With increasing life expectancy and younger patients opting for transcatheter heart valves, durable, non calcifying and anatomically conforming synthetic leaflet materials hold great potential.
The purpose of this in-vitro study is to characterize various potentially suitable materials and investigate their effects on the hydrodynamic behaviour for transcatheter heart valves (THV).
Materials and Methods
To assess the suitability of different synthetic materials, heart valve prototypes are built up using the same supporting stent frame structure and occluder body geometry as a commercially available 27mm THV. The CE mark product with pericardial leaflets is used as a benchmark, due to its previously characterized and clinically proven excellent flow characteristics.
The prototype’s materials are selected based on: Young's modulus, elongation and tensile strength. Additionally, composite materials with tailored mechanical properties are developed and included into the assessment.
The prototypes’ hydrodynamic performance is benchmarked in a pulse duplicator (HDTi 6000, BDC Laboratories) according to the ISO 5840-3.
The effective orifice area, pressure gradient in forward flow and leakage volume are derived from the pulse duplicator tests. For a better understanding of the leaflet opening, high speed videos are processed to calculate the maximal visual orifice area during systole.
Results
Polymers of the family of PTFE, PU and PET in form of fabrics or films were identified as having a high potential for the application as heart valve leaflets due to their excellent hemocompatibility and the experience of their intravascular applications in the cardiovascular field. Especially combinations of fabric reinforced polymers like TSPCU films with knitted PET reinforcements seem to offer favorable mechanical properties with Young‘s modulus and elongation data comparable to native tissue and tensile forces high enough to withstand the high forces exerted on the leaflets during the heart cycle.
The benchmark tests show that the flexibility of the leaflet material has a great influence on the hydrodynamic performance of the prosthesis. With a Young's modulus of 20.4 / 108.4 MPa and a visual opening area of 4.59 cm2 and a mean pressure drop of 5.2 mmHg, the composite material TSPCU with PET knit mesh reinforcement shows the best proximity to the reference values 4.26 cm2 (VOA) and 7.3 mmHg (mean PD) of the pericardial valve. Of the single layer materials investigated, the pure TSPCU with a thickness of 0.15 mm shows the best proximity to the reference with a visual opening area of 3.83 cm2 and a mean pressure drop of 6.6 mmHg.
Conclusions
THV prototypes with synthetic leaflets can be designed to perform similarly to pericardial valves regarding their hydrodynamic performance. Thereby the flexibility of the investigated materials correlates with their hydrodynamic behavior. In addition to the hydrodynamic performance, the aspect of fatigue strength must be included in leaflet development. Therefore, reinforced composites are directly considered in addition to the homogenous pure materials because of their higher tensile strength and crack growth resistance. Those dedicated composite materials can be designed and manufactured with tailored flex properties imitating the native tissue.
https://dgk.org/kongress_programme/ht2023/aV456.html