SYMPOSIA PAPER Published: 01 January 2007
STP45241S

Prediction of Failure in Existing Heart Valve Designs

Source

Artificial heart valves must be designed to survive greater than 109 cycles over 40 years of operation. Thus, fatigue represents one of the primary driving forces for safe operation of these devices. The inability to maintain the long term performance of critical devices in the future may lead to catastrophic failure and patient loss of life. The Bjork-Shiley convexo-concave (BSCC) heart valve provides an excellent case study in heart valve design. Approximately 86 000 valves were implanted from 1979 to 1987 and approximately 1 % of the valves experienced failure due to fatigue. Failures of this type are likely to yield a 70 % mortality rate in patients. To understand the conditions that produced failure, a detailed engineering assessment was conducted to determine valve designs, manufacturing processes, and physiologically related loading conditions that gave rise to an increased risk of failure. The material used in constructing the valve, Haynes 25, possesses good long crack threshold fatigue properties (ΔKth=4.5 MPa√m). However, continued operation of the valves produced cracking under certain physiological circumstances. These assessments indicate that a small subset of valves may operate under conditions that are close to the boundary between continued safe operation and catastrophic failure. These findings should be considered when using materials with inherently lower threshold fatigue properties. Crack growth data show that Nitinol has a threshold stress intensity factor ≈2 MPa√m, or less than half that of Haynes 25. Thus, current heart valve designs that use Nitinol should incorporate lessons learned from analyses of the BSCC heart valve to assess the likelihood of premature valve failure due to repeated loading.

Author Information

Koppenhoefer, Kyle
43230, Columbus, OH
Crompton, Jeffrey
43230, Columbus, OH
Dydo, James
43230, Columbus, OH
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Details
Developed by Committee: F04
Pages: 77–86
DOI: 10.1520/STP45241S
ISBN-EB: 978-0-8031-6237-2
ISBN-13: 978-0-8031-4511-5