The impact of imperfect frame deployment and rotational orientation on stress within the prosthetic leaflets during transcatheter aortic valve implantation

Abstract

TAVI devices are manufactured with cylindrical frames. However, the frames are rarely cylindrical post-deployment since deformation due to localised under expansion can be induced by calcified material on the native valve leaflets exerting irregular forces upon the frame. Consequently, the leaflets within a deformed TAVI device may undergo elevated stress during operation, which may lead to premature device failure.Using computational analysis a complete TAVI device model was simulated undergoing deployment into an aortic root model derived from CT data for a patient with severe calcific aortic stenosis, followed by a pressure simulated cardiac cycle. The complete analysis was performed eight times, each with the device at a different rotational orientation relative to the native valve, with an increment spacing of 15°.The TAVI device frames consistently featured significant distortions associated with bulky calcified material at the base of the non-coronary sinus. It was found that the average von Mises stress in the prosthetic valves was only increased in one of the cases relative to an idealised device. However, the maximum von Mises stress in the prosthetic valves was elevated in the majority of the cases.Furthermore, it was found that there were preferable orientations to deploy the prosthetic device, in this case, when the prosthetic leaflets were aligned with the native leaflets. As device orientation deviated from this orientation, the stresses in the valve increased because the distance between the prosthetic commissures decreased. This potentially could represent a sufficient increase in stress to induce variation in device lifespan.