Can the pinwheeling index serve as a surrogate for accelerated leaflet degeneration in transcatheter heart valves?

Transcatheter heart valve (THV) replacement is an advancing field, with various valve designs incorporating features like flexible frames to improve valve hemodynamics, durability, and patient outcomes. Leaflet pinwheeling, a common metric, is thought to negatively impact long-term durability. This study investigates the pinwheeling index and its correlation with stress distribution across different THV designs. Three THV designs were created using an optimization framework, each with a nominal size of 26-mm and varying leaflet coaptation heights of 10-mm, 13-mm, and 16-mm. Each valve design was evaluated under two conditions: one with a rigid frame and one with a flexible frame. The valves were implanted with a 90 % area expansion ratio, and their performance was assessed by examining key mechanical parameters, including the pinwheeling index and maximum in-plane principal stress under a diastolic loading condition. At a coaptation height of 10-mm, the pinwheeling index was 0 % for both frame types. At 13-mm, the rigid frame maintained a low index of 2 %, while the flexible frame increased slightly to 4 %. At 16-mm, the index rose for both frames, with the rigid frame at 7 % and the flexible frame at 10 %. The study found that leaflet stress was unrelated to the pinwheeling index. While flexible frames may reduce stress and improve long-term durability, they increase the pinwheeling index. Therefore, the traditional pinwheeling index may not reliably predict accelerated leaflet degeneration across different valve designs in comparative analyses. A comprehensive evaluation incorporating computational modeling, digital image correlation, and experimental validation is crucial for preclinical assessments.