Correspondence

Strut Separations in Björk–Shiley Mitral Valves

N Engl J Med 1995; 333:1714-1715December 21, 1995

Article

To the Editor:

O'Neill et al. (Aug. 17 issue)1 described a radiographic method for the detection of strut separation in Björk–Shiley convexo-concave mitral valves that had a reasonable sensitivity (83 percent) and high specificity (99.7 percent). The authors suggest that this method may be useful for screening patients with this type of mechanical heart valve, since the elective removal of valves with a defect in one leg of the outlet strut will prevent death from subsequent mechanical failure of the second leg.

The alternatives to screening are direct elective surgery without screening on the one hand, and expectant management (observation) on the other. Direct surgery carries a risk of operative mortality, and observation carries a cumulative risk of mechanical failure with an associated high mortality. For a 61-year-old patient with no coexisting condition and a valve with a risk of mechanical failure of 0.99 percent per year (averages from O'Neill et al.1), the mortality rate associated with reoperation may be estimated as 2 percent2 and the cumulative mortality caused by failure as 4.5 percent.3 Therefore, screening may result in a mortality reduction of at most 2 percent, as compared with direct surgery. This maximal benefit will not be achieved for several reasons. First, strut separation and mechanical failure may occur between two consecutive screening visits, even with short intervals such as every six months.1 Furthermore, the estimated sensitivity of the screening method may be too optimistic, since some strut separations were undetected. Moreover, the reproducibility of the method in other centers may be low, as indicated by the poor kappa values for outside observers.1 Finally, surgical mortality will increase during follow-up, because of increasing age and the possible development of additional coexisting conditions.

We conclude that the case for selective screening as a useful alternative to observation or direct elective surgery remains to be proved.

Ewout W. Steyerberg, M.Sc.
Marinus J.C. Eijkemans, M.Sc.
J. Dik F. Habbema, Ph.D.
Erasmus University, 3000 DR Rotterdam, the Netherlands

3 References

1. 1

   O'Neill WW, Chandler JG, Gordon RE, et al. Radiographic detection of strut separations in Björk-Shiley convexo-concave mitral valves. N Engl J Med 1995;333:414-419
   Full Text | Web of Science | Medline

2. 2

   Piehler JM, Blackstone EH, Bailey KR, et al. Reoperation on prosthetic heart valves: patient-specific estimates of in-hospital events. J Thorac Cardiovasc Surg 1995;109:30-48
   CrossRef | Web of Science | Medline

3. 3

   van der Meulen JH, Steyerberg EW, van der Graaf Y, et al. Age thresholds for prophylactic replacement of Björk-Shiley convexo-concave heart valves: a clinical and economic evaluation. Circulation 1993;88:156-164
   Web of Science | Medline

Author/Editor Response

Dr. O'Neill replies:

To the Editor: We concur with Steyerberg et al. that radiographic screening of Björk–Shiley convexo-concave valves has not been shown to decrease the risk of outlet-strut fracture. Unfortunately, sample size and logistic considerations preclude prospective, randomized testing of this technique. We hope that the completion of screening of 900 patients and the subsequent follow-up of this cohort will show a decreased incidence of outlet-strut fracture as compared with historical controls.

We strongly disagree with Steyerberg et al. regarding the value of routine explantation of these valves. Since most patients have had these valves in place for more than 10 years, on average the patients are older than when they had their original operations (61±11 years in our study).1 Older age alone will increase operative mortality. The risk of surgery is in fact greater in this cohort. To date, 805 patients have undergone radiographic screening and 27 patients have undergone prophylactic explantation because of abnormal results of radiographic examinations. There have been four operative deaths (15 percent mortality). De Mol et al.2 reported that no deaths occurred in 27 operations. The patient group was younger (mean age, 51), and their surgery was performed at one highly regarded center. Although no deaths occurred, 3 patients had protracted postoperative courses, and 16 patients underwent needless surgery, since the valves were fully intact. Given the known clinical risk of explantation and the continuously aging patient population, reliable predictors of valve failure must be developed before prophylactic explantation. We are confident that radiographic screening will prove to be such a test.

William W. O'Neill, M.D.
William Beaumont Hospital, Royal Oak, MI 48073

2 References

1. 1

   O'Neill WW, Chandler JG, Gordon RE, et al. Radiographic detection of strut separations in Björk-Shiley convexo-concave mitral valves. N Engl J Med 1995;333:414-419
   Full Text | Web of Science | Medline

2. 2

   de Mol BA, Kallewaard M, McLellan RB, van Herwerden LA, Defauw JJ, van der Graaf Y. Single-leg strut fractures in explanted Björk-Shiley valves. Lancet 1994;343:9-12
   CrossRef | Web of Science | Medline

Citing Articles (3)

Citing Articles

1. 1

   Bas A. de Mol, Manon E. Cromheecke, Janny G. Groen, Gerard Faber, Maurits S. van der Heiden, Leo Ongkiehong. (2001) The Complexity of External Acoustic Detection of Defects in Björk-Shiley Convexoconcave Heart Valves. Artificial Organs 25:1, 63-67
   CrossRef

2. 2

   Bas A. de Mol, Manon E. Cromheecke, Janny G. Groen, Gerard Faber, Maurits S. van der Heiden, Leo Ongkiehong. (2001) The Complexity of External Acoustic Detection of Defects in Bjork-Shiley Convexoconcave Heart Valves. Artificial Organs 25:1, 63-67
   CrossRef

3. 3

   Günter Hufnagel, Sabine Pankuweit, Bernhard Maisch. (1998) Therapie der dilatativen Kardiomyopathie mit und ohne Entzündung. Medizinische Klinik 93:4, 240-251
   CrossRef