Effect of endovascular stent strut geometry on vascular injury, myointimal hyperplasia, and restenosis.
OBJECTIVE
Early restenosis and the development of myointimal hyperplasia in stented blood vessels have been attributed to deep vascular injury with fracture of the internal elastic lamina (IEL). The purpose of this study was the evaluation of the vascular wall response to superficial injury (without IEL rupture) after balloon angioplasty and intravascular stent placement in porcine arteries and the determination of the effect of stent strut geometry on the degree of vessel injury and early restenosis.


METHODS
Balloon-expandable stainless-steel stents were placed into the iliac arteries of 10 Sinclair miniature swine that had been fed an atherogenic diet. A Palmaz stent, with rectangular struts and smooth corners, was randomly assigned to one iliac artery (group 1), and a novel stent, which was designed and manufactured in the laboratory with thicker struts and sharper corners specifically to induce large wall stress concentrations, was placed in the contralateral iliac artery (group 2). Intravascular ultrasound scan was used in all deployments to ensure accurate balloon sizing and to avoid stent overexpansion and deep vascular injury. At 90 days after implantation, the animals were killed, the stented vessels harvested, and histomorphometric analysis performed.


RESULTS
Deployment of novel stents in group 2 resulted in a statistically higher incidence rate of deep vascular injury (fracture of the IEL) compared with group 1, despite identical balloon size used for deployment (with Student t test, P <.05). Vessels with deep injury showed a 10-fold increase in myointimal thickening compared with those vessels in which the IEL remained intact. A statistically higher restenosis rate was observed for group 2 (33.5% +/- 19.90%) compared with group 1 (20.39% +/- 14.70%). For both stent designs, there was a trend toward lower degrees of restenosis within the mid-portion of the stent. For superficially injured arteries in both groups, no correlation was observed between the amount of vessel wall/medial layer compression and the development of restenosis from myointimal hyperplasia.


CONCLUSIONS
Maintenance of an intact IEL is an important factor in the prevention of myointimal hyperplasia and restenosis in stented porcine iliac arteries. The alteration of stent strut height and geometry does not significantly affect restenosis and the development of myointimal hyperplasia in vessels with superficial injury. Superficial injury elicits a response that is independent of stent strut geometry and vessel wall compression. Stent strut profile may, however, increase local vessel wall stress concentrations, leading to IEL rupture and an exaggerated response to injury.
Sullivan
Timothy M
TM
Academic Department of Surgery, Greenville Hospital System, SC 29605, USA. tsullivan@ghs.org
Ainsworth
Stephen D
SD
Langan
Eugene M
EM
Taylor
Spence
S
Snyder
Bruce
B
Cull
David
D
Youkey
Jerry
J
Laberge
Martine
M
D000818:Animals; D019917:Blood Vessel Prosthesis Implantation; D004195:Disease Models, Animal; D005500:Follow-Up Studies; D006083:Graft Occlusion, Vascular / Q000209:etiology*; D006965:Hyperplasia / Q000209:etiology*; D016014:Linear Models; D011183:Postoperative Complications / Q000209:etiology; D012720:Severity of Illness Index; D015607:Stents; D013552:Swine; D017211:Treatment Failure; D017539:Tunica Intima / Q000293:injuries* / Q000473:pathology*; D014656:Vascular Surgical Procedures