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| MISCELLANEOUS - HISTORY |
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| Year : 2015 | Volume
: 1
| Issue : 3 | Page : 289-293 |
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Development of mechanical heart valves - an inspiring tale
P Rajashekar
Department of Cardiothoracic Surgery, All India Institute of Medical Sciences, New Delhi, India
| Date of Web Publication | 23-Feb-2016 |
Correspondence Address:
P Rajashekar
Department of Cardiothoracic Surgery, All India Institute of Medical Sciences, New Delhi
India
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/2395-5414.177309
The historical evolution of the prosthetic heart valves from the first attempts with the Hufnagel's valve in the treatment of the aortic insufficiency to the Starr-Edwards' ball valve and later the tilting disc valves (Bjork-Shiley etc.,) and finally the bileaflet valves (St. Jude) are discussed. The Indian contribution with Chitra valve is also described. Keywords: Chitra valve, history, mechanical valves, prosthetic valves
How to cite this article:
Rajashekar P. Development of mechanical heart valves - an inspiring tale. J Pract Cardiovasc Sci 2015;1:289-93 |
| Introduction | |  |
Valve replacement surgery has a long, important, and inspiring history. [1],[2],[3],[4],[5] The attempts to surgically correct valvular heart disease through valvuloplasty started in the 1920s, but the results had been discouraging. C. Walton Lillehei, Henry Bahnson, and many other surgeons tried to attach individual polymer leaflets, but the results were poor because of the subsequent rupture.
The development of prosthetic heart valves involved a search for biologically compatible materials and hemodynamically tolerant designs. Several demonstrations and analysis were carried out by trial and error methods, but no satisfactory mechanism was found to achieve a hemodynamically stable, implantable, and durable heart valve. This review is an effort to discuss the innovations and designing efforts involved in the development of mechanical prosthetic heart valves. The search of avoiding thromboembolic complications of mechanical prosthetic valves and lifelong anticoagulation and associated side effects lead to bioprosthetic tissue valves which were developed later in the history but are not included in the present discussion.
| Necessity is the Mother of Invention | | |
The first steps
The need of prosthetic heart valves was recognized long ago but seemed like an impossible vision until 1952. Dr. Charles Hufnagel implanted an acrylic ball valve prosthesis into the descending aorta of a 30-year-old woman to correct aortic valve insufficiency in 1952 at Georgetown Medical Center in Washington, DC, who could lead a normal life after the surgery [Figure 1]. [1],[2] Hufnagel's invention was a methylcrylate chamber containing the methylcrylaye ball in the middle, which was "implanted quickly into the descending aorta using a nonsuture technique." More than 200 implanted Hufnagel valves functioned for as long as 30 years with no significant wear. No anticoagulation was used. The drawback to this model, besides the mortality and cumbersome insertion during the brief cross-clamp period, was that patients could hear the plastic ball bouncing around inside them. At a later stage, a hollow nylon ball coated with silicone rubber was used for designing the valve instead of the methacrylate ball which eventually reduced the valve noise.
Hufnagel valves and his experiments on biocompatible materials successfully proved that synthetic materials could be used to create heart valves. The major hitch of Hufnagel valves was that it could only be positioned in descending aorta and not inside the heart and, therefore, had poor hemodynamics. Because of these reasons, it failed to resolve the diseased valve, instead it alleviated the symptoms.
| Coming of the Caged Ball Valve | | |
Dr Harken working with Mr W. C. Birtwell from Davol Rubber Company, Rhode Island, started the modern era of prosthetic valve replacement by the insertion of his double cage-ball valve into the aortic orifice below the coronary Ostia following excision of the diseased cusps. The valve was fabricated with stainless steel. Dr. Harken was concerned that the ball could intrude into the aortic wall. Thus, he designed his valve with a second outer concentric cage. The valve was implanted in 17 patients initially, of which only two could survive. Both the patients required successive valve replacement, one at 3 years for peri-valvular leak and another at 22 years for bacterial endocarditis. The ball valve removed after 22 years had no deterioration. The Harken's valve model did not have the benefit of the "heat curing process." [3],[4]
In the mid-1960s, another successful valve was introduced, called as Starr-Edwards Ball Valve [5],[6],[7]] - which was actually an improved version of Hufnagel's ball-valve which could be implanted in the heart after excision of the diseased valve. A silastic ball with circular sewing wing was used in designing of the valve was slightly smaller in size and was caged from both the sides [Figure 1].
Albert Starr, a physician, and Lowell Edwards, an electrical engineer, simplified the caged-ball valve using a single titanium cage, a silastic ball, and a sewing ring covered with Teflon. The Starr-Edwards valve was first implanted in the mitral position in 1960, and later in the aortic position. The valve became commercially available in 1965. In comparison to Hufnagel's valve, with the caged-ball valve, the ease of implantability was more. It had a sewing ring which made the process of suturing of valve easy for surgeons. The silastic ball of the valve had a tendency to absorb liquid which malformed it or at times resulted in jamming. Moreover, the obstacle to the laminar blood flow used to cause high pressure gradients, which was observed more in patients with a small aortic root.
| Further Developments | | |
In the early 1960s, many of the surgeons recognized the obstacles faced during implant, especially in the placement of prosthetic valves in the heart. Dr. Magovern Senior Chief of Cardiothoracic Surgery and Mr. Harry Cromie [Figure 2], an engineer worked together at the University of Pittsburgh Medical Center and developed a ball valve. [8] He was concerned more about the time taken to suture or fix the valve into the heart and this outlook made him approach the development of prosthetic valve in a different way. He designed the valve in a manner that it eradicated the requirement of suturing for fixation of prosthetic valve. The procedure was based on mechanical fixation which requires only a few minutes. The essential feature of this fixation was the use of multiple curved pins to hold the valve in the aortic annulus. The valve was for the 1 st time implanted in 1962 and was used for many years in both mitral as well as aortic positions. The production of the valve was stopped in 1980 due to various reasons, although Magovern continued to implant the valve for the next couple of years. A study by Dr. Magovern, collected the data of 25 years, which showed that the valve was used in approximately 4,798 cases. The data analyzed by them showed that the Magovern-Cromie valve was safe, durable, and efficient. The valve-related morbidity observed was in the lower expected ranges for prosthetic aortic valves: Ball variance, 0.3%/patient-year; paraprosthetic leak, 0.41%/patient-year; valve endocarditis, 0.43%/patient-year; valve thrombosis, 0.04%/patient-year; and embolic events, 3.95%/patient-year. The incidence of aortic valve reoperation was 0.76%/patient-year. The 5-year, 10-year, and 20-year probability of survival corrected for normal mortality was 77%, 64%, and 52% for all discharged patients.
In 2008, the longest functioning Magovern-Cromie Sutureless prosthetic aortic valve was reported. The valve was explanted 42 years after implant.
In 1963, Smeloff along with a mechanical engineer at California State University, [9] Sacramento designed a valve to employ a "FULL-FLOW" orifice concept. The valve design comprised a double set of cages permitting the silicone elastomer ball to rest on the smaller inflow cage during valve closure. As the valve was one of its kind, therefore commercial manufacturing of it was then transferred to Cutter Laboratories, Berkley California in 1966. In 1989 at the World Congress on Valve replacement, San Diego, Dr. Smeloff reported that 50,000 Smeloff valves had been implanted worldwide, with no structural failure for 22 years of use.
Braunwald [10] developed a flexible polyurethane-dacron fabric mitral valve prosthesis with attached Teflon-tape chordae tendoneae. The valve was implanted in March, 1960. Dr. Braunwald observed that the fabric was infiltrated by fibrous connective tissue and she speculated that applying fabric to the metal cage of a ball valve might reduce thrombus formation. Thereafter, she started working with cutter laboratories to develop a cloth covered caged ball valve. They covered the struts with a knit dacron tubing and the inflow ring with an ultrathin polypropylene mesh fabric. The valve was used clinically from 1968 onwards. Results obtained were good and low incidence for valve-related complications were observed. Approximately 475 valves were implanted. However, after several years of clinical use cases were reported of fabric wear and silicone poppet abrasion in aortic valves leading to poppet escape. Thus, production of the Braunwald-Cutter valve ceased in 1979.
| Use of Pyrolytic Carbon for the Fabrication of Prosthetic Heart Valves | | |
Dr Michael DeBakey and Harry Cromie of Surgitool introduced a ball valve in 1967. In 1969, Dr. Jack Bokros at the General Atomic Company, LaJolla, California introduced a new carbon material pyrolytic carbon poppet which replaced the polyethylene poppet. The pyrolyte ball was intended to limit ball variance; unfortunately, the relatively hard ball and soft titanium cage led to strut wear and some instances of strut fracture. The fabrication of a hollow ball of pyrolytic carbon (pyrolyte) was a landmark research in mechanical valve development. It was originally developed for the encapsulation of nuclear fuel rods, and became over the next decade, the principal biomaterial for virtually all new mechanical valves.
Dr Bokros' [11] found that highly polished pyrolytic carbon will not bond with heparin and in canine in vivo screening tests, the Bokros material proved to be the most thrombo resistant, nonheparinized material that they had evaluated. Encouraged by their findings, Bokros subsequently developed the ball poppet for the DeBakey-Surgitool valve and the discs and leaflets for virtually all mechanical valves developed over the next 30 years.
| Coming of the Nontilting Disc Valves | | |
Kay-Shiley disc valve
Dr Jerome Kay, Professor of Cardiac Surgery at the University of Southern California Medical Center, and a valve engineer, Mr Donald Shiley collaborated together and introduced the Kay-Shiley disc valve. [12] It was the first disc valve that achieved worldwide use beginning in 1965. It was designed with a low profile. It was a reliable mitral prosthesis that utilized a stellite housing and a flat silicone elastomer disc. Unfortunately, there were problems with wear of the silicone elastomer disc and hence was replaced with a Delrin polymer disc in 1975. Valve durability was markedly improved with the Derlin disc. Approximately, 12,000 of these Kay-Shiley valves were implanted worldwide at mitral and tricuspid positions.
To prevent the disc impingement by the left ventricular wall, Dr. Kay modified the standard Kay-Shiley valve and added a muscle-guard onto it. It was used by Dr. Kay primarily, but was not used worldwide by other surgeons.
Beall-Surgitool disc valve
Following the trend, Dr. Arthur Beall, Baylor college of Medicine in Houston in collaboration with Mr. Howard Cromie, Surgitool developed a Teflon disc valve in the mid 1960s. [13] Over a period of 10 years of clinical existence, the valve was redesigned 5-time. Post this changes in design of the valve, almost 5,000 valves were implanted at the mitral position. In 1985, the production was discontinued due to the fabric wear on the annular opening.
| The Tilting Disc Valve in the 1970s | | |
In the mid-1970s the tilting disc valve were introduced. These included the Bjork-Shiley convexo-concave (BSCC) tilting disc valve, Lillehei-Kaster tilting disc valve, Omniscience tilting disc valve, Omnicarbon tilting disc valve and Hall-Kaster and Medtronic-Hall tilting disc valves [Figure 2].
The very first tilting disc model, i.e., BSCC tilting disc was implanted in 1975. [14],[15],[16],[17] The valve was designed in a manner so that a large flow through the orifice on the backside of the open disc could be obtained. Both the stellite housing and concave pyrolyte disc were used. The inlet and outlet struts were modified such the disc could make a slide forward and down movement of about 2 mm, thereby achieving the desired enlargement of the valve orifice. However in a few years of its use, cases were reported of an inordinate number of fractures at the weld site of the small c-shaped outflow strut. Bjork reported the hazard function and mechanical failure among the series of BSCC heart valves. The trend was observed for almost 7-year follow-up period. The 7-year actuarial incidence of mechanical failure among these valves was found to be 12.5% and many of the patients with these valves was considered for prophylactic replacement.
Hall-Kaster and Medtronic-Hall tilting disc valves
Dr. Kari Victor Hall, Chairman, Department of Surgery, Rikshospitalet, Oslo, Norway and Robert Kaster developed the Hall-Kaster valve which was used in 1977 for the 1 st time. The design of the valve, comprised a unique tilting prolyte disc with a small central perforation for a thin metal strut that guides the disc during opening and closing of the valve. It was widely used throughout the world. In 1987 minimal mechanical engineering changes were done in the design of the valve. The manufacturing and distribution of the valve was taken over by Medtronic. More than 300,000 Hall-Kaster and Medtronic-Hall valves have been used worldwide with no reports of structural failure. [18],[19],[20],[21],[22]
| Bileaflet Valves | | |
Just after the era of tilting disc models, the bileaflet heart valve model was introduced in 1979. The valves usually consist of two semicircular leaflets that rotate about struts attached to the valve housing. [23],[24],[25]
The bileaflet model had advantages over earlier models. The design of the valve was such that it resulted in a greater effective orifice area (2.4-3.2 cm 2 ). They were the least thrombogenic valves in comparison to other prosthetic valves. The types of bileaflet valves developed were Gott-Dagette bileaflet valve, Kalke-Lillehei bileaflet valve, St. Jude Medical bileaflet valve and Carbomedics bileaflet valve [Figure 3].
The Gott-Daggett bileaflet valve was the very first model of bileaflet design and was introduced in the late 1960s. It was implanted in approximately 500 patients at both mitral and aortic positions. The clinical outcome was relatively good. Despite of bileaflet design, the valve had one disadvantage. A relatively stagnant blood flow in the area of the superstrut used to capture the flexible leaflets, was observed. This area was occasionally the site of thrombus; however, no clinical episodes of thromboembolism were reported. For this reason, the valve was withdrawn from the market in 1966; the patients who were implanted with this valve were followed for more than 25 years. No deterioration of the flexible silicone-coated Teflon leaflets were reported during this period or even later on.
| St. Jude Medical Bileaflet Valve | | |
The St. Jude Medical bileaflet valve was implanted in 1977 for the 1 st time. Mr. Manny Villafana, founder of Cardiac Pacemaker St. Jude Medical was the implementer for the development of St. Jude Medical bilefalet valve. The valve was primarily designed by an individual engineer Xinon (Chris) Posis, and he took suggestions from the cardiovascular surgeon Dr. Demetre Nicoloff, University of Minnesota. Furthermore, both of them worked together and took suggestions from other surgeons and fellow engineers. Working with Jack Bokros, the engineers Posis and Hanson modified the initial pivot mechanism and came up with the concept of a leaflet-tab rotating in a "butterfly recess" in the inner wall of the housing. Doctor Nicoloff implanted the first St. Jude valve on October 3, 1977. The design of the valve remained unchanged for over a period of 26 years. Following this, St. Jude Medical introduced their Regent Valve in 1999 which incorporated a housing design that significantly improved the orifice size of smaller aortic prostheses. With more than 1.3 million St. Jude valves implanted, it is the most widely used prosthetic valve in the world.
| Indian Prosthetic Valve | | |
The TTK Chitra valve was developed in Sri Chitra Institute [Figure 4] in Trivandrum and first implanted in December 1990. M. S Valiathan was the surgeon who was the main force behind the development of the Chitra valve and the current valve is the 4 th generation valve. More than 75000 have been implanted. It is a tilting disc valve. [26] The Chitra tilting disc valve has an integrally machined cobalt-based alloy cage, an ultra-high molecular-weight polyethylene disc, and a polyester suture ring.
Between December 1990 and January 1995, 306 patients underwent isolated aortic valve replacement ([AVR], n = 101) or mitral valve replacement ([MVR], n = 205) at six institutions in India. The early mortality rate was 6.9% (seven after AVR; 14 after MVR). A total of 285 survivors was followed up until September 1998; total follow-up was 1212 patient-years (pt-yr) (AVR, 445 pt-yr; MVR, 767 pt-yr).
There were 52 late deaths. Thirty-five deaths were valve-related. One AVR patient and 12 MVR patients developed valve thrombosis, and embolic episodes occurred in 25 patients. Bleeding events and infectious endocarditis occurred infrequently. There was no incidence of paravalvular leak or structural dysfunction of the valve. Actuarial survival rates at 7 years were 82.4 ± 4.0% for AVR and 65.2 ± 5.0% for MVR. Freedom from all valve-related mortality and morbidity at 7 years was 81.5 ± 4.1% after AVR, and 64.2 ± 5.1% after MVR. [27]
| Conclusion | | |
Over the last 60 years, a remarkable progress has been achieved in mechanical valves. There are a number of valve substitutes available in the market, but none of them are completely achieving the standards laid by Harken for an ideal valvular substitute. Two of the six mechanical heart valves currently available for implantation (the Starr-Edwards ball valve and the St. Jude Medical bileaflet valve) are virtually unchanged from the original models implanted. Four other mechanical valves approved for implantation (Omniscience, Omnicarbon, Medtronic-Hall, and Carbomedics valves) have been in use for more than a decade with essentially no mechanical failure. Pyrolytic carbon, a compatible and virtually indestructible biomaterial adapted from the nuclear fuel industry, has enabled a lot of progress. There will always be room for improvement in mechanical valves. Eventually, with the right valve design and the right valve material, it is conceivable that we may someday have a mechanical valve that does not require lifelong anticoagulation therapy.
Acknowledgements
Ms Neha Sharma, Clinical Research Associate for collecting historical material related to the article.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]
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