PATIENT FACTORS ASSOCIATED WITH STRUT FRACTURE IN BJORK-SHILEY 60-DEGREES CONVEXO-CONCAVE HEART-VALVES

Background Previously established predictors of outlet strut fracture in Bjork-Shiley convexo-concave (CC) valves include larger valve size, larger opening angle (70 degrees versus 60 degrees), younger age at i mplant, and date of manufacture. We sought to identify patient charact eristics that might be predictive of strut fracture and to refine the estimates associated with previously identified predictors. Methods an d Results We conducted a case-control study of CC60 degrees valves imp lanted in the United States and Canada and manufactured between Januar y 1, 1979, and March 31, 1984. Cases included all valves with verified outlet strut fractures reported to the manufacturer from January 1979 through January 1992. Up to 10 controls were selected for each case. Control valves were matched according to implanting surgeon and were r equired to have been functioning at least as long as their matched cas e valves. Case and control medical records were reviewed for informati on on patient medical history before the valve implant. There were 96 case and 634 control valves for which clinical data were available. Pa tient age and valve size and implant position were confirmed as import ant determinants of fracture. There was a strong inverse gradient of r isk with age. The risk of fracture was 42% lower for each 10-year incr ement of patient age at time of implant. Large mitral valves were at g reatest risk of strut fracture, with the largest mitral valves (33 mm) estimated to be 33 times more likely to fracture than the smallest (2 1 to 25 mm) aortic valves. Date of manufacture was also associated wit h risk; valves welded from mid-1981 through March 1984 were more likel y to fracture than those manufactured in 1979 and 1980. Body surface a rea <1.5 m(2) was associated with 1/16 the risk of body surface area g reater than or equal to 2.0 m(2). No other patient factor was strongly associated with the risk of strut fracture. Conclusions Few patient f eatures identifiable in the implant record are predictive of strut fra cture. Our analysis supports previous work in identifying valve size, patient age, and date of manufacture as predictors of fracture and add s body surface area. A number of these associations suggest that condi tions associated with higher cardiac output may also place patients at increased risk.