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BJORK-SHILEY VALVE X-RAY IMAGING STUDY RESULTS

This article was originally published in The Gray Sheet

Executive Summary

BJORK-SHILEY VALVE X-RAY IMAGING STUDY RESULTS "confirm exploratory nature" of an x-ray technique designed to identify valves in which one leg has separated from the valve, Shiley Heart Valve Research Center President Philip Hedger says in a Feb. 5 press release from parent firm Pfizer. Because the procedure has resulted in one false positive diagnosis and one "possible" false negative diagnosis, "caution is still warranted before considering whether to make this procedure available to additional patients with convexo/concave valves outside this study," Hedger maintains. The Feb. 5 release outlines preliminary results of an SHVRC- sponsored study of the imaging procedure. The study has evaluated 181 patients as of Feb. 10. In addition to the one false positive and potential false negative result, the study has found four (2.2%) patients with single-leg separated valves. Single-leg separation may be a precursor to valve fracture, which has a high mortality rate. Identification of the problem would enable patients to undergo replacement surgery to avert possible valve fracture. The study population is limited to patients with large 60 degrees convexo/concave valves placed in the mitral position; these patients are thought to have the highest risk for valve fracture. The study of the valve imaging method was initiated in September 1992 at the William Beaumont Hospital in Royal Oak, Michigan ("The Gray Sheet" Oct. 12, I&W-4). The primary diagnostic tool used to study valve structure is a Siemens Hicor computer- assisted x-ray system. Until recently, the procedure also involved an analysis of valve sound recordings. Elaborating on the "false positive" result, Pfizer says that the initial x-ray image and acoustic analysis indicated a "probable" single-leg separation, and that further "analysis of the valve sound recording led to a reconsideration of the valve's original x-ray image, which was then found to be 'minimally suspicious.'" After a second x-ray image showed a "probable" valve defect, the patient elected to have the valve replaced. The device was found to be normal upon explantation. "In planning our research, we were particularly concerned about false positives," Hedger commented. "One of our primary objectives has been to do everything that we can scientifically to reduce the risk of false-positive findings that could necessarily expose patients to the risks of valve replacement surgery." The "possible false negative" case involved a patient who was diagnosed as having a normal Shiley valve and died suddenly three months later. Because the valve is not available for examination, "it is impossible to know if its x-ray examination produced a 'false negative' finding," according to Shiley. Hedger concludes: "Although the x-ray technique continues to look promising, two independent advisory panels of physicians . . . still counsel caution." He adds that the technique "will not be more widely available until the FDA has reviewed and approved the study's data." Researchers at William Beaumont offer a different interpretation of the "false positive" event. Investigators conducting the study say that the "false positive" case resulted from incorrect interpretation of acoustic patterns, not an incorrect x-ray diagnosis. According to the investigators, the x-ray correctly identified the valve as normal, but the patient decided to have the valve removed because the valve sound recordings suggested a defect. After further analysis of several additional patients who displayed abnormal sound patterns, the use of valve acoustics as a diagnostic tool was abandoned. Researchers are expecting to complete the screening of the 300 patients allowed under an FDA investigational device exemption in the next several weeks. Six-month followup examinations will then be conducted, with final results anticipated in about a year.
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