The improved Björk-Shiley tilting disc valve prosthesis

The Björk-Shiley convexo-concave heart valve experience from the perspective of the supervisory panel

The 20-year activities of a medical supervisory panel appointed under the terms of a settlement agreement of the Bowling v. Pfizer class action suit involving the Björk-Shiley convexo-concave (BSCC) heart valve are detailed. Of approximately 86,000 valves implanted, catastrophic failure of the valve was reported in 663 patients from 1978 to 2012. In 1994, a 7-member medical panel consisting of cardiologists, cardiovascular surgeons, epidemiologists, and a nontechnical chairman was appointed by the federal court. The panel collected clinical and manufacturing data, supported epidemiologic studies assessing risk factors for valve fracture, and developed guidelines for payment for explanting potentially defective valves in patients. Three sets of guidelines, based on comparisons of estimated risks of valve fracture versus risks of valve replacement surgery, were issued by the panel to help guide patients and their physicians in decisions about explanting valves. In addition, the panel supported research directed at identifying valves at risk for outlet strut fracture. The primary techniques evaluated included analyzing acoustic signals from the valves, imaging valves for potential cracks in the struts, and structural analyses of Björk-Shiley convexo-concave valves, but none proved applicable for large-scale surveillance of the patient population. The panel also became a patient advocate and acted as an intermediary between the manufacturer and the attorneys initiating the legal settlement. The panel's experiences may help inform future strategies for guideline development for other medical devices or procedures involving risk-benefit comparisons.

Twenty-Five–Year Experience With the Björk-Shiley Convexoconcave Heart Valve

BACKGROUND

The first Björk-Shiley convexoconcave (BSCC) prosthetic heart valves were implanted in 1978. The 25th anniversary provided a stimulus to summarize the research data relevant to BSCC valve fracture, patient management, and current clinical options.

METHODS AND RESULTS

Published and unpublished data on the risks of BSCC valve fracture and replacement were compiled, and strategies for identifying candidates for prophylactic valve reoperation were summarized. By December 2003, outlet strut fractures (OSFs), often with fatal outcomes, had been reported in 633 BSCC valves (0.7% of 86,000 valves implanted). Fractures still continue to occur, but average rates of OSFs in 60 degrees valves are now <0.1% per year. OSF risk varies markedly by valve characteristics, especially valve angle and size, with weaker effects associated with other manufacturing variables. OSF risks are mildly lower among women than men but decline sharply with advancing age. The risks of valve replacement typically greatly exceed those of OSF. By comparing individualized estimated risks of OSF versus valve replacement, guidelines have been developed to identify the small percentage of BSCC patients (mostly younger men) who would be expected to have a gain in life expectancy should reoperative surgery be performed.

CONCLUSIONS

Twenty-five years after the initial BSCC valve implants, fractures continue to occur. Continued monitoring of BSCC patients is needed to track and quantify risks and enable periodic updating of guidelines for patients and their physicians.

Outlet strut fracture of Björk-Shiley convexo concave heart valves: the UK cohort study

OBJECTIVE

To investigate the risk of outlet strut fracture (OSF) in Björk-Shiley convexo concave (BSCC) valves in relation to patients' clinical and valve characteristics.

DESIGN

A cohort of 2977 patients with 3325 valves with a follow up of 18 years.

SETTING

38 cardiac implantation centres in the UK.

RESULTS

56 OSF events were reported with 43 occurring in mitral and 13 in aortic valves. The overall OSF rate was 0.17%/year. No dominant clinical factor of risk was found, but multiple regression analysis identified age, body surface area, valve size, shop order fracture rate, and manufacturing period as risk factors for OSF. A 4% (95% confidence interval (CI) 2% to 6%) decrease in the risk of OSF was observed for each advancing year of age and a fivefold (95% CI 2 to 13) increase in risk for a 0.5 m(2) increase in body surface area. The association between the risk of OSF and valve size was not constant over time. Excess risks among 31 mm and 33 mm sizes (mainly mitral valves) decreased over time while that for 23 mm (almost all aortic valves) increased. The risk of OSF increased by 40% (95% CI 20% to 50%) for a unit increase in the fracture rate of other valves in the same batch. For valves manufactured during 1981 to 1984 the risk of OSF was 4 (95% CI 2 to 12) times greater than for valves manufactured before 1981.

CONCLUSIONS

The OSF rates for 60 degrees BSCC valves observed in the UK are the highest among all monitored populations. The changing patterns of mitral and aortic valve OSF rates over time observed in this study have not been identified previously and highlight the need for continued monitoring of patients with the BSCC valve.

Outlet strut fracture of Björk-Shiley convexo concave heart valves: the UK cohort study

OBJECTIVE

To investigate the risk of outlet strut fracture (OSF) in Björk-Shiley convexo concave (BSCC) valves in relation to patients' clinical and valve characteristics.

DESIGN

A cohort of 2977 patients with 3325 valves with a follow up of 18 years.

SETTING

38 cardiac implantation centres in the UK.

RESULTS

56 OSF events were reported with 43 occurring in mitral and 13 in aortic valves. The overall OSF rate was 0.17%/year. No dominant clinical factor of risk was found, but multiple regression analysis identified age, body surface area, valve size, shop order fracture rate, and manufacturing period as risk factors for OSF. A 4% (95% confidence interval (CI) 2% to 6%) decrease in the risk of OSF was observed for each advancing year of age and a fivefold (95% CI 2 to 13) increase in risk for a 0.5 m2 increase in body surface area. The association between the risk of OSF and valve size was not constant over time. Excess risks among 31 mm and 33 mm sizes (mainly mitral valves) decreased over time while that for 23 mm (almost all aortic valves) increased. The risk of OSF increased by 40% (95% CI 20% to 50%) for a unit increase in the fracture rate of other valves in the same batch. For valves manufactured during 1981 to 1984 the risk of OSF was 4 (95% CI 2 to 12) times greater than for valves manufactured before 1981.

CONCLUSIONS

The OSF rates for 60° BSCC valves observed in the UK are the highest among all monitored populations. The changing patterns of mitral and aortic valve OSF rates over time observed in this study have not been identified previously and highlight the need for continued monitoring of patients with the BSCC valve.

Disk embolization of a Björk-Shiley convexo-concave mitral valve: a cause of sudden cardiovascular collapse and mesenteric ischemia

Strut fracture and disk embolization of a Björk-Shiley convexo-concave valve is uncommon, but it should always be considered as a cause of sudden cardiovascular collapse in patients with such valves. Recognition of this clinical scenario is essential, given the importance of early diagnosis and the prevalence of these valves worldwide. We present a fatal case of disk embolization of a mitral prosthesis presenting with cardiogenic shock and mesenteric ischemia.

In vivo accuracy of two radiographic systems in the detection of Björk-Shiley convexo-concave heart valve outlet strut single leg separations

OBJECTIVE

Modified cineradiographic systems have been used clinically to detect partially broken outlet struts in normally functioning Björk-Shiley convexo-concave heart valves. Almost all such valves were explanted, presuming that full failure would likely follow. Inasmuch as the clinical setting only rarely permits examination of normally rated valves, the accuracy of radiographic detection cannot be clinically defined. This study uses the clinical radiographic technique in sheep implanted with known-status convexo-concave valves, comparing its accuracy and that of a newly developed, geometric image magnification radiography system.

METHODS

Twenty-one sheep with mitral convexo-concave valves were studied on both systems. Five were used for extensive training. When operators were expert with both systems, images of four intact valves and 12 valves with outlet strut single leg separations, along with a seventeenth single leg separation valve used for calibration, were integrated into 112 image sets organized into a balanced incomplete block design for evaluation by eight trained, blinded reviewers.

RESULTS

Cineradiography sensitivity was 24% versus 31% for direct image magnification. The odds ratio for detection of single leg separation by direct image magnification versus cineradiography was 2.0 (95% confidence interval, 0.76 to 5.9; p = 0.13). Cineradiography specificity was 93% versus 90% for direct image magnification. Sensitivity and specificity varied markedly by reviewer, with sensitivity ranging from 8% to 55% and specificity from 51% to 100% for the combined technologies.

CONCLUSIONS

The data support the need for more intensive training for convexo-concave valve imaging and further investigation of unconventional radiographic technologies. Clinical cineradiography of convexo-concave valves may detect as little as 25% of valves having a single leg separation, underestimating the prevalence of single leg separations and thereby implying more rapid progression to full fracture than is actually the case.

Tricuspid valve replacement. Fifteen years of experience with mechanical prostheses and bioprostheses

Tricuspid valve replacement is not a common operation. The purpose of this study was to examine the early and late results in 60 patients who underwent 28 (47%) bioprosthetic and 32 (53%) mechanical tricuspid valve replacements. All operations took place between January 1978 and June 1993 during which period a total of 4741 patients underwent valve replacement operation. Mean patient age was 50 +/- 15 (18 to 75) years. Forty-one patients (68%) were female and 19 patients (32%) were male. Forty-nine patients (82%) were in New York Heart Association class III or IV before operation. Forty-five patients (75%) were undergoing repeat cardiac valve operation. Seventeen patients (28%) had complex congenital cardiac problems. Operation was urgent in 15 patients (25%). The hospital mortality rate was 27% (16 patients). All patients with hospital death were in New York Heart Association class III or IV, were having repeat operations, or had complex congenital disease. Low output syndrome was observed in 21 patients (35%). Reoperation because of bleeding was required in seven patients (12%). Thirteen patients (22%) required permanent (epicardial lead) pacemaker implantation. Mean follow-up is 75 +/- 45 months (maximum 173 months) and 100% complete for the 44 patients who left the hospital. There have been 14 deaths (32%). Nine of these patients (64%) had mechanical valves and five (36%) had bioprostheses. Of the 11 cardiac deaths, three were valve related (bioprostheses). Three patients (10%) required reoperation because of tricuspid valve prosthetic failure (1 thrombosed mechanical valve, 2 failed porcine valves). Of the remaining 30 patients, 20 (67%) are in New York Heart Association class I or II. Seventeen patients have mechanical valves and 13 have bioprostheses. Twenty-six patients (90%) are receiving warfarin. Thromboembolism (transient ischemic attack) has occurred in one patient with a mechanical valve who also had a previous cerebrovascular accident. In this group there has been no hemorrhage, endocarditis, or new pacemaker requirement. Actuarial survival for the whole series is 37% +/- 9% and for the hospital survivors is 50% +/- 12% at 15 years. Linearized rates of valve-related complications are not different between groups. Tricuspid valve replacement is a beneficial procedure for patients with structural tricuspid valve disease, many of whom have other valvular or congenital disease. Contemporary mechanical prostheses and bioprostheses are equally effective in the tricuspid position. Mechanical valves should be considered for tricuspid replacement in young patients and in patients with mechanical valves implanted in the left side of the heart.

Detection of Björk-Shiley Mitral Valve Dysfunction via Doppler Echocardiography

Fifty-eight patients with a Björk-Shiley (B-S) mitral valve were examined to study applicability of Doppler echocardiography in diagnosing and predicting the severity of prosthetic valve dysfunction. The effect of valve replacement on the hemodynamic performance at rest and during bicycle exercise was determined from serial echocardiographic data. The high pressure gradient group in which peak pressure gradients were assumed to be more than 15mmHg at rest, showed negative values of percent change in both stroke volume index (%ΔSVI) and left ventricular end-diastolic volume index (%ΔEDVI). All patients with high pressure gradients had poor exercise response of the left ventricle, whereas most patients with low pressure gradients showed good exercise response. The high pressure gradient group had significantly smaller mitral valve area than did the low pressure group. This suggests that impairment of inflow caused by the artificial valve, namely, prosthetic valve stenosis, is possibly a significant factor causing left ventricular dysfunction—notably a decrease in stroke volume during exercise. Reoperation was performed with good results in 5 of 58 patients because of high pressure gradients across the mitral valve prosthesis caused by tissue overgrowth. We conclude the high pressure gradient group is considered to be a reserved cohort of reoperation and periodical measurement of the pressure gradient via Doppler echocardiography can predict prosthetic valve dysfunction before it deteriorates significantly.

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.

Myocardial energy metabolism in the induction phase of cardioplegia in relation to myocardial temperature during open heart surgery

Changes in myocardial high energy phosphate and lactate concentrations during initiation of cardioplegia for open heart surgery were studied in 21 patients and related to their individual myocardial temperatures. Left ventricular myocardial biopsies were taken 10 min post aortic cross-clamping and were analysed for ATP, creatine phosphate (CP), creatine (C) and lactate. The patients were divided into three groups according to the achieved myocardial temperature: 6-10 degrees C, 11-15 degrees C and 16-24 degrees C. The results indicated that optimal myocardial protection during the induction phase of the cardioplegia was obtained in the 11-15 degrees C group in which the highest ATP concentration and simultaneously lowest lactate concentration was maintained.

Cineradiographic functional evaluation of the Björk-Shiley monostrut prosthesis. A follow-up study of 46 consecutive patients

In 46 patients, 51 Björk-Shiley monostrut valves were studied with high-speed cineradiography 9 months after implantation. Each valve was viewed in lateral, frontal and oblique projections for 10-12 heart beats. In the aortic valves the opening time was 0.04-0.067 (mean 0.052) and closing time 0.04-0.067 (mean 0.046) sec. In all these valves the maximum opening angle was 70 degrees. Disc rotation could be monitored in 29/31 valves, and during 10 heart beats averaged 20 degrees. Disc slide of 2.0-2.5 mm was seen in 27/31 valves. It occurred during the last 40-50 degrees of opening and the first 20-40 degrees of closing. In mitral valves with sinus rhythm (12/20), the opening time was 0.053-0.106 (mean 0.073) and closing time 0.040-0.106 (mean 0.061) sec. Mean disc rotation (recorded in 17/20 valves) during 10 heart beats was 25 degrees, and disc slide of 2.0-2.5 mm was found in all but one case, mainly during the last 50 degrees of opening and the first 30 degrees of closing. The valve opened to 70 degrees in all but one patient, in whom the disc clearly impinged against the left ventricular wall and opened only to 35-50 degrees at rest. At reexamination a year later the patient was asymptomatic, in sinus rhythm, and the disc had regained full movement with 70 degrees opening.

The Monostrut Björk-Shiley heart valve

To avoid the possibility of a fracture of the welded two-armed outflow strut of the Björk-Shiley heart valve, since 1982 it has been machined from one piece of Haynes 25 in the form of a monostrut valve without welds. Of the first 864 patients with a monostrut Björk-Shiley valve implanted, 268 have now been followed up to 3 years. The clinical findings, as well as absence of hemolysis, excellent hemodynamics even with a narrow aortic root as demonstrated by transseptal cardiac catheterization and excellent functional improvement are reported. No valve thrombosis in patients receiving anticoagulant therapy was observed with valves in either the aortic or the mitral position and there was no case of mechanical failure.

Early clinical evaluation of a new Björk-Shiley valve prosthesis with integral monostrut

We evaluated preliminary results of valve replacement with a new Björk-Shiley valve prosthesis with integral monostrut. Sixty-five valves were implanted in 56 patients (18 aortic, 30 mitral, 7 double, 1 triple). The age of the patients ranged from 30 to 62 years, and they were followed up for 7-17 months (mean, 12.5 months). There were three operative deaths (5.3%) not related to the prosthesis and no late deaths. Minor cerebral thromboembolism occurred in one patient 2 weeks after surgery despite anticoagulant therapy. Intraoperative transvalvular pressure gradients across the 23-mm aortic and 27-mm mitral valve prostheses were insignificant. Real-time two-dimensional echocardiography revealed no regurgitation at the moment of valve closure in 20 randomly selected patients. Though the data accumulated so far are still relatively incomplete and the follow-up periods short, the clinical results obtained here were satisfactory, warranting further use of this new Björk-Shiley valve prosthesis with integral monostrut for longer follow-up studies.

Experience with outlet strut fracture of the Björk-Shiley convexoconcave mitral valve prosthesis

Within a period of 15 months, we encountered five patients with outlet strut fracture of the Björk-Shiley convexoconcave mitral valve prosthesis. All of the patients had acute failure of the left side of the heart and pulmonary edema. The diagnosis was made by review of the chest roentgenogram which showed features of pulmonary edema; both the outlet strut and the tilting disc were missing from the mitral prosthesis. The "missing" components might be found in the left side of the heart or in the course of the thoracic aorta. Emergency reoperation was carried out on three patients, and there were two survivors. It is essential to recognize this potentially fatal complication and undertake immediate surgical intervention. We performed the original valvular replacement operations in four of the five patients. The probability of outlet strut fracture occurring in our series of 237 patients with a Björk-Shiley convexoconcave mitral valve prosthesis is 1.69%, or 0.076 per 100 patient months.

Hemodynamic evaluation of the integral monostrut Björk-Shiley prosthesis in the aortic position

Between May, 1983, and November, 1984, the new integral monostrut Björk-Shiley prosthesis was used for aortic valve replacement in 62 patients. The prosthesis is machined from a solid piece of cobalt alloy and has no welded joints. The traditional U-shaped outlet strut has been replaced by a projecting metal finger that holds the disc in place. The disc opens to 70 degrees and is convexoconcave. Successful transseptal heart catheterization was performed in 23 patients an average of 6 months following operation to evaluate the hemodynamic performance of the prosthesis. The mean peak-to-peak gradient was 7.73 +/- 7.49 mm Hg (+/- standard deviation). In five valves it was 0, and in only three was it higher than 15 mm Hg. Significant peak gradients were directly related to the valve index (valve area/body surface area). Mean systolic gradient at rest was 12.7 +/- 6.27 mm Hg and did not increase after exercise. Effective orifice areas were adequate, and the discharge coefficient ranged from 0.77 for the 21-mm prosthesis to 0.48 for the 29-mm prosthesis. Minimal regurgitation, which was washed out on the next systole, was observed with all sizes of the prosthesis. Disc opening was maximal (70 degrees) in all but one of the observed instances. Longer clinical follow-up is required, but the new integral monostrut Björk-Shiley prosthesis, with its important design changes and excellent hemodynamic performance, appears to be a promising aortic valve substitute.

The monostrut strength

The fatigue endurance limit for Haynes 25 from which the Björk-Shiley (B-S) valve is made is 4900 kg per square centimeter (70000 pounds per square inch). A welded strut may have a variation of fatigue endurance limit from 4900 kg per square centimeter (70000 pounds per square inch) in an incomplete weld with phase segregation. To avoid a weld with this variation, the monostrut has been developed, where the valve is made by electrochemical machining from one piece of Haynes 25. The homogenous outflow monostrut will then have a stable fatigue endurance limit of 4900 kg per square centimeter (70000 pounds per square inch). In a pulse duplicator at a pulse rate of 120 and a peak ventricular pressure of 200 mmHg, the maximum inservice tensile stresses for the 29 mm valve outflow strut do not exceed 700 kg per square centimeter (9800 pounds per square inch). Therefore, a seven times safety limit is present for the monostrut under maximal physiological stress conditions. The struts in the B-S monostrut valve cannot be fractured even under extreme experimental conditions and never under peak physiological conditions.

A computer-aided method to evaluate the function of implanted Björk-Shiley prosthetic heart valves

Evaluation of the function of implanted prosthetic valves is important in early diagnosis of valve dysfunction. Björk-Shiley valves contain two radiopaque rings, which are projected as ellipses in cineradiography. From these ellipses the actual valve opening angle can be calculated. A computer-aided method was developed that enables measurement of ellipse characteristics reliably, independent of projection angle and valve opening. It is demonstrated that calculated and real opening angles differ less than 2 degrees with this method. Using the same technique the tilting angle of the valve ring during the cardiac cycle is computed for evaluation of progression of valve dehiscense in case of a paravalvular leak. Application of the method to patient data is illustrated by three cases. The method is suitable for use by technicians. It can be implemented on a small microprocessor system. The method proved to be a powerful tool in the evaluation of patients with implanted Björk-Shiley valves.

Thrombotic obstruction of Bjork-Shiley valves--diagnostic and surgical considerations

We have evaluated 12 patients with thrombotic obstruction of the Bjork-Shiley valve since 1975, 11 in the mitral and 1 in the aortic position. During this period 442 patients with 303 mitral (181 plano-convex and 122 convexo-concave) and 205 aortic (112 plano-convex and 93 convexo-concave) Bjork-Shiley valves were available for follow-up. The incidence of thrombosis for the plano-convex model was 1.06% per patient year for the mitral position and 0.19% per patient year for the aortic position. The new convexo-concave model has brought down the incidence to 0.78% per patient year for the mitral (P less than 0.01) and 0% per patient year for the aortic valve. The onset of symptoms was acute (less than 15 days) in 41.7% and subacute (greater than 15 days) in 58.3% patients. All patients presented with pulmonary edema. Evidence of inadequate anticoagulation was present in only 3 (25%) patients. Reduction of prosthetic sounds and appearance of a new murmur was highly suggestive of valve thrombosis. Echocardiography and cinefluoroscopy was very useful for the instant recognition of this condition and had obviated the need for cardiac catheterisation in the last 6 patients. Emergency surgery was obligatory in all. Thrombectomy alone was successful in 9 patients. Three patients required replacement of the prosthesis. There was one operative death (mortality 8.3%). The long-term follow-up of these patients (3-82 months, mean 34 months) is excellent. We conclude that thrombotic obstruction of the Bjork-Shiley valve is often not related to inadequate anticoagulation, and more than half of the patients do not present with abrupt onset of symptoms. The convexo-concave model has significantly reduced this problem. Emergency surgery with thrombectomy is the procedure of choice for clotted prostheses.

Early results of valve replacement with the Björk-Shiley convexoconcave prosthesis

The Björk-Shiley convexoconcave prosthetic valve has design characteristics that may result in a lower incidence of thromboembolic complications than the conventional spherical Björk-Shiley prosthesis. We evaluated the results of valve replacement with the convexoconcave prosthesis in 248 patients receiving 301 prosthetic valves between March, 1979, and June, 1981. One hundred thirteen patients had aortic valve replacement (AVR), 73 had mitral valve replacement (MVR), and 62 had multiple valve replacement. Two hundred nine (84%) were in New York Heart Association Class III or IV. The median duration of follow-up was 13 months, and follow-up information was available for 246 (99%) of the patients. The actuarial incidence of freedom from thromboembolism at two years was 98% in the AVR group, 97% in the MVR group, and 87% in the group having multiple valve replacement. There were no documented episodes of valve thrombosis or mechanical failure and no fatal thromboembolic complications. The absence of valve thrombosis is in marked contrast to the results reported with the spherical disc valve. Although longer follow-up is necessary, it appears that the convexoconcave design represents a major improvement in the Björk-Shiley prosthesis.

Long-term results of cardiac valve replacement with the Delrin-disc model of the Björk-Shiley valve prosthesis

One hundred two Björk-Shiley valve prostheses with the Delrin-disc occluder were implanted in 83 patients between January, 1971, and July, 1972. Fifty-eight were in the mitral position, 42 in the aortic, and 2 in the tricuspid. Complete follow-up until 1981 was obtained in 93% of the patients (mean follow-up, 66.8 months). Hospital mortality was 18% and late mortality, 19%. Survival according to actuarial methods was 84.8% at 5 years and 78.1% at 9 years after operation. Thromboembolism was detected in 8.8% of patients but caused no deaths. The incidence was 1.2% and 1.5% per year in those patients treated with Coumadin and antiplatelet agents, respectively. Reoperation was necessary in 13% of the patients. Most survivors (72%) are in New York Heart Association Functional Class I, despite a preoperative status of Class III or IV in 57% of the patients. Hospital mortality may be due to poorer understanding of patient management and less refined techniques of myocardial protection. Long-term survival with this prosthesis is similar to that in more recent studies, and rates of thromboembolism and malfunction compare favorably with other prosthetic valves.

Bileaflet, tilting disc and porcine aortic valve substitutes: in vitro hydrodynamic characteristics

The desire for a low profile mechanical valve with better fluid dynamic performance led to the design and development of the St. Jude Medical bileaflet prosthesis. Comparative in vitro flow studies indicate that it has better pressure drop characteristics than the Björk-Shiley (convexo-concave) and Carpentier-Edwards porcine valves in current clinical use, especially in the small sizes. In the 21 to 27 mm aortic valve size range the St. Jude valve has an average performance index of 0.66, compared with 0.46 and 0.32 for the Björk-Shiley and Carpentier-Edwards valves, respectively. In contrast, the St. Jude valve has larger regurgitant volumes than both the Björk-Shiley and Carpentier-Edwards valves. Velocity measurements with a laser-Doppler anemometer indicate relatively centralized flow with small amounts of turbulence downstream of the St. Jude valve. The flow is unevenly distributed between the central and side orifices. The turbulent shear stresses are, however, large enough to cause sublethal or lethal damage to blood elements. Wall shear stresses are smaller than those measured downstream of the Björk-Shiley valve. Regions of flow separation were observed just downstream from the sewing ring, which could lead to excess tissue growth along the sewing ring. The results of this study indicate that overall in vitro fluid dynamic performance of the St. Jude valve is superior to that of the two other commonly used prostheses.

Optimal insertion technique for the Björk-Shiley valve in the narrow aortic ostium

The Björk-Shiley tilting disc valve was used for aortic valve replacement (AVR) in 250 consecutive patients between 1977 and 1982. One hundred and ninety-six patients had isolated AVR, and 54 had combined procedures (double- or triple-valve replacement in 31, associated coronary artery bypass grafting in 20, and miscellaneous procedures in 3). A special technique for inserting large Björk-Shiley valves without using outflow patches or annuloplastic procedures was developed. This method included allowing the right portion of the aortic incision to end about 0.5 cm above the noncoronary sinus; the use of simple interrupted sutures; placement of the prosthetic sewing ring on top of the annulus of the noncoronary sinus, thereby tilting the valve slightly in the outflow tract; and routine orientation of the major opening of the valve toward the annulus of the noncoronary sinus. This orientation resulted in the largest effective orifice area at postoperative catheterization. None of the male patients received a valve smaller than 23 mm, and none of the female patients were given a valve smaller than 21 mm. The convexoconcave model of the Björk-Shiley valve was used in 71% of the patients. An outflow patch was required only in 1 patient with concomitant supravalvular stenosis of the aorta. The combination of adequate myocardial protection, comparatively short aortic cross-clamping times, and the use of large, properly oriented Björk-Shiley valves resulted in satisfactory postoperative hemodynamics in all patients. In fact, none of the 196 patients undergoing isolated AVR and only 5 (9%) of the 54 patients undergoing combined procedures required postoperative inotropic stimulation. There were no operative deaths, and all patients left the hospital in good condition. The Björk-Shiley tilting disc valve is a reliable and well-functioning aortic valve substitute that is particularly suited for patients with narrow aortic ostia. With attention to certain details in the insertion technique, encouraging clinical results can be obtained with this prosthesis.

A case of strut fracture of the new Björk-Shiley mitral valve prosthesis

We treated a 61-year-old Japanese man with a strut fracture of the new Björk-Shiley mitral valve. This fracture occurred about two months after mitral valve replacement. Emergency reoperation was performed as soon as the chest X-ray showed the fracture, despite the presence of cardiopulmonary shock. He died on the 3rd postoperative day. Similar reported cases of literature are reviewed.

Assessment of the opening angle of implanted Björk-Shiley prosthetic valves

A method has been developed in which cineradiography is used for the assessment of the opening angle of implanted Bjork-Shiley prosthetic valves. The method is based on the fact that the ring and the disc, which are known to be circular, appear to be elliptical on x-ray films. The spatial position of the valve can be retrieved from the characteristics of these ellipses when vectoranalysis is applied. The method's accuracy does not depend on the position of the patient with respect to the direction of the x-ray beam. The accuracy of the method was demonstrated with the use of a phantom valve. The difference between the measured and the real opening angle was -0.7 +/- 1.8 degrees (mean +/- SD). Results were reproducible in patients to within -0.1 +/- 1.8 degrees. In 18 patients with normally functioning valves it could be demonstrated with frame-by-frame analysis (interval between frames 20 msec) that the valves opened very rapidly up to about 60 degrees. Closing patterns varied. In one of our patients with valvular thrombosis insufficient valvular opening could be demonstrated by our method before the patient's complaints drew attention to the valvular dysfunction.

Cineradiographic evaluation of the convexo-concave Björk-Shiley prosthetic valve in mitral position

The in vivo function of the convexo-concave Björk-Shiley prosthetic valve implanted in mitral position was evaluated with a simple cineradiographic procedure. The maximum opening angle of the tilting disc, calculated from the maximum and the minimum diameter of the radiopaque marker embedded in the disc when viewed elliptically, was 56 +/- 2 degrees and was not affected by tachycardia up to 160 beats per min. The time required for disc opening was almost the same as that for disc closure, and these times shortened in proportion to increase in pulse rate. Disc rotation, quick or slow, could be observed in all patients. Excellent function of the convexo-concave Björk-Shiley prosthesis was demonstrated by cineradiography. Any dysfunction of the disc opening is easily demonstrable, not only from measurement of the disc's maximum opening angle, but also from evaluation of the distance, on en face view, between the characteristic internal rim disc marker and the small strut delineating the small valve orifice when the disc is fully open.

Long-term effects of prosthetic materials

The surgical repair of the various types of congenital cardiac defects often requires the use of prosthetic materials, both bioprosthetic and synthetic. Patches have proved highly effective in many applications and locations. All prosthetic valves have significant limitations, and particularly disappointing was the observation that bioprosthetic valves undergo accelerated degeneration in younger patients. The extracardiac conduit allowed corrective operation for several complex types of anomalies, but it suffers the double jeopardy of premature degeneration of its integral tissue valve (if any), and progressive peel formation within its lumen. A threat of infection exists in the presence of prosthetic materials, especially valves. These known limitations of prosthetic devices as well as possible potential late complications not yet fully elucidated are sufficient indication for periodic, perpetual surveillance of patients who have received cardiac prostheses.

Strut fracture and disc embolization of a Björk-Shiley mitral valve prosthesis: localization of embolized disc by computerized axial tomography

The case of a patient who survived strut fracture and embolization of a Björk-Shiley mitral prosthetic disc is presented. Prompt surgical treatment was directly responsible for survival. In addition, computerized axial tomography of the abdomen aided in localizing and retrieving the embolized disc, which was lodged at the origin of the superior mesenteric artery. A review of similar case reports from the literature supports our conclusions that the development of acute heart failure and absent or muffled prosthetic heart sounds in a patient with a Björk-Shiley prosthetic heart valve inserted prior to 1978 should raise the possibility of valve dysfunction and lead to early reoperation.

Dysfunction of the Björk-Shiley prosthesis. Report of 32 cases

We present 32 cases of dysfunction of the Björk-Shiley valvular prosthesis, representing 3.01% of the 1,063 BS prostheses implanted at this clinic. The complications observed were thrombosis of the prosthesis, suture dehiscence with or without endocarditis and disc-suture interference. In selected, favourable cases, we prefer thrombectomy with generous washing of the prosthesis and rotation of the disc, without removal of the disc from the prosthesis. Furthermore, when the dehiscence does not exceed 1/3 of the circumference of the ring, we have achieved very good results with single sutures supported on Teflon patches. Subsequent failures of this procedure were not of a technique nature, but rather due to the poor condition of the patients. In situations of clinical emergency, the diagnosis of valvular dysfunction may suffice as indication of surgery, further diagnostic measures being postponed in view of the data of the physical exploration.

Haemodynamic evaluation of the convexo-concave Björk-Shiley prosthesis in patients with narrow aortic annulus

A late haemodynamic re-evaluation at rest and during exercise was performed in 22 patients with isolated aortic valvular disease and narrow aortic annulus, operated upon with the convexo-concave Björk-Shiley prosthesis. The 21 mm prosthesis had been inserted in 11 patients and the 23 mm one in the other 11 patients. Left ventricular pump function improved and was normalized in half of the patients. The mean systolic pressure difference across the 21 mm convexo-concave prosthesis was 16.2 +/- 8.1 mmHg at rest and 20.7 +/- 7.9 mmHg during exercise (32 +/- 10 watts). It was 14.9 +/- 6.0 mmHg at rest and 18.6 +/- 6.3 mmHg during exercise (34 +/- 156 watts) across the 23 mm convexo-concave prosthesis. Compared with the earlier investigated standard model Björk-Shiley prosthesis, the 21 mm convexo-concave version creates a lower resistance to blood flow (less than 0.01), whereas no such difference could be demonstrated in the two models of 23 mm tissue diameter. It was concluded that the new convexo-concave tilting disc valve constitutes an improvement over the standard model in the management of the narrow aortic annulus permitting insertion of a 21 mm prosthesis.

Late thrombotic malfunction of the Björk-Shiley tilting disc valve in the tricuspid position. Principles for recognition and management

Among 52 consecutive patients surviving tricuspid valve replacement with the Björk-Shiley tilting disc valve, follow-up extends between 1/2-9 years, mean 4.9 years. Four patients suffered thrombotic obstruction of their tricuspid prosthesis on 8 occasions, an incidence of 3.2%/year. Ebstein's anomaly and deficient anticoagulation were identified as likely contributory factors, but the complication remained unexplained in 2/8 instances. Thrombotic malfunction of the tricuspid prosthesis seems to constitute a relatively benign clinical entity with mild manifestations and diagnostic possibilities by non-invasive methods. Relief by means of thrombolytic treatment in the form of streptokinase (Kabikinase) (4) or replacement of the clotted prosthesis (4) involved neither disabling complications nor mortality. Our clinical observations and experimental studies suggest that thrombolytic therapy is effective, provided that prosthetic malfunction is due to a recent red clot, whereas encapsulation of the prosthetic disc by organized white-grey pannus necessitates re-operation. Streptokinase treatment should be attempted before surgery, but it is hardly meaningful to proceed for more than 24 hours. Restored prosthetic function within this time limit indicates the likely resolution of a red clot.

Surgical treatment of Ebstein's anomaly. Early and late results in seven consecutive cases

The surgical treatment of Ebstein's anomaly is discussed on the basis of our experience with 7 patients who underwent operation at this clinic during the last ten years. The age of the patients (2 males, 5 females) ranged from 17 to 47 years (mean 27 years) at the time of operation. Two patients were in functional class II and five in classes III or IV (N.Y.H.A.). The Wolff-Parkinson-White syndrome was concomitant in 2/7 cases and patent foramen ovale or atrial septal defect (ASD) with right-to-left shunt was present in 6/7 cases. The valvular anomaly was typical in 5 patients and stenosis of displaced tricuspid leaflets into right ventricular outflow region was detected in two patients. Tricuspid valve replacement (TVR) with disc valve prosthesis was performed in 5 patients (Björk-Shiley model in 4 cases, Kay-Shiley model in one) and tricuspid valve commissurotomy in two patients. All six patients with interatrial communication underwent closure of this communication simultaneously. One patient had concomitant epicardial mapping and attempted division of the anomalous conduction pathways was unsuccessful. This patient died on the 14th postoperative day from ventricular fibrillation. No other early or late mortality was recorded. Life-long anticoagulation therapy was introduced in all 5 patients with TVR. Thrombotic malfunction of the prosthetic valves necessitated re-operation and new prosthetic valve replacement in two patients 15 and 16 months after the first TVR. One of these patients had recurrent prosthetic thrombosis twice which was successfully treated with streptokinase. The other patient's prosthesis is functioning well 18 months after re-operation. All 6 long-term survivors were improved and remained in good condition, in functional class I, 1, 3, 3, 8, 9, and 10 years, respectively, after operation.

Comparison between the in vitro flow dynamics of the standard and the convexo-concave Björk-Shiley tilting disc valve prostheses

In the new convexo-concave model of the Björk-Shiley prosthesis the disc pivots 2.5 mm downstream, creating a space between the disc and the ring when the disc tilts open. Its flow dynamics were compared with those of the standard model under steady flow rates 0--32 1/min of a water-glycerin mixture employed as blood-analogous test fluid. The following results are valid for corresponding sizes of the conventionally used 21, 23, 25, 27, 29 and 31 mm prosthetic valves of the two models. The transprosthetic pressure fall varied directly, but in a parabolic fashion with the steady flow rate for all the partial and full flow orifices. The resistance to flow 0--32 1/min for the full flow orifice of the convexo-concave prosthesis was in average 16% lower than that of the standard model, with highly significant differences for the 21 and 23 mm prostheses (p less than 0.001). There was a redistribution of flow towards the smaller prosthetic opening from 23% (S.D. +/- 1.4) for the standard model to 30% (S.D. +/- 2.4) for the convexo-concave model (p less than 0.001). The minimum steady flow rate required to maintain the convexo-concave disc in completely open position (60 ml/sec) was only half that (37--50%) required for the standard disc (125 ml/sec) (p less than 0.001). Regurgitation through the closed prosthesis varied directly and linearly with the driving pressure and was slightly but definitely lower with the convexo-concave model than with standard model. The main features of the new design are decreased resistance to flow, redistribution of the flow within the prosthesis in order to prevent stasis along its smaller orifice, diminished opening resistance and reduced regurgitation. It is concluded that the flow dynamics of the convexo-concave model Björk-Shiley prosthesis constitute a significant improvement over those of the standard model.