Serendipity and the development of heparin and carbon surfaces.

In the early 1960s, bileaflet valves fabricated with polymer housings routinely thrombosed within a few hours after implantation in the canine heart. In a serendipitous series of events, the authors found a way to bond heparin to these bileaflet valves using a coating of graphite-carbon and benzalkonium chloride. Over the ensuing 30 years, improved heparin coatings have been developed by other investigators for bonding to various biomedical devices; currently, about 25% of oxygenators used in this country utilize heparin coatings to minimize surface activation of clotting factors. Also, and somewhat serendipitously, a pyrolytic carbon material developed in the 1960s as a coating for nuclear fuel rods was submitted to the authors' laboratory for possible coating with benzalkonium and heparin. This carbon coating, developed at Gulf General Atomic, Inc, would not bond heparin, but it proved to be the best rigid material available for prosthetic valve construction; more than one million pyrolytic carbon valves have been clinically implanted over the last 29 years.

Mechanical heart valves: 50 years of evolution.

The past 50 years have witnessed remarkable progress in the development of safe, hemodynamically favorable mechanical heart valves. Starr-Edwards aortic and mitral ball valves introduced in the mid-1960s, continue to be used successfully worldwide. More than 100,000 Omniscience and Omnicarbon tilting-disc valves have been implanted since 1978 with essentially no mechanical failure; similar results have been obtained with more than 300,000 Hall-Kaster and Medtronic-Hall tilting-disc valves over the past 25 years. Pyrolytic carbon, originally used to encapsulate nuclear fuel rods, has been adapted for the fabrication of discs, leaflets and the housings for more than 2 million mechanical valves. The St. Jude bileaflet valves, totally fabricated from pyrolytic carbon, have remained virtually unchanged in design since their introduction in 1977. More than 1.3 million of these valves have been implanted worldwide with virtually no reported failures of the carbon leaflets or housings. Similarly, pyrolytic carbon bileaflet Carbomedics valves have been implanted in more than 500,000 patients since 1986. Now, 50 years after Dr Gibbon's seminal achievement, patients with debilitating valve disease can have elective valve replacement (mechanical or tissue) with an operative mortality approaching 1% to 2% and a low lifetime complication rate.

Development of a carbon-coated, central-hinging, bileaflet valve.

Between April 1963 and January 1966, 86 patients at the University of Wisconsin Hospital underwent aortic or mitral valve replacement, or both, with a carbon-coated, central-hinging, bileaflet valve. A 25-year follow-up has been obtained on 43 of these patients discharged with an aortic prosthesis, 13 patients discharged with a mitral prosthesis, and 2 patients discharged with double prostheses. The mean implantation time was 7.2 years, 9.0 years, and 9.5 years, respectively. The longest aortic valve implantation time was 24.2 years in a patient who had her bileaflet valve prophylactically replaced, and the longest mitral implantation time is 24 years in a patient who is doing well with her original prosthesis. We are not aware of any patient among the approximately 700 receiving this valve around the world who has developed fatigue-failure of the silicone-impregnated Teflon fabric leaflet. This valve has demonstrated unexpected durability and has provided some design and biomaterial concepts that are used in a number of current prosthetic valves.

Development of an artificial heart valve.

When I reviewed the 21-year results with the Björk-Shiley tilting disc valves, I found out that to date, we still have to use these disc valves and all mechanical heart valves with anticoagulation therapy. The highest incidence of valve-related postoperative deaths after aortic valve replacements in Stockholm was anticoagulation-related bleeding, which continued at a rate of about 1% year after year. There is a need to improve the quality of life for heart valve patients, especially for children, for young females who want to have children, for the older generation who are on medical treatment, and for all patients in whom long-term anticoagulation of a perfect quality is impossible to guarantee. A series of tests on goats has been performed, using the Björk-Shiley Monostrut valve used in 2,024 patients at the Karolinska Hospital in Stockholm and in 75,000 patients worldwide for up to 8 years with a modification of a microporous surface. In the mitral position, this modified partially microporous-surfaced Björk-Shiley Monostrut valve has permitted goats to live for 5 years with four normal pregnancies without anticoagulation therapy.

The Björk-Shiley Delrin tilting disc heart valve: historical perspective, design and need for scientific analyses after 25 years.

The Björk-Shiley Delrin (BSD) tilting disc heart valve was first used clinically in 1969. It is estimated that up to 24,000 BSD heart valves were implanted between 1969 and 1981, of which 7,000 may still be implanted in patients. The BSD valve provided a low-profile, quiet prosthesis with excellent hemodynamics. There have been only two reports of mechanical failure due to inlet strut fracture. Recent reports of wear of the Delrin disc combined with wear as observed on explanted BSD valves after 17-20 years in patients stimulated the formation of a Scientific Advisory Panel by Shiley to review the status of the BSD heart valve and make recommendations regarding patients living with BSD heart valves. The studies presented in this Supplement of The Journal of Heart Valve Disease summarize some of the scientific investigations conducted by Shiley and those recommended by this Panel. The material reviewed by the Panel included: (i) clinical publications on BSD heart valves; (ii) seventy-three explanted BSD heart valves returned to Shiley over the past 25 years; (iii) BSD valves subjected to accelerated wear tests; (iv) unimplanted BSD heart valves in Shiley's inventory; (v) in vitro studies of static leakage and pulsatile regurgitation of explanted and unimplanted "control' BSD heart valves; (vi) two Christiansen hip prostheses explanted from patients after five and 13 years; (vii) implant data for the BSD heart valve from the Karolinska Hospital, Stockholm, Sweden; and (viii) test reports for studies and analyses conducted by Shiley for the BSD heart valve. This article gives an overview of and introduction to the studies of the BSD heart valve presented in the following papers.

The unnatural history of valvular heart disease: late results with silastic ball valve prostheses.

The development of prosthetic heart valves successfully arrested the dismal natural history of valvular heart disease for thousands of patients. The experiences of numerous investigators provided a setting wherein the design and implantation of the silastic ball valves led to improved survival with both aortic and mitral valve replacement. Refinement of the caged-ball design was based on clinical and laboratory findings. In the mitral position, valve related thromboembolism was reduced from 38% to 3%. With the aortic prostheses the problem of ball variance was overcome by reducing trauma to the poppet and altering its heat curing process. In 1967 a completely cloth covered valve was introduced to reduce further the thromboembolic rate. Significant improvement in the embolus-free rate was ultimately found to be dependent on the year of operation with introduction of the time-frame concept. The current mitral silastic ball valve, Model 6120, yields an actuarial survival of 72 (+/- 3%), 54 (+/- 5%), and 37 (+/- 5%) for five, ten and fifteen years respectively. For aortic valve replacement, current Model 1260, the actuarial survival is 71 (+/- 2%), 58 (+/- 3%) and 48 (+/- 4%) for five, ten and fifteen years respectively. Late results are compared to other valvular prostheses.

Conduit-mounted cardiac valve prostheses: a review of their uses, design and in vivo performance.

Although providing an historical overview of the development and clinical applications of conduit-mounted prosthetic heart valves, with elementary explanations of operative techniques, this review concentrates on the impact of design and surgical considerations on their in vivo performance. Areas showing potential for design improvement of mechanical prostheses are highlighted, both in terms of haemodynamic efficiency and haemocompatibility. Comparisons are drawn throughout the paper with conventional valve prostheses, and the key features where they differ significantly are pointed out. It is concluded that there is considerable scope for further worthwhile development.

Reflections on the development of valvular prostheses.

Surgical attempts to open obstructed heart valves in the 1940s led to the eventual development of valvular prostheses, accompanied by the parallel development of methods of sustaining extracorporeal circulation; biocompatible materials; and engineering designs. Early problems encountered included the incidence of thrombotic phenomena, audibility of valvular noise, impaired flow dynamics, and hemo-incapability. These problems have been solved with increasing success with the creation of new plastics, the ball valve design, and improved manufacturing processes.

Mitral replacement: clinical experience with a ball-valve prosthesis. Twenty-five years later.

The purpose of this report is to review the results of mitral valve replacement since a first report in the Annals of Surgery in 1961, in order to determine the relative importance of new valve designs versus other surgical variables. The continued use of the silastic ball valve in its 1966 configuration (Model 6120), by providing a comparative data base for other new prosthetic valves, allows this analysis. For a valid comparison with the tilting disc (Bjork-Shiley) and the porcine (Hancock and Carpentier-Edwards) valves, only results with the silastic ball valves implanted during comparable time frames should be used. (Formula: see text) Thus, there are no significant differences in the results obtained with the silastic ball valve in time frames comparable to other contemporary valves introduced in the early 1970s. Improved results, therefore, must be non-prosthetic valve related.

Porcine valves.

To date, the glutaraldehyde porcine aortic valve xenograft has proved a good choice for valve replacement in both the aortic and mitral positions. Late thromboembolisms in the absence of long-term anticoagulation is virtually nonexistent in aortic valve replacement and very low in mitral valve replacement patients without a predisposing history. The hemodynamic performance of the porcine xenograft is adequate and comparable to that of mechanical prostheses. The potential for improved hydrodynamic function, particularly of very small sized valves, is great and already being realized. In spite of over 8 yr of xenograft experience, long-term durability remains the primary concern. Histologic study suggests that these valves undergo progressive postimplantation morphological alteration. However, to date, the incidence of tissue failure is very low. Although detailed reports of long-term valve series are surprisingly few, at present, there is no valve replacement device with a 10-yr experience proven structural integrity and a negligible incidence of valve-related morbidity. It will be 3-4 yr before a significant number of porcine xenograft patients either reach this point or experience valve failure. While this review of the valve literature does not permit a statistical comparison of valve types, we feel that it does allow us to attempt a general projection. On the basis of combined survival and valve-related complication rates, at 4 yr, the porcine xenograft appears to be a better choice than the mechanical prosthesis. Excessive tissue failure during the next 3-4 yr might reverse this opinion. However, even if an increase in valve failure does occur, the advantage of noncatastrophic disfunction and decreased valve-related complications may balance the risk of reoperative morbidity and mortality and continue to favor the porcine exnograft. Thus we could speculate that: (1) The tissue valve would be the valve of choice if (A) durability of 10 yr or more is proven, and valve complications with the xenograft remain as presently reported; (B) the incidence of valve complications with the mechanical prostheses at 10-yr follow-up continues to increase. (2) Mechanical prostheses would be the valves of choice if (A) xenograft valve failure is greater than 20% at 10 yr of follow-up; (B) the incidence of valve complications with the mechanical prostheses remains unchanged. (3) The choice of xenograft versus mechanical prosthesis will remain an open issue if valve failure and related complications with both types of device remain below 20% at 10-yr follow-up...