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Ann Thorac Surg 2000;69:1612-1621
© 2000 The Society of Thoracic Surgeons

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Our surgical heritage

Evolution of mechanical heart valves

^a Department of Surgery, Wright State University Medical School, and University of Dayton, Dayton, Ohio, USA

Address reprint requests to Dr Dewall, 421 Thornhill Rd, Dayton, OH 45419

	Abstract

Top Abstract Introduction Ball valves Pyrolite carbon for mechanical... Nontilting disc valves Tilting disc valves Bileaflet valves References

 
The need for prosthetic heart valves was long recognized but seemed an impossible dream before 1952 when Dr Charles Hufnagel [1] clinically introduced a ball valve that he placed into the descending thoracic aorta for treatment of aortic valvular insufficiency. Fulfillment of that dream became a reality with the advent of extracorporeal circulation in the early 1950s. Development of prosthetic heart valves involved the search for biologically compatible materials and hemologically tolerant designs. Success could not be achieved without the union of these two factors. As there was no satisfactory mechanism to scientifically achieve this goal, trial and error was the method of choice. The development of prosthetic heart valves became the purview of the cardiovascular surgeon who often collaborated with engineers. To distinguish one valve from another each prosthesis often became identified with the surgeon developer.

The development of bioprostheses occurred later in the development of artificial heart valves and constitutes a separate subject not covered in this presentation.

	Introduction

Top Abstract Introduction Ball valves Pyrolite carbon for mechanical... Nontilting disc valves Tilting disc valves Bileaflet valves References

 
The purpose of this article is to illustrate the evolution of thought in the design and development of mechanical heart valves and to identify the surgeons whose efforts led to a given design. This report is not inclusive of all valves that were developed, but only those that had historical interest and had at least minimal clinical application. No attempt is made to compare one valve with another. Most of these valves failed in their clinical trials, and only several valves have current clinical usefulness. The authors give greater emphasis to some valves and individuals as they believe that those valves and individuals had more impact on current surgical practice than some others. Only valves of United States origin are included in this article.

	Ball valves

Top Abstract Introduction Ball valves Pyrolite carbon for mechanical... Nontilting disc valves Tilting disc valves Bileaflet valves References

 
Hufnagel descending aortic ball valve, 1951
Charles Hufnagel, MD (1916 to 1989) received his medical degree from Harvard University Medical School in 1941. He continued his surgical training at Harvard, including work in the surgical research laboratory, where he developed an interest in the use of methacrylate tubes as an artificial blood conduit. An appointment as professor of experimental surgery brought him to Georgetown University in Washington, DC, in 1950. In 1951 he described a methacrylate ball contained in a methacrylate tube [1]. The ball sat snugly at the proximal end of the tube during diastole, and three bulbous pouches that opened around the ball in its systolic position at the distal portion of the tube allowed blood to flow in one direction. The prosthesis was positioned into the descending thoracic aorta, secured by nylon rings containing teeth on its inner surface to hold the aorta to the prosthesis. The valve was designed for use in patients with aortic insufficiency.

After proper investigation in animal models, Dr Hufnagel’s heart valve (Fig 1A) was deemed safe for clinical application. Its first clinical use was in October 1952. More than 200 individuals received the Hufnagel prosthesis. No anticoagulation was used. Hufnagel ball valves were recovered 30 years after implantation, without showing wear.

View larger version (43K): [in this window] [in a new window]   Fig 1. (A) The Hufnagel ball valve was developed in 1951 and applied clinically before the availability of heart-lung machines. It was placed in the descending thoracic aorta for patients with aortic insufficiency. (B) The Bahnson fabric aortic cusp valve saw clinical use in 1960. Flexible leaflet valves for both aortic and mitral applications composed of either fabric or silicone-covered fabric were tried in the late 1950s and early 1960s by several investigators. The development of heart-lung machines in the mid-1950s made possible the direct approach to valve surgery. (C) A double cage identified the Harken-Soroff ball valve of 1960. The outer cage served to separate the valves struts from the aortic wall. (D) The Starr-Edwards ball valve of 1960 continues today in its clinical use. It demonstrated that a double cage was unnecessary. (E) The Magovern-Cromie ball valve of 1962 had a rapid fixation mechanism of multiple curved pins mobilized from the cloth ring of the valve to attach the prosthesis to the native valve annulus. It incorporated an open cage to prevent streamers of clot forming at the junction of crossing struts. (F) The Lillehei-Cruz-Kaster prosthesis in 1963 introduced the tilting disc concept to prosthetic valves. (G) The Gott-Daggett prosthesis of 1963 incorporated a silicone-impregnated fabric disc fixed at its diameter to a polycarbonate ring. The valve was carbon-coated, which led to the development of Pyrolyte carbon used in components of almost all prosthetic valves made from the late 1960s on. (H) UTC-Barnard Aortic Prothesis 1963. UTC refers to the University of Cape Town. This modified disc or plunger valve was made in the US.

Overview of fabric and fabric-coated valves and silicone rubber valves
In the time between Dr Hufnagel’s ball valve and the availability of the ball valve prostheses from Dwight Harken, MD, and Albert Starr, MD, in 1960, innovators’ efforts were directed toward developing flexible leaflet, silicone, and urethane-coated fabric prosthetic valves. These pioneering efforts came from David Long, MD, working with C. Walton Lillehei, MD, Robert Frater, MD (at the Mayo Clinic), Earl B. Kay, MD, Nina Braunwald, MD, and others. Valves of this type ultimately were unsatisfactory.

Bahnson flexible fabric cusp valve, 1960
Henry Bahnson, MD, (1920 to present), writing from Johns Hopkins University Hospital, began clinical placement of jersey knit Teflon aortic cusps in 1960 [4]. From one to three cusps could be used. These efforts were limited, as, within 24 months after implantation, stiffening and tearing of the leaflets often occurred because of fibrin deposition and ingrowth of connective tissue. Doctor Bahnson also tried valves made of nylon fabric impregnated with silicone. The use of flexible fabric valves (Fig 1B) proved to be disappointing.

Harken ball valve, 1960
Dwight Harken, MD, (1910 to 1993) gained heart surgery experience repairing heart wounds during World War II. Early in his career in Boston, he received much acclaim for his innovations in closed mitral valve surgery. With his background in heart surgery, he turned his attention to devising a caged ball valve (Fig 1C) using a silicone rubber ball for the poppet. His concept incorporated a larger cage surrounding the primary ball cage to shield the prosthesis from incursions into the wall of the aorta [5]. Doctor Harken’s first successful use of his caged ball valve was in March 1960. He later discontinued the use of the second, larger cage after Dr Albert Starr demonstrated that it was unnecessary.

Doctor Harken subsequently developed a discoid silicone poppet valve with crossing struts [6], the Harken-Surgitool low profile valve. Clinical use of this valve began in 1968.

Starr-Edwards caged ball valve, 1960
The general and thoracic surgical education of Albert Starr, MD (1926 to present) took place at the Bellevue and Presbyterian Hospitals of Columbia University. Doctor Starr moved to the University of Oregon in 1957, where he met Lowell Edwards, a semiretired engineer with many patents to his credit. One notable invention was a centrifugal high-altitude booster fuel pump that was used, at one time, in 85% of the military aircraft engines during World War II. Doctor Starr and Mr Edwards found a mutual interest in the development of prosthetic heart valves.

Their first design was a silicone rubber bileaflet valve. This approach proved to be unsuccessful. Their attention was then focused on a caged ball valve (Fig 1D) with a methacrylate cage and silicone rubber poppet. Success with canine surgery using this valve encouraged Dr Starr to begin a clinical trial, which took place on September 21, 1960 [7].

A Stellite-21 cage, monocast by the lost wax technique, soon replaced the methacrylate cage. Stellite-21, an alloy of cobalt, chromium, molybdenum, and nickel [7], was proved by orthopedists to be biocompatible. The silicone rubber balls used in the early trials absorbed lipids. This caused ball variance, the manifestation of which was a change in the shape of the ball, which could lead to ball fractures. Hollow Stellite-21 balls for a time replaced the silicone rubber balls. In 1965 a different curing process of the silicone rubber balls resolved the ball variance problem, again permitting the use of silicone rubber poppets. Fabric was introduced in 1968 to cover all of the metal exposed on the valves, including the struts. The fabric tended to deteriorate, so this innovation was discontinued. Five Starr-Edwards ball valve models were produced from 1960 to 1972. A Starr-Edwards nontilting disc mitral valve was introduced in 1970 [8].

In 1961, Mr Edwards moved his Oregon manufacturing facilities to Santa Ana, CA. Several engineers who worked at Edwards Laboratories later developed their own production companies. These include the late James Bentley of Bentley Laboratories, the late Donald Shiley of Shiley Laboratories, Warren Hancock of Hancock Laboratories, and George Siposs of American Omni Medical, Inc.

Magovern-Cromie ball valve, 1962
George Magovern, MD (1923 to present), from the Allegheny General Hospital in Pittsburgh, PA, worked with Henry Cromie, a machinist partner and founder of Surgitool, to produce a mobile pin fixation method for their open-caged silicone rubber ball valve (Fig 1E). The initial fixation mechanism that they tried contained horizontal curved pins, which emerged from the prosthesis sewing ring upon activation with the valve holder. Their first clinical application came in 1962, at which time their valve had a closed cage. As the junction of the two struts became a source of streamer clots, they converted their cage to an open cage [9].

Improvements were made from the horizontal fixation mechanism to a fixation mechanism incorporating 24 curved pins, which were activated from the upper plate of the valve ring against 24 similar pins that moved from the lower plate to encompass a circular ring of valvular annulus.

Smelloff-SCDK-Cutter ball valve, 1964
In 1961, Edward Smelloff, MD (1925 to present) and Robert Cartwright, MD, from the Sutter Memorial Hospital, and Trevor Davey, ME and Boris Kaufman, MS, professors of mechanical engineering at the California State University in Sacramento, initiated a heart valve research project [10]. The partners considered many valve configurations and elected to pursue a ball valve concept. They chose a double closed-cage design. The smaller cage held the ball at its equator in the valve ring during diastole. The second cage retained the ball during systole. The cage was machined from a single bar of titanium. The valve was named after the original inventors and was known as the SCDK valve (Fig 2J). Its first clinical application was in 1964 [11].

View larger version (38K): [in this window] [in a new window]   Fig 2. (I) In the mid-1960s a number of nontilting disc valves were developed. In 1965 the Cross-Jones caged disc valve contained a disc poppet of silicone rubber reinforced with a titanium ring to add stiffness to the disc. The retaining struts did not meet, forming an open cage. (J) The Smelloff-Cutter prosthesis in 1966 introduced a new concept. With this valve a silicone rubber poppet was sized to seat within the ring of the valve housing, clearing the ring by a few thousandths of an inch. (K) The UCT-Barnard mitral prosthesis first used in 1962 represented an early disc valve concept. The disc was free-floating and retained by a centrally located peg. (L) The Kay-Suzuki disc valve of 1964 had a closed cage and a radiotranslucent disc. Discs in the early models of nontilting disc valves developed notching from rubbing against the struts and became dysfunctional. When Pyrolyte was introduced for poppets in the late 1960s, the notching problem was solved. (M) The Lillehei-Nakib toroidal disc valve in 1967 contained a disc with a large perforation in its center. During the closure the disc would sit on a central spindle sealing the central hold. (N) With the Beall-Surgitool valve in 1967, velour fabric covered the orifice, with a Teflon poppet. As the poppet tended to notch on the parallel struts, Pyrolyte carbon was later used for the poppet. (O) The Davila prosthesis of 1968 incorporated a novel modified disc poppet. The poppet mechanism was a cylinder with one end a closed plate or a disc, which was connected by four struts to a flared ring. During systole the ring would catch the annulus of the prosthetic valve. (P) The flexible fabric valves of the early 1960s, after some months of implantation, developed a smooth endothelial covering. Based on this observation, the Braunwald-Cutter valve was developed. This ball valve prosthesis was totally covered with fabric, including the struts. The silicone poppet was abraded by the fabric. Later, using a Pyrolyte ball, the fabric on the struts shredded. (Q) The Björk-Shiley prosthesis, beginning in 1969, was the first extensively used tilting disc prosthesis. The disc was held in place by two wire struts, one on each side of the disc. The disc used initially was made of the plastic Delrin, which would swell in a fluid medium and lock up. This was replaced with a Pyrolyte disc. After a period of time, the struts would fracture in some of the valves, releasing the disc. (R) The Lillehei-Kaster 1970 prosthesis contained a tilting disc, which was smooth on both surfaces and retained in place and through the disc excursions by means of two lateral struts. The seating was made of titanium and the disc of Pyrolyte. Some of the original patients in whom this prosthesis was used continue to do well. (S) The 1973 biconical disc Cooley-Cutter valve placed a Pyrolyte poppet at the equater of the housing.

DeBakey-Surgitool caged ball valve, 1967
During the mid-1960s, Michael DeBakey, MD (1908 to present) became concerned about ball variance that occurred in some valves. Working with Harry Cromie of Surgitool he developed a closed cage aortic ball valve that was similar in design to the Starr-Edwards valve [12]. Their first design incorporated a titanium poppet with a Dacron-covered ring and struts. Their second model incorporated an orifice of high molecular weight polyethylene that could only be gas-sterilized. This led to a change in the orifice material to pyrolytic carbon in their third model valve. The first use of Pyrolyte in heart valves came in 1969 for the ball in the DeBakey ball valve. The Pyrolyte ball was used in a titanium cage the orifice of which was Pyrolyte-coated and had bare struts. The ball caused excessive wear on the titanium struts, leading to its discontinuation. A low-profile, nontilting disc in a cage mitral valve soon followed the third model prosthesis.

Braunwald-Cutter ball valve, 1968
Nina Starr Braunwald, MD (1928 to 1992) received her general surgery training at New York Bellevue Hospital, after which she became a surgical fellow in Dr Charles Hufnagel’s laboratory at Georgetown University Medical Center. After her Georgetown experience, she joined the cardiothoracic surgery staff at the National Heart Institute in Washington, DC.

In 1959, Dr Braunwald developed a flexible polyurethane mitral valve prosthesis with attached Teflon chordae tendineae [13]. It was first used clinically on March 11, 1960. Between 1960 and 1963 Drs Braunwald and Andrew Morrow, MD, implanted 23 flexible Teflon aortic prostheses [14]. They noted that patients did not experience arterial emboli despite the absence of anticoagulation. The leaflets functioned well for a few months, then became stiff and immobile.

Mitral and aortic fabric prostheses that were recovered after various periods of implantation revealed complete covering and infiltration with a tightly adherent layer of fibrous connective tissue. Doctor Braunwald reasoned that the cloth covering of metal surfaces on the more durable caged ball and disc valves would diminish the rate of thromboembolism.

Doctor Braunwald worked with Cutter Laboratories to incorporate her ideas of cloth covering to a caged ball valve. Implantation in human subjects of the Braunwald-Cutter cloth-covered prosthesis (Fig 2P) began in 1968. They used an open cage prosthesis in which struts were covered with a knit Dacron tubing. The inflow ring was covered with an ultra–thin polypropylene mesh fabric. In clinical use, the valve suffered from strut covering disruption and abrasion of the silicone poppet.

In 1968, Dr Braunwald moved to the University of California at San Diego with her husband, Gene Braunwald, MD, a cardiologist. In 1972 they moved to Boston, where she became an associate professor of surgery at Harvard Medical School.

Doctor Nina Braunwald died of breast cancer in 1992. She received a Distinguished Member award from the Association of Women Surgeons in 1992. In addition, the Nina Starr Braunwald Award from the same association was established in her name. The award is given annually to a woman surgeon in recognition of outstanding contributions of women to surgery. The Thoracic Surgery Foundation for Research and Education also awards the Nina S. Braunwald Research fellowship for women, and the Nina S. Braunwald Career Development award for women.

	Pyrolite carbon for mechanical valves

Top Abstract Introduction Ball valves Pyrolite carbon for mechanical... Nontilting disc valves Tilting disc valves Bileaflet valves References

 
A major contribution to mechanical heart valves was provided by Jack Bokros, PhD (1935 to present), who invented a pyrolytic carbon that he called Pyrolyte. This was used as a component of most of the mechanical heart valves since 1969. More than 2 million valves with Pyrolyte components have been used since its introduction for use in heart valves. Doctor Bockros’ career began in 1958 with the General Atomic Company in San Diego, CA, where he was charged with the task of developing a seal for pellets of uranium thoride, a nuclear fuel. This was accomplished in 1963 by using a pyrolytic carbon that coated the uranium pellets.

Pyrolyte coating [15] involves a retort containing a given quantity of heart-resistant particles (ie, sand or ceramic beads) that are suspended by an inflow of a hydrocarbon gas such as propane flowing into the retort at a variable rate (ie, 10 L/min). This is called the fluidized medium. The retort is oxygen-free and is maintained at a temperature of 1,200°C to 1,500°C by an electric furnace while the article to be coated is suspended in the fluidized media. The heat separates the propane into elemental carbon and hydrogen (pyrolysis). The carbon then fuses to the desired article as well as to the surrounding (bead) particles.

Doctor Bokros found that the carbon coating was uniform but not sufficiently hard. Hardness is desirable, as it is related to wear resistance. Adding methyltrichlorosilane (MTS) to the inflow of the hydrocarbon gas caused the formation of 4% to 12% silicone carbide in the carbon coating, producing the proper hardness. The thickness of the carbon coating could be altered by changing the variables in the retort of temperature, time of exposure, type of hydrocarbon gas used, type of flotation, size of item being coated, and other variables.

Vincent Gott, MD, developed an exquisite test for blood biocompatibility of materials in 1961 (see Gott-Daggett valve). A chance reading of the Gott paper by Dr Bokros in 1955 led to applying to Pyrolyte the Gott material testing system, which found Pyrolyte to have exceptional biocompatibility.

The Pyrolyte division of General Atomic was sold to Intermedics in 1979, and the company moved to Austin, TX. Doctor Bokros later formed a new, separate company in Austin, called the Medical Carbon Research Institute and developed a silicone-free pyrolytic carbon. He used this new pyrolytic carbon for the bileaflet valve on his design of the On-X Valve. Other bileaflet valves will likely emerge in the future, including a new design from Medtronic, Inc, the Novadyne valve from Medical, Inc, and others.

	Nontilting disc valves

Top Abstract Introduction Ball valves Pyrolite carbon for mechanical... Nontilting disc valves Tilting disc valves Bileaflet valves References

 
Barnard-Goosen valves, 1962
Christian Barnard, MD (1922 to present) was a surgical resident in the service of Dr C. Walton Lillehei at the University of Minnesota in the mid-1950s. In 1958 he returned to his home base at the University of Cape Town Groote Schur Hospital in South Africa. It was there that he became the first surgeon to successfully transplant a human heart. Doctor Barnard’s chief perfusionist was Carl Goosen, who designed a mitral prosthesis in 1962 and an aortic prosthesis in 1963 [16]. Both valves (Figs 1H and 2K) were modified discs with attached restraining projections. They experienced a modest success until newer valves were developed. Both valves were made in the United States. The UTC prefix on these valves refers to the University of Cape Town.

Kay-Suzuki caged disc valve
Earl Kay, MD (1910 to present) was the codeveloper of the Kay-Cross rotating disc blood oxygenator in 1956. In 1958 Dr Kay became chief of cardiovascular surgery at St Vincent’s Hospital in Cleveland, OH, where he began investigating several mitral valve prosthesis designs. He first used Teflon fabric, polyurethane-coated leaflets with attached Teflon threads that served as artificial chordae tendineae. The chordae were sewn to the papillary muscles or were passed through them and fastened to the outer myocardium over Teflon pledgets. Doctor Kay also experimented with a Teflon fabric trileaflet valve encased in a Teflon cylinder for aortic valve replacement.

As these ventures were unsatisfactory, his attention focused upon a low profile, caged disc configuration that he believed would be an improvement over the caged ball. He and Akio Suzuki, MD, began experimentation in 1963 with a low profile, closed cage disc prosthesis (Fig. 2L) [17]. Their first clinical application of this valve occurred in 1964. Four short studs projected from the inner edge of the annulus to prevent the disc from cocking. It used a Teflon disc, which would develop notching over time because of rubbing against the cage struts.

Cross-Jones caged lens prosthesis, 1965
Frederick Cross, MD (1921 to present) obtained his surgical education under Owen Wangensteen, MD, at the University of Minnesota from 1948 to 1953. After completing his residency at Minnesota, he returned to Cleveland, his hometown, and joined forces with Earl Kay, MD. In 1956 the two surgeons developed the Kay-Cross Disc Pump-Oxygenator.

In 1959, Dr Cross became Chief of Cardiothoracic Surgery at St Luke’s Hospital in Cleveland. There he and Richard Jones, PhD, a physiologist, proceeded to develop the Cross-Jones heart valve lens prosthesis (Fig 2I) [18]. They initiated their work in May 1964, with their first clinical implant taking place on January 5, 1965. They used an open titanium cage with a totally covered ring of woven Teflon. The disc poppet was of silicone, reinforced with a titanium ring to increase its rigidity. This valve, as with all nontilting disc valves, was subject to poppet notching by the struts.

Kay-Shiley disc valve with muscle guard, 1965
Jerome Kay, MD (1921 to present) worked in the department of surgery at the Los Angeles County General Hospital. Doctor Kay and Donald Shiley of Shiley Laboratories pooled their thoughts and devised a caged valve with a Stellite orifice containing a silicone rubber disc. The disc was retained by two parallel struts similar to the placement of struts in the Beall valve. As some difficulties were experienced with their early designs because of interference from the ventricular wall muscle, a muscle guard was introduced on their later model [19, 20].

Lillehei-Nakib toroidal valve, 1967
C. Walton Lillehei, MD (1918 to 1999) at the University of Minnesota in 1953 became internationally known as a significant innovator in open heart surgery. His reputation brought many students from all over the world to study with him, one of whom was Ahmad Nakib, MD, from Beirut, Lebanon. He and Dr Lillehei devised the Toroidal heart valve (Fig 2M) [21]. The first clinical implants were done by Dr Lillehei in 1967. The valve was entirely made of machined titanium, including the poppet, which had a round, Lifesaver shape and was called a toroid. During systole the toroid poppet permitted a central as well as a peripheral flow, and during diastole the toroid sat on the orifice of the valve as well as on a central plug closing the center port. The toroid was retained by four struts.

Beall-Surgitool disc valve, 1967
The surgical career of Arthur Beall, MD (1929 to present) developed at the Baylor College of Medicine in Houston, TX, where he still works. There he conceived of the Beall-Surgitool Teflon disc valve (Fig 2N), which incorporated a seating ring with two parallel wire strut retainers to control the excursions of the disc [22]. Five design changes evolved over the first 10 years of its clinical existence. Each change brought increased knowledge, promoted better hemodynamic efficiencies, and compensated for disc wear, structural failures, and other problems. Later models used a thicker Teflon disc, followed by use of a Pyrolyte disc.

Davila-Sierra sliding cage disc valve, 1967
Julio Davila, MD (1921 to present) devised a unique occluder for a mitral valve prosthesis (Fig 2O) [23] while at the Temple University Department of Surgery in Philadelphia, PA. His polypropylene occluder was a hollow cylinder capped with a disc for the ventricular side and an open ring for the atrial side. The walls of the cylinder were fenestrated using four struts to connect the atrial ring with the ventricular disc, and the cylinder was flared at both ends to retain it in the supporting metal orifice.

Cooley-Cutter biconical disc prosthesis, 1973
Denton Cooley, MD (1920 to present) received his surgical training at Johns Hopkins University School of Medicine in 1944. His surgical practice started at Baylor College of Medicine in Houston, TX, in 1951. In 1969 he became Surgeon-in-Chief of the Texas Heart Institute, where he now continues his career.

In the mid-1960s, he worked with Domingo Liotta, MD, to devise an eccentrically hinged disc valve. As this valve did not function well, they developed the Cooley-Liotta-Cromie prosthesis, which was a modified Starr-Edwards ball valve using a titanium ball and a complete cage covering of Dacron velour. However, cloth wear and hemolysis led to its early discontinuation. In 1966, the Cooley-Bloodwell-Cutter prosthesis was introduced, which was a low-profile silicone rubber disc valve. Its retaining structure was four open-ended struts of titanium with a Dacron-covered orifice. Thrombosis and embolization problems led to its discontinuation in 1968.

A revised Cooley-Cutter prosthesis (Fig 3S) [24] was introduced in 1971. Its retaining mechanism was two sets of struts on the inlet and outlet positions of the valve in the Smellof-Cutter style, with an equator seating silicone disc. As the silicone disc exhibited excessive wear, Pyrolyte carbon was substituted. In 1973 the poppet was converted to a biconical disc.

View larger version (45K): [in this window] [in a new window]   Fig 3. (T) The Wada-Cutter valve from 1966 was an early attempt to make a tilting disc prosthesis. In this case the Teflon disc contained two major notches matched to mating notches in the housing, which fixed the disc to the housing. Hemodynamically the valve worked well, however, it developed excessive wear at the hinge mechanism. (U) The St Jude heart valve was the first bileaflet valve to achieve major success beginning in 1976. Pyrolyte was used for the leaflets as well as the housing. (V) The Medtronic-Hall-Kaster valve was developed in 1976 and continues to be used. It Pyrolyte disc has a central perforation through which curved wire struts guide its course. (W) The Bjork-Shiley monostrut valve was developed to compensate for the weak support of the wire struts used previously. The two legged outflow strut was replaced with a single catch strut, machined in titanium as part of the housing. (X) The Omniscience valve was introduced in 1978 to replace the Lillehei-Kaster valve. The only change was to replace the extended struts with two tabs as the catch mechanism. This valve had a titanium housing and a Pyrolyte disc. The Omnicarbon Valve was introduced in 1984 and contains both disc and housing structures made of pyrolytic carbon. Both valves retain clinical usefulness.

	Tilting disc valves

Top Abstract Introduction Ball valves Pyrolite carbon for mechanical... Nontilting disc valves Tilting disc valves Bileaflet valves References

 
Lillehei-Cruz-Kaster tilting disc valve, 1963
Anatolio Cruz, MD (1933 to present) from the Philippines, while in the service of Dr C. Walton Lillehei, in 1963 devised a heart valve (Fig 1F) with a free-floating disc tilting on the edge of an orifice ring. The excursion of the disc was retained by a cage [25]. Although the valve had good hemodynamic qualities, an area of stasis existed between the open disc and the aortic wall, which negated its usefulness. This work represents the introduction of the tilting disc concept into heart valve design.

Wada-Cutter tilting disc heart valve, 1966
Juro (Jerry) Wada, MD (1922 to present) came to the United States in 1950 as the first surgical trainee from occupied Japan. He served as a surgical fellow in the department of Owen Wangensteen, MD, at the University of Minnesota. Doctor Wada received additional surgical experience at a number of surgical departments in this country. Returning to Japan in 1958, he became Chief of Cardiovascular Surgery at the Sopporo Medical School.

In 1966, Dr Wada designed the Wada-Cutter disc heart valve (Fig 3T) [26]. One-third of the Teflon discoid occluder was depressed several millimeters and parallel to the main occluder body. The disc was notched at the junction of the main body with the depressed portion. The notches of the leaflet fit into and pivoted on paired matching protrusions in the titanium annulus. Production was discontinued in 1974 because of excessive wear of the Teflon occluder.

Lillehei-Kaster tilting disc prosthesis, 1970
Robert Kaster (1933 to present) received an electrical engineering degree from the University of Minnesota in 1951. His interest turned to prosthetic heart valves when he began working in the laboratory of Dr Lillehei. The deficiencies of the Cruz prosthesis became apparent to him in 1965. To eliminate the area of stasis behind the open Cruz valve, he moved the pivot point forward to a cord measuring about one-third of the circumference of the orifice. Lateral guides were used to replace the cage of the Cruz valve. This configuration became the Lillehei-Kaster (Fig 3R) valve [27].

In Minneapolis, Mr Kaster met Dr Bokros to evaluate Pyrolyte for the disc of the Lillehei-Kaster valve. Up to that time, Delrin and plastics were used for the discs; however, they proved to be unsatisfactory because of excessive wear. In tests by Mr Kaster, Pyrolyte proved to be wear-resistant and subsequently was selected as the material of choice for the disc. In November 1967, Mr Kaster moved to New York Cornell Medical Center with Dr. Lillehei and continued the development of the Lillehei-Kaster prosthesis. The initial implants of the Lillehei-Kaster valve, which was produced by Medical, Inc, of Minneapolis, began in 1970 and still function well in many patients.

Omniscience, 1978, and Omnicarbon, 1984, valves
The Omniscience [28] and the Omnicarbon [29] valves (Fig 3X) are direct descendants of the Lillehei-Kaster prosthesis. The only change was the replacement of the retaining rails of the latter by abbreviated earlike guards. The Omniscience valve has a titanium cage and Pyrolyte disc, whereas the Omnicarbon valve is all Pyrolyte. Both valves are currently used.

Björk-Shiley tilting disc valve, 1969
Viking Björk, MD (1919 to present) was born in Sweden. In 1948 he developed the rotating disc oxygenator recording the first use of an oxygenator with a surviving animal [30]. In 1966, he was appointed Chairman of the Department of Surgery at the Karolinska Institute in Stockholm, Sweden. After clinical experience with ball heart valves Dr Björk was attracted to the low profile of the Wada prosthesis. He later was confronted with a number of problems in his use of the Wada valve and believed that improvements could be made.

Doctor Björk worked with Donald Shiley of Shiley Laboratories in California. After diligent efforts, they developed a tilting disc heart valve (Fig 3Q) [31, 32]. Their disc retainer used two U-shaped wire struts welded to a Stellite orifice. They selected Delrin to use in the disc of their design, only to discover later that Delrin absorbs water, which altered the shape of the disc after implantation. This deficiency was corrected by the use of Pyrolyte for their disc.

Later the longevity of their Pyrolyte disc valve was compromised as the outflow wire retainer of the disc tended to fracture at its weld joint, releasing the disc. This was corrected by the use of a monostrut for the outflow retainer (Fig 3W). The monostrut was machined as an integral part of the orifice ring involving no weld joint [32].

Medtronic-Hall-Kaster tilting disc, 1977
Karl Victor Hall, MD (1917 to present) was the chairman of the Department of Surgery at the Rikshospitalet in Oslo, Norway. As a cardiac surgeon, Dr Hall used the available valves of the time until the mid-1970s, when he sensed that improvements could be made in the tilting disc concept.

To accomplish his goal, Dr Hall needed financial help and scientific support. Arne Woien, a friend, physicist, and businessman, came to his aid. As prosthetic heart valve expertise was not available in Norway, Mr Woien suggested that they contact Mr Robert Kaster, who had returned to Minneapolis from New York. In 1974, Medtronic, Inc, of Minneapolis distributed the Lillehei-Kaster valve. Mr Woien was the Medtronic European representative. It was through this connection that Mr Woien and Mr Kaster met.

Doctor Hall, Mr Woien, and Mr Kaster worked together to develop a satisfactory design, which incorporated a Pyrolyte disc containing a small central perforation. The disc was designed to slide over a guidewire through its central perforation to tilt open [33]. Prototypes were made in Minneapolis, followed by the first clinical implant in 1977. With Medtronic design and engineering input, the name of the valve (Fig 3V) was changed to the Medtronic-Hall Valve. With proper orientation, the Medtronic nonoleaflet valve was advantageous in aortic valve replacement over a bileaflet prosthesis [34].

	Bileaflet valves

Top Abstract Introduction Ball valves Pyrolite carbon for mechanical... Nontilting disc valves Tilting disc valves Bileaflet valves References

 
Gott-Daggett valve, 1963
Vincent Gott, MD (1927 to present) was a Lillehei student at Minnesota. After completing his residency at Minnesota in 1960 he moved to the University of Wisconsin at Madison. It was there that he devised a biocompatibility test that placed test materials into the inferior vena cava of animals. The resistance to clotting of the material was a measure of its biocompatibility. Working with these blood compatibility experiments, Dr Gott became acquainted with Dr Ronald Daggett, a professor of mechanical engineering at the University. As they had a mutual interest in prosthetic heart valves, they devised a flexible bileaflet prosthesis (Fig 1G) [35].

Their valve was a polycarbonate ring containing a disc of Teflon fabric impregnated with silicone rubber. The valve components were coated with colloidal graphite sterilized in benzalkonium chloride and rinsed in heparin. This treatment induced resistance to clotting of the valve. Open-ended restraining struts several millimeters long projected from the inside edge of the ring to support the flexible fabric disc, which was held in place by a bar located across the diameter of the disc and fused to the retaining ring. The first clinical application of the Gott valve occurred in 1963. Some of these valves have stayed functional for 25 years.

In 1965 Dr Gott accepted the post as Chief of Cardiac Surgery at Johns Hopkins Medical School in Baltimore. Jack Bokros, PhD, who was now familiar with Dr Gott’s work on the biocompatibilities of materials, worked with Dr Gott to test the blood compatibility of Pyrolyte. The success of these tests led to the use of pyrolytic carbon components in most of the prosthetic heart valves devised from the late 1960s on.

Lillehei-Kalke bileaflet prosthesis, 1965
Bhagavant Kalke, MD, began work in Dr Lillehei’s Minneapolis laboratory in 1964 and continued with Dr Lillehei after their move to Cornell Medical School in 1967. Doctor Kalke’s bileaflet design positioned the leaflets to open with their hinging axis toward the periphery of the metal annulus. As this did not work well, the pivot axis was moved to the diameter of the retaining ring. A single wire guard placed 90 degrees from the main hinging axis of the leaflets and extending over the leaflets aided the control of leaflet excursions [36]. The valve was basically a bileaflet valve, as is known today, with the exception of the controlling guard. In 1968 Surgitool made one titanium valve that was used clinically by Dr Lillehei at the New York Cornell Medical Center.

St Jude bileaflet prosthesis, 1976
In 1976, Xinon C. (Chris) Posis, an industrial engineer, became interested in prosthetic heart valves and approached Demetre Nicoloff, MD, a cardiovascular surgeon at the University of Minnesota. The design by Mr Possis was a floating hinge valve with the pivots near the periphery of the retaining annulas and with a central opening. Doctor Nicoloff expressed an interest in working with Mr Possis.

At this time, Mr Possis and Dr Nicoloff approached Manuel Villafana, the founder of Cardiac Pacemakers, Inc, with the Possis heart valve design; Mr Villafana was receptive to the idea and formed a development company.

Subsequently, Mr Villafana and his engineers determined that the valve leaflets hinged at the periphery of the rigid annulus and opening centrally was not a workable design. From that realization evolved the concept of having the floating hinges of the leaflets located near the central axis of the rigid housing and opening to the outer edge of each leaflet, leaving a small central opening. It was agreed that the valve, with the exception of the sewing ring, would be made of Pyrolyte carbon. Working with Dr Bokros at Carbomedics, this was accomplished. An extensive series of calf implants of the valve proved successful. Doctor Lillehei, who had returned from New York Cornell Medical Center, encouraged Dr Nicoloff to proceed with clinical cases. The St Jude valve (Fig 3U) was first employed by Nicoloff on October 3, 1977 [37].

It was suggested by Mr Villafana that they call their new valve the Nicoloff valve. Doctor Nicoloff declined. At that time, Mr Villafana’s son was recovering from a serious illness. The St Jude valve was proposed as a name by Mr Villafana. Church liturgy teaches that St Jude Thaddeus is the patron saint of difficult cases. After inquiries to whether such a name would be acceptable, Mr Villafana received affirmative replies.

Doctor Nicoloff was asked to be the medical director of the new company; however, he declined because of the demands of his clinical practice. He suggested that Dr C.W. Lillehei become the Medical director, a post that Lillehei held until his death in 1999.

The story of a heart valve prosthesis can be told in a few words. No words, however, can relate the many hours of thought and research that produces each design. New developers learn from the good and bad experience of others.

	Acknowledgments

 
Personal communications with the following individuals was most helpful and appreciated: Eugene Braunwald, MD, for background information concerning Nina Braunwald, MD; Arthur C. Beall, Jr, MD, for background information concerning Beall, DeBakey, and Cooley valves; Jack Bokros, PhD, for background information concerning the origins of Pyrolyte carbon and its production; Frederick Cross, MD, for background information concerning the Cross-Jones and the Kay-Suzuki valves; William Cuthbertson, for aid in photographing the diagrams of valves; Robert W.M. Frater, MD, for background information concerning the Barnard-Goosen valves; Vincent L. Gott, MD, for background information concerning the Gott-Daggett valve and the work with Jack Bokros, PhD, that led to the development of Pyrolyte carbon; Keith Johnson, BS, who, as an engineer working with Medtronic, Inc, provided information concerning the Medtronic-Hall-Kaster valve; Shelly Johnson, who, as an officer with Medical, Inc, provided information concerning the Lillehei-Kaster, Omniscience, and Omnicarbon valves; Robert Kaster, for background information concerning his role in the development of several different valves discussed here; C. Walton Lillehei, MD, PhD, for background information concerning his role in valve development (these conversations took place 9 months before his death); Demetre M. Nicoloff, MD, for background information on the development of the St. Jude valve and related topics; Gene Stobbs, who, as an engineer with Medical, Inc, provided information on the production of pyrolytic carbon; Manuel Villafana, for background information concerning the development of the St. Jude prothesis and related activities; and Arne Woien, for background information on the development of the Medtronic-Hall-Kaster prosthesis; Rosalyn Sterling Scott, MD, from the Cleveland Clinic, for providing information relative to the acknowledgments and awards given to Nina Braunwald, MD.

	References

Top Abstract Introduction Ball valves Pyrolite carbon for mechanical... Nontilting disc valves Tilting disc valves Bileaflet valves References

 

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