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J Thorac Cardiovasc Surg 1995;110:566
© 1995 Mosby, Inc.

LETTERS TO THE EDITOR

Mid-term follow-up after heart valve replacement with CarboMedics bileaflet prostheses

Department of Cardiac Surgery
Massachusetts General Hospital
Boston, MA 02114

To the Editor:

I read with interest the article by de Luca and associates ¹ concerning valve replacement with the CarboMedics bileaflet prosthesis, and I commend them for providing valuable information to help surgeons evaluate the recently approved CarboMedics valve (CarboMedics, Inc., Austin, Tex.). The authors have carefully adhered to the published guidelines for reporting valve-related complications ² in virtually all areas. The completeness of their follow-up and the detail of their presentation are admirable.

One area of their report has results that appear to be misleading, namely, the presentation of linearized rates of valve-related complications reported for aortic, mitral, and double valve replacement. The presentation of accurate information is important, because on page 1163 of their report the authors state that their incidence of thromboembolic complications is low, at 0.5%/pt-yr, compared with other series. Analysis of the information provided in the Results section on page 1160 reveals that the linearized rates calculated for the individual events are probably erroneous. For example, the authors state on page 1160 that thromboembolic events were observed in seven patients. If the cumulative patient follow-up was 478 patient-years, as stated on page 1159, then the linearized rate for thromboembolism would be 1.5%/pt-yr, not 0.5%/pt-yr.

A further difficulty arises when the authors present linearized rates segregated according to valve procedure. Although they do not provide us with a breakdown of the individual events by operative procedure, their report of the linearized rates of thromboembolism for aortic (0.35%/pt-yr), mitral (0.8%/pt-yr), and double valve replacement (0.3%/pt-yr) cannot be correct. Linearized rates for valve-related complications separated according to valve operation must be divided by the patient-years of follow-up for only that valve operation group to accurately represent the linearized rate. The authors appear to have generated a "linearized rate" by dividing the percentage of patients free of an event actuarially by the follow-up interval of 3 1/2 years.

Similar computational errors can be found in the presentations of valve-related death, anticoagulant-related hemorrhage, nonstructural valvular dysfunction, prosthetic valve endocarditis, and incidence of reoperation. In terms of sustaining the high quality of their report, I ask that de Luca and colleagues generate accurate linearized rates for the valve-related complications that they have noted for the combined and separate operative procedures. This information would be valuable for cardiac surgeons who are seeking to generate data ³ that allow comparison of the various available prostheses, with an aim toward finding the most appropriate prostheses for their patients.

References

1. de Luca D, Vitale N, Giannolo B, et al. Mid-term follow-up after heart valve replacement with CarboMedics bileaflet prostheses. J THORAC CARDIOVASC SURG 1993;106:1158-65.[Abstract]
   
2. Edmunds LH, Clark RE, Cohn LH, et al. Guidelines for reporting morbidity and mortality after cardiac valvular operations. J THORAC CARDIOVASC SURG 1988;96:351-3.[Medline]
   
3. Akins CW. Mechanical cardiac valvular prostheses. Ann Thorac Surg 1991;52:161-72.[Abstract/Free Full Text]
   

This Article Alert me when this article is cited Alert me if a correction is posted 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): Cary W. Akins Permission Requests Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Akins, C. W. Search for Related Content PubMed PubMed Citation Articles by Akins, C. W.