[Clinical study of "stent creep" in porcine bioprosthesis]

Stent creep is often associated with malfunction of bioprosthesis. We measured the inward bending angle of the stent-post showing maximum bending (IBA) on 42 mitral porcine xenografts retrieved 1 to 12 yrs (mean 7.7 yrs) postoperatively at reoperation. Patients were 12 men and 28 women, ranging in age from 26 to 58 yrs. Mean +/- S.D. for IBA was 12.7 +/- 4.2 degrees(ds) in 14 valves being implanted for less than 7 yrs and 16.9 +/- 5.5 ds in 28 valves longer than 8 yrs (p less than 0.05). There was a significant difference in IBA between 36 valves of 25-29 mm size (16.3 +/- 5.1 ds) and 6 valves of 31 mm (10.3 +/- 5.5 ds) (p less than 0.05), but no significant difference between 23 Hancock valves (15.5 +/- 4.4 ds), 10 Angell-Shiley valves (16.2 +/- 8.6 ds) and 9 Carpentier-Edwards valves (14.4 +/- 3.7 ds). IBA showed a tendency to have large valve in the heart with small left ventricular end-systolic volume. The results showed that stent creeping phenomenon was not related to the material or design of stent-post, but tended to increase with passage of time in place. Furthermore, it was suggested that stent creep was induced by the mechanism of compression of the stent by the left ventricular wall.