Introduction

As the population ages, the number of reported age-associated diseases increases. One of these diseases is atherosclerosis. Although atherosclerosis can occur in any arterial location, one critical location is at the carotid bifurcation, as it restricts blood flow to the internal carotid artery and, hence, the brain. Stroke is the third leading cause of death, and the leading cause of adult disability in the United States. More than 80% of these strokes are ischemic in nature, and 35% to 40% of ischemic strokes are direct results of large-vessel atherosclerosis (1). Carotid end-arterectomy (CEA), surgical removal of plaque, was pioneered in the 1950s and has become established as the preferred intervention for treating carotid artery stenosis.

In the late 1990s, the first carotid angioplasty/stenting procedures were conducted (2-5), whereby, via a catheter and under fluoroscopic observation, a balloon (with or without a balloon-expandable stent) was placed at the level of the stenosis and used to expand the narrowing. This procedure represented a potential alternative to CEA and a significant development in the field of endovascular intervention. However, the rates of risk associated with those early procedures—approximately 10% (3,6,7)—did not compare favorably with complication rates for CEA. The 1991 North American Symptomatic Carotid Endarterectomy Trial (NASCET) documented significant benefits of CEA for symptomatic patients who had stenosis of >70% and reported an overall rate of 6.5% for perioperative stroke or death and a rate of 2% for permanent disability or death (8). It is important to recognize, however, that these results were achieved with specific sets of patient and surgeon selection criteria that limit the validity of comparisons to the few existing studies of carotid stenting. For example, centers were excluded from the NASCET if their rates of complication were >6%. Complication rates <6% for CEA might be found among experienced surgeons who perform the procedure frequently but are not as common in the wider community; hence, this biased selectivity became the major criticism of the collaborative work. The 1995 Asymptomatic Carotid Atherosclerosis Study (ACAS) (9), which reported benefit from surgery in patients with stenosis >60%, used an even more selective surgical complication rate of 3%. Even so, data from both of these studies is frequently utilized to make patient management decisions.

The Carotid Revascularization Endarterectomy versus Stent Trial was initiated to develop comparable data for the 2 procedures but has been slow to achieve patient enrollment and is still underway. Given the improvements in technology in carotid stenting, including the development of distal protection devices, carotid stenting might well be proven to be a viable alternative to CEA. However, until that time, its use is likely to remain limited to 2 patient populations: those who are poor surgical candidates for CEA and those who suffer restenosis.

In part, because the NASCET excluded high-risk surgical candidates, resistance to the use of carotid stenting for such patients has been considerably less. The benefit of carotid stenting in these patients was given further support by the Stenting and Angioplasty with Protection in Patients at High Risk for Endarterectomy (SAPPHIRE) study (10,11), which showed slightly improved outcomes and shorter hospitalizations in patients with endovascular treatment, compared to those with surgical treatment. In 2005, the Centers for Medicare and Medicaid Services approved Medicare coverage for carotid stenting for high-risk CEA patients with symptomatic stenosis >70% and for high-risk CEA patients who are enrolled in Category B investiga-tional device exemption clinical trials and have symptomatic stenosis between 50% and 70% or asymptomatic stenosis >80% ( 12 ).

Restenosis, or recurrent stenosis, is a condition that is present in approximately 20% of patients who receive CEA (13-16). Its etiology has a biphasic distribution. In the first 24 months post CEA, restenosis usually represents intimal hyperplasia from the surgical manipulation. After 2 years, it is more commonly due to recurrent atherosclerotic disease. Intimal hyperplasia is smooth and easily expanded by balloon angioplasty. Embolic phenomena are rare, as the lesion is not as friable as atheromatous plaque. The risk of repeat surgery is approximately 12%, and increases in these patients (6,17) due to risk of nerve injury at the prior operative site. Therefore, carotid angioplasty, with or without stents, is commonly performed in this patient population.

When making the recommendation for carotid angioplasty/stenting, it is important to consider the marginal improvements of outcome. From a procedural viewpoint, it has become easier to perform these interventions. Hence, now the more difficult question must be addressed: which patients truly benefit from the revascularization? For the surgical opening of the carotid artery, NASCET has made it clear that patients who have 69% or greater stenosis with symptoms referable to the distribution should be treated (8). ACAS additionally provided proof that patients with 80% or greater stenosis would benefit, even if asymptomatic (9). The SAPPHIRE study demonstrated that patients with high degrees of stenosis who are poor candidates for CEA can still benefit from revascularization in the form of carotid stenting. The length of time that a patient needs to live after the procedure to reap the benefits of the risks involved, and the therapy that current medical management can provide for patients without intervention remain unclear factors. For example, with the introduction of Statin medications, a 20% to 35% reduction in stroke has been documented in patients with atherosclerotic disease (18-20). The NASCET study did not take these newer drugs into account; therefore, the marginal improvement of risk from surgical or endovascular repair might now be reduced.

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