PROGRESSIVE VASCULAR REMODELING AND REDUCED NEOINTIMAL FORMATION AFTER PLACEMENT OF A THERMOELASTIC SELF-EXPANDING NITINOL STENT IN AN EXPERIMENTAL-MODEL

Despite the improvements afforded by intracoronary stenting, restenosi s remains a significant problem, The optimal physical properties of a stent have not been defined. We compared the vascular response to a th ermoelastic self-expanding nitinol stent with a balloon-expandable tub ular slotted stainless steel stent in normal porcine coronary arteries , Twenty-two stents (11 nitinol and 11 tubular slotted) were implanted in II miniature swine, The nitinol stents were deployed using the int rinsic thermal properties of the metal, without adjunctive balloon dil ation, The tubular slotted stents were implanted using a noncompliant balloon with a mean inflation pressure of 12 atm. Intravascular ultras ound (IVUS) and histology were used to evaluate the vascular response to the stents, The mean cross-sectional area (CSA) of the nitinol sten ts (mm(2)) as measured by IVUS increased from 8.13 +/- 1.09 at implant to 9.10 +/- 0.99 after 28 days (P = 0.038), while the mean CSA of the tubular slotted stents was unchanged (7.84 +/- 1.39 mm(2) vs, 7.10 +/ - 1.07 mm(2), P = 0.25). On histology at 3 days, the tubular slotted s tents had more inflammatory cells adjacent to the stent wires (5.7 +/- 1.5 cells/0.1 mm(2)) than the nitinol (3.9 +/- 1.3 cells/0.1 mm(2), P = 0.016), The tubular slotted also had increased thrombus thickness ( 83 +/- 85 mu) than the nitinol stents (43 +/- 25 mu, P = 0.0014). Afte r 28 days, the vessel injury score was similar for the nitinol (0.6 +/ - 0.3) and the tubular slotted (0.5 +/- 0.1, P = 0.73) designs. The me an neointimal area (0.97 +/- 0.46 mm(2) vs. 1.96 +/- 0.34 mm(2), P = 0 .002) and percent area stenosis (15 +/- 7 vs. 33 +/- 7, P = 0.003) wer e significantly lower in the nitinol than in the tubular slotted stent s, respectively. We conclude that a thermoelastic nitinol stent exerts a more favorable effect on vascular remodeling, with less neointimal formation, than a balloon-expandable design, Progressive intrinsic ste nt expansion after implant does not appear to stimulate neointimal for mation and, therefore, may provide a mechanical solution to prevent in -stent restenosis. (C) 1998 Wiley-liss, Inc.