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Development of an artificial heart valve
CLASSICS IN THORACIC SURGERY
Development of an Artificial Heart Valve Viking 0 . Bjork, MD Karolinska Hospital, Stockholm, Sweden, and Desert Heart Institute Foundation, Rancho Mirage, California
When I reviewed the 21-year results with the BjorkShiley 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 anticoagulationrelated 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 Bjork-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 Bjork-Shiley Monostrut valve has permitted goats to live for 5 years with four normal pregnancies without anticoagulation therapy. (Ann Thorac Surg 1990;50:2524
I
Something more radical had to be done. I then replaced the aortic leaflets with the Bahnson Teflon cusps, sewn in ”free-hand.” This method resulted in calcification and cusp rupture within 1 to 2 years. In a few survivors, I could replace the Bahnson cusps with the Starr-Edwards ball valves. However, in the patients with narrow aortic roots, the Starr-Edwards ball valve (size 8A) gave a gradient of 70 mm Hg, and 6 of 8 patients died. Something better was needed. I made aortic cusps out of the patient’s own pericardium, but they wore out and ruptured within 6 months. Better results were obtained with the patient’s own fascia lata. However, even the fascia lata cusp shrunk down and calcified within 4 to 5 years. I then used the Kay-Shiley flat disc valve for aortic valve replacement. The Kay-Shiley valve gave a gradient as high as was obtained with the ball valve, but the patients with Kay-Shirley valves could tolerate tachycardia during exercise without a decrease in blood pressure better than patients with ball valves. I went to Hokkaido, Japan, to visit Dr Juro Wada, who was using the Wada-Cutter Valve. I started using this hinged tilting disc valve and found that the gradient was substantially lower, ie, only one half of the gradient found in the Kay-Shiley valve. Later fibrin formation in the hinge caused malfunction of the occluding mechanism. The localized wear in the hinge then caused embolization of the disc. I had learned that the tilting-disc concept could diminish the pressure gradient, but the hinge had to be avoided. Donald Shiley presented his ideas of a valve with a free-floating disc (without a hinge), and with some improvements of a prototype, I immediately knew we had to try this idea. With this Delrin disc valve in the aortic position, there was a 15-year actual survival of 55% in the first 150 cases, compared with a 76% survival for Swedes of similar age and sex. After 20 years of follow-up, the Delrin disc is still functioning well in the first 14 surviving patients I have investigated.
t is estimated that about 100,000 patients worldwide have an artificial heart valve implanted each year. These man-made heart valves are produced from various materials and of various designs. It was not so long ago that no prosthetic heart valves were available. During the early 1950s, dilation of calcified aortic valves was the first treatment available in Sweden. I used Bailey’s ”Cadillac” dilator, first guided by a wire with a spherical tip, which could be palpated in the root of the aorta before the dilator was pushed through the calcific valve. The crack of the calcific valve could be heard when the dilator was opened. The dilation caused a very small change or decrease in valvar gradient, and there was usually a restenosis within 1 or 2 years. When the gradient did decrease considerably, valvar insufficiency developed. In my first 22 patients with dilation, long-term results were bad. Severe regurgitation occurred when a bicuspid aortic valve was dilated. As the results were not good, I had to be careful with the selection of patients. First, I had to develop a better procedure for exact diagnosis with catheterization of the left side of the heart before attempting further to treat calcified valves. I used an 18-cm long needle that was introduced at the upper border of the ninth rib, 2 fingerwidths to the right from the posterior midline. The needle, touching the vertebral body, then entered the left atrium. A catheter was introduced through the left atrium and passed through the left ventricle out into the aorta. On withdrawal, the pressures in all portions of the left side of the heart could be recorded. When I had the heart-lung machine with the spinning disk oxygenator available in 1958, I started manual decalcification of the aortic cusp. This method was more effective in reducing the pressure gradient. Unfortunately, the gradients did return in 1 to 2 years. Address reprint requests to Dr Bjork, do Frid, Runbergsv 8, 19148 Sollentuna, Sweden. 0 1990 by The Society of Thoracic Surgeons
0003-4975/90/$3.50
152
CLASSICS BJORK ARTIFICIAL HEART VALVE
In 1971, the Delrin disc was exchanged with a disc of pyrolytic carbon (later called the "conical" disc). The pyrolytic carbon disc eliminated the problems associated with sterilizing the Delrin disc, which could retain water and swell, and it provided a considerable increase in durability. In 1975, the conical disc was replaced with a spherical disc that incorporated a radiopaque marker in the disc. On screening, it was then easy to verify the function of the disc movement. (I call both the conical and spherical discs "flat" discs in contrast to the convexoconcave discs.) In the whole group of 1,657 patients with aortic valve replacement, with Bjork-Shiley valve models, the 15-year actuarial survival was 54%. Twenty-five percent of late deaths were valve related, 8.3%were mainly of anticoagulation-related bleeding, and 5.4%, of thromboembolic complications. In 764 patients with mitral valve replacement using all models, the 15-year actuarial survival was 51% compared with 82% of healthy Swedes (matched control population of the same sex and age). The valve-related cause of death in these 764 patients was dominated by valve thrombosis in lo%, embolism in 3%, and anticoagulation-related fatal bleeding in 4%. From the beginning, both the inflow and outflow struts were welded into the valve ring. Of 1,100 patients with a flat disc, I had one inflow strut rupture. The inflow strut was then made an integral part of the valve ring for the convexoconcave disc valve, after which no inflow strut ruptured. The main thing was now to improve the valve flow to diminish thromboembolic complications. In 1976, I implanted the first convexoconcavedisc valves, in which the configuration of the disc was changed mainly to improve the flow through the smaller flow area and thereby diminish thromboembolic complications. When open, the fluid forces would cause the disc to slide out of the orifice by 2 mm, eliminating the low-flow area caused by the disc edge touching the orifice in the earlier valve models with a flat disc. As a result of the earlier inlet strut fracture, the inlet strut was made an integral part of the convexoconcave valve ring. In 1978, the report of an outlet strut fracture was received in the United States. Then we decided that a single-piece valve, later known as the Monostrut valve, should be developed. In the mean time, the opening angle was increased from 60 degrees to 70 degrees. This change would reduce the opening forces on the outlet strut. The 70-degree opening angle was also important to avoid a vortex formation behind the smaller hole and to diminish the gradient, making the valve suitable for narrow aortic roots. During one week in March 1982, I experienced my first two outlet strut ruptures in large 70-degree mitral valves. This was a shock, and I immediately stopped using the large convexoconcave valve model and would only use the Monostrut valve. Review of clinical results of the convexoconcave valve models, both with 60-degree and 70-degree opening angles, showed that the thromboembolic complications were reduced by 50% over the earlier models with a flat
Ann Thorac Surg 1990;50 1 5 1 4
Fig I . The Bjork-Shiley Monostrut mitral heart valve with 70-degree convexoconcave disc opening. Notice the space between the edges of the disc and the valve ring as the disc slides out 2 mm in the open position.
disc, with exactly the same anticoagulation treatment and identical rate of bleeding complications. At 5 years of follow-up, a 1.2% rate of thrombosis was encountered in patients with the convexoconcave disc valve in the mitral position, as compared with a 7.1% rate in patients with the earlier flat disc valves. The 2-year mortality, however, was 2% higher, mainly because of rupture of the outflow strut. The 7-year actuarial survival was 9% better, ie, 80% for patients with the convexoconcave disc as compared with 71% for patients with the earlier flat disc valve. To date, the monostrut valve has been used, without rupture, in 2,024 patients at the Karolinska Hospital in Stockholm and in more than 75,000 patients worldwide, outside the United States. The Monostrut disc opens to 70 degrees, which is important (Fig 1).There were no episodes of thrombosis or fatal embolism in our first group of patients with Bjork-Shiley Monostrut valves. Detailed follow-up has shown a 1.2% embolism rate in 180 patients who had aortic valve replacement and a 3.1% embolism rate in 101 patients with mitral valve replacement. Anticoagulation-related bleeding was found in 2.2% of these patients, and proved fatal in 0.5%. As of today, no mechanical valve can be left without anticoagulation therapy. In my first aortic valve replacement series, I left 32 patients for 12 months without anticoagulation therapy. This resulted in 15.6 thromboembolic complications per 100 patient-years. These patients had to be put back on anticoagulation therapy. In 1978, the carbon-coated sewing ring was introduced. This sewing ring was developed to reduce the tissue overgrowth in the fabric cuff and thereby maintain a smoother surface of the sewing ring. To date, the importance of the
Ann Thorac Surg
CLASSICS BJORK ARTIFICIAL HEART VALVE
1990;501514
carbon-coated sewing ring has been impossible to determine owing to the small complication rate of the overall series and the limited number of both Teflon cloth sewing rings and carbon-coated Dacron cloth sewing rings. In 1976, MacGregor and co-workers described a microporous metal coating perpetuating endothelialization on metal surfaces in the bloodstream. MacGregor and coworkers' work was tested. Microporous-surfaced rings were introduced into the superior vena cava of goats. Larger porous surfaces caused clotting, but a porosity size of 20 pm produced a thin, translucent, nonvascularized endothelialized covering (Fig 2). In 1984, 19 goats had a Monostrut valve with porous coating implanted over the entire flange surface, and 10 goats were implanted with a Monostrut valve as controls. The valves were implanted in the mitral position of the goats, as thromboembolic complications in the mitral position of humans were double those of the aortic position. All goats were treated humanely; however, no anticoagulation therapy was provided. The goats were killed between 1 and 1% years. All the polished Monostrut controls had a different degree of thrombosis, originating from the suture ring or growing over the groove to the valve ring. No thrombosis was attached to the polished struts. The porous metal Monostruts showed an endothelialized covering from the sewing ring to the metal orifice ring, but never over the center of the orifice where the disc seats. The struts were never completely covered. The contact area of the struts where the disc continuously seats had a tendency to build up a thrombus (37%). Additional valves were porous-coated; however, in these valves the contact areas of the struts were polished, and the valves were implanted. When explanted after 2% years, the valves looked excellent and had no thrombus formation (Fig 3). The longest porous-coated mitral Monostrut valve implants are now 5 years. The goats are currently healthy, one goat is pregnant for the fourth time, and all goats are scheduled to be killed in the near future.
153
Fig 3. The modified porous-surfaced Bjork-Shiley 25-mm Monostrut mitral valve after 2 % years without anticoagulation therapy in a gout (viewed from the left atrium). The carbon-coated Tefon suture ring is covered with a thin, smooth, and glistening endothelium continuing over the groove and upper part of the valve ring.
In conclusion, the porous-coated Monostrut valve should be used. I would suggest a clinical trial be initiated with the porous-coated Monostrut valve as described. Patients would have the normal anticoagulation therapy for the first 3 months, after which they should be weaned off. I would prefer to bring the patients into the hospital for 1 week to be weaned off the warfarin or dicumarol treatment during heparin administration and then discontinue heparin administration, leaving the patients without anticoagulation therapy. The incidence of emboli should be less than the incidence of anticoagulation-related bleedings. In case of an embolus, anticoagulation therapy should be started. In the pursuit of improved quality of life for heart valve patients, a clinical investigation of the porous-coated Monostrut valve has to be done. This is a definite step forward, and it is especially needed for children, for young females who want to have children, for the older generation who are on medical treatments that do not allow anticoagulation drugs, for patients with sickle-cell anemia, and for all patients in whom long-term anticoagulation of a perfect quality is impossible to guarantee.
Bibliography
Fig 2. A valve ring of 15-mm diameter surfaced with microspheres of an average size of 20 p m inscrted into the superior vena cava of a goat and explanted after 6 months when it was covered with a
smooth, thin, translucent neointima continuous with the intima of the superior vena cava and the right atrium.
1. Rodriguez LE. Hernodynamic and angiographic findings in patients with isolated aortic valvular disease before and after insertion of ball-valve prosthesis. Scand J Thorac Cardiovasc Surg 1970;4(Suppl5). 2. Bjork VO. Experience with the Wada-Cutter valve prosthesis in the aortic area. J Thorac Cardiovasc Surg 1970;60:26. 3. Bjork VO. A new tilting disc valve prosthesis. Scand J Thorac Cardiovasc Surg 1969;3:1-10. 4. Bjork VO. The pyrolytic carbon occluder for the Bjork-Shiley tilting disc valve prosthesis. Scand J Thorac Cardiovasc Surg 1972;6:109-13.
154
CLASSICS BJORK ARTIFICIAL HEART VALVE
5. Bjork VO, Henze A. Management of thromboembolism after aortic valve replacement with the Bjork-Shiley tilting disc valve. Scand J Thorac Cardiovasc Surg 1975;9183-91. 6. Bjork VO, Henze A. Ten years' experience with the BjorkShiley tilting disc valve. Scand J Thorac Cardiovasc Surg 1979;78:331. 7. Bjork VO. The improved Bjork-Shiley tilting disc valve prosthesis. Scand J Thorac Cardiovasc Surg 1978;12814. 8. Bjork VO. Advantages and long-term results of the BjorkShiley valve. Cardiovasc Med 1982;1:293-304. 9. Bjork VO, Henze A, Hindmarsh T. Radiopaque marker in the tilting disc of the Bjork-Shiley heart valve. J Thorac Cardiovasc Surg 1977;73:563-9. 10. Bruss KH, Reul H, Van Gilse F, Knott E. Pressure drop and velocity yields at four mechanical heart valve prostheses: Bjork-Shiley standard, Bjork-Shiley concave-convex, HallCaster and St Jude Medical. Life Support Syst 1983;1:8-22. 11. Bjork VO. The optimal angle of the Bjork-Shiley tilting disc valve prosthesis. Scand J Thorac Cardiovasc Surg 1981; 15:223-7. 12. Bjork VO. Metallurgical and design development in response to mechanical dysfunctions in Bjork-Shiley heart valves. Scand J Thorac Cardiovasc Surg 1985;19:1-12. 13. Bjork VO, Lindblom D. The Monostrut Bjork-Shiley heart valve. J Am Coll Cardiol 1985;6:1142-8. 14. Bjork VO, H e m e A, Lindblom D. The Monostrut strength. Scand J Thorac Cardiovasc 1985;9:13-9. 15. Woo YR, Yoganathan A. In vitro pulsative flow measurements in the vicinity of mechanical heart valves in the mitral flow chamber. Life Support Syst 1986;4:115-39. 16. Yoganathan AP, Reamer HH, Corcoran WH, Hamson JC. The Bjork-Shiley aortic prosthesis: flow characteristics of the
Ann Thorac Surg 1990;50:1514
17. 18. 19. 20. 21. 22. 23. 24. 25. 26.
present model vs the convexo-concave model. Scand J Thorac Cardiovasc Surg 1980;14:1-5. Lindblom D. Long-term clinical results after aortic valve replacement with the Bjork-Shiley prosthesis. J Thorac Cardiovasc Surg 1988;95:658-7. Bjork VO. Optimal orientation of the 60" and the 70" BjorkShiley tilting disc valves. Scand J Thorac Cardiovasc Surg 1982;16:113-8. Lindblom D. Long-term clinical results after mitral valve replacement with the Bjork-Shiley prosthesis. J Thorac Cardiovasc Surg 1988;95:321-3. Lindblom D, Bjork VO, Semb BKH. Mechanical failure of the Bjork-Shiley valve. Incidence, clinical presentation and management. J Thorac Cardiovasc Surg 1986;92:894. Lindblom D, Lindblom U, Henze A, Bjork VO, Semb BKH. Three-year clinical results with the monostrut Bjork-Shiley prosthesis. J Thorac Cardiovasc Surg 1987;94:3443. Macgregor DC, Pilliar RM, Wilson GJ, et al. Porous metal surfaces: a radical new concept in prosthetic heart valve design. Trans Am SOCArtif Intern Organs 1976;22:64&53. Bjork VO, Sternlieb JJ. Artificial heart valve testing in goats. Scand J Thorac Cardiovasc Surg 1986;20:97-102. Bjork VO, Wilson Gregory J, Stemlieb Jack J, Kaminsky David B. The porous metal-surfaced heart valve. J Thorac Cardiovasc Surg 1988;95:1067-82. Bjork VO, Stemlieb JJ, Kaminsky DB. Optimal microporous surface for endothelialization of mitral valves in the blood stream. Scand J Thorac Cardiovasc Surg (in press). Bjork VO, Stemlieb JJ, Kaminsky DB. Modified porous metal-surfaced Bjork-Shiley Monostrut heart valve. Scand J Thorac Cardiovasc Surg (in press).
Development of an Artificial Heart Valve Viking 0 . Bjork, MD Karolinska Hospital, Stockholm, Sweden, and Desert Heart Institute Foundation, Rancho Mirage, California
When I reviewed the 21-year results with the BjorkShiley 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 anticoagulationrelated 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 Bjork-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 Bjork-Shiley Monostrut valve has permitted goats to live for 5 years with four normal pregnancies without anticoagulation therapy. (Ann Thorac Surg 1990;50:2524
I
Something more radical had to be done. I then replaced the aortic leaflets with the Bahnson Teflon cusps, sewn in ”free-hand.” This method resulted in calcification and cusp rupture within 1 to 2 years. In a few survivors, I could replace the Bahnson cusps with the Starr-Edwards ball valves. However, in the patients with narrow aortic roots, the Starr-Edwards ball valve (size 8A) gave a gradient of 70 mm Hg, and 6 of 8 patients died. Something better was needed. I made aortic cusps out of the patient’s own pericardium, but they wore out and ruptured within 6 months. Better results were obtained with the patient’s own fascia lata. However, even the fascia lata cusp shrunk down and calcified within 4 to 5 years. I then used the Kay-Shiley flat disc valve for aortic valve replacement. The Kay-Shiley valve gave a gradient as high as was obtained with the ball valve, but the patients with Kay-Shirley valves could tolerate tachycardia during exercise without a decrease in blood pressure better than patients with ball valves. I went to Hokkaido, Japan, to visit Dr Juro Wada, who was using the Wada-Cutter Valve. I started using this hinged tilting disc valve and found that the gradient was substantially lower, ie, only one half of the gradient found in the Kay-Shiley valve. Later fibrin formation in the hinge caused malfunction of the occluding mechanism. The localized wear in the hinge then caused embolization of the disc. I had learned that the tilting-disc concept could diminish the pressure gradient, but the hinge had to be avoided. Donald Shiley presented his ideas of a valve with a free-floating disc (without a hinge), and with some improvements of a prototype, I immediately knew we had to try this idea. With this Delrin disc valve in the aortic position, there was a 15-year actual survival of 55% in the first 150 cases, compared with a 76% survival for Swedes of similar age and sex. After 20 years of follow-up, the Delrin disc is still functioning well in the first 14 surviving patients I have investigated.
t is estimated that about 100,000 patients worldwide have an artificial heart valve implanted each year. These man-made heart valves are produced from various materials and of various designs. It was not so long ago that no prosthetic heart valves were available. During the early 1950s, dilation of calcified aortic valves was the first treatment available in Sweden. I used Bailey’s ”Cadillac” dilator, first guided by a wire with a spherical tip, which could be palpated in the root of the aorta before the dilator was pushed through the calcific valve. The crack of the calcific valve could be heard when the dilator was opened. The dilation caused a very small change or decrease in valvar gradient, and there was usually a restenosis within 1 or 2 years. When the gradient did decrease considerably, valvar insufficiency developed. In my first 22 patients with dilation, long-term results were bad. Severe regurgitation occurred when a bicuspid aortic valve was dilated. As the results were not good, I had to be careful with the selection of patients. First, I had to develop a better procedure for exact diagnosis with catheterization of the left side of the heart before attempting further to treat calcified valves. I used an 18-cm long needle that was introduced at the upper border of the ninth rib, 2 fingerwidths to the right from the posterior midline. The needle, touching the vertebral body, then entered the left atrium. A catheter was introduced through the left atrium and passed through the left ventricle out into the aorta. On withdrawal, the pressures in all portions of the left side of the heart could be recorded. When I had the heart-lung machine with the spinning disk oxygenator available in 1958, I started manual decalcification of the aortic cusp. This method was more effective in reducing the pressure gradient. Unfortunately, the gradients did return in 1 to 2 years. Address reprint requests to Dr Bjork, do Frid, Runbergsv 8, 19148 Sollentuna, Sweden. 0 1990 by The Society of Thoracic Surgeons
0003-4975/90/$3.50
152
CLASSICS BJORK ARTIFICIAL HEART VALVE
In 1971, the Delrin disc was exchanged with a disc of pyrolytic carbon (later called the "conical" disc). The pyrolytic carbon disc eliminated the problems associated with sterilizing the Delrin disc, which could retain water and swell, and it provided a considerable increase in durability. In 1975, the conical disc was replaced with a spherical disc that incorporated a radiopaque marker in the disc. On screening, it was then easy to verify the function of the disc movement. (I call both the conical and spherical discs "flat" discs in contrast to the convexoconcave discs.) In the whole group of 1,657 patients with aortic valve replacement, with Bjork-Shiley valve models, the 15-year actuarial survival was 54%. Twenty-five percent of late deaths were valve related, 8.3%were mainly of anticoagulation-related bleeding, and 5.4%, of thromboembolic complications. In 764 patients with mitral valve replacement using all models, the 15-year actuarial survival was 51% compared with 82% of healthy Swedes (matched control population of the same sex and age). The valve-related cause of death in these 764 patients was dominated by valve thrombosis in lo%, embolism in 3%, and anticoagulation-related fatal bleeding in 4%. From the beginning, both the inflow and outflow struts were welded into the valve ring. Of 1,100 patients with a flat disc, I had one inflow strut rupture. The inflow strut was then made an integral part of the valve ring for the convexoconcave disc valve, after which no inflow strut ruptured. The main thing was now to improve the valve flow to diminish thromboembolic complications. In 1976, I implanted the first convexoconcavedisc valves, in which the configuration of the disc was changed mainly to improve the flow through the smaller flow area and thereby diminish thromboembolic complications. When open, the fluid forces would cause the disc to slide out of the orifice by 2 mm, eliminating the low-flow area caused by the disc edge touching the orifice in the earlier valve models with a flat disc. As a result of the earlier inlet strut fracture, the inlet strut was made an integral part of the convexoconcave valve ring. In 1978, the report of an outlet strut fracture was received in the United States. Then we decided that a single-piece valve, later known as the Monostrut valve, should be developed. In the mean time, the opening angle was increased from 60 degrees to 70 degrees. This change would reduce the opening forces on the outlet strut. The 70-degree opening angle was also important to avoid a vortex formation behind the smaller hole and to diminish the gradient, making the valve suitable for narrow aortic roots. During one week in March 1982, I experienced my first two outlet strut ruptures in large 70-degree mitral valves. This was a shock, and I immediately stopped using the large convexoconcave valve model and would only use the Monostrut valve. Review of clinical results of the convexoconcave valve models, both with 60-degree and 70-degree opening angles, showed that the thromboembolic complications were reduced by 50% over the earlier models with a flat
Ann Thorac Surg 1990;50 1 5 1 4
Fig I . The Bjork-Shiley Monostrut mitral heart valve with 70-degree convexoconcave disc opening. Notice the space between the edges of the disc and the valve ring as the disc slides out 2 mm in the open position.
disc, with exactly the same anticoagulation treatment and identical rate of bleeding complications. At 5 years of follow-up, a 1.2% rate of thrombosis was encountered in patients with the convexoconcave disc valve in the mitral position, as compared with a 7.1% rate in patients with the earlier flat disc valves. The 2-year mortality, however, was 2% higher, mainly because of rupture of the outflow strut. The 7-year actuarial survival was 9% better, ie, 80% for patients with the convexoconcave disc as compared with 71% for patients with the earlier flat disc valve. To date, the monostrut valve has been used, without rupture, in 2,024 patients at the Karolinska Hospital in Stockholm and in more than 75,000 patients worldwide, outside the United States. The Monostrut disc opens to 70 degrees, which is important (Fig 1).There were no episodes of thrombosis or fatal embolism in our first group of patients with Bjork-Shiley Monostrut valves. Detailed follow-up has shown a 1.2% embolism rate in 180 patients who had aortic valve replacement and a 3.1% embolism rate in 101 patients with mitral valve replacement. Anticoagulation-related bleeding was found in 2.2% of these patients, and proved fatal in 0.5%. As of today, no mechanical valve can be left without anticoagulation therapy. In my first aortic valve replacement series, I left 32 patients for 12 months without anticoagulation therapy. This resulted in 15.6 thromboembolic complications per 100 patient-years. These patients had to be put back on anticoagulation therapy. In 1978, the carbon-coated sewing ring was introduced. This sewing ring was developed to reduce the tissue overgrowth in the fabric cuff and thereby maintain a smoother surface of the sewing ring. To date, the importance of the
Ann Thorac Surg
CLASSICS BJORK ARTIFICIAL HEART VALVE
1990;501514
carbon-coated sewing ring has been impossible to determine owing to the small complication rate of the overall series and the limited number of both Teflon cloth sewing rings and carbon-coated Dacron cloth sewing rings. In 1976, MacGregor and co-workers described a microporous metal coating perpetuating endothelialization on metal surfaces in the bloodstream. MacGregor and coworkers' work was tested. Microporous-surfaced rings were introduced into the superior vena cava of goats. Larger porous surfaces caused clotting, but a porosity size of 20 pm produced a thin, translucent, nonvascularized endothelialized covering (Fig 2). In 1984, 19 goats had a Monostrut valve with porous coating implanted over the entire flange surface, and 10 goats were implanted with a Monostrut valve as controls. The valves were implanted in the mitral position of the goats, as thromboembolic complications in the mitral position of humans were double those of the aortic position. All goats were treated humanely; however, no anticoagulation therapy was provided. The goats were killed between 1 and 1% years. All the polished Monostrut controls had a different degree of thrombosis, originating from the suture ring or growing over the groove to the valve ring. No thrombosis was attached to the polished struts. The porous metal Monostruts showed an endothelialized covering from the sewing ring to the metal orifice ring, but never over the center of the orifice where the disc seats. The struts were never completely covered. The contact area of the struts where the disc continuously seats had a tendency to build up a thrombus (37%). Additional valves were porous-coated; however, in these valves the contact areas of the struts were polished, and the valves were implanted. When explanted after 2% years, the valves looked excellent and had no thrombus formation (Fig 3). The longest porous-coated mitral Monostrut valve implants are now 5 years. The goats are currently healthy, one goat is pregnant for the fourth time, and all goats are scheduled to be killed in the near future.
153
Fig 3. The modified porous-surfaced Bjork-Shiley 25-mm Monostrut mitral valve after 2 % years without anticoagulation therapy in a gout (viewed from the left atrium). The carbon-coated Tefon suture ring is covered with a thin, smooth, and glistening endothelium continuing over the groove and upper part of the valve ring.
In conclusion, the porous-coated Monostrut valve should be used. I would suggest a clinical trial be initiated with the porous-coated Monostrut valve as described. Patients would have the normal anticoagulation therapy for the first 3 months, after which they should be weaned off. I would prefer to bring the patients into the hospital for 1 week to be weaned off the warfarin or dicumarol treatment during heparin administration and then discontinue heparin administration, leaving the patients without anticoagulation therapy. The incidence of emboli should be less than the incidence of anticoagulation-related bleedings. In case of an embolus, anticoagulation therapy should be started. In the pursuit of improved quality of life for heart valve patients, a clinical investigation of the porous-coated Monostrut valve has to be done. This is a definite step forward, and it is especially needed for children, for young females who want to have children, for the older generation who are on medical treatments that do not allow anticoagulation drugs, for patients with sickle-cell anemia, and for all patients in whom long-term anticoagulation of a perfect quality is impossible to guarantee.
Bibliography
Fig 2. A valve ring of 15-mm diameter surfaced with microspheres of an average size of 20 p m inscrted into the superior vena cava of a goat and explanted after 6 months when it was covered with a
smooth, thin, translucent neointima continuous with the intima of the superior vena cava and the right atrium.
1. Rodriguez LE. Hernodynamic and angiographic findings in patients with isolated aortic valvular disease before and after insertion of ball-valve prosthesis. Scand J Thorac Cardiovasc Surg 1970;4(Suppl5). 2. Bjork VO. Experience with the Wada-Cutter valve prosthesis in the aortic area. J Thorac Cardiovasc Surg 1970;60:26. 3. Bjork VO. A new tilting disc valve prosthesis. Scand J Thorac Cardiovasc Surg 1969;3:1-10. 4. Bjork VO. The pyrolytic carbon occluder for the Bjork-Shiley tilting disc valve prosthesis. Scand J Thorac Cardiovasc Surg 1972;6:109-13.
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CLASSICS BJORK ARTIFICIAL HEART VALVE
5. Bjork VO, Henze A. Management of thromboembolism after aortic valve replacement with the Bjork-Shiley tilting disc valve. Scand J Thorac Cardiovasc Surg 1975;9183-91. 6. Bjork VO, Henze A. Ten years' experience with the BjorkShiley tilting disc valve. Scand J Thorac Cardiovasc Surg 1979;78:331. 7. Bjork VO. The improved Bjork-Shiley tilting disc valve prosthesis. Scand J Thorac Cardiovasc Surg 1978;12814. 8. Bjork VO. Advantages and long-term results of the BjorkShiley valve. Cardiovasc Med 1982;1:293-304. 9. Bjork VO, Henze A, Hindmarsh T. Radiopaque marker in the tilting disc of the Bjork-Shiley heart valve. J Thorac Cardiovasc Surg 1977;73:563-9. 10. Bruss KH, Reul H, Van Gilse F, Knott E. Pressure drop and velocity yields at four mechanical heart valve prostheses: Bjork-Shiley standard, Bjork-Shiley concave-convex, HallCaster and St Jude Medical. Life Support Syst 1983;1:8-22. 11. Bjork VO. The optimal angle of the Bjork-Shiley tilting disc valve prosthesis. Scand J Thorac Cardiovasc Surg 1981; 15:223-7. 12. Bjork VO. Metallurgical and design development in response to mechanical dysfunctions in Bjork-Shiley heart valves. Scand J Thorac Cardiovasc Surg 1985;19:1-12. 13. Bjork VO, Lindblom D. The Monostrut Bjork-Shiley heart valve. J Am Coll Cardiol 1985;6:1142-8. 14. Bjork VO, H e m e A, Lindblom D. The Monostrut strength. Scand J Thorac Cardiovasc 1985;9:13-9. 15. Woo YR, Yoganathan A. In vitro pulsative flow measurements in the vicinity of mechanical heart valves in the mitral flow chamber. Life Support Syst 1986;4:115-39. 16. Yoganathan AP, Reamer HH, Corcoran WH, Hamson JC. The Bjork-Shiley aortic prosthesis: flow characteristics of the
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present model vs the convexo-concave model. Scand J Thorac Cardiovasc Surg 1980;14:1-5. Lindblom D. Long-term clinical results after aortic valve replacement with the Bjork-Shiley prosthesis. J Thorac Cardiovasc Surg 1988;95:658-7. Bjork VO. Optimal orientation of the 60" and the 70" BjorkShiley tilting disc valves. Scand J Thorac Cardiovasc Surg 1982;16:113-8. Lindblom D. Long-term clinical results after mitral valve replacement with the Bjork-Shiley prosthesis. J Thorac Cardiovasc Surg 1988;95:321-3. Lindblom D, Bjork VO, Semb BKH. Mechanical failure of the Bjork-Shiley valve. Incidence, clinical presentation and management. J Thorac Cardiovasc Surg 1986;92:894. Lindblom D, Lindblom U, Henze A, Bjork VO, Semb BKH. Three-year clinical results with the monostrut Bjork-Shiley prosthesis. J Thorac Cardiovasc Surg 1987;94:3443. Macgregor DC, Pilliar RM, Wilson GJ, et al. Porous metal surfaces: a radical new concept in prosthetic heart valve design. Trans Am SOCArtif Intern Organs 1976;22:64&53. Bjork VO, Sternlieb JJ. Artificial heart valve testing in goats. Scand J Thorac Cardiovasc Surg 1986;20:97-102. Bjork VO, Wilson Gregory J, Stemlieb Jack J, Kaminsky David B. The porous metal-surfaced heart valve. J Thorac Cardiovasc Surg 1988;95:1067-82. Bjork VO, Stemlieb JJ, Kaminsky DB. Optimal microporous surface for endothelialization of mitral valves in the blood stream. Scand J Thorac Cardiovasc Surg (in press). Bjork VO, Stemlieb JJ, Kaminsky DB. Modified porous metal-surfaced Bjork-Shiley Monostrut heart valve. Scand J Thorac Cardiovasc Surg (in press).