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Acs0602 Asymptomatic Carotid Bruit
 

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    Acs0602 Asymptomatic Carotid Bruit Acs0602 Asymptomatic Carotid Bruit Document Transcript

    • © 2004 WebMD, Inc. All rights reserved. ACS Surgery: Principles and Practice 6 VASCULAR SYSTEM 2 ASYMPTOMATIC CAROTID BRUIT — 1 2 ASYMPTOMATIC CAROTID BRUIT Claudio S. Cinà, M.D., Sp.Chir. (It.), M.Sc., F.R.C.S.(C), Catherine M. Clase, M.B., B.Chir., M.Sc., and Aleksandar Radan, M.D., B.Sc., B.F.A. Assessment of Asymptomatic Carotid Bruit The term bruit refers to any noise detected on auscultation in the hours or causes death.9 Amaurosis fugax is a transient (< 24 hours) neck.The conventional method of auscultation is to use the bell of loss of vision in one eye or a portion of the visual field.9 If a patient the stethoscope and listen over an area extending from the upper with a carotid bruit has a history of any of these conditions in the ip- end of the thyroid cartilage to just below the angle of the jaw.1-3 The silateral eye or brain, then the bruit is regarded as neurologically principal reason why bruits in the neck are matters of some concern symptomatic, and the relevant question at that point is whether the is that they may reflect underlying occlusive carotid artery disease, patient has significant carotid stenosis and may be a candidate for which carries an increased risk of stroke. carotid endarterectomy on that basis. Given the substantial differ- In what follows, we outline a problem-oriented approach to the ences between the management of patients with symptomatic bruits workup of patients found to have cervical bruits at the time of rou- and those with asymptomatic bruits, the distinction between these tine or focused vascular examination. two patient groups is crucial. The history is of critical importance in the diagnosis of TIA be- Clinical Evaluation cause most TIAs last less than 4 hours,10 which means that patients typically are not seen by physicians during the period of neurologic deficit.11 Patients should be specifically asked about transient focal CAROTID BRUITS VERSUS problems with vision, language, facial paresis, dysarthria, and arm OTHER CERVICAL SOUNDS or leg numbness or weakness. A 1984 study reported good interob- Clinical assessment begins server agreement (κ = 0.65) [see Table 1] between clinicians diagnos- with evaluation of the character ing previous ischemic episodes.12 Assigning a probable neurologic of the bruit and examination of territory to a TIA or stroke, however, proved more difficult: for TIAs, the precordium and the cervical the interobserver agreement between two independent neurologists structures. Carotid bruits must be distinguished from other sounds asked to distinguish between carotid and vertebrobasilar events was heard in the neck.Venous hums are relatively common, being report- relatively poor (κ = 0.31).12 There is some evidence that using a stan- ed in 27% of young adults.4 They tend to have a diastolic compo- dardized protocol for the diagnosis of previous ischemic episodes nent, are louder when the patient sits or turns the head away from might improve this low interobserver agreement (e.g., to κ = 0.6512 the side of auscultation, and disappear when the patient lies down or κ = 0.7713). Similar difficulties attend diagnosis of stroke by means or when the Valsalva maneuver is performed.4 Ejection systolic mur- of history and physical examination.14 murs of cardiac origin may radiate into the neck, but generally, they Many patients with a possible TIA or stroke will have undergone are bilateral, are louder within the chest, and are less audible distal- neurologic imaging. Such imaging is unhelpful if it yields negative ly in the neck5; the same is true of bruits arising in other intratho- results; however, in some cases, it reveals the presence of an infarct, racic vessels.6,7 No definitive clinical sign has yet been identified that thereby confirming the ischemic nature of the event and establish- clearly differentiates bruits from transmitted cardiac murmurs. On occasion, a bruit may be heard over the thyroid gland; however, this finding is extremely rare and is usually accompanied by thy- Table 1 Quantification of Interobserver Agreement* romegaly and other features of autoimmune thyroid disease.5 In dialysis patients, a bruit may be generated by the increased flow re- κ† Strength of Agreement sulting from the creation of an arteriovenous fistula in the forearm.8 ≤ 0.2 Poor SYMPTOMATIC VERSUS ASYMP- > 0.2, ≤ 0.4 Fair TOMATIC CAROTID BRUITS > 0.4, ≤ 0.6 Moderate > 0.6, ≤ 0.8 Good Transient ischemic attacks > 0.8, ≤ 1 Very good (TIAs) are defined as brief epi- sodes of focal loss of brain func- *Reliability (how closely an assessment agrees with another similar assessment on a second occasion or by a second observer) and validity (how closely the assessment tion that can usually be localized agrees with another criterion or a gold standard) are the key properties of any assess- ment. When agreement between two observers is poor, the assessment in question, to a specific portion of the brain whether it is a physical finding, a clinical diagnosis, or an interpretation of a diagnostic supplied by a single vascular sys- test, is lacking in reliability; if more reliable methods are available, they should be consid- ered instead. In clinical medicine, however, more reliable methods are not always avail- tem.9 By arbitrary convention, able. When this is the case, the physician must use a relatively unreliable assessment as such an ischemic episode is considered a TIA if it lasts less than 24 the best available alternative, while remaining aware of its limitations.118 † κ is a statistical measure used to quantify agreement between two or more observers. hours; a similar episode, in the absence of evidence of trauma or hem- It takes a value between 0 and 1, where 0 represents agreement no better than that orrhage, is considered an ischemic stroke if it lasts more than 24 expected by chance alone and 1 represents perfect agreement.118
    • © 2004 WebMD, Inc. All rights reserved. ACS Surgery: Principles and Practice 6 VASCULAR SYSTEM 2 ASYMPTOMATIC CAROTID BRUIT — 2 Noise is detected on auscultation of neck Determine nature of cervical sound. Sound is carotid bruit Distinguish symptomatic bruits from asymptomatic bruits; the decision affects treatment. Bruit is symptomatic Bruit is asymptomatic Perform vascular risk assessment, looking for vascular risk factors (e.g., ↑BP, ↑lipids, diabetes, smoking) and vascular disease (e.g., ischemic cardiac disease, peripheral vascular disease). Initiate modification of vascular risk. Determine subsequent management approach. Assessment of Risk associated with CE is low (Goldman class I or II) Asymptomatic Carotid Bruit Assess risk of carotid stenosis. Risk of carotid stenosis is high Risk of carotid stenosis is low Risk factors include ↑age, ↑BP, smoking, peripheral vascular disease. Assess risk of stroke. Risk of stroke is high Risk of stroke is low Risk factors include age > 70, male sex, ↑BP, ↑lipids, diabetes, smoking, ischemic cardiac disease, peripheral vascular disease. Consult patient preferences regarding surgical treatment. Patient prefers surgical management Patient prefers medical management Determine presence and degree of carotid stenosis with duplex ultrasonography and carotid angiography. Severe stenosis is present Moderate stenosis is present Minimal or no stenosis is present Perform prophylactic CE. Reevaluate with duplex ultrasonography every 1– 2 yr unless patient status changes.
    • © 2004 WebMD, Inc. All rights reserved. ACS Surgery: Principles and Practice 6 VASCULAR SYSTEM 2 ASYMPTOMATIC CAROTID BRUIT — 3 Sound is venous hum, radiating cardiac murmur or intrathoracic bruit, or thyroid bruit Patient is to be assessed as candidate for Patient is to be managed carotid endarterectomy (CE) conservatively Determine level of risk associated with procedure. Risk associated with CE is high (Goldman class ≥ III) Continue modification of vascular risk. Educate patient regarding symptoms and signs of stroke. Carry out nonsurgical follow-up. Re-refer patient promptly if he or she ever becomes symptomatic.
    • © 2004 WebMD, Inc. All rights reserved. ACS Surgery: Principles and Practice 6 VASCULAR SYSTEM 2 ASYMPTOMATIC CAROTID BRUIT — 4 ing its location. For a bruit to be regarded as symptomatic on the Table 2 Annual Risk of Stroke basis of imaging studies, at least one infarct must be seen in the ap- propriate ipsilateral anterior vasculature. Patient Population Annual Risk of Stroke It is evident that distinguishing between symptomatic and asymp- tomatic bruits on clinical grounds may be difficult; nonetheless, it Population without bruits, age > 60 yr19,43,44 0.86% (95% CI, 0.8–0.9) Population with bruits, age > 60 yr19,20,43 2.1% (95% CI, 0.6–8.5) is worthwhile to make the effort because the risk of stroke in the Male population without bruits, age > 60 yr19,24 0.9% (95% CI, 0.1–3.0) asymptomatic population is quite different from that in the sympto- Male population with bruits, age > 60 yr19 8.0% (95% CI, 0.2–38.0) matic population. For example, whereas the Asymptomatic Carotid Female population without bruits, age > 60 yr24 2.0% (95% CI, 0.8–4.2) Atherosclerosis Study (ACAS), which included patients believed on Female population with bruits, age > 60 yr19 2.4% (95% CI, 0.7–5.5) clinical grounds to be neurologically asymptomatic, reported an overall stroke rate of 6.2% at 2.7 years in its medically managed group,15 the North American Symptomatic Carotid Endarterecto- gestive heart failure, or peripheral vascular syndrome) will occur in the my Trial (NASCET), which included patients assessed as neurolog- next 5 years is greater than 20%.22,37 In such patients, consultation ically symptomatic (i.e., with a history of amaurosis fugax,TIA, or of formulas or tables is unnecessary, and all modifiable risk factors minor stroke), reported a stroke rate of 26% at 3 years in its med- should be aggressively managed (target BP < 140/90; target ratio of ically managed group.16 total cholesterol to high-density lipoprotein [HDL] cholesterol < 4).22 In determining whether a unilateral bruit is symptomatic or A meta-analysis of randomized, controlled trials showed that as- asymptomatic, the physician should concentrate primarily on is- pirin reduced the risk of subsequent stroke, MI, and death from vas- chemic deficits in the ipsilateral hemisphere (i.e., those causing focal cular events for patients who had previously experienced a cere- contralateral motor or sensory deficits) and ipsilateral amaurosis fu- brovascular event, MI, or unstable angina.38 Other meta-analyses of gax. However, symptoms referable to the contralateral carotid ar- randomized, controlled trials39,40 were unable to confirm the effec- tery, even if no bruit is heard on that side, might prompt evaluation tiveness of aspirin in preventing cerebrovascular events in asympto- of the patient for symptomatic carotid stenosis on the contralateral matic patients or in patients with TIAs or strokes of noncardiac (and side.The absence of a bruit by no means excludes the diagnosis: ca- presumably vascular) origin41; however, one randomized, controlled rotid bruits are absent in 20% to 35% of patients with high-grade trial involving hypertensive patients at modest vascular risk found stenosis of the internal carotid artery.17 In the NASCET subgroup that aspirin reduced the risk of vascular events, if not the risk of in which the physical finding of a carotid bruit was compared with stroke.42 In the absence of contraindications, we recommend that as- angiographic imaging of the carotid system, the presence of a focal pirin be considered for all patients who have established vascular dis- ipsilateral carotid bruit had a sensitivity of 63% and a specificity of ease elsewhere and for all patients who have a bruit in association 61% for high-grade (70% to 99%) stenosis; the absence of a bruit with any vascular risk factors. did not significantly change the probability of significant stenosis in INDICATIONS FOR SURGICAL this population (pretest 52%, posttest 40%).18 INTERVENTION Workup of patients with symptomatic bruits is beyond the scope of this chapter. Accordingly, the ensuing discussion focuses on as- The absolute risk of stroke is sessment of patients with asymptomatic bruits. increased in the presence of a ca- rotid bruit. In population-based VASCULAR RISK ASSESSMENT studies, the annual risk of stroke Vascular diseases and other vascular risk factors are common in was 2.1% (95% confidence in- patients with asymptomatic carotid bruits. Hypertension is twice as terval [CI], 0.6 to 8.5)19,20,43,44 common in patients who have bruits as in those who do not19; for persons who had a carotid smoking, ischemic heart disease, and peripheral vascular disease are bruit and 0.86% (95% CI, 0.8 to 0.9) for those who did not.19,43,44 also more prevalent.20,21 Consequently, detection of a bruit should These figures represent an absolute risk increase for stroke of 1.24% prompt a thorough vascular risk assessment. Standard vascular risk a year and a relative risk for stroke of 2.4. The mean patient age in factors—hypertension, hyperlipidemia, diabetes, and smoking—can these studies was approximately 65 years, and sex distribution and be integrated into risk profiles for particular patients by using either prevalence of risk factors for atherosclerotic disease were similar in the New Zealand risk tables (http://www.nzgg.org.nz/library/gl_ patients with bruits and those without bruits. Even after adjustment complete/bloodpressure/appendix.cfm) or the formula and spread- for age, sex, and the presence of hypertension, the presence of a ca- sheets provided by Anderson et al.22,23 The probability of stroke for rotid bruit remained an independently significant variable, with a various follow-up periods may be quantified by using the Framing- relative risk of 2.0.19 ham stroke-risk profile.24 From age, systolic blood pressure, dia- betes, smoking, cardiovascular disease, atrial fibrillation, and left ven- Table 3 Prevalence of Carotid Stenosis in Patients tricular hypertrophy, probability of stroke may be calculated for men with Bruits and in Healthy Volunteers and women according to a point system.24 Smoking cessation should be recommended to all patients,25-27 Patient Population Prevalence of Carotid Stenosis and hypertension should be controlled (BP < 140/90).28-31 De- pending on a patient’s individual risk profile, dietary and pharma- Overall population with cervical bruits cologic management of hyperlipidemia may also be warranted.32-34 > 35% stenosis20,56-58,119 58% (95% CI, 55–60) Diabetic control should be optimized.35,36 > 60%–75% stenosis56-58 21% (95% CI, 18–24) Patients should be asked specifically about any concurrent vascu- Healthy volunteers* lar disease—in particular, symptoms suggestive of ischemic heart dis- Age > 70 yr89 5.1% (95% CI, 2.6–9.0) ease or of claudication or rest pain. In patients with established vascu- Age ≤ 70 yr89 1.5% (95% CI, 0.2–5.3) lar disease, the risk that future vascular events (e.g., coronary-related *In healthy volunteers, the incidence of asymptomatic carotid stenosis is significantly death, myocardial infarction [MI], new angina, stroke,TIA, new con- correlated with age (P < 0.01) and with the presence of hypertension (P < 0.005).
    • © 2004 WebMD, Inc. All rights reserved. ACS Surgery: Principles and Practice 6 VASCULAR SYSTEM 2 ASYMPTOMATIC CAROTID BRUIT — 5 nonfatal MI was 2% (95% CI, 1.1 to 3.9), whereas for patients in Table 4 Necessary Criteria for Offering class III or IV, the corresponding figure was 21% (95% CI, 9.2 to an Interventional Approach to Selected 39.9) [see Table 5]. Given that 50 prophylactic carotid endarterec- tomies would have to be performed to prevent one stroke over the Patients with Carotid Bruits subsequent 3-year period (i.e., the number needed to treat [NNT] Center-specific criteria is 50), it is clearly unacceptable to perform this procedure in a pop- Either ulation facing a 21% incidence of MI or death, in which for every 5 DUS is documented to have a > 90% PPV for stenosis > 50% on patients undergoing the operation, one would experience an MI or angiography and is used alone die (i.e., the number needed to harm [NNH] is only 5). Further or consideration of prophylactic carotid endarterectomy in patients for DUS has a lower PPV and is used as a screening test only, and angiography in patients with cerebrovascular disease has a whom the procedure carries a high risk is not warranted. documented complication (stroke or death) rate of around 1% Surgeon-specific criterion High Risk of Carotid Stenosis Perioperative rate of stroke or death is < 3% for carotid Cohort45,54-60 and population- endarterectomy based19,61,62 studies suggest that DUS—duplex ultrasonography PPV—positive predictive value patients with asymptomatic ca- rotid bruits are more likely to have significant carotid stenosis Given the low absolute risk of stroke in asymptomatic patients if they are older, are hyperten- with bruits [see Table 2], the low prevalence of surgically relevant sive, smoke, or have advanced stenosis in patients with bruits [see Table 3], and the small (and peripheral vascular disease. In only marginally statistically significant) absolute benefit of carotid one study, hemodynamically significant stenosis (i.e., > 50%) was endarterectomy in patients with asymptomatic stenosis,45,46 we found by means of ultrasonography in 32% of patients scheduled to and others47-51 do not believe that further investigation with a view undergo peripheral vascular procedures but in only 6.8% of those to carotid endarterectomy is mandatory in the asymptomatic pop- scheduled to undergo coronary artery bypass grafting (CABG).63 ulation. Many surgeons may prefer to manage these patients con- (All figures for degree of stenosis in this chapter are determined ac- servatively, reevaluating them promptly if they become sympto- cording to the formula used in NASCET [see Table 6 and Figure 1].) matic [see Discussion, below]. Other surgeons may wish to pursue Further consideration of carotid endarterectomy may be war- a more interventional strategy with selected patients, in which case ranted in patients with vascular risk factors or known peripheral further evaluation with an eye to surgical treatment depends on vascular disease; in the absence of these findings, the risk of signifi- the presence of the following key findings in a given patient: (1) cant carotid stenosis is low. Further evaluation is unnecessary for low risk associated with carotid endarterectomy, (2) relatively high patients who are younger, do not smoke, are not hypertensive or di- risk of carotid stenosis, and (3) high risk of stroke if carotid steno- abetic, and are not known to have peripheral vascular disease. sis is documented. In addition, the patient’s preferences should be consulted: no patient should be subjected to further evaluation who High Risk of Stroke is not prepared to undergo surgical treatment if such management Within the group of patients is recommended. Patients who, on the basis of any of these crite- with asymptomatic carotid ste- ria, are not suitable candidates for intervention will not benefit nosis, there is only limited direct from imaging studies and should be managed medically. evidence for the existence of sub- Finally, surgeons and centers who are contemplating offering groups of patients at higher risk prophylactic carotid endarterectomy for asymptomatic stenosis for stroke. Men seem to be at should be able to document that their rates of stroke or periopera- higher risk for stroke than wom- tive death for this procedure are lower than 3% [see Table 4].When en are: in the medical arm of complication rates exceed this threshold, the value of carotid endar- ACAS, the incidence of stroke or death at 2.7 years was 7.0% (95% terectomy becomes negligible, and surgeons may find themselves CI, 4.9 to 9.4) for men and 4.9% (95% CI, 2.7 to 8.0) for women. doing more harm than good.45,46 Gender-related differences aside, however, identification of other subgroups at higher risk relies on extrapolation of data from other Low Risk Associated with populations at risk for artery-to-artery embolism. Data from Carotid Endarterectomy NASCET indicate that for symptomatic patients with greater than In NASCET and ACAS, pa- 70% carotid stenosis, the presence of a higher number of identifi- tients were excluded if they had able clinical risk factors (age > 70 years; male sex; systolic or dias- coexisting medical disease likely tolic hypertension; the occurrence of a cerebrovascular event within to produce significant mortality the preceding 31 days; the occurrence of a more serious cerebrovas- and morbidity (e.g., cardiac val- cular event, namely, stroke rather than a TIA or amaurosis fugax; vular or rhythm disorders, un- smoking; MI; congestive heart failure; diabetes; intermittent claudi- controlled hypertension or dia- cation; or hyperlipidemia) was associated with a higher annual betes, unstable angina pectoris, or MI in the previous 4 months)16; stroke risk. For patients with zero to three risk factors, the annual accordingly, the results of these trials are not generalizable to pa- stroke risk was 6.6%; for those with four or five, 9.2%; and for those tients who have such conditions. Further evidence for the impact of with six or more, 15.8%. Data from the same study indicate that operative risk on outcomes is provided by a retrospective review of among patients with a contralateral asymptomatic stenosed carotid 562 patients who underwent carotid endarterectomy for sympto- artery, patients with zero to three risk factors have an annual stroke matic and asymptomatic disease in a large community hospital.52 risk of 1.4% in the territory of the asymptomatic stenosis; those For patients in Goldman class I or II,53 the overall rate of death or with four or five, 2.8%; and those with six or more, 3.8%.64
    • © 2004 WebMD, Inc. All rights reserved. ACS Surgery: Principles and Practice 6 VASCULAR SYSTEM 2 ASYMPTOMATIC CAROTID BRUIT — 6 Obesity is another risk factor for stroke.49,50 Some 60% of pa- Table 5 Cardiac Risk Assessment* tients who experience a stroke before 65 years of age have a body mass index greater than 24 kg/m2.49 This finding, in conjunction Weighted Score on Cardiac Risk Index with a history of smoking, was found to predict 60% of strokes in Parameter men in this age group.50 Goldman Detsky Eagle Patients with carotid bruits who do not have significant systemic Age > 70 yr 5 5 1 risk factors or other vascular disease are at low absolute risk for stroke and are unlikely to benefit from carotid endarterectomy; MI 1 hence, further investigation is not warranted.5,18,49 Patients with nu- < 6 mo 10 10 merous (i.e., six or more) clinical risk factors [see Table 7] are at rela- > 6 mo 5 tively high risk for stroke, and it is in this population that most of the Angina 1 benefit from carotid endarterectomy is likely to be concentrated. Class III 10 Class IV 20 Patient Preference for Surgical Unstable 10 Intervention Diabetes 1 Before pursuing the diagno- sis of carotid stenosis with im- Operation Emergency 4 10 aging techniques, the surgeon Aortic, abdominal, or thoracic 3 must discuss prophylactic sur- gical intervention with the pa- CHF 11 1 tient. The essential question is, < 1 wk 10 if significant stenosis is docu- > 1 wk 5 mented, will the patient wish to undergo carotid endarterectomy? ECG It should be remembered that at this point in the workup, we are Rhythm other than sinus 7 5 considering only those patients (1) for whom the cardiac risk > 5 PVCs/min 7 5 associated with the procedure is acceptably low and (2) who are Poor medical status† 3 5 considered to be at relatively high risk for stroke if carotid steno- sis is demonstrated. Risk of Perioperative Cardiac Events Patients should be informed that if they are found to have signifi- cant carotid stenosis, their risk of stroke is 6.3% over the ensuing Low 0–12 (class I, II) 0–15 0 2.7 years if they do not undergo operation and 4.0% over the same Intermediate 13–25 (class III) 16–30 1–2 period if they do.15 They should also be informed that these figures High > 25 (class IV) > 30 ≥3 take into account a 3% risk of perioperative stroke or death (2.7% *The Goldman cardiac risk index53 is a multifactorial index of cardiac risk in patients under- risk of stroke and 0.3% risk of death).15 The 2.3% absolute risk re- going noncardiac surgery. Modifications have been proposed by Detsky,121-123 who includ- duction associated with surgical treatment translates into an NNT ed angina and institution-specific perioperative cardiac event rates in the model. The Eagle index124-126 is another risk index based on five clinical variables. Despite the lack of con- of 43, meaning that 43 patients would have to undergo endarterec- sensus regarding the relative merits of these tools for preoperative cardiac risk assessment, stratification of patients into risk categories is helpful in assessing the risk and benefits of a tomy to prevent one stroke over the next 2.7 years. procedure such as carotid endarterectomy. Given the front-loaded risks of surgery, some patients will prefer † PaO2 < 60 mm Hg; PaCO2 > 50 mm Hg; K+ < 3 mmol/L; serum HCO3 < 20 mmol/L; serum urea > 18 mmol/L; creatinine > 260 µmol/L; abnormal ALT; signs of chronic liver disease; a simple risk-modification strategy to a strategy including both risk bedridden from cardiac causes. modification and surgical intervention. In such cases, carotid imag- CHF—congestive heart failure MI—myocardial infarction PVC—premature ventricular contraction ing is not necessary, because knowledge of the degree of stenosis will not affect subsequent management. than 50% stenosis (determined by means of angiography, the gold standard), DUS had a sensitivity of 91% (95% CI, 89 to 94) and a Investigative Studies specificity of 93% (95% CI, 88 to 95).67 Given a disease prevalence The purpose of investigation of approximately 41% in patients referred for DUS, these findings of asymptomatic neck bruits is to translate into a positive predictive value of 90% and an accuracy of identify persons with significant 92%.67 A subsequent prospective study of patients (both sympto- carotid stenosis who are at in- matic and asymptomatic) in whom carotid endarterectomy was being creased risk for cerebrovascular considered reported a sensitivity of 100% and a specificity of 98% for disease65,66 and who are likely to greater than 60% stenosis, with a positive predictive value of 99%.68 benefit from carotid endarterec- At centers where DUS has been internally validated in com- tomy. In the absence of other sig- parison with angiography and where this level of performance nificant findings, cervical bruits are not sufficiently predictive of sig- has been documented, the surgeons may choose to proceed to nificant carotid stenosis or ischemic stroke to be useful in selecting surgery without angiography.68-70 At centers where DUS is less candidates for noninvasive imaging.51 Noninvasive testing is a rea- reliable, however, it should be regarded as a screening test, and sonable step in patients with the characteristics listed above, but angiography should be performed when DUS suggests greater routine screening of all patients with asymptomatic carotid bruits is than 50% stenosis. not warranted.51 CAROTID ANGIOGRAPHY DUPLEX ULTRASONOGRAPHY As an invasive procedure, carotid angiography carries a significant Duplex ultrasonography (DUS) should be performed bilaterally.A risk of morbidity and mortality. All centers performing carotid an- meta-analysis conducted in 1995 found that for detecting greater giography for cerebrovascular disease should audit their stroke rates
    • © 2004 WebMD, Inc. All rights reserved. ACS Surgery: Principles and Practice 6 VASCULAR SYSTEM 2 ASYMPTOMATIC CAROTID BRUIT — 7 Table 6 Conversion between Different Methods of Measuring Degree of Carotid Stenosis Severity of Disease Method Minimal Moderate Severe Occlusion ECST* 24%–57% 58%–69% 70%–81% 82%–99% 100% NASCET 0%–29% 30%–49% 50%–69% 70%–99% 100% † CC method 35%–56% 57%–61% 62%–80% 81%–99% 100% *Conversion from ECST to NASCET was done according to the following formula: ECST % stenosis = 0.6(NASCET % stenosis) + 40.127 † The relation of the NASCET method to the CC method is linear, with a ratio of 0.62 between the distal internal carotid diameter and the common carotid diameter.117 periodically. Since 1990, four prospective studies71-74 have addressed greater degrees of stenosis would be associated with greater risk of the question of the risks associated with angiography in patients with stroke.This finding may be explained either by the fact that duplex atherosclerotic cerebrovascular disease. When the data from these ultrasound was the sole imaging criterion or that plaque morpholo- studies were pooled, the risk of permanent neurologic deficit or death gy plays a greater role in determining stroke risk than degree of ste- was 1.1% (95% CI, 0.6 to 2.0).75 In ACAS, the 1.2% of patients in nosis. Furthermore, unlike previous studies, many of the patients in the intervention arm who experienced stroke or died after angiogra- the ACST were receiving lipid-lowering drugs and other antiplatelet phy accounted for 40% of the strokes and deaths attributable to sur- agents. As Barnett pointed out in his discussion of the ACST article, gical intervention.15 Angiographic complication rates significantly the perioperative stroke rate must be low for the results of this study worse than these will adversely impact the risk-benefit ratio associat- to be generalized.81 In the ACST, the risk of stroke or death within ed with surgical intervention. Centers that consistently record rela- 30 days of undergoing carotid endarterectomy was 3.1%. tively high angiographic complication rates should not offer evalua- Technical details of carotid endarterectomy are discussed else- tion for and surgical treatment of asymptomatic carotid disease. where [see 6:9 Surgical Treatment of Carotid Artery Disease]. PATIENT EDUCATION Management All patients with asymptomatic carotid bruits, whether they are CAROTID ENDARTERECTOMY undergoing prophylactic endarterectomy or not, should be carefully At this point in management, it is reasonable to offer surgical treat- advised regarding the symptoms and signs of stroke, TIAs, and ment of asymptomatic disease to patients with greater than 50% ste- amaurosis fugax and should be strongly encouraged to seek urgent nosis. ACAS15 and two meta-analyses45,46 that included other trials of medical attention if such problems arise. Patients who experience surgical therapy for asymptomatic carotid stenosis documented a one of these untoward events should undergo full reevaluation for small and marginally statistically significant benefit from prophylactic stroke risk factors (e.g., hypertension, hyperlipidemia, diabetes, smok- carotid endarterectomy in asymptomatic patients with greater than ing, and atrial fibrillation); in the absence of atrial fibrillation (which 50% to 60% carotid stenosis. Because the absolute benefit is small, we do not consider it obligatory to pursue the diagnosis or to follow Internal an invasive strategy in patients identified solely on the basis of an Carotid Artery asymptomatic bruit; however, patients possessing all the characteris- External Carotid Artery tics listed earlier [see Indications for Surgical Intervention, above] probably constitute a group that is particularly able to benefit from B surgical intervention. Patients with higher degrees of stenosis are at higher risk for stroke and are therefore most likely to benefit.76-79 The degree of stenosis and the presence or absence of plaque ul- ECST Method ceration may modify the final decision for or against operative man- C–A x 100% Stenosis agement [see Discussion, Subgroup Analyses for Potential High- C A Risk Factors, below]. In May 2004, the United Kingdom Medical Research Council C NASCET Method Asymptomatic Carotid Surgery Trial (ACST) collaborative group B–A x 100% Stenosis reported the results of a prospective, randomized trial of carotid B endarterectomy in asymptomatic patients.80 More than 3,000 pa- tients were randomly assigned either to undergo immediate carotid D CC Method endarterectomy or to be placed on indefinite deferral. In the patients D–A referred for immediate carotid endarterectomy, one half underwent D x 100% Stenosis endarterectomy within 1 month of referral; 88% underwent endar- terectomy within 1 year. Combining the rate of perioperative events Common Carotid Artery and nonperioperative strokes, the 5-year results indicate a stroke rate of 6.4% in the group undergoing immediate carotid endarterecto- Figure 1 Carotid angiography remains the gold standard for de- my, as compared with 11.8% in the deferral group.These findings termining the extent of carotid arterial disease. Several methods are strikingly similar to the ACAS findings. However, the ACST of reporting angiographically defined stenosis have been described found a similar benefit for women. In addition, in the ACST, no dif- in the literature.115 The most commonly used methods are those ference was found in the degree of stenosis and the benefit of adopted by the NASCET and ECST investigators, though the so- surgery—an interesting observation, because one would expect that called common carotid (CC) method has its advocates as well.116,117
    • © 2004 WebMD, Inc. All rights reserved. ACS Surgery: Principles and Practice 6 VASCULAR SYSTEM 2 ASYMPTOMATIC CAROTID BRUIT — 8 ter a stroke.75 Performing endarterectomy early reduces the risk pe- Table 7 Risk Factors for Stroke128,129 riod for recurrent stroke and may therefore increase the potential benefit of the intervention; the usual approach is to perform the Age > 70 yr Smoking (or history of smoking) procedure within a week or two of a patient’s first neurologic event. Male sex > 80% carotid stenosis Management of cardiovascular risk factors and concurrent vascu- Hypertension* Presence of ulceration lar disease should continue. In the absence of concurrent vascular Hyperlipidemia Ischemic heart disease† disease, patients may be referred back to the family practitioner, in- Diabetes Peripheral vascular disease ternist, or cardiologist in place of specific surgical follow-up. *Defined as systolic BP > 160 mm Hg or diastolic BP > 90 mm Hg. † MI or CHF. FOLLOW-UP OF PATIENTS WITH LOWER-GRADE STENOSIS Carotid stenosis progresses in about one quarter of patients with asymptomatic carotid stenosis monitored with DUS over a 2-year should prompt consideration of prophylactic anticoagulation82-84), a period.87 In a population of asymptomatic patients with bruits who change in antiplatelet therapy should be considered. Both ticlopi- were referred to a vascular laboratory, 282 stenotic carotid arteries dine85 and clopidogrel86 are more effective than aspirin in preventing (average stenosis, 50%) were followed for 38 ± 18 months. Progres- stroke. (Ticlopidine is associated with reversible but severe neutro- sion of stenosis, defined as an increase in degree of stenosis to 80% penia in fewer than 1% of cases; accordingly, monitoring for this or beyond, occurred in 17% of arteries, and 2% became complete- complication is indicated.) ly occluded. Progression was associated with an increase in stroke If a patient who is a surgical candidate experiences a TIA or risk of 4.9% at 1 year, 16.7% at 3 years, and 26.5% at 5 years. In stroke as a result of an ischemic event in the carotid region in the comparison, the estimated stroke risk in an asymptomatic popula- absence of atrial fibrillation, he or she must be promptly referred tion of patients with 50% to 79% stenosis was 0.85%, 3.6%, and back to the vascular surgeon.This possibility should be clearly ex- 5.4% for the same three periods (P = 0.001).76 plained to patients once the initial evaluation is complete and they Although carotid stenosis, once identified, tends to progress over have been referred back to their primary care physicians. Patients time,20,54,76,88 the data are currently insufficient to permit recommenda- referred back to a vascular surgeon under these circumstances tion of routine ultrasonographic or other surveillance for all patients should then be regarded as having symptomatic carotid disease. A with neck bruits outside a research setting. In our view, reevaluation subgroup analysis of patients with symptomatic stenosis reported every 1 to 2 years with noninvasive diagnostic tests is a reasonable ap- that carotid endarterectomy performed soon after a nondisabling proach to patients (1) who are already known to have greater than 50% stroke was not associated with a significantly higher operative com- stenosis, (2) who do not undergo surgery, and (3) who are at high risk plication rate than endarterectomy performed 30 days or longer af- for stroke, are surgical candidates, and are not averse to surgery. Discussion Epidemiology Economic Considerations In cross-sectional and population-based studies, the overall prev- A cogent argument in favor of pursuing a surgical strategy in at alence of greater than 75% carotid stenosis has been low. A 1992 least some patients was made by a 1997 economic analysis,90 which study reported a 2.3% prevalence in men and a 1.1% prevalence in demonstrated that although prophylactic endarterectomy in patients women; there was a significant (P < 0.0001) increase with age with with asymptomatic carotid stenosis did not reduce societal costs ap- each decade from 65 years to beyond 85 years, but there were no preciably, it was nonetheless, at a cost of $8,000/quality-adjusted life significant differences between men and women.62 In the Framing- year (QALY), within the range of many interventions considered by ham study population, the incidence of greater than 50% stenosis society to be cost-effective. It should be pointed out, however, that was 8% (95% CI, 6.5 to 9.8).61 In a study of healthy volunteers, the this economic analysis addressed only carotid endarterectomy in pa- incidence of greater than 50% stenosis was 5.1% (95% CI, 2.6 to tients with identified carotid stenosis, not screening strategies for pa- 9.0) in patients 70 years of age or older and 1.5% (95% CI, 0.2 to tients with bruits, and consequently did not consider costs associat- 5.3) in younger patients.89 ed with investigation and follow-up to the point of recommendation The pooled risk of greater than 60% to 75% stenosis in patients for or against carotid endarterectomy in the broader group of pa- with carotid bruits referred for noninvasive vascular evaluation at an tients with bruits.These costs would alter the economic analysis sub- average age of 65 years is reported to be 21% (95% CI, 18 to 24),56-58 stantially, and if they are included, it is far from clear whether the re- which is three to four times the prevalence expected on the basis of sulting overall cost/QALY would still be acceptable.To date, no trial population-based studies.Thus, five persons with neck bruits must or economic analysis of a screening strategy has been published. be screened to detect one patient with moderate to severe carotid stenosis.The absolute benefit of surgery is small and of borderline Screening Issues statistical significance. In ACAS, as noted (see above), the relative risk reduction for an ipsilateral major stroke or perioperative death For the reasons previously discussed, we do not feel justified in over a 2.7-year period was 36.5% (95% CI, 27.5 to 47.1), the abso- recommending routine screening for patients with asymptomatic lute risk reduction was 2.3% (95% CI, 0.2 to 7.0), and the NNT carotid bruits. Given the available evidence, we believe that such pa- was 43 (95% CI, 14 to 500); the number of patients that would have tients may reasonably be managed in either of two ways. One to be screened with DUS to prevent one stroke over a 3-year follow- choice is simply to conclude that screening patients with carotid up period was 250 (95% CI, 70 to 2,500). bruits as possible candidates for carotid endarterectomy has not
    • © 2004 WebMD, Inc. All rights reserved. ACS Surgery: Principles and Practice 6 VASCULAR SYSTEM 2 ASYMPTOMATIC CAROTID BRUIT — 9 PLAQUE ULCERATION AND PLAQUE STRUCTURE been proved to be a useful intervention and to concentrate instead on general vascular risk reduction.The other, which is appropriate At present, there are no subgroup analyses examining the effect in centers where noninvasive or invasive diagnostic tests reach ac- of plaque ulceration on the ability of asymptomatic patients to ben- ceptable standards with an acceptable degree of risk and where the efit from surgical treatment. In NASCET, however, when sympto- procedure is done by surgeons whose documented perioperative matic patients with 70% to 99% stenosis were considered, those stroke and death rates are less than 3%, is to take a selective ap- with angiographic evidence of plaque ulceration were at higher risk proach that addresses various issues related to stroke risk, cardiac for stroke than those without ulceration92 and derived greater bene- risk, and patient preferences before noninvasive tests are ordered. fit from surgery.75 Angiography had a sensitivity of 46% and a speci- ficity of 74% in the detection of ulcerated plaques, with a positive predictive value of 72%.93 A 1994 study reported that when ulcera- Subgroup Analyses for Potential High-Risk Factors tion was detected with B-mode imaging in patients with asympto- Given the small absolute risk reduction reported by ACAS15 matic carotid stenosis, the incidence of silent cerebral infarction de- and by the two meta-analyses of all asymptomatic carotid stenosis tected by magnetic resonance imaging was 75%, compared with an trials,45,46 it would be useful to be able to identify one or more incidence of 25% when ulceration was absent.94 high-risk groups within the broader group of patients identified as It has also been suggested that carotid plaques of differing struc- having stenosis. tures may have differing embolic potentials.95 DUS can distinguish between fibrous plaques (which are highly echogenic) and plaques SEX with high concentrations of lipid and necrotic material (which are ACAS included a subgroup analysis addressing the effect of sex echolucent). Echolucent plaques are more frequently associated on ability to benefit from surgery: the absolute reduction in the risk with neurologic symptoms and computed tomography–proven ce- of perioperative stroke or death or ipsilateral stroke at 2.7 years was rebral infarction.95-97 Interobserver reliability for plaque echostruc- 3.6% (95% CI, 1.1 to 9.9) for men and 0.5% (95% CI, 0.01 to 2.7) ture, however, seems to be highly variable, ranging from good (κ = for women. 0.79) for greater than 70% stenosis95 to average (κ = 0.51) for greater than 40% stenosis98 to poor (κ = 0.29) for greater than 80% DEGREE OF STENOSIS stenosis.99 A 1994 report found no correlation between the pres- In asymptomatic patients stratified according to their ultrasono- ence or type of symptoms and plaque structure as determined by graphically determined degree of stenosis, the risk of stroke is low DUS.100 The true importance of carotid plaque echomorphology both for patients with less than 30% stenosis (4% cumulative event and surface characteristics as predictors of cerebrovascular events rate at 3 years) and for those with 30% to 74% stenosis (9% cumu- remains to be defined. lative event rate at 3 years); it is highest for those with greater than CONTRALATERAL DISEASE 75% stenosis (21% cumulative event rate at 3 years).20 The Euro- pean Carotid Surgery Trialists (ECST) study,47 using angiographic It has been suggested that the presence of contralateral carotid dis- data from the asymptomatic carotid arteries of 2,295 patients, re- ease is a risk factor for future cerebrovascular events. In NASCET pa- ported that the Kaplan-Meyer estimate of stroke risk at 3 years was tients with greater than 70% stenosis,101 contralateral occlusion signif- only 2% and remained low (< 2%) when patients with less than icantly increased the benefit of surgery with respect to the incidence 79% stenosis were considered; stroke risk increased to 9.8% for pa- of stroke or death, but contralateral high-grade stenosis did not.75 tients with 70% to 79% stenosis and to 14.4% for those with 80% ASYMPTOMATIC CEREBRAL INFARCTION to 99% stenosis. In a population of patients referred to a vascular laboratory with asymptomatic carotid stenosis on DUS who were The presence of areas of asymptomatic cerebral infarction ipsilat- followed for a mean of 38 months, the incidence of stroke was 2.1% eral to the area of carotid stenosis on head CT may identify patients in patients with 50% to 79% stenosis and 10.4% in those with great- who would benefit from surgery.102 In asymptomatic patients with er than 80% stenosis.76 carotid stenosis, the incidence of silent strokes demonstrated by CT In ACAS, there were too few strokes to permit subgroup analysis has been reported to be 10% in patients with 35% to 50% stenosis of the effect of degree of stenosis on ability to benefit from carotid on DUS, 17% in those with 50% to 75% stenosis, and 30% in endarterectomy. In both ECST79 and NASCET,75,77,78,91 however, those with greater than 75% stenosis.103 The incidence of silent higher degrees of stenosis in symptomatic patients were consistent- cerebral infarctions demonstrated by MRI in the same type of pop- ly observed to be associated with higher stroke risk as well as with ulation has been reported to be 42%, increasing to 75% for greater greater ability to benefit from surgical treatment [see Table 8]. than 50% stenosis.94 Use of CT and MRI of the brain in risk strati- Table 8 Effectiveness of Surgery by Degree of Stenosis in Patients with Symptomatic Carotid Stenosis75 Degree Relative Risk Reduction Absolute Risk Reduction Number Needed to Treat of Stenosis or Increase or Increase or Harm 70%–99% RRR, 48% (95% CI, 27–63) ARR, 6.7% (95% CI, 3.2–10) NNT, 15 (95% CI, 10–31) 50%–69% RRR, 27% (95% CI, 5–44) ARR, 4.7% (95% CI, 0.8–8.7) NNT, 21 (95% CI, 11–125) ≤ 49% RRI, 20% (95% CI, 0–44) ARI, 2.2% (95% CI, 0–4.4) NNH, 45 (95% CI, 22–∝) ARI—absolute risk increase ARR—absolute risk reduction NNH—number needed to harm NNT—number needed to treat RRI—relative risk increase RRR—relative risk reduction
    • © 2004 WebMD, Inc. All rights reserved. ACS Surgery: Principles and Practice 6 VASCULAR SYSTEM 2 ASYMPTOMATIC CAROTID BRUIT — 10 fication of patients with asymptomatic carotid stenosis is controver- CI, 2.1 to 4.5), the MI rate is 5.2% (95% CI, 3.6 to 6.9)—a non- sial and currently is not advised. significant increase—and the mortality is 4.7% (95% CI, 3.4 to 6.4).109 For cohorts in which CABG was done first and carotid ste- CONCLUSIONS nosis was treated on its own after the cardiac procedure, the stroke Although only limited data on patients with asymptomatic steno- rate is 3.5% (95% CI, 1.0 to 9.0), the MI rate is 2% (95% CI, 0.2 to sis are available, we believe that consideration of sex, degree of steno- 6.0), and the mortality is 0.8% (95% CI, 0.02 to 4.8).110-112 sis, and possibly the presence of plaque ulceration may be helpful in We recommend against a combined surgical approach in patients making the final decision on whether to offer carotid endarterecto- with asymptomatic carotid stenosis. Given the equivalent stroke rate my to these patients; at present, plaque morphology is insufficiently and the lower MI rate and mortality, we believe that the preferred reliable to be a useful guide to clinical management. strategy in patients with bruits is first to proceed with CABG if indi- cated and then to determine whether the patient should be further Special Situations evaluated as a candidate for carotid endarterectomy in the same manner as other elective patients would be. RESTENOSIS OR PREVIOUS CAROTID SURGERY Patients who have previously undergone carotid surgery have Effect of Center-Specific Variations on Risk-to-Benefit Ratio been excluded from most studies of asymptomatic patients; when they have been included in trials addressing symptomatic stenosis, In ACAS, 1.2% of the overall 2.7% perioperative stroke rate was they have experienced increased rates of perioperative complica- accounted for by strokes occurring after angiography. Centers where tions.16,50 Patients in whom restenosis occurs after an earlier carot- ultrasonography has been documented to have high predictive val- id endarterectomy should be advised against surgery while they ues may avoid this risk by proceeding directly from ultrasonography remain asymptomatic.15 It is therefore unnecessary to follow pa- to surgery. If these complications had been avoided in ACAS, the tients with ultrasonography after carotid endarterectomy if no absolute risk reduction would have been more substantial: 3.43% symptoms develop. (95% CI, 1.1 to 9.9), corresponding to an NNT of 29 (95% CI, 1 to 80). The true perioperative combined stroke and death rate PREOPERATIVE ASSESSMENT FOR CORONARY ARTERY BYPASS achieved in this study was 1.5%, a result that is definitive of excel- GRAFTING lence in the surgical management of carotid endarterectomy and Some 20% to 30% of patients undergoing assessment for CABG that constitutes a useful quality assurance measure for centers and are found to have carotid bruits,49,104 and 5% to 20% have greater individual surgeons. than 50% stenosis on DUS105-107 or ocular plethysmography.108 In asymptomatic patients with carotid stenosis who are undergoing Issues for the Future CABG, there is no direct evidence favoring prophylactic carotid endarterectomy either before or in conjunction with CABG. Co- It is possible, perhaps likely, that in the future, magnetic reso- hort studies including symptomatic and asymptomatic carotid ste- nance angiography67 and three-dimensional CT angiography,113,114 nosis indicate that patients undergoing CABG and carotid endarter- together with DUS, will replace angiography as preferred imaging ectomy in the same operation have a stroke rate of 6% (95% CI, 4.6 methods for diagnosing internal carotid artery stenosis. As for surgi- to 7.8), an MI rate of 4.6% (95% CI, 3.1 to 6.5), and a mortality of cal treatment and screening, further data on patients with asympto- 4.7% (95% CI, 3.4 to 6.4).109 For cohorts in which carotid endarter- matic carotid stenosis are necessary before definitive recommenda- ectomy was performed before CABG, the stroke rate is 3.2% (95% tions can be made. References 1. Chambers BR, Norris JW: Clinical significance of Cerebrovascular Diseases III. 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Eliasziw M, Smith RF, Singh N, et al: Further com- tients with symptomatic severe carotid stenosis and ments on the measurement of carotid stenosis from contralateral carotid stenosis or occlusion: results angiograms. North American Symptomatic Carotid Acknowledgment from nascet. North American Symptomatic Carotid Endarterectomy Trial (NASCET) group. Stroke Endarterectomy Trial (NASCET) group. J Neuro- 25:2445, 1994 Figure 1 Laurie Grace.