Surveillance of asymptomatic carotid artery stenosis: Not all plaques are created equal

Asymptomatic carotid artery stenosis is associated with a low overall risk of progression to stroke or transient ischemic attack, especially in the era of contemporary medical care with antiplatelet agents, statins, and anti-hypertensive therapy. Despite these advancements, development of a cerebrovascular event from a carotid artery lesion can have catastrophic consequences. As a result, providers caring for patients with asymptomatic carotid artery stenosis face a clinical conundrum: how does one judiciously manage valuable resources in surveillance and invasive management, while maintaining an aggressive enough approach to identify and treat patients before the development of disabling stroke? Current guideline recommendations address the approach to asymptomatic carotid stenosis very generally and define the diagnosis broadly as a greater than 50% stenosis ¹ but do not provide guidance on risk stratification. A refinement to this definition is needed, with a more targeted approach that can inform the appropriate surveillance interval and whether other risk factors might help inform subsequent management.

The authors of two manuscripts published in this issue of Vascular Medicine provide important evidence to address knowledge gaps regarding frequency of surveillance of asymptomatic carotid artery stenosis. Hamilton and colleagues used retrospective data from a large multidisciplinary practice to assess the progression of mild asymptomatic carotid disease in 440 carotid arteries by duplex ultrasonography over a period of 3 to 5 years. ² The authors reported an overall low rate of progression (~5.5%) across measurements, with only one patient (0.2%) progressing to severe carotid stenosis. While these data support the historical impact of more intensive medical therapy in slowing the progression of atherosclerotic disease, the study also identifies specific risk factors associated with progression of disease. The presence of hypertension, diabetes mellitus, peripheral vascular disease, male sex, and lower intensity or lack of statin use, were all associated with disease progression. These characteristics are not surprising, given their association with overall cardiovascular mortality and morbidity, but may serve as a starting point to help clinicians discern who to image on a more frequent basis. The authors suggest increasing the time interval for repeat carotid artery duplex studies among patients with mild asymptomatic carotid artery stenosis and without significant risk factors, thereby lessening costs by limiting screening exams in an emerging era of value-based health care. Extrapolating these findings to the converse, however, they also suggest that patients with other manifestations of systemic atherosclerosis may benefit from more frequent surveillance imaging.

In a second manuscript, Masoomi and colleagues investigated the utility of additional duplex ultrasound features to predict disease progression among patients with asymptomatic carotid artery stenosis. ³ The authors utilized retrospective data from carotid artery duplex studies performed at their institution and identified ultrasound features readily captured by current imaging methods that were associated with an increased risk of ipsilateral ischemic stroke or transient ischemic attack. The authors hypothesized that external carotid artery stenosis predicts cerebrovascular outcomes. Consistent with this, the presence of external carotid artery stenosis has previously been associated with overall mortality. ⁴ Although certain measures of plaque morphology, area, and embolic potential have been previously studied to attempt to identify ‘high-risk’ plaque, these measurements are not readily available to most clinicians and institutions, and are not yet appropriate in standard imaging practice. ⁵ The authors instead used the combination of internal and external carotid artery stenosis progression to identify patients at increased risk for neurologic events. They found that the combination of internal and external carotid artery stenosis progression was associated with a nearly fourfold increase in the odds of ipsilateral stroke or transient ischemic attack, even after adjusting for demographic and clinical characteristics. ⁴ Utilizing current and guideline-recommended methodology for carotid artery imaging (e.g. duplex ultrasonography), as well as ultrasound parameters that are consistently and readily captured in clinical practice (e.g. external carotid artery velocities), the authors identified a method by which higher risk patients can be identified for either more intensive surveillance or even earlier intervention.

While both of the manuscripts published in this issue are single-center studies, they will help further refine the assessment and treatment of asymptomatic carotid artery stenosis. Prior analyses have begun to characterize at-risk groups as well as other duplex features associated with both progression of stenosis and the risk of neurologic events^6–8; however, more comprehensive and broadly applicable analyses remain lacking. With that said, identifying key high- and low-risk groups within larger cohorts of patients with asymptomatic carotid artery stenosis is an important first step. Ultimately, a clinically applicable risk score is necessary to aid clinicians in the management of patients with asymptomatic carotid artery stenosis. Such a risk score should be discerning enough to suggest optimal intervals for surveillance examinations and further identify thresholds for intervention, but it also needs to be broadly accessible to practitioners with ‘real-world’ use and implementation kept in mind during development. With some investigators already calling for more targeted strategies for intervention in severe asymptomatic disease ⁹ and randomized trials in revascularization forthcoming, ¹⁰ upstream evaluation of asymptomatic carotid artery disease will likely need to follow suit. Not all plaques are created equal, and clinicians should strive to assess and treat them accordingly.