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Publication:
Surgical Technology International XV - Cardiovascular Surgery
Article title:
Advanced Technologies for Cardiac Valvular Replacement, Transcatheter Innovations and Reconstructive Surgery

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Author(s)

W. R. Eric Jamieson, M.D., F.R.C.S. (C.), F.A.C.S., F.A.C.C.
Professor of Surgery and Director of Clinical Cardiac Surgery Research
University of British Columbia
St. Paul's Hospital, Vancouver General Hospital
Vancouver, Canada

Abstract
Since the 2002 Surgical Technology International monograph on valvular prostheses, there have been significant developmental and investigative advances. Aortic bioprostheses and mechanical prostheses have undergone design changes to optimize hemodynamics and prevent patient-prosthesis mismatch to have a potential satisfactory influence on survival. There has been continual technological improvements striving to bring forward advances that improve the durability of bioprostheses and reduce the thrombogenicity of mechanical prostheses. There also has been a continuance to preserve biological tissue with glutaraldehyde, rather than clinically evaluate other cross-linking technologies, by controlling or retarding calcification with therapies to control phospholipids and residual aldehydes. The techniques of mitral valve reconstruction have now been well established and new annuloplasty rings have been designed for the potential of maintaining the anatomical and physiological characteristics of the mitral annulus. Several objectives exist for annuloplasty, namely remodeling of the length and shape of the dilated annulus, prevention of dilatation of the annulus, and support for the potentially fragile area after partial-leaflet resection. Currently, there exists an emergence of catheter-based therapies for management of aortic stenosis and mitral regurgitation. For management of selected populations with critical aortic stenosis, techniques for aortic valve substitution have been developed for both antegrade and retrograde catheter techniques, as well as apical transventricular implantation. Mitral regurgitation has been addressed by experimental transcoronary sinus, stent-like devices and transventricular, edge-to-edge leaflet devices. The devices, descriptions and pictorial images comprise this monograph.

INTRODUCTION

 

The purpose of this communication is to provide a current overview of modern cardiac valvular devices, marketed and under investigational protocols, for replacement and reconstruction, as well as innovative technologies and devices for transcatheter valvular replacement and intervention.

 

Background

 

Surgical Technology International has published invited monographs by the author on valvular technology for replacement and reconstruction during the past ten years, previously in 1995, 1998, and 2002.1-3 Valvular interventional therapies have been the domain of cardiac surgeons since the 1960s, except for balloon dilation of congenital aortic or pulmonary stenosis and percutaneous balloon mitral valvuloplasty of rheumatic mitral stenosis. Balloon aortic valvuloplasty was evaluated in the mid 1980s, but is not considered an alternative to aortic valve replacement in patients suitable for surgery.
Since the 2002 publication,1-3 developmental and investigative emphasis has been on three fronts, namely: 1) optimizing hemodynamics of aortic bioprostheses and mechanical prostheses to prevent patient-prosthesis mismatch and the potential influence on survival; 2) continuance to preserve biological tissue with glutaraldehyde, rather than clinically evaluate other cross-linking technologies, by controlling or retarding calcification with therapies to control phospholipids and residual aldehydes; and 3) transcatheter technologies as therapies for management of aortic stenosis and mitral regurgitation.
Advancements in cardiac valvular replacement devices during the past 25 years have left residual problems with biological and mechanical prostheses. Extensive developments were introduced to reduce or eliminate valve-related complications, namely thromboembolism, anticoagulant-related hemorrhage, and structural failure; as well as optimize hemodynamic performance. Residual problems persist with both biological and mechanical prostheses. Structural failure of porcine and pericardial bioprostheses persist over time, with leaflet degeneration and dystrophic calcification. Thrombus formation from blood stasis and the resultant thromboembolic phenomena, despite anticoagulant management, remain continuing problems with mechanical prostheses.
Current mechanical prostheses have been developed to eliminate structural failure, facilitate intraoperative leaflet positioning, and facilitate radio-opacity for evaluation of prosthesis function. Present biological valvular prostheses have been developed with tissue preservation, together with stent designs, that contribute to preservation of anatomical characteristics and biomechanical properties of the leaflets. Current mechanical and biological prostheses are designated in Tables I and II. Developmental and investigational transcatheter devices are designated in Table III. Current devices to support reconstructive atrioventricular valvular procedures are designated in Table IV.
For the past 30 years, there has been a choice of bioprostheses and mechanical prostheses for cardiac valve replacement surgery. These developments during the past two decades have been introduced to reduce or eliminate valve-related complications—namely: thromboembolism, thrombosis—as well as anticoagulant-related hemorrhage with mechan- ical prostheses, and structural failure of bioprostheses. The prostheses designs have facilitated optimal hemodynamic performance. Prostheses, both the current and advanced generation, illustrated in this article have not significantly altered the incidence of these valve-related complications.
Surgical management of valvular heart disease is not limited to use of porcine and bovine pericardial bioprostheses and mechanical prostheses. Valvular reconstructive techniques, for mitral valve predominately over aortic valve, have been developed and popularized. Mitral valve reconstruction has provided superior results for degenerative disease over chronic rheumatic disease. Aortic valve reconstruction has been used primarily for manifestations of congenital disease.
Biological prostheses have not been limited to heterographic tissue. The allograft (homograft) has long been used as a substitute for any aortic valve either as a cryopreserved valve, or a hypothermic “homovital” valve, obtained from hearts explanted at transplantation. The allograft is usually implanted as a subcoronary valve, or as an aortic root replace- ment with reconstruction of the coronary ostia. The allograft is limited by availability and usually reserved for management of native and prosthetic valve endocarditis.
The pulmonary autograft is another alternative for aortic valve replacement, especially in children for reconstruction of complex congenital disease. The autograft is recommended for children because it remains viable, grows in proportion to somatic growth, and the annulus and sinotubular junction is increased in size to the normal range. Experience of the pulmonary autograft in young to middle-aged adults in the past decade is currently becoming available.

 

Prosthetic Failure Modes
Several identified modes of failure of valvular prostheses have been attributed to the structural components of the prostheses. Structural valve deterioration has been the predominant valve-related complication of glutaraldehyde-preserved biological prostheses. Porcine, or bovine pericardial bioprostheses, fail over extended periods of implantation related to age at implantation by dystrophic calcification, primary stress-related tears, or perforations or tears secondary to minimal or moderate calcification. The prosthetic failure modes of mechanical prostheses have been structural failure, predominantly historical; and thromboembolic phenomena, including thrombosis.