mechanical heart valve prostheses must satisfy three basic requirements: biocompatibility, efficiency and durability. Over the past 25 years of clinical use, pyrolytic carbon has proven to be biocompatible and thromboresistant, and is therefore the material of choice for mechanical heart valve prostheses. However, in recent years the material has been questioned in this application because it is brittle and susceptible to subcritical crack growth. This has raised concerns regarding the structural reliability of prostheses constructed from this material. This paper describes the application of the damage tolerance methodology to assess the structural integrity of heart valve prostheses made of pyrolytic carbon. In particular, an analysis of the CarboMedics Prosthetic Heart Valve (CPHV) is presented. A new measure of fatigue lifetime, the fatigue safe-life index, is introduced. Additionally, the degradation of structural integrity from cavitation erosion is examined. It is shown that structural integrity, especially for brittle materials, is not just a function of design, but involves the entire manufacturing process. The damage tolerance method can be applied to assess and ensure the structural integrity of pyrolytic carbon prosthetic heart valve components.