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Ann Thorac Surg 1998;66:1871
© 1998 The Society of Thoracic Surgeons
a Department of Surgery, Emory University School of Medicine, Atlanta, GA, USA
To the Editor
We thank Doctors Chanda, Kuribayashi, and Abe for their attention to the work on the AOA (Biomedical Design Inc., Atlanta, GA) antimineralization technique for bioprosthetic valves [1, 2]. We reply to correct the misconceptions outlined in their communication [3].
The AOA process for treating bioprosthetic heart valves with the anticalcification agent compound alpha-aminooleic acid was conceived and developed by Drs Jean-Marie and Nadia Girardot. In a collaborative effort we tested the anticalcification effect of alpha-aminooleic acid in juvenile sheep in 1989, a widely appreciated model for the study of bioprosthetic valve calcific degeneration. For this study, stented bioprostheses treated with an initial iteration of the AOA process were compared with control, untreated valves implanted in the mitral position. This early AOA process proved extremely efficacious in preventing calcification [1]. It had one apparent shortcoming: unsolubilized particles of 
-aminooleic acid in the valve treatment solution abraded the cuspal tissue. This initial AOA process has not been applied to any valve prepared for human implantation.
This abrasion problem was overcome by refining the AOA process, which included a straightforward filtration procedure. The refined AOA process was tested in 1991 in a second juvenile sheep study. Because the valve under evaluation was the Freestyle porcine aortic root, heterotopic placement was necessary as the small diameter LVOT of juvenile sheep would not accommodate a clinical size bioprosthesis. The implantation model for this study was the valved apico-aortic conduit. Again, -aminooleic acid proved extremely efficacious against accelerated calcification. This second sheep study and extensive additional studies to assess safety of the final AOA process [2] led in 1992 to a recommendation by the Food and Drug Administration (FDA) for clinical trials of the stentless AOA-treated Freestyle heart valve. Some results from this second study were published en passant in 1994 [3]; the study was published in detail in The Annals in 1997 [4].
The authors were concerned about variability in calcium levels in the control valves in not only our experiments but those of others [5]. This speaks to the very nature of having, for each study, a control group to compare with the experimental group, which serves as an internal check in a given experiment. The statistical variability in calcium values is perfectly expected in the typical small numbers of animals studied in this type of work.
We are not privy to the inner workings of the FDA, and thus do not have access to that decision-making process and cannot speak directly to these issues. Through direct communication with representatives of the corporation that has brought the AOA process to clinical reality (Medtronic, Inc, Minneapolis, MN), we find that the FDA has had access to preclinical anticalcification data, preclinical hemodynamic data, preclinical wear testing data, and results from the initial human implantations in Europe, Canada, Australia, and other nations. The FDA was obviously quite satisfied with those data, and the AOAII process was approved for use in the United States in 1997 for the stentless root-pressure fixed Freestyle valve. Early favorable clinical experiences with this valve have been reported [6–8]. We await FDA approval of the stented version of the AOA-treated bioprosthesis.
The undersigned have no financial interest in the AOA technique.
References
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