Anatomical, Structural, and Device-Tissue Characterizations of the Atrioventricular Valves, and Associated Structures: Implications for Transcatheter Valve Repairs and/or Replacement Therapies

Abstract

Objective: This thesis aims to characterize the biophysical features of human cardiac atrioventricular (AV) valves, so to aid in the future designs and implementations of percutaneous repair and/or replacement therapies. There remain numerous unanswered questions concerning the complex anatomies and biomechanical properties of the AV valves, and associated structures. To address these questions, various types of investigations were performed, including: (1) anatomical, (2) structural/biomechanical, and (3) device-tissue characterizations. Methods: The anatomical characterizations, focused on the tricuspid valve, were studied using preserved human heart specimen with varying cardiac histories and disease states from the Visible Heart® Library. The biomechanical properties of fresh valvular tissue, and associated cardiac structures, were quantified using a digital force testing system. Visible Heart® testing models were employed as means to study the device-tissue interactions relative to the transcatheter replacement valves and repair techniques. Results: Chapters 1 and 2 detail the traditional dissections and 2D measurements of static tricuspid valves that were supplemented using real-time functional imaging and reconstructions. The right atrioventricular valve was found to have 4 functional leaflets in more than 40% of heart specimens, with the inferior region being the most variable area of the valve. The proximities between the tricuspid annuli and the right coronary artery, for hearts with atrioventricular valve regurgitation, averaged 5.3 mm, which is less than currently deployed anchor lengths. These distances were most frequently located at the posterior annular regions (40%) or adjacent to the posteroseptal commissure (53%). Chapters 3 and 4 are focused on quantifying the rupture and puncture forces of the human chordae tendineae and swine fossa ovalis, respectively. The mitral chordae failed at greater average stresses (22 MPa) but significantly lower strains (49%) compared to the tricuspid chordae (19 MPa; 63%). Chordae are more susceptible to rupture near the leaflet junction (54%). The average fossa ovalis needle puncture forces are significantly lower using radiofrequency needles (179 gf) systems compared to transseptal needles (243 gf). The sheath crossing forces, when normalized to tissue thickness, and atrial septal defect sizes increased with sheath size. The chordae and fossa ovalis are examined in relation to chordal repair and transseptal puncture procedures, respectively. Chapter 5, 6, and 7 supplement the aforementioned tissue studies with functional heart experiments using Visible Heart® apparatus methodologies. Transcatheter repair and replacement procedures are directly visualized using multimodal imaging to study the specific device-tissue interactions. In-vitro pilot studies illustrate that a successful tricuspid edge-to-edge repair could be performed using transcatheter suturing. The reanimated swine hearts demonstrated characteristics of acute tricuspid regurgitation. Transcatheter aortic valve replacement (TAVR) implantation and catheter-based techniques were also visualized as prospective investigations for transcatheter mitral valve replacement (TMVR) applications. Conclusion: Overall, the experiments summarized in this thesis comprise of anatomical, structural, and device-tissue interaction studies that can serve as implications for transcatheter AV valve repair/replacement systems.