Biological replacement heart valves: Identification and evaluation

Abstract

Valvular heart disease is a worldwide problem. While most valvular disease is of inflammatory etiology in developing countries, in the developed world, most valvular heart disease today is degenerative. Regardless of the cause, valvular heart disease ultimately ends up as stenosis or incompetence and leads to progressive cardiac changes and secondary involvement of other organs in the body. Most patients with significant valvular heart disease need valve replacement. Annually, approximately 60,000 patients in the United States undergo heart valve replacement, while, worldwide, the number is over 250,000. Patients who undergo valve replacement lead a better lifestyle than those managed medically. In spite of significant progress in the development of prosthetic heart valves, prosthesis-related problems continue. It is therefore critical for pathologists and other medical staff to be able to recognize prostheses and their associated problems for further progress to be made in the development and improvement of prosthetic heart valves. Worldwide, over 55% of implanted prosthetic heart valves are mechanical valves and about 45% are biological. In many countries, the proportion of biological prostheses implanted is increasing fairly rapidly. At the same time, the repair of native heart valves is also increasing. In a previous article in this journal (Butany et al. Cardiovasc Pathol 12(1)), we have discussed the identification and evaluation of mechanical heart valve prostheses. In this article, we discuss the identification of replacement heart valves (having biological tissue components) and some of their salient features. Biological replacement heart valves may be divided into bioprosthetic valves, which usually have aldehyde-treated porcine aortic valve tissue or bovine pericardial tissue mounted on a fabric-covered stent and tissue heart valves, which are homograft aortic valves or autografts (the hosts own, e.g., pulmonary valve autografts). In spite of the progress made, contemporary heart valve substitutes still do not meet all the criteria for an optimal valve, as enunciated over 50 years ago by Dwight Harken et al. [1]. All prosthetic heart valves (including mechanical valves) have a fabric-covered sewing cuff that surrounds the base of the prosthesis, which provides attachment site to suture the valve (mechanical or biological) into the native valvular annulus, from which the native valve has usually been removed. Bioprosthetic heart valves or biological tissue valves generally imitate the flow and materials properties, that is, the design, of the native counterpart. This is a much closer match than mechanical valves. The most essential component of the bioprosthesis is made of biological tissues, usually porcine aortic valves or a threecusp valve made of bovine pericardium. A popular though somewhat limited (availability) type of valve is the tissue or homograft valve, which is usually a cadaveric aortic or pulmonary valve harvested and prepared for use as a replacement valve. Today, homografts are often cryopreserved after previous preparation and are then made available for use as replacement valves.