Pathophysiology of superficial femoral artery in-stent restenosis.

Peripheral artery disease (PAD) is an emerging problem especially with aging population and increase in the incidence of diabetes and metabolic syndrome. The disease is histologically characterized by the presence of moderate to severe calcification and fibrous plaques as compared to coronary and carotid atherosclerotic disease, which are richer in necrotic core. Endovascular therapy for the superficial femoral artery (SFA), at least in the United States, has been largely limited to balloon angioplasty and stenting and these are considered safe and relatively effective therapies. However, the patency rates remain low even at one year and restenosis is a growing and challenging problem. Recently the development of newer devices, i.e., drug-eluting stent, and drug coated balloon are showing greater efficacy and are being adopted into daily practice. In this review, we will present the morphologic characteristics of the underlying SFA atherosclerotic disease and discuss in-stent restenosis and the mechanisms that may be involved in the induction of excessive smooth muscle cell proliferation and deposition of proteoglycans and collagen, that lead to restenosis.

Unique demands of the femoral anatomy and pathology and the need for unique interventions.

With the aging of the population the incidence of peripheral artery disease (PAD) is increasing, which is histologically characterized by fibrocalcific intimal plaques as well as underlying Mönckeberg's medial calcinosis as compared to coronary and carotid artery disease. Superficial femoral artery (SFA) is one of the longest and most dynamically active vessels in the body undergoing torsion, compression, flexion, and extension from leg motion, and is known to be more susceptible to atherosclerosis because of low shear stress or spiral flow, best appreciated in the long segment in its lesser curvature. Endovascular interventions are now considered the first-line strategy for the treatment of PAD patients presenting with claudication or critical limb ischemia, where physiologic stresses on the arterial wall, anatomic considerations, and lesion characteristics impact on their success. Stent fracture and malapposition, are a common phenomenon in PAD which are attributed to severe calcification and fibrosis along with greater motion of the lower extremity, that result in the dampening of the efficacy of stenting and balloon angioplasty. Better designs of self-expanding stents have resulted in either reduction in stent fracture rates or its elimination at least in the short-term follow-up studies, to date. Although drug-eluting stents (DES) have reduced restenosis rates in the coronary circulation, this benefit has not been consistently observed in PAD. However, recent clinical studies utilizing novel Zilver-PTX self-expanding stent (DES) have demonstrated favorable patency rate. Also, in patients with critical limb ischemia, better outcomes have been reported for below-the-knee utilization of DES. Nevertheless, drawbacks of stent technology remain and interests in the greater use of drug-coated balloons (DCB) for PAD have emerged. Randomized controlled trials have consistently shown superiority of DCB over uncoated balloons in reducing neointimal formation in patients with SFA disease. Moreover, there is a growing interest in atherectomy as an alternative treatment strategy for PAD, thus decreasing plaque burden with possibly avoidance of barotrauma. The results from registries support the effectiveness of the atherectomy devices; however, prospective randomized controlled trials are needed to confirm their benefit.

Vascular remodeling after coronary stent implantation.

Drug eluting stents (DES) have significantly reduced restenosis when compared to BMS and are considered the standard of care in the treatment of symptomatic coronary artery disease. However, late stent thrombosis has emerged as a major concern with the use of first generation DES. Pathologic studies of patients dying from late DES thrombosis (first generation sirolimus-eluting stents and paclitaxel-eluting stents) showed that DES are associated with delayed healing characterized by poor endothelialization of stent struts and persistence of fibrin as compared to BMS. Additional risk factors for LST include long lesions, left main coronary artery, bifurcation stenting, ruptured plaques, and hypersensitivity reactions. Currently, the next generation DES are being developed to optimize the three major components of DES: the stent platform, the polymer coating and the drug. New technologies include biodegradable polymers and stents, polymer free drug delivery and prohealing approaches. Further preclinical testing and evaluation through large clinical trials are needed to determine the safety and efficacy of future DES in clinical practice.