Carotid Artery Stenosis

Stroke is the third leading cause of death in developed countries and the leading cause of morbidity. The majority of strokes (85%) are ischemic in nature, and the most common source of occlusion is thought to be intracranial embolic disease from the ipsilateral carotid artery. Recurrent strokes are a significant concern, as these often occur in the same vascular territory as the initial stroke and are associated with 65% mortality.  Determining the difference between hemodynamic and embolic causes in the presence of internal carotid artery stenosis is important for identifying the source of ischemia, which usually presents as a classic stroke or transient ischemic attack (TIA). Symptoms may include contralateral motor or sensory deficits and amaurosis fugax. Hemodynamic compromise may present similarly to a classic stroke or TIA, but may also be less predictable and atypical. Patients have reported symptoms, eg, limb shaking, retinal claudication, headache from large pulsatile external carotid artery collaterals, syncope, and generalized fatigue. One-third of all strokes are related to cervical carotid disease. The mechanism of cervical carotid stroke is usually embolization from a carotid bifurcation plaque, but hemodynamic compromise due to stenosis may also play a role. The risks of embolization and hemodynamic compromise increase with the degree of carotid artery stenosis. The benefit of carotid endarterectomy depends on the degree of stenosis, with greater benefit associated with higher levels of stenosis. Carotid endarterectomy is not a benign procedure, with an estimated 4% to 7% risk of stroke and death within the first 30 days of surgery. This is related to many factors, but primarily to the manipulation of intraluminal plaque. Periprocedural morbidity can also be difficult to quantify accurately because the natural history of stroke and TIA also results in a certain percentage of recurrent stroke and death. Therefore, determining the stenosis levels at which the risk of carotid endarterectomy is outweighed by the benefit of medical management alone is essential. Optimal medical management should be applied to all patients and includes lipid-lowering agents, hypertension control, and diabetes management. Timing of Carotid Endarterectomy The timing of intervention for carotid stenosis remains controversial, as conflicting evidence exists regarding the risks and benefits across different treatment windows. The landmark North American Symptomatic Carotid Endarterectomy Trial (NASCET) and European Carotid Surgery Trial (ECST), both published in 1991, demonstrated that carotid endarterectomy for symptomatic carotid stenosis performed within 6 months of a symptomatic event reduces the rate of recurrent stroke. The greatest clinical benefit occurred when carotid endarterectomy was performed within 2 weeks of the ischemic event. These findings led to recommendations that carotid endarterectomy be performed within 14 days of an ischemic event, with some guidelines recommending an even shorter window, including carotid endarterectomy within 48 hours of the index event. A later analysis from the Swedish Vascular Registry (Swedvasc), published in 2012, reported higher perioperative complication rates when carotid endarterectomy was performed within 48 hours of the ischemic event compared with when performed 3 to 7 days after the event (11.5% versus 3.6%). This study also found no increased risk of embolic events when carotid endarterectomy was performed at 8 to 14 days after the event. More recent guideline-based approaches recommend first classifying the index event as a TIA or a stroke, then tailoring the timing accordingly. Carotid endarterectomy within 48 hours may be considered after a TIA, whereas carotid endarterectomy performed between 3 and 7 days may be considered after a stroke. An important exception includes patients with recurrent or worsening TIAs, also referred to as crescendo TIAs, who benefit from early intervention to reduce further neurologic compromise. Multiple patient-specific factors continue to influence decision-making regarding optimal timing of carotid endarterectomy. Asymptomatic Carotid Artery Stenosis Another major area of controversy involves significant carotid artery stenosis in asymptomatic patients, defined as patients without neurologic symptoms for the preceding 6 months. Three randomized controlled trials evaluated carotid endarterectomy versus optimal medical management in asymptomatic carotid stenosis, typically defined as stenosis greater than 50%: the Veterans Affairs Cooperative Study Group, the Asymptomatic Carotid Atherosclerosis Study (ACAS), and the Asymptomatic Carotid Surgery Trial-1 (ACST-1). These studies generally demonstrated a reduction in stroke risk among patients undergoing carotid endarterectomy; however, important limitations were present, including a low incidence of ischemic stroke in both treatment groups, restriction of participation to surgeons with low complication rates in 2 trials, and substantial advances in medical therapy since the trials were conducted. Asymptomatic carotid stenosis is commonly defined as a narrowing of the proximal internal carotid artery by 50% or more at its cervical origin due to atherosclerosis. This diagnosis applies to patients without a history of recent ischemic stroke or transient ischemic attack involving the ipsilateral carotid territory within the preceding 6 months. Carotid stenosis is generally defined as 50% or greater narrowing, although many studies use 60% or greater, with stenosis exceeding 70% classified as severe carotid stenosis. Recognition and management remain clinically important because asymptomatic carotid stenosis may not appear to be a decisive risk factor for ischemic stroke, yet it serves as a strong marker of systemic atherosclerotic disease and is associated with increased risk of coronary artery disease and mortality. Carotid artery stenosis represents a major cause of ischemic stroke due to atherosclerotic disease. The presence or absence of recent transient ischemic attack or stroke plays a central role in major treatment decisions. Management of symptomatic carotid stenosis follows a more uniform and straightforward decision pathway for carotid revascularization. In contrast, significant controversy exists regarding the management of asymptomatic carotid stenosis for revascularization, resulting in multiple differing guideline recommendations. Mechanistically, hemodynamic compromise may result in transient ischemic attacks or stroke, while embolization from carotid bifurcation plaque represents the most common cause of cervical carotid stroke. Although risks of embolization and hemodynamic compromise increase with greater stenosis severity, more recent studies demonstrate that plaque composition and structural characteristics are strong predictors of stroke risk and clinical behavior in carotid artery stenosis. Over the past 3 decades, the best medical therapy for asymptomatic carotid stenosis has changed substantially. During the Asymptomatic Carotid Atherosclerosis Study (ACAS) era in the 1990s, recommended medical therapy primarily consisted of aspirin alone. Contemporary optimal medical therapy now includes multiple antiplatelet strategies, strict control of blood pressure and blood glucose, lipid-lowering agents, and comprehensive lifestyle modification, including smoking cessation, obesity management, regular exercise, and dietary optimization. These advances have significantly reduced stroke risk in medically managed patients. The 5-year ipsilateral stroke risk decreased from 11% in the 1995 ACAS trial to 3.6% in the 2010 Asymptomatic Carotid Surgery Trial-1 (ACST-1). A systematic review and meta-analysis of 11 studies demonstrated a decline in stroke risk from 2.8% to 1.4% between 1985 and 2007. Best medical therapy alone now reduces annual ipsilateral stroke risk to approximately 1%. A 2023 systematic review analyzing 73 studies and 28,265 patients with asymptomatic carotid stenosis managed medically showed that ipsilateral ischemic stroke decreased by 24% every 5 years of recruitment. Given the markedly reduced stroke risk with modern medical therapy, the benefit of carotid revascularization procedures, including carotid endarterectomy and carotid artery stenting, has become more limited in asymptomatic patients. However, select high-risk patients may still benefit from intervention. These include patients with severe stenosis (80% to 99%), microembolic signals detected on transcranial Doppler, echolucent or ulcerated plaques on duplex ultrasound, reduced cerebrovascular reserve, documented progression of stenosis, and silent embolic infarcts identified on neuroimaging. Carotid Artery Stenosis and Coronary Artery Disease  Because carotid stenosis reflects systemic atherosclerosis, a substantial proportion of patients with severe carotid disease also have concomitant CAD. In patients requiring coronary artery bypass graft surgery (CABG) who also have severe (>70%) but asymptomatic carotid stenosis, the timing of carotid intervention relative to cardiac surgery remains an important clinical question. A randomized controlled trial involving 185 patients demonstrated significant benefit when carotid endarterectomy was performed either before or at the same time as CABG, compared with patients undergoing carotid endarterectomy 1 to 3 months after CABG. The delayed carotid endarterectomy group experienced a significantly higher risk of perioperative or delayed stroke.