Transcatheter heart valve (THV) replacement has become a well-established intervention, initially focusing on the aortic and pulmonary valves, and now expanding to include other heart valves, such as the mitral and tricuspid valves (Popma et al., 2019, Mack et al., 2023). This evolution in THV technology has been driven by the development of various valve designs, each incorporating unique features aimed at improving valve hemodynamics, long-term durability, and patient outcomes. Some THVs are inspired by the design principles of surgical bioprosthetic valves, drawing on the extensive experience from traditional valve replacement procedures. For example, devices like the Evolut (Medtronic), Navitor (Abbott), and ACURATE neo2 (Boston Scientific) aortic valve systems feature flexible frames (Fig. 1a–c). These flexible frames could be advantageous in reducing leaflet stress, as previously demonstrated in surgical valves (Hamid et al., 1985, Christie and Barratt-Boyes, 1991). In contrast, some intra-annular valves, such as the SAPIEN family of devices (Edwards Lifesciences), use rigid frames to provide structural support to the valve after implantation in calcified native leaflets (Fig. 1d). In addition to differences in frame design, the leaflet shapes vary substantially among different valve designs. The various approaches to valve design underscore the range of strategies employed to optimize the structural integrity and hemodynamic performance of THVs.

THVs are often oversized relative to the anatomical dimensions of the patient's heart, with manufacturers providing a range of recommended annulus sizes for each valve size. This sizing strategy is designed to ensure the THV fits securely within the annulus. However, this approach frequently caused valve underexpansion, which subsequently resulted in a phenomenon known as leaflet pinwheeling. Leaflet pinwheeling occurs when the valve is not deployed in its intended shape, leading to localized bending of the leaflet material and excessive wrinkling or folding along the free edges (Fig. 2a and b) (Azadani et al., 2017). According to ISO 5840 guidelines for testing THVs, pinwheeling refers to the folding of leaflet-free edges caused by excessive leaflet redundancy. To quantify leaflet pinwheeling, the guideline proposes the use of a “pinwheeling index (PI),” a metric that can be defined based on the degree of leaflet folding after valve deployment. As shown in Fig. 2c, the pinwheeling index is determined using the following formula: pinwheeling index (PI)=Lactual-LidealLideal×100%. In this equation, Lactual represents the actual curvature length measured from the center of the free edge to the frame, while Lideal denotes the direct distance between the same two points. In accordance with ISO guidelines and FDA recommendations, THV manufacturers are required to perform standardized hydrodynamic testing to assess hemodynamic, structural, and durability performance. This includes visual inspections to detect potential issues such as leaflet pinwheeling, improper coaptation, and structural deterioration.

Leaflet pinwheeling is believed to compromise the valve's long-term durability by diminishing its resilience, causing early fatigue damage, and accelerating tissue degradation (Martin and Sun, 2014, Gunning et al., 2015). This issue has roots in surgical bioprosthetic valves, which have traditionally been prone to pinwheeling—a major failure mechanism causing early fatigue in valves like the Ionescu–Shiley—while the Edwards Perimount valve has demonstrated 18 years of durability without experiencing pinwheeling (Gunning et al., 2015). Nonetheless, the deployment of THVs differs significantly from that of surgical bioprosthetic valves, which typically include a surgical ring for stabilization. Furthermore, the design of THV leaflets and frames can vary greatly from one valve to another. Consequently, the goal of this study was to reevaluate the traditional pinwheeling index commonly utilized in preclinical testing and investigate whether leaflet stress, a marker of mechanical damage and long-term durability (Rodriguez-Gabella et al., 2017, Kostyunin et al., 2020), correlates with the pinwheeling index across different valve designs. This is important as the management of valvular heart disease shifts toward a lifetime care approach, making a thorough comparison of valve designs increasingly essential.