Understanding Stroke Risks in Carotid Artery Stenting

Why Less Invasive Doesn't Mean Lower Stroke Risk in Carotid Artery Stenting

Carotid artery stenting (CAS), while less invasive than carotid endarterectomy (CEA), does not equate to a reduced risk of stroke. On the day of the procedure, the risk of experiencing a stroke is 4.7%, with an additional 2.5% chance within the following 30 days. The majority of these strokes are ischaemic, occurring primarily on the side of the stent insertion. Various factors contribute to this risk, including embolisation, thrombosis within the stent, dissection of the internal carotid artery (ICA) or common carotid artery (CCA), haemorrhagic stroke, and intracranial haemorrhage.

Protection devices are designed to prevent embolic strokes during the procedure, but their effectiveness can be compromised by incomplete deployment, incorrect positioning, or insufficient removal of debris. If a stroke occurs during CAS, it is critical to treat the patient immediately without waiting for extra imaging. Therapy can include mechanical thrombectomy, possibly alongside intra-arterial thrombolysis, which is less effective due to the nature of the embolus. For acute thrombosis in the stent, a thrombolytic agent like rTPA may be used. Prior carotid intervention does not alter the management of acute ischemic stroke. Therefore, a neuro-interventional team should ideally be available at facilities performing CAS to address these challenges swiftly.

Stroke Incidence Following Carotid Artery Stenting

Carotid artery stenting (CAS) carries a risk of stroke, which is an important consideration for both practitioners and patients. According to a meta-analysis of patients involved in randomized controlled trials, the risk of experiencing a stroke on the day of the stenting procedure is 4.7%. In the subsequent period, from day 1 to day 30 after the procedure, an additional 2.5% of patients experience a stroke.

The majority of these strokes, approximately 94%, are ischaemic in nature, and 91% occur on the same side as the stented internal carotid artery (ICA). These figures underscore the importance of monitoring and preventive strategies to mitigate the risk of stroke following CAS.

Patients at Higher Risk for Stroke After Carotid Artery Stenting

Certain patients are at an elevated risk of experiencing a stroke following carotid artery stenting (CAS). Anatomical challenges significantly contribute to this risk, especially for those less experienced in CAS procedures. Features such as a type III aortic arch, where the gap between the brachiocephalic artery's starting point and the top of the arch is greater than double the left common carotid artery's diameter, can complicate the procedure. Similarly, a "bovine arch" formation, where the brachiocephalic artery and left common carotid artery originate together, increases complexity. Other anatomical risk factors include severe atheroma in the aortic arch, a compromised or blocked external carotid artery, sharply angled distal internal carotid arteries, long sections of narrowing, and very narrow stenoses.

Clinical studies have highlighted additional risk factors. In the CREST study, plaques longer than 13 mm or with multiple lesions distant from the stenosis were linked to a heightened stroke risk. Age is another factor: patients with high age-related white matter changes on imaging showed greater stroke rates peri-operatively. CAS posed a higher stroke risk than carotid endarterectomy (CEA) in patients with a high ARWMC score. Moreover, complications within the first week of CAS are more prevalent, especially for symptomatic patients. Additional factors include urgent interventions, chronic obstructive pulmonary disease, and an ASA grade over 3, which have been identified as independent predictors of post-operative stroke.

What Randomised Comparisons with Surgery Measured

Randomised controlled trials (RCTs) comparing carotid artery stenting (CAS) with carotid endarterectomy (CEA) have provided insights into the risks associated with each procedure. One key finding from these trials is the higher rate of stroke or death within the first seven days after symptom onset in patients undergoing CAS compared to those undergoing CEA, with rates of 8.3% for CAS versus 1.3% for CEA. This results in a relative risk of 6.7, indicating a significantly higher risk for CAS in this early period.

The trials also explored anatomical risk factors that might influence outcomes. The Delphi Anatomical Risk score, which considers features like arch type and stenosis characteristics, was validated as a predictor of stroke or transient ischemic attack (TIA) in CAS patients. However, this score did not correlate with peri-operative stroke in the ICSS trial. In contrast, the CREST trial identified plaque features, such as plaque length greater than 13 mm, as risk factors for stroke after CAS, although these were not linked to non-ischemic brain lesions (NIBLs) in the ICSS-MRI substudy.

Further analysis indicated that patients with high age-related white matter change (ARWMC) scores undergoing CAS had higher rates of peri-operative stroke compared to those with lower scores. This association was not observed in CEA patients, highlighting a specific risk factor for CAS. Additionally, urgent interventions and patient comorbidities like COPD and higher ASA grades were identified as independent predictors of post-operative stroke in both CAS and CEA, with a stronger association noted in CAS.

Deciding Between Carotid Artery Stenting and Carotid Endarterectomy

Choosing between carotid artery stenting (CAS) and carotid endarterectomy (CEA) involves weighing different risk factors and outcomes. A meta-analysis indicated that CAS poses a higher risk of stroke or death within the first seven days following symptom onset compared to CEA. Specifically, 8.3% of CAS patients experienced these adverse events, compared to just 1.3% for those undergoing CEA. This suggests that CEA might be a safer option in the immediate postoperative period.

Certain anatomical features can make CAS more challenging, especially for less experienced practitioners. For example, a Type III aortic arch or a common origin of the brachiocephalic artery with the left common carotid artery are factors associated with increased procedural difficulty. Furthermore, individuals with a high Delphi Anatomical Risk Score are at greater risk for stroke or transient ischemic attack after CAS.

Plaque characteristics also influence the risk. In the CREST study, plaques longer than 13 mm or those with sequential lesions linked to the ICA stenosis raised the stroke risk in CAS. However, the ICSS-MRI substudy did not find these features to correlate with higher rates of new ischemic brain lesions on MRI.

Another consideration is the age-related white matter change (ARWMC) score. An ARWMC score above 7 is associated with a higher incidence of stroke during the peri-operative period for CAS but not for CEA. This score also correlated with silent cerebral embolization during procedures like transcatheter aortic valve implantation.

Despite these insights, some gaps remain. For instance, real-world data on managing strokes arising from ICA thrombosis or M1/M2 embolic occlusions post-stenting is limited. Although guidelines suggest treating these incidents similarly to strokes without prior intervention, this area lacks robust clinical trial evidence. The findings emphasize the need for a neuro-interventional service in facilities conducting CAS to enhance patient outcomes.