Interpreting a 20-year experience with the Biocor porcine bioprosthesis

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CTSNet classification: 35.2, 35.3.3, 35.4.2

To the Editor:

With greatest interest we read the recent article by Drs Mykén and Bech-Hausen.¹ The authors reported on a 20-year experience of 1712 patients with the Biocor porcine bioprosthesis. The study reported excellent long-term prosthetic valve durability in both the aortic and mitral positions over a 20-year period. Comparing the data with those for other types of bioprostheses, the Biocor devices were shown to rival the best valves around.

A few comments and a word of caution seem to be appropriate and of interest to the readership of the Journal to interpret these data. The authors correctly state that comparisons with other long-term studies are difficult because of differing baseline characteristics.¹ Comparisons are subsequently provided and summarized in Table 5; however, considerations concerning some key patient cohort differences are lacking.², ³, ⁴ These include the following.

First, the continuing patient enrollment during a 20-year period resulted in a limited mean follow-up time: 6.0 ± 4.5 years for aortic valve replacement (AVR) and 6.2 ± 5.6 years for mitral valve replacement. This strategy tends to underestimate events in comparison with similar studies with a much shorter enrollment period like the cited 20-year Edwards Clinical Communiqué, which had a mean follow-up time of 9.0 ± 5.5 years.²

Second, the authors report the actuarial freedom from reoperation because of structural valve deterioration (SVD), which is inherently lower than the freedom from SVD. Therefore the direct comparison with the freedom from SVD as reported by several other studies tends to underestimate the number of events in the current study.³, ⁴

Third, the long inclusion period has resulted in an uneven age distribution over time. Given the mean age difference between the originally reported 10-year experience and the current 20-year report, patients in the AVR and mitral valve replacement cohorts, respectively, must on average have been about 7 and 5 years older during the second decade of the study than during the first decade.¹, ⁵ Therefore a high number of patients with a relatively short follow-up time might contribute to an underestimation of the incidence of SVD in the elderly groups.²

A further comment is directed at the intriguing incompleteness of Table 5.¹ Age-stratified event rates for AVR from several studies are cited in the last column, headed by the Biocor's 20-year freedom from reoperation because of SVD being 92.1% ± 3.9% in patients aged 65 years and older and 44.5% ± 9.2% in those younger than 65 years. However, for 2 studies these readily available data are provided as mean overall rates only.³, ⁴ The excellence of these results in the elderly patient groups makes these data indispensable for the overall perspective. The 68% ± 12% overall freedom from SVD in Aupart and colleagues' 18-year Perimount experience³ thus breaks down into 99% ± 1% for patients aged greater than 70 years, 77% ± 12% for those aged 60 to 70 years, and 45% ± 15% for those aged less than 60 years. In Yankah and associates' 17-year Mitroflow experience,⁴ the 67.0% ± 4.9% freedom from SVD in similar age groups breaks down into 93.0% ± 3.0%, 60.1% ± 6.4%, and 45.7% ± 13.5%, respectively.

We congratulate the authors with the realization of their study spanning so many years and hope to see further results and adequate comparisons in future publications.

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References 

1. Mykén PS, Bech-Hansen O. A 20-year experience of 1712 patients with the Biocor porcine bioprosthesis. J Thorac Cardiovasc Surg. 2009;137:76–81
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2. Clinical Communiqué: Carpentier-Edwards Perimount pericardial aortic bioprosthesis 20 year results. Irvine, Calif: Edwards Lifesciences; 2003. Available at: http://www.edwards.com/products/heartvalves/perimountaorticcommuniquepdf.htm. Accessed April 6, 2009.
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3. Aupart MR, Mirza A, Meurisse YA, Sirinelli AL, Neville PH, Marchand MA. Perimount pericardial bioprosthesis for aortic calcified stenosis: 18-year experience with 1,133 patients. J Heart Valve Dis. 2006;15:768–776
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4. Yankah CA, Schubel J, Buz S, Siniawski H, Hetzer R. Seventeen-year clinical results of 1,037 Mitroflow pericardial heart valve prostheses in the aortic position. J Heart Valve Dis. 2005;14:172–179
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5. Mykén PS, Caidahl K, Larsson S, Berggren HE. 10-year experience with the Biocor porcine bioprosthesis in the aortic position. J Heart Valve Dis. 1994;3:648–656
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