Mechanical heart valve prostheses:: identification and evaluation (erratum)
Introduction
Prosthetic heart valves have been in use for over 40 years. The first heart valve substitute was actually placed in the descending thoracic aorta by Hufnagel (Hufnagel valve) in 1952 [1]. With the availability of cardiopulmonary bypass, the first orthotropic heart valve replacements were performed in 1960 [2], [3]. Today, patients with significant valvular lesions, stenotic or regurgitant, are routinely managed by the replacement (or repair) of the diseased valve. Heart valve prostheses are generically classified as mechanical heart valves (MHVs), which have only synthetic or nonbiological components and bioprosthesis (or tissue valves), which are made, at least in part, of biological components [4].
Worldwide, the number of prosthetic heart valves implanted is around 250,000 and is increasing at the rate of 5–7% per year [5]. Of all valves implanted, 60,000–75,000 are implanted in the United States of America. Worldwide, approximately 55% of implanted prosthetic heart valves are mechanical and 45% biological. In developed countries, percentages are reversed with biological valves holding 55% of the market. The use of MHVs is increasing at the rate of 3–5% per year, while bioprosthesis implants are increasing at 8–11% per year [5].
All MHV prostheses have a similar basic structure with three essential components: (1) the occluder, (2) the housing and (3) the sewing ring. The occluder is usually one or more rigid moveable parts which may be a ball (as in the Starr-Edwards valves), a disc (free floating as in the Bjork-Shiley valves) or a hinged leaflet, which may be circular or semi-circular. The housing may include a cage-like structure that helps the occluder to move by guiding and restricting its movement and a valve base or body, which is a ring made of metal (alloy) or a graphite coated with pyrolytic carbon, and supports the cage/struts and provides the “seat” for the occluder. The occluder fits in the housing, which has the fabric-sewing cuff attached to it, to allow implantation of the device. Most contemporary MHV prostheses have pyrolytic carbon as a major component, while some have metal components also. The sewing cuff is made with synthetic fabrics, with or without a “filler” between the layers of the fabric. Other refinements of this basic structure may be seen.
MHV prostheses can be divided into two kinds based on their flow pattern, those with lateral flow such as the ball in cage valves and those with more central flow such as the tilting disc and bileaflet valves.
Prosthetic heart valves of every kind work on the simple principle of passive movement, wherein closure depends on the pressure gradients and changes of blood flow in the heart. The competency of valve substitutes is generally related to the structure of the prosthesis and, more specifically, the way the prosthesis occluder is seated. Most MHV prostheses have a minimal degree of incompetence built in (1–5%) to allow “backwash” of the components to inhibit thrombosis.
The features of an ideal heart valve were enunciated by Harken et al. [3] in 1962 and have since been modified [6]. To this day, these criteria are not fulfilled by any one prosthetic heart valve.
Prostheses are frequently associated with complications that impact significantly on the patient's prognosis after heart valve replacement surgery [7]. Prosthetic heart valves are increasingly seen and will continue to be seen by surgical pathologists when they are removed at reoperation or when a patient who has had one or more valves replaced comes to autopsy. There are many excellent reviews available on the pathology of heart valve prostheses and many more will be available in the future about the current generation of prostheses [8], [9]. This paper and another on bioprostheses, which will follow in a subsequent issue of this journal, are meant to provide the pathologist with a ready reference to contemporary prosthetic heart valves, in an effort to help identify them and to familiarize themselves with major known complications associated with particular devices. A few of these valves have been used for many years and a good body of literature is available about them. Many others have been in use for relatively short periods and definitive information about them is not yet available. The detailed examination of these prostheses by skilled pathologists will have an immense impact on the accumulation of a body of information about these devices. This will help in deciding the value of individual types of devices and to compare different devices with each other.
Heart valve prostheses have many common complications. These include prosthesis-related complications such as device failure, whether design- or materials-related. Complications may also be related to the host, including infections and tissue overgrowth. The lifelong use of anticoagulants is mandatory for all patients with MHV prostheses. This treatment is associated with its own set of complications, such as hemorrhage. Many of these complications necessitate urgent removal of the device and its replacement. A working knowledge about each device is clearly essential when examining these explanted devices.
Numerous heart valve substitutes have been designed over the last 50 years. Many of these are no longer in use. In this paper, we have described heart valve prostheses that are currently being implanted in North America and, as well, the rest of the world. We have also described some that, though discontinued, continue to be explanted, and hence will be seen by pathologists for many years to come. We have excluded many that have been discontinued long ago, whose implant numbers were small and are highly unlikely to be seen today. Explanted prostheses if not easily identified should be referred to a pathologist with an interest in prosthetic heart valves, for detailed analyses. We have divided MHVs by occluder types and then described them (where necessary) alphabetically (by manufacturers names). The authors do not have any bias whatsoever for or against any manufacturer or for that matter any particular prosthetic heart valve.
Section snippets
The Starr-Edwards prosthesis
Model: Starr-Edwards 1260 (other Starr-Edwards mechanical prostheses include model 1000, 1200, 2300, 2310, 2320, 2400, 6000, 6120, 6300, 6310, 6320 and 6400).
Type: Caged ball.
Technical information: Manufactured and sold by Edwards Lifesciences (formerly Baxter Healthcare). The Starr-Edwards ball in cage model was the first commercially available mechanical prosthetic heart valve; introduced clinically in September of 1960 [10]. The aortic model 1260 was first implanted in 1968 and is still in
The AorTech Ultracor mechanical valve
Model: AorTech Ultracor U19A–U29A (aortic) and U23M–U33M (mitral).
Type: Single leaflet/tilting disc valve.
Technical information: AorTech Europe (Strathclyde, UK) markets the Ultracor valve. This prosthesis obtained the CE mark in 1995 and in its first 4 years of implantation, approximately 14,000 valves have been implanted worldwide [18].
Size range and available dimensions: The AorTech Ultracor model is available with sewing cuff diameters ranging from 19 to 29 and 23 to 33 mm for the aortic
The advancing the standard (ATS) open pivot bileaflet valve
Model: ATS open pivot bileaflet valve standard series and ATS open pivot bileaflet AP (advanced performance) series.
Type: Bileaflet valve; aortic and mitral positions.
Technical information: Manufactured and sold by ATS Medical; the standard series is designed for intra-annular placement; the AP series is designed for the supra-annular position [41].
Size range and available dimensions: Standard series (Fig. 8A,C)—aortic: 19–31 mm, mitral: 19–33 mm [42]. AP series (Fig. 8A,D)—aortic: 16–28 mm,
Acknowledgments
We gratefully acknowledge Ms. Melissa Skarban for her help in preparing this manuscript. We thank ATS valves, Edwards Life Sciences, Medtronic Heart Valves Division, Sorin Biomedica and St. Jude Medical for assistance with technical information, illustrative material either in electronic or hard copy photographs or the use of their websites on which illustrative material and technical data were available. We are particularly thankful to Ms. Sandra Schlehuber and Prof. Martin Guenther who
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2012, Surgical Pathology ClinicsCitation Excerpt :Finally, care should be taken not to over-interpret changes to the valve introduced during the surgical procedure to remove it; communication with the surgeon or reference to the operative note can be helpful in such instances. Of the numerous iterations on the mechanical heart valve design over the past 50 years, the vast majority can be classified into one of four main categories: caged ball, caged disc, tilting disc, and bileaflet tilting disc valves (Figs. 1 and 2).3,10–12 The caged ball design (see Fig. 1A) relies on a freely movable ball occluder that is held in place by a wire cage attached to the orifice ring.