In vivo assessment of stent recoil in normal porcine arteries: evaluation of contemporary stent designs

Coronary Stent Failure: Fracture, Compression, Recoil, and Prolapse

Current-generation coronary drug-eluting stents are associated with low rates of restenosis and target lesion revascularization. However, several mechanisms of stent failure remain clinically important. Stent fracture may occur in areas of excessive torsion or angulation. Longitudinal stent deformation is related to axial stent compression owing to extrinsic forces or secondary devices that disrupt stent architecture. Stent recoil occurs when a stent does not deploy at its optimal cross-sectional area. Tissue prolapse between stent struts may also predispose patients to adverse outcomes. Prevention, recognition, and treatment of these stent failures are necessary to optimize patient outcomes after percutaneous coronary interventions.

Impact of stent design on clinical outcome after coronary stent implantation

Coronary stents have considerably improved both immediate and late results after coronary angioplasty, by limiting elastic recoil and vascular remodeling, but their use does not eliminate restenosis, caused mainly by neointimal hyperplasia. Stents are now implanted in over 70% of percutaneous coronary interventions. More than 50 coronary stents have already been approved in Europe and over 20 stents are commercially available in the USA, raising the question: which device is best suitable for which lesion? Several in vitro experiments revealed significant differences in expansion characteristics of coronary stents, related to the strut design and metallic composition. Animal studies were performed to determine the influence of stent design on the patterns and extent of neointimal hyperplasia. However, the clinical results of randomized trials comparing stent types in humans have not always reflected laboratory findings. This article is a critical overview of experimental and clinical data concerning the impact of stent design on the early and late clinical outcome after coronary stent implantation.

Chronic stent recoil plays an important role in restenosis of the right coronary ostium

OBJECTIVE

The efficacy of coronary stenting of aorto-ostial atherosclerotic lesions is still unclear. We investigated the frequency and mechanism of stent restenosis at this particular lesion.

METHODS

Fifty-five consecutive patients with 64 native aorto-ostial lesions in the right coronary artery (RCA, n = 38) and the left main trunk (LM, n = 26) were treated by conventional stenting. Determinants of angiographic restenosis were established. The mechanism of stent restenosis was evaluated using post-stenting and follow-up intravascular ultrasound (IVUS) findings.

RESULTS

Restenosis was more frequent in the RCA than in the LM (50% compared with 19%, P < 0.03) and determinants included diabetes mellitus (63% compared with 21%, P < 0.03), calcium deposition (58% compared with 5%, P < 0.003), smaller stent cross-sectional area (SA) (as demonstrated by post-stenting IVUS studies, 8.1 +/- 1.4 mm compared with 10.2 +/- 2.2 mm, P < 0.01), larger plaque burden (64 +/- 6% compared with 57 +/- 8%, P < 0.03) and less circular expansion at the aorto-coronary junction. Serial IVUS examination was performed in 11 patients with restenosis of the right coronary ostium. The mean reduction in the SA was 21% at the aorto-coronary junction (6.4 +/- 1.9 mm, P < 0.003), whereas the SA at the distal edge was unchanged. Thirty-three per cent of late luminal loss was due to chronic stent recoil.

CONCLUSION

These findings suggest that stenosis of the right coronary ostium is a high-risk lesion for stent restenosis. In addition to excessive intimal growth, chronic stent recoil might be an important etiologic factor at this particular location.

Comparison of the morphological changes of restenosis after the implantation of various types of stents in a swine model

BACKGROUND

Stent design causes the differences of restenosis rate, but the morphological differences after the various types of stent implantation have not been clarified.

DESIGN

Seven types of stents were implanted in pig coronary arteries to clarify how the mechanism of restenosis differs with coil stents and tube stents.

METHODS

The left anterior descending coronary arteries (LADs) of pigs were injured using coronary angioplasty balloons (diameter: 3.0 mm; length: 20 mm; balloon/artery ratio: 1 : 2). Fourteen days after the injury, four types of coil stents (Cordis, Wiktor, GR-I, and GR-II) and three types of tube stents (Palmaz-Schatz, gfx, and Multilink) were implanted, and the LADs were extracted 28 days after the implantation.

RESULTS

The proliferated neointima was eccentric in the coil stents and concentric in the tube stents. Although there was no significant difference in the area of neointima, the area of the lumen was significantly larger in the tube stents than in the coil stents ( < 0.01) because of the larger area of stent. Cells positive for anti-proliferating cell nuclear antigen antibody were mainly observed around the stent struts, and most of these cells were also positive for either anti-macrophage or anti-smooth muscle actin antibodies.

CONCLUSIONS

Compared to the coil stents, the tube stents induce less negative remodelling including stent recoil, resulting in a wider luminal area. In order to prevent restenosis, it is crucial to implant a stent that will cause less negative remodelling.