The Monostrut Björk-Shiley heart valve

Diamond Anniversary of Mechanical Cardiac Valve Prostheses: A Tale of Cages, Balls, and Discs

This year marks the 60th anniversary of the first aortic and mitral valve replacements using mechanical artificial prosthesis. The first caged-ball devices represented a milestone in cardiac surgery and in the treatment of valvular disease. The following decades witnessed a great evolution in mechanical valve technology providing, through frustrating complications and stimulating successes, more reliable models to be safely used in the clinical setting. This review pays tribute to pioneers of this field who made currently available the most advanced models of mechanical prostheses with extended records of durability and performance, to be used as reliable alternatives to biological devices.

Mechanical heart valve prostheses:

Mechanical heart value prostheses have been in use since the 1950s. Many prostheses have been used for a while and then discontinued. Today, there are a large number and variety of prostheses in use and an even larger variety that are in place in patients. These may be explanted at any time for a number of reasons. It is essential for the practicing pathologist to be able to identify the prosthesis and be aware of some of its reported complications and modes of failure. This article, and a second one on bioprosthetic heart valves, is designed as a ready reference guide to heart valve prostheses, their important identifying features, their common complications, and modes of failure. It should help in the accurate identification of explanted prosthetic valves and more definitive reports. This accuracy of identification as well as tracking of abnormalities noted will, we hope, permit the identification of new failure modes and the recording of causes of failure of new (or even modified) prosthetic heart valves.

The Spanish Monostrut Study Group: a ten-year experience with 8,599 implants

BACKGROUND

The Monostrut valve is a pyrolytic carbon, tilting-disc prosthesis with no welds. After the first implantation in Spain in May 1983, the Spanish Monostrut Study Group was established to evaluate prospectively the performance of the valve using uniform protocols.

METHODS

During a 10-year period, 8,599 Monostrut valves were implanted in 7,317 patients in 22 centers. Mean age was 53.3 +/- 11 years. Of the total group, 3,229 underwent aortic valve replacement, 2,806 had mitral valve replacement, and 1,282 had double valve replacement. Follow-up was 96% complete, with a mean period of 4.3 years and a total of 29,155 patient-years.

RESULTS

The operative mortality rate was 7.2%. The 10-year probability of freedom from valve-related complications and linearized rates (event/100 patient-years in parentheses) were as follows: structural deterioration, 100% (0); nonstructural dysfunction, 96% +/- 0.5% (0.51); thromboembolism, 82.9% +/- 1.5% (1.32); anticoagulant-related hemorrhage, 87.6% +/- 1.4% (0.98); and prosthetic valve endocarditis, 96.1% +/- 0.5% (0.48). There were five obstructive valve thromboses (0.017/100 patient-years). Actuarial freedom from reoperation was 95% +/- 0.5% at 10 years. Actuarial freedom from all valve-related morbidity was 70.2% +/- 1.6%; freedom from all valve-related morbidity and mortality (including operative and sudden deaths) was 62.6% +/- 2% (70.1% +/- 2% for aortic valve replacement, 56.9% +/- 2% for mitral valve replacement, and 59.8% +/- 3% for double valve replacement; p < 0.0001). Clinically, 5,988 patients (94%) are in New York Heart Association class I-II.

CONCLUSIONS

The Monostrut valve has shown no structural failures and a low rate of valve-related complications over a 10-year period in a large patient population.

Doppler-derived pressure differences in normally functioning aortic valve prostheses. Studies in Björk-Shiley monostrut and Biocor porcine prostheses

To determine the normal range of maximum and mean Doppler-derived pressure differences for mechanical and bioprosthetic valves in the aortic position, Doppler echocardiography was performed on 239 stable patients with normally functioning Björk-Shiley monostrut (BSM, n = 185) or Biocor porcine (n = 54) prostheses. The interval from aortic valve replacement to echocardiography was 3-9 days. Maximum and mean pressure differences were significantly greater in 21 mm than in 25 or 27 mm BSM prostheses. The pressure differences in 23 mm BSM valves did not diverge significantly from those in 21, 25 or 27 mm valves. The mean pressure difference did not exceed 30 mm Hg in any type or size of studied prosthesis. No significant differences were found in pressure gradients in comparisons between BSM and Biocor prostheses of corresponding sizes. The calculated velocity ratio for BSM prostheses was not significantly influenced by the valve size. We suggest that the normal range of Doppler-derived maximum and mean pressure differences determined in this study be adopted as reference in evaluations of aortic BSM and Biocor valve prostheses.

Early and late results of aortic valve replacement. A series of 510 patients

Aortic valve replacement was performed in 510 patients (Björk-Shiley valves in 93%), with concomitant surgical procedures in 146 cases. The patients were grouped according to technique of myocardial protection: Group I (n = 98) selective coronary perfusion, group II (n = 82) topical cooling, and group III (n = 330) cold crystalloid cardioplegia and topical cooling. The early mortality rate was 5.7% overall: Among patients with isolated aortic valve replacement in groups I, II and III it was 8.4, 1.7 and 1.3%, respectively, and among those with additional surgery 40.0, 12.5 and 8.4%. Myocardial infarction and low cardiac output were responsible for 65.5% of the early deaths. Follow-up ranged from 2 months to 16 11/12 years, totalling 2,859 patient years. In patients with isolated aortic valve replacement and Björk-Shiley prosthesis, the incidence of valve-related late complications/100 patient years was 0.49 for thromboembolism, 0.82 for anticoagulant-related haemorrhage and 0.49 for prosthetic valve endocarditis. There was no thrombotic encapsulation in aortic position. Survival at 5 and 10 years was 83% and 72%. Aortic valve replacement is a safe procedure and concomitant operations do not unreasonably increase risks.

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.

Analysis of Doppler-obtained velocity curves in functional evaluation of mechanical prosthetic valves in the mitral and aortic positions

A total of 145 patients with 160 mechanical prostheses of the Björk-Shiley or Starr-Edwards type (15 with double mitral plus aortic valves) underwent clinical and Doppler echocardiography analysis. In the mitral position (85 valves) 10 patients with valve-related symptoms, calculated prosthetic area less than or equal to 1 cm2, or mean transprosthetic gradient greater than 10 mm Hg by Doppler echocardiography were predefined as abnormal. Seven patients had operations, and prosthetic obstruction was confirmed in all. All patients had higher pulmonary pressures (p less than 0.001) before valve replacement. Clinical presentation was variable; however, all those with proved prosthetic thrombosis had a fulminant course and distinctive velocity curves on Doppler. In the 75 patients predefined as normal, calculated valve area (2.3 +/- 0.6 cm2, mean +/- SD, range 1.3 to 3.7 cm2) and mean gradient (4.9 +/- 1.7 mm Hg, range 1.5 to 9.5 mm Hg) were widely spread and were independent of prosthetic size greater than or equal to 27 mm. Clinically 37 of 75 patients were moderately to severely limited. Mean gradient above 5 mm Hg was associated with a higher incidence of chronic atrial fibrillation (p less than 0.05), significant tricuspid regurgitation, failure of the right side of the heart, and significant functional limitation (p less than 0.02 for all). In the aortic position (75 valves) peak gradients were 28.2 +/- 15 mm Hg (8 to 80 mm Hg). Mean gradients were 18 +/- 9.6 mm Hg (6.5 to 46.5 mm Hg). Averaged gradients derived from the average of peak and late systolic gradients were 22.4 +/- 12.7 mm Hg (6 to 62 mm Hg). In all five abnormal patients (two with endocarditis and three with hemodynamic decompensation) but also in 18 of 70 clinically normal valves, peak gradients were greater than or equal to 36 mm Hg (ranges 36 to 65 mm Hg in both). Gradients were unrelated to symptoms or to the duration of the valve in situ (3 weeks to 20 years). Gradients correlated with prosthetic size (r = 0.57) and were higher (p less than 0.001) across small (19 to 23 mm) versus large (25 to 31 mm) valves. Regurgitation was present in 40% of the mitral prostheses. It was detected in 32% of the mitral prostheses defined as normal and was estimated as mild in most. Aortic regurgitation was present in all five abnormal aortic prostheses, significant in four, and in 26 of the valves (37%) defined as normal, significant in two.(ABSTRACT TRUNCATED AT 400 WORDS)

Heart valve replacement with the Björk-Shiley Monostrut valve: early results of a multicenter clinical investigation

To evaluate the clinical performance of the Björk-Shiley Monostrut prosthesis, five centers combined their early experience. Between May, 1982, and June, 1985, 537 prostheses were implanted in 486 patients at these centers: 246 patients had aortic valve replacement (AVR), 163 underwent mitral valve replacement (MVR), and 47 had double-valve replacement (DVR). Thirty patients underwent other, more complex procedures. Concomitant cardiac procedures were performed in altogether 25%. Overall hospital (30 days) mortality was 5.1% (3.6% for AVR, 4.3% for MVR, 8.3% for DVR, and 16.6% for other procedures). The patients were followed up at 6- to 9-month intervals from 6 to 48 months (mean follow-up, 33 months). Follow-up was 99.6% complete. Late mortality was 7.2%. The three-year survival rate was 91.0% for AVR, 92.3% for MVR, and 76.2% for DVR. There was no structural failure of the prosthesis. No instances of valve thrombosis and fatal thromboembolism occurred in anticoagulated patients. The three-year incidence of freedom from thromboembolic events (including TIA) was 89.8% for AVR, 94.9% for MVR, and 90.2% for DVR. Preoperative and postoperative data for the assessment of mechanical hemolysis was available in 60% of the patients. The degree of mechanical hemolysis was low and did not change with time. Although the follow-up is still short, the Björk-Shiley Monostrut prosthesis appears to represent an improvement over previous Björk-Shiley models, particularly with regard to durability.