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J Thorac Cardiovasc Surg 1994;107:631-0631
© 1994 Mosby, Inc.

Letters to the Editor

Clinical evaluation of the Omniscience cardiac valve prosthesis (J THORAC CARDIOVASC SURG 1992;103:259-66)

Cardiac Surgical Unit
Massachusetts General Hospital
Boston, MA 02114

To the Editor:

I read with interest the article by Akalin and associates, ¹ "Clinical Evaluation of the Omniscience Cardiac Valve Prosthesis," and commend them for providing valuable information that surgeons may use to evaluate the Omniscience prosthesis. 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.

There is one area in the report where the results appear to be somewhat misleading, however, namely the linearized rates of valve-related complications found in Table IV. Akalin and coworkers ¹ state on page 262 of their report that their cumulative follow-up was 407.9 patient-years, which is reasonably accurately approximated by multiplying the number of their patients (200) by the mean follow-up period (2.03 years). Analysis of the information found in Table IV reveals that the linearized rates calculated for the individual events separated according to mitral valve replacement, aortic valve replacement, and double valve replacement were generated by dividing the individual number of events by the total follow-up time of 407.9 patient-years. This is valid only for the valve-related complications for the entire group of 200 patients. Linearized rates for valve-related complications separated according to valve operation must be divided by the patient-years of follow-up for that valve operation group to be represented by the accurate linearized rate.

The differences in the linearized rates calculated for the individual valve-related complications separated by valve operation could differ significantly from those stated in the table. For example, for the first complication listed in Table IV, thromboembolism for patients undergoing mitral valve replacement, Akalin and associates report four complications, which they find to have a linearized rate of 1.0%. A closer approximation to the true patient-years of follow-up for these patients would be obtained by multiplying the number of patients (128) by the mean length of follow-up (2.03 years), which would yield an approximate follow-up of 260 patient-years. Dividing the four complications by 260 patient-years yields a linearized rate of 1.5%.

In terms of sustaining the high quality of this report, I ask that Akalin and colleagues generate the accurate linearized rates for the valve-related complications that they have noted for the 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. Akalin H, Çorapçioglu ET, Özyurda U, et al. Clinical evaluation of the Omniscience cardiac valve prosthesis. J THORAC CARDIOVASC SURG 1991;103:259-66.[Abstract]
   
2. Edmunds LH, Clark RE, Cohn LH, Miller DC, Weisel RD. 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 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 Articles by Akins, C. W.