Asymptomatic carotid stenosis

Asymptomatic carotid bruits occur in 4% of the US population older than 40 years, and the annual stroke rate in these individuals is 1.5%.

This same population has an annual mortality rate of 4%, primarily from complications of heart disease. The presence of a carotid bruit is, therefore, a better predictor of arteriosclerotic disease than of stroke. As of 2014 the current AHA/ASA guidelines for management of asymptomatic carotid stenosis include the following:

• Patients with asymptomatic carotid stenosis should be prescribed a statin and aspirin. They should also be screened for conditions that are risk factors for stroke, with appropriate institution of medical therapy and lifestyle modifications.

• Individuals with greater than 50% stenosis should undergo serial annual ultrasonography to identify progression.

• It is reasonable to consider CEA in patients with greater than 70% stenosis if the perioperative complication risk for stroke, myocardial infarction, and death is less than 3%. However, the benefit of CEA over best medical therapy is controversial.

• For patients undergoing CEA, aspirin is recommended perioperatively and postoperatively, unless contraindicated.

• Prophylactic carotid artery stenting (CAS) might be considered in select patients with stenosis that is greater than or equal to 60% on angiography or stenosis that is greater than or equal to 70% on ultrasonography, but the benefit of CAS over best medical therapy is not proven.

• In patients at high risk for complications related to revascularization that might result from either CEA or CAS, the effectiveness of revascularization versus medical therapy is not well established.

Contemporary intensive medical management (also called best medical therapy), which includes the more widespread and aggressive use of statins, newer antiplatelet agents, and lifestyle modifications (eg, cessation of smoking), as well as improvements in pharmacologic therapy for treatment of diabetes and hypertension, seems to have altered the prognosis in those assigned to medical therapy, which may now be equivalent or superior to outcomes from revascularization procedures. Furthermore, because most ischemic strokes due to carotid stenosis are preceded by a TCI, some experts feel that medical management should be the preferred treatment, and that physicians should wait until symptoms occur in the patient before subjecting a patient to the risks associated with revascularization. The Carotid Revascularization Endarterectomy Versus Stenting Trial-2 (CREST-2) study is now under way; it will compare outcomes in patients treated with best medical therapy versus those who undergo CEA.

Symptomatic carotid stenosis

Patients with TCI, transient monocular visual loss (TMVL), or previous stroke resulting from carotid stenosis are considered symptomatic. The risk of stroke within 1 year of onset of symptoms is 8% in patients with TCI; the risk thereafter is approximately 6% per year, with a 5-year risk of 35%–50%. Current AHA/ASA guidelines for management of symptomatic carotid stenosis are as follows:

• For patients with recent (within the past 6 months) TCI or ischemic stroke and severe (70%–99%) ipsilateral carotid artery stenosis, CEA is recommended if the perioperative morbidity and mortality risk is less than 6% and the patient’s life expectancy is greater than 5 years.

• For patients with recent cerebrovascular events and moderate ipsilateral stenosis (50%–69%), CEA is recommended, depending on patient-specific factors such as age, sex, and other comorbidities.

• There is no benefit of CEA or CAS in a patient with stenosis of less than 50%.

• Surgery may be performed within 2 weeks of a TCI or stroke.

• CAS can be considered as an alternative to CEA in symptomatic patients when the patient is at low risk for endovascular intervention and an internal carotid artery stenosis of greater than 70% is indicated by noninvasive imaging or an internal carotid artery stenosis of greater than 50% is indicated by catheter angiography. CAS may also be considered in other selected patients.

Carotid artery stenting versus carotid endarterectomy

The first CREST study randomly assigned patients with asymptomatic or symptomatic carotid disease to CEA or CAS. The primary endpoint of the trial—a composite of any stroke, MI, or death within 30 days of the procedure and ipsilateral stroke during long-term follow-up—was similar in both groups, including the rate of ipsilateral stroke at 31 days to up to 4 years after the procedure. The study showed that:

• Endarterectomy had a greater benefit in older patients (≥70 years).

• Stenting was more beneficial in patients in younger age groups (<60 years).

• There was a greater incidence of stroke and death at 30 days in the stenting group versus the endarterectomy group, but the incidence of MI was significantly lower in the CAS group.

• Despite the higher rate of stroke associated with stenting, at 1-year follow-up there were no significant differences in any quality-of-life measure between the CEA and CAS groups.

Transient monocular visual loss and cardioaortic causes of ischemic stroke

In addition to cerebral conditions, ocular conditions such as TMVL and retinal TCIs can be associated with carotid stenosis. The ophthalmologist is often the first physician to see a patient with TMVL; the TMVL is usually embolic, with either a carotid or a cardiac source. The annual stroke rate among patients with isolated TMVL, retinal infarcts, or TCIs is approximately 2%, 3%, and 8%, respectively. Untreated individuals with TMVL, retinal infarcts, or TCIs have a 30% risk of MI and an 18% risk of death over a 5-year period. A cardiac source of embolization should be excluded for all patients presenting with isolated TMVL. Transthoracic echocardiography (TTE) can identify multiple potential cardiac causes for embolism and, as expected, the diagnostic yield is highest if the clinical history and physical examination suggest a cardiac source such as atrial fibrillation, rheumatic mitral stenosis, diffuse atherosclerosis, left ventricular aneurysm, or clinical endocarditis. Transesophageal echocardiography (TEE) is superior to transthoracic echocardiography in diagnosing a cardioembolic source, except for a left ventricular thrombus, which is better seen on TTE. Because TEE is invasive and uncomfortable and may not be tolerated well by the patient, TTE is recommended first in the evaluation of a potential cardioaortic source of stroke. If the results from TTE imaging are negative, the use of TEE would then be indicated. TEE is the best imaging modality to use to rule out atheromatous plaques in the ascending aorta, a patent foramen ovale, a left atrial appendage clot, or other causes of “cryptogenic” stroke. TEE is also superior for identifying certain anatomic abnormalities, but the identification of intracardiac thrombi or tumors with TEE is rare (<3%). Therefore, whether the use of TEE will become routine in the evaluation of cryptogenic stroke remains to be seen. Other modalities used in the diagnosis of cardioembolic sources of stroke include inpatient telemetry, ambulatory Holter monitoring, loop recorders, and surgically implantable cardiac monitors.

If evidence suggests that a carotid lesion is the cause of the TMVL, or if venous stasis retinopathy is present, duplex ultrasonography should be performed to determine whether vessel wall disease or carotid stenosis is present.

The following approach should be considered for a patient presenting with a cerebral or retinal transient ischemic attack (TIA):

• emergency department or urgent outpatient evaluation or hospital admission if the event occurred within the previous 48 hours

• patient evaluation for the presence of risk factors associated with atherogenesis: hypertension, diabetes mellitus, obesity, hyperlipidemia, and smoking

• institution of appropriate medical therapy

• evaluation by appropriate testing for the presence of a cardiac source of emboli

• determination using duplex ultrasonography of the possibility of carotid stenosis

If ipsilateral carotid stenosis exceeds 70%, if bilateral carotid stenosis greater than 50% is present, or if long-term evidence indicates progressive disease, CEA should be considered—but only if the surgeon’s perioperative stroke and death rate is less than 6%. Otherwise, antiplatelet therapy with aspirin (325 mg/day), aspirin/extended-release dipyridamole combination, or clopidogrel should be initiated. A patient presenting with TIA symptoms who has previously undergone CEA should be evaluated and treated similarly. Special attention should be paid to evaluating patients for the presence of early restenosis and thrombosis.

For further discussion of TIA and TMVL, see BCSC Section 5, Neuro-Ophthalmology.

Ophthalmic considerations Giant cell arteritis (GCA), which may present as TMVL, should always be considered in the differential diagnosis of TMVL and may warrant further laboratory investigation depending on age (>50 years). For more on GCA and TMVL, see BCSC Section 5, Neuro-Ophthalmology.

• Katsanos AH, Giannopoulos S, Frogoudaki A, et al. The diagnostic yield of transesophageal echocardiography in patients with cryptogenic cerebral ischaemia: a meta-analysis. Eur J Neurol. 2016;23(3):569–579.

  Meschia JF, Bushnell C, Boden-Albala B, et al; American Heart Association Stroke Council, Council on Cardiovascular and Stroke Nursing, Council on Clinical Cardiology, Council on Functional Genomics and Translational Biology, Council on Hypertension. Guidelines for the primary prevention of stroke: a statement for health care professionals from the American Heart Association/American Stroke Association. Stroke. 2014;45(12):3754–3832.

  Safian RD. Asymptomatic carotid stenosis: revascularization. Prog Cardiovasc Dis. 2017;59(6):591–600.

Excerpted from BCSC 2020-2021 series: Section 1 - Update on General Medicine. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.