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J Thorac Cardiovasc Surg 1994;108:177-178
© 1994 Mosby, Inc.

LETTERS TO THE EDITOR

Valve thrombosis and strut fracture with the Björk-Shiley valve

Division of Cardiothoracic Surgery
Department of Surgery
Huddinge University Hospital
S-141 86 Huddinge, Sweden

To the Editor:

I read with great interest the article by Orszulak and associates ¹ from the Mayo Clinic on their long-term results with the Björk-Shiley tilting disc valve (Shiley, Inc, Irvine, Calif.). Their main conclusions seem to be that (1) performance of the Björk-Shiley valve is similar to that of other mechanical valves, (2) modifications in valve design (i.e., the introduction of the convexo-concave disc) have not reduced the threat of valve thrombosis, and (3) elective explantation of any of these valves (for risk of outlet strut fracture) is not warranted.

Inasmuch as my colleagues and I ^2-7 have published a numberof papers on the long-term results with the Björk-Shiley valve based on the experience with more than 3000 valves, with a 99% follow-up covering more than 17,000 patient-years and with postmortem examinations in 75% of all fatalities, I would like to add some perspective to two of their conclusions:

I found that in 809 mitral valve replacements the actuarial incidence of valve thrombosis was almost sixfold lower among 451 patients with convexo-concave valves than among 358 patients with spherical disc valves (p < 0.0005). This reduction in valve thrombosis was achieved without any change in the incidences of embolism or anticoagulant-related bleeding, probably reflecting an unchanged level of the anticoagulant treatment over the years. ² In our experience with 1758 aortic valve replacements ³ there were no differences in thromboembolism with different valve models. The findings in the Mayo clinic series ¹ seem similar to ours; allvalve thromboses in mitral valves occurred in spherical disc valves whereas 20% of aortic valve thromboses occurred in convexo-concave valves. The convexo-concave prostheses constituted approximately 30% of all aortic prostheses in the Mayo series, but with a much shorter follow-up. In conclusion, and in contrast with the authors' statement, I believe that the findings by Orszulak and associates corroborate our findings that the convexo-concave design in fact dramatically reduced the risk of valve thrombosis in mitralvalves. Inasmuch as the complication was mainly a mitral valve problem, the importance of this finding should not be underestimated.

Even though the convexo-concave design probably reduced the risk of valve thrombosis among mitral valves, it introduced a new problem—strut fractures. ^5,6 Despite this, Orszulak and coauthors could not document any case of strut fracture among their 356 fatalities. As they pointed out, a modest number of autopsies (32%) and a large number of sudden unexplained deaths (17%) "leaves doubt as to the true prevalence of valve-related problems." Furthermore, it is important to note that strut fracture of Björk-Shiley valves is mainly a problem with the 70-degree convexo-concave valve, which was never used in the United States. ⁵ In fact, we found the actuarial incidence of strut fracture among early produced, large (i.e., 29 to 33 mm), 70-degree convexo-concave valves to be as high as 12.5% at 7 years, representing a linearized incidence of 2.0%/patient-year. ⁶ For this particular group of 70-degree prostheses, we ^6,7 and others ⁸ have recommended elective explantation although Blackstone and Kirklin ⁹ have advised against such reoperations. We ⁷ have performed a small series of prophylactic replacements. It should be noted that the risk of strut fracture among the valves referred to as "high-risk valves" by Orszulak and associates (i.e., 29 to 33 mm 60-degree convexo-concave valves) is much less than the corresponding risk among large 70-degree valves, and I agree that these 60-degree valves need not to be explanted as a pure prophylactic measure. In the case of need for reoperation for other reasons (periprosthetic leakage or valve thrombosis), I would suggest valve replacement (as opposed to local repair) for any welded convexo-concave Björk-Shiley valve. ⁷

The Monostrut valve (without any welds), which combines the advantage of the convexo-concave disc with improved durability, has now been available outside the United States for 11 years. We ¹⁰ have not observed any case of strut fracture or valve thrombosis in patients with this valve who are receiving anticoagulants, and no strut fractures have been reported elsewhere.

References

1. Orszulak TA, Schaff HV, DeSmet J-M, Danielson GK, Pluth JR, Puga FJ. Late results of valve replacement with the Björk-Shiley valve (1973 to 1982). J THORAC CARDIOVASC SURG 1993;105:302-12.[Abstract]
   
2. Lindblom D. Long-term clinical results after mitral valve replacement with the Björk-Shiley prosthesis. J THORAC CARDIOVASC SURG 1988;95:321-33.[Abstract]
   
3. Lindblom D. Long-term clinical results after aortic valve replacement with the Björk-Shiley prosthesis. J THORAC CARDIOVASC SURG 1988;95:658-67.[Abstract]
   
4. Lindblom D, Lindblom U, Åberg B. Long-term clinical results after combined aortic and mitral valve replacement. Eur J Cardiothorac Surg 1988;2:347-54.[Abstract]
   
5. Lindblom D, Björk VO, Semb BK. Mechanical failure of the Björk-Shiley valve: incidence, clinical presentation, and management. J THORAC CARDIOVASC SURG 1986;92:894-907.[Abstract]
   
6. Lindblom D, Rodriguez L, Björk VO. Mechanical failure of the Björk-Shiley valve: updated follow-up and considerations on prophylactic rereplacement. J THORAC CARDIOVASC SURG 1989;97:95-7.[Abstract]
   
7. Ericsson A, Lindblom D, Semb G, et al. Strut fracture with Björk-Shiley 70 degrees convexo-concave valve: an international multi-institutional follow-up study. Eur J Cardiothorac Surg 1992;6:339-46.[Abstract]
   
8. Birkmeyer JD, Marrin CAS, O'Connor GT. Should patients with Björk-Shiley valves undergo prophylactic replacement? Lancet 1992;340:520-23.[Medline]
   
9. Blackstone E, Kirklin JW. Recommendations for prophylactic removal of heart valve prostheses. J Heart Valve Dis 1992;1:3-14.[Medline]
   
10. Lindblom D. Lindblom U, Henze A, Björk VO, Semb BK. Three-year clinical results with the Monostrut Björk-Shiley prosthesis. J THORAC CARDIOVASC SURG 1987;94:34-43.[Abstract]
    

This Article Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Dan Lindblom Permission Requests Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Lindblom, D. Search for Related Content PubMed PubMed Citation Articles by Lindblom, D.