Mitral regurgitation (MR) has a prevalence of approximately 2 % (Enriquez-Sarano et al., 2009) and can lead to severe complications such as left heart failure and even mortality (Trichon et al., 2003, Carabello, 2009). A prevalent method to address this issue involves remodeling or strengthening the mitral annulus using an annuloplasty ring (Acker et al., 2014). This technique offers significant benefits, including rapid restoration of cardiac function and elimination of the need for lifelong anticoagulation after the procedure.

The principle of mitral valve repair is to suture the annuloplasty ring to the mitral annulus and reduce mitral regurgitation by contracting the mitral annulus. As the annulus contracts, the annuloplasty ring is subjected to complex biomechanical loads during cardiac beating.

Mitral annuloplasty rings (MAR) are classified according to their stiffness into three types: hard, soft, and semi-rigid (Rausch et al., 2012). Research indicates that rigid rings maintain a constant area of the mitral valve orifice after implantation, whereas soft rings demonstrate a regular pattern of cyclic dilation throughout the cardiac cycle (Kronzon et al., 2009). Since stiff rings are not conducive to achieving and restoring physiological motion of the mitral annulus, they may lead to undesirable mitral valve tissue stress and reduced MV capacity in the long time (Sacks et al., 2019). Therefore, the future trend of MAR may be less stiff and restores physiological motion of the mitral annulus (Purser et al., 2011, Ncho et al., 2020, Frishman et al., 2022). However, the deformation rate of flexible rings in vivo is greater than stiff rings (Okada et al., 1995).

This increased flexibility, while beneficial, raises concerns about the possible compromise in structural stiffness and the subsequent implications for fatigue life, making it a subject of equal importance as the tearing of human mitral annular tissue (Bauer et al., 2006, De Caleya et al., 1983, Galiñanes et al., 1986).

To reduce the risk of fatigue damage to MAR in-vivo, the first edition of the international standard “ISO 5910–2018(E): Cardiovascular implants and extracorporeal systems – Cardiac valve repair devices” mandated in vitro evaluation of the devices; e.g., A validated stress/strain analysis (e.g. finite element analysis) under simulated in-vivo conditions should be performed on key structural components of the repair device. The repair device should be tested under appropriate loads while simulating device function in an appropriate environment or representative target implant site to a minimum of 400 million cycles required to demonstrate in-vitro device durability.

In implementing the standard, the small deformation of the rigid ring in-vivo resulted in a larger fatigue safety factor, so both finite element analysis and in-vitro fatigue testing allowed for a large margin of error. However, the deformation of the flexible MAR is much larger under the same load, more accurate stress/strain analysis and in-vitro testing to assess fatigue risk for flexible rings is important.

Current numerical analyses have modelled these loads as uniformly distributed forces (Baillargeon et al., 2015, Seki et al., 2019) or as concentrated points (Chiariello et al., 2021), derived from numerical models (Purser et al., 2011) or data from left ventricular simulation devices (Seki et al., 2019). On the other hand, in-vitro studies have typically applied concentrated displacement loads longitudinally (anterior-posterior) (Purser et al., 2011) and transversely (left–right) (Seki et al., 2019) to simulate in-vivo deformation of the annuloplasty ring.

This article identifies limitations in existing studies. In numerical analyses, the in-vivo fixation of the MAR to the annular tissue through uniformly distributed sutures suggests uniform pressure loads may not be the most accurate representation. Additionally, the ability of in-vitro simulation devices to accurately mimic annular motion remains unvalidated. Regarding in-vitro testing, it is proposed that different types of MAR should be subjected to varying test loads to ensure that the in-vitro tests accurately reflect the in-vivo forces.

This paper introduces a novel approach for the simulation and in-vitro testing of MAR. The study categories the rings into open-end and closed-end types and employs finite element analysis to simulate and analyze the deformation of different mitral valve forming rings under uniform concentrated loads. Subsequently, the article explores fatigue loading methods aimed at aligning MAR deformation with that observed in-vivo. It aims to enhance and optimize existing in-vitro fatigue testing methods. The final optimized in-vitro fatigue method more accurately reflects in-vivo loading conditions. Combining, for the first time, effective stress/strain analysis under simulated in vivo conditions with in vitro durability assessment, the study seeks to make in-vitro evaluation of mitral valve-forming rings more scientific, efficient and economical. Given on the innovative product and clinical use increasing trend of flexible rings, the research in this paper is highly significant.