On the Mechanics of Transcatheter Aortic Valve Replacement

Abstract

Transcatheter aortic valves (TAVs) represent the latest advances in prosthetic heart valve technology. TAVs are truly transformational as they bring the benefit of heart valve replacement to patients that would otherwise not be operated on. Nevertheless, like any new device technology, the high expectations are dampened with growing concerns arising from frequent complications that develop in patients, indicating that the technology is far from being mature. Some of the most common complications that plague current TAV devices include malpositioning, crimp-induced leaflet damage, paravalvular leak, thrombosis, conduction abnormalities and prosthesis-patient mismatch. In this article, we provide an in-depth review of the current state-of-the-art pertaining the mechanics of TAVs while highlighting various studies guiding clinicians, regulatory agencies, and next-generation device designers.

Keywords: Minimally invasive; Paravalvular leak; Stent; TAVR; Thrombosis; Transcatheter aortic valve; Valve-in-valve.

Fig. 1

Transcatheter aortic valves FDA-approved for clinical use in the U.S. The figure is from Kheradvar et al (2015),1 with permission

Fig. 2

Types of valvular leakages in (a) Edwards SAPIEN valve and (b) CoreValve.

Fig. 3

Segmented CT scans presenting reconstructed 3D models of the aortic root and calcific lesions overlaid with positions of paravalvular leak after TAVR based on respective transesophageal echocardiography scans. Red arrows correspond to PVL at cusp side and orange arrows correspond to PVL at commissure between two cusps. Green, blue and yellow denote the calcification in the right coronary, non-coronary and left coronary cusps respectively.

Fig. 4

Time taken for a given number of particles to exit the sinus at the highest supra-annular deployment

Fig. 5

Reduced motion leaflet identification images of different prosthetic and surgical valves presented in Makkar et al 2015 with respect to their corresponding sinuses. LCA denotes Left Coronary Artery and RCA Right Coronary Artery

Fig. 6

Risks associated with supra-annular deployment of a Transcatheter Aortic Heart Valve

Fig. 7

Valve in Valve (ViV) arrangement using a stented valve as the surgical valve and a transcatheter aortic valve as the Valve-in-Valve

Fig. 8

Evolution of the aortic valve area as the configuration of the valves change in the case of (a) a surgical heart valve implantation originally and (b) a transcatheter aortic heart valve implantation originally. The value of 1.00 corresponds to a healthy aortic valve area and is taken to be 3.5 cm².

Fig. 9

(a) Pre- and (b) post-deployment geometries of the aortic root of Case 1. (c) full and (d) local views of the deformed the aortic root and balloon deployment indicates annulus tearing under the left coronary ostium due to dislodgement of calcification into the vulnerable part of the aortic sinus. Adopted from Wang et al. Biomech Model Mechanobiol (2015) 14:29–38

Fig. 10

(Left) SHG microscopy images compare the structural changes of intact and crimped pericardial tissues at depths of 10, 40, and 60 microns for crimping sizes of 18Fr over time. (Right) SEM images show intact (A, C, and E) and crimped (B, D, and F) states of three different pericardial leaflets at 18Fr, 16Fr, and 14Fr, respectively. Comparison of SEM images demonstrates substantial changes on the surface microstructure due to crimping, which increased with reduction of the collapsed profile. The images are adapted with permission from Alavi et al Annals of Thoracic Surgery (2014).4

Fig. 11

Verhoeff Van Gieson (VVG) staining of two cross sections extracted from Uncrimped (A) and crimped (B) bovine pericardial leaflets, respectively. Image A demonstrates intact elastin fibers (long black thin lines) in a cross section of an intact pericardial leaflet and image B shows fragmented elastin (short black thin lines) fibers in a stent-crimped leaflet. Elastin fibers in both cross sections were pointed by black arrows. Bars are 100 μm. The images are adapted from Sinha and Kheradvar (2015) 118

Fig. 12

Von Kossa and Trichrome staining of a cross section extracted from a crimped bovine pericardial leaflet. Both cross sections were extracted from the same location in the leaflet and then were stained for calcification and ECM investigations. A1 and B1 are mosaic images ( 10 stitched images) of Van Kossa and Trichrome staining of the cross section, respectively. A2 and B2 are two magnified local images to compare the calcification versus ECM. Image A2 and B2 show hydroxyapatite deposition and collagen fibers in the same location of tissue. Black and white arrows represent the calcified and damaged ECM zones in the leaflet. Bars are 600 μm and 100 μm in mosaic and magnified images, respectively. The images are from Kheradvar

Fig. 13

Panel A shows the presence of fresh thrombus (arrow), and panel B indicates the severe calcification and rupture of leaflets in a CoreValve. The images are taken from Richardt et al., NEJM, 2015 with permission.

Fig. 14

Macroscopic images of a TTEHV prior and after implantation in sheep pulmonary position. The valves were fabricated using biodegradable scaffolds and in vitro culture of vascular derived cells. The valves were decellularized prior to implantation to provide an off-the-shelf characteristic. The images were adapted from Driessen-Mol et al., 2014.