The carotid arteries are two large blood vessels located on either side of the neck that supply blood to the brain. Carotid Artery Disease (CAD), also known as carotid stenosis, occurs when fatty deposits called plaque build up inside these arteries, a process known as atherosclerosis. This plaque accumulation causes the artery to narrow or become blocked, which significantly increases the danger of an ischemic stroke if a piece of plaque breaks off. The determination of whether surgical intervention is appropriate depends on medical guidelines that evaluate the degree of blockage and the patient’s symptoms. This article explains the specific percentage thresholds and clinical considerations used to decide when surgery is necessary to reduce stroke risk.
How Blockage is Measured
Measuring the percentage of carotid artery blockage is a technical process that relies on more than simple visual estimation. The primary diagnostic tool used is the Carotid Duplex Ultrasound, which combines traditional ultrasound imaging with Doppler technology to assess blood flow dynamics. This method allows physicians to estimate the degree of stenosis by measuring the velocity of blood flow through the narrowed section, as a higher velocity indicates a more severe constriction.
The calculation of the stenosis percentage is standardized, primarily using the criteria established by the North American Symptomatic Carotid Endarterectomy Trial (NASCET). The NASCET method determines the percentage of narrowing by comparing the diameter of the residual lumen at the point of maximum blockage to the diameter of the normal internal carotid artery located further down the vessel. This calculation provides a reliable and reproducible measure of the severity of the disease.
While ultrasound is the initial screening tool, further tests like Computed Tomography Angiography (CTA) or Magnetic Resonance Angiography (MRA) may be used to confirm the degree of stenosis. The use of a standardized calculation method, such as NASCET, is fundamental because the major clinical trials that set the surgical thresholds were based on this specific measurement technique.
Criteria for Asymptomatic Patients
An individual is classified as asymptomatic if they have not experienced any stroke-related symptoms, such as a Transient Ischemic Attack (TIA) or a stroke, that are directly attributable to the blocked carotid artery. For this group, the general threshold for considering surgical intervention, such as Carotid Endarterectomy (CEA) or stenting, is a stenosis of 70% or greater. This recommendation stems from large-scale studies that demonstrated a modest long-term benefit in stroke prevention for patients with high-grade stenosis.
The decision to intervene at this level is subject to a careful risk-benefit analysis, as the potential benefit must outweigh the procedural risks of the surgery itself. Current guidelines suggest that revascularization procedures should only be performed if the combined risk of perioperative stroke and death is very low, typically below 3%.
Blockages measuring between 50% and 69% are usually managed with intensive medical therapy, including antiplatelet drugs and high-intensity statins, rather than immediate surgery. Aggressive medical management has significantly reduced the annual stroke rate in asymptomatic patients, leading to ongoing debate about the long-term value of surgery for this group.
Procedural intervention is generally reserved for those with a life expectancy of at least five years, ensuring they live long enough to realize the stroke prevention benefit. Factors such as plaque ulceration, the presence of microemboli, or a rapidly progressing blockage can also prompt consideration for intervention, even if the stenosis is slightly below the 70% threshold.
Criteria for Symptomatic Patients
A patient is considered symptomatic if they have recently suffered a TIA or a non-disabling stroke that is directly linked to the carotid artery being evaluated. For this patient group, the threshold for intervention is significantly lower because the recent neurological event indicates a highly unstable plaque that poses an immediate and high risk of a future stroke. This instability justifies a more aggressive treatment approach.
The greatest benefit from surgical intervention is observed in symptomatic patients with a high-grade stenosis ranging from 70% to 99%. In these cases, Carotid Endarterectomy is strongly recommended, provided the procedural risk is acceptably low, often defined as a combined stroke and death rate below 6%. Intervention is typically recommended as soon as possible, ideally within two weeks of the most recent neurological event, to prevent a recurrent stroke.
For symptomatic patients with moderate stenosis, defined as a blockage between 50% and 69%, there is still a moderate benefit from intervention. Surgery is often considered for these patients, particularly if they are younger or have other high-risk plaque characteristics. Conversely, for blockages less than 50%, medical therapy remains the standard of care, as the risk of the procedure generally outweighs the benefit of stroke prevention.
Comparing Surgical and Stenting Procedures
Once the percentage threshold and symptomatic status indicate the need for intervention, the choice is typically between two primary revascularization options: Carotid Endarterectomy (CEA) and Carotid Artery Stenting (CAS).
Carotid Endarterectomy (CEA)
CEA is the traditional, open surgical procedure where the artery is opened, and the plaque is physically removed to restore normal blood flow. This method is often considered the standard of care due to its long track record of durable stroke prevention.
Carotid Artery Stenting (CAS)
CAS is a less invasive, endovascular procedure where a catheter is threaded through the blood vessels. A balloon is used to open the blockage, and a stent is deployed to keep the artery open.
The choice between CEA and CAS is not based on the percentage of blockage but rather on the patient’s individual clinical profile and anatomy. Patients who may be poor candidates for open surgery, such as those with severe heart or lung conditions, previous neck radiation, or a history of prior neck surgery, are often better suited for stenting.
While stenting may carry a lower risk of certain periprocedural complications like myocardial infarction and nerve injury, endarterectomy has historically demonstrated a lower risk of periprocedural stroke, particularly in older patients. Patient age is a significant factor, with CEA generally preferred for patients over 70 years old due to the slightly increased stroke risk associated with CAS in this age group. The decision ultimately involves a collaborative discussion between the patient and a multidisciplinary team, weighing the specific risks of each procedure against the patient’s overall health and anatomical considerations.