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Carotid Bruits: David L. Simel, MD, MHS, discusses the clinical examination for carotid bruits.
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Carotid Bruits: David L. Simel, MD, MHS, discusses the clinical examination for carotid bruits.
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Upload Date:
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Language: EN.
Segment:0 .
>> I'm Joan Stephenson, Editor of JAMA's Medical News and Perspectives Section. Today, I have the pleasure of once again speaking with Dr. David Simel. This time, on the topic of carotid bruits, which is discussed in Chapter 9 of the Rational Clinical Exam which is co-authored by Dr. Simel. Dr. Simel, why don't you introduce yourself to our listeners? >> Yes, I'm the Editor of the Rational Clinical Examination Series. And I'm a General Internist based at the Durham Veterans Affairs Medical Center in Duke University.
>> Dr. Simel, what is the prevalence of carotid artery bruits in the general population? >> Well, the prevalence varies by ages. So, we need to consider a broad range of probabilities. But in patients 50 years or older, the probability varies from about 0.05 to 1% at that lower end of the range, up to say about the 90-year-old patient where the prevalence can be as much as 10%. >> What's the best way for a clinician to hear a carotid bruit in the clinical setting?
>> Well, the first thing you need to do before you listen for the bruit is to consider whether or not the patient is an asymptomatic or a symptomatic patient. And the symptoms we are referring to are those of a transient ischemic attack or the symptoms in which a patient has already had a stroke. So, once we've considered whether we're dealing with the asymptomatic or symptomatic patient and decide to listen for a bruit, we place either the diaphragm or the bell of the stethoscope over the course of the carotid in an area just behind the upper end of the thyroid cartilage to just below the angle of the jaw.
Now, there are not methods that have been studied that show any one approach is better than any other. The bruits are typically heard during systole. So, some listeners might also palpate the radial artery for timing. Sometimes the examiner will mistake a referred systolic heart murmur for a bruit. But by marching down the neck towards the precordium with the stethoscope, the heart murmur will usually be heard during the entire course and will be loudest over the precordium.
>> If a clinician discovers an asymptomatic carotid bruit in an adult patient, what are the implications? >> Well, we found only two studies that totaled 275 asymptomatic patients, that it allowed us to determine the likelihood ratios for the presence or absence of a bruit. And in those two studies, the presence of a bruit had a likelihood ratio of 6. So, in other words, those patients would be 6 times as likely as the average risk patient to have carotid stenosis.
While the absence of a bruit had a likelihood ratio of 0.45. So, the absence of a bruit decreases the likelihood by about a half. However, we only had two studies, and these didn't include as many patients as we would have liked to make this assessment. So, what we did in our review was we looked for studies of the predictive value of a bruit. Now, the predictive value tells us the percentage of patients with a bruit who will prove to have a carotid stenosis.
And in the three studies we found of predictive value, the result was that about 22% of 1,300 patients with an asymptomatic bruit had a carotid stenosis. Now, the problem with those data is that the predictive value depends on the prevalence of disease. So, a listener to this podcast couldn't assume or shouldn't assume that their patient will automatically have a 22% probability of carotid stenosis just because they've heard a bruit.
So, we had to do some back-calculations. And what we were able to deduce is that across a range of prior probabilities of carotid stenosis of say 3 to 8%, which would be the prior probability in the appropriate age range where you would be considering carotid stenosis, the likelihood ratio for the presence of a bruit ranges from 4 to 10. Which confirmed the results of the two studies with complete data. >> To what likelihood does the presence or absence of a carotid bruit reflect the likelihood that the symptomatic patient has carotid stenosis?
>> So, in the symptomatic patient, we're now dealing with a different situation. And what we would like to decide in the symptomatic patient is whether or not that patient might be an appropriate patient for whom carotid endarterectomy is a viable option based on their age and overall surgical risk. And in those patients for whom a carotid endarterectomy could be considered, about 10 to 30% of the symptomatic patients will have a surgically amenable carotid stenosis.
Now, the presence of a bruit in a symptomatic patient has a much better specificity than sensitivity. And that means that the presence of a bruit is useful in identifying patients most likely to have a carotid stenosis. However, because of the relatively low sensitivity, the absence of a bruit in the symptomatic patient does not allow us to rule out stenosis. So, that creates a problem. Now, from three studies that included almost 2,300 symptomatic patients, the presence of a bruit has a likelihood ratio of 3.
So, those patients will be about 3 times as likely to have a carotid stenosis. And the likelihood ratio negative was 0.49. So, a decreased likelihood. But these are results not just for any stenosis, but for a stenosis of 70 to 99%. Now, that 70 to 99% stenosis range is important because that is a range where you might consider your patient for an endarterectomy. So, among symptomatic patients, the presence of a bruit makes them 3 times more likely to have a significant carotid stenosis.
Now, one could easily argue that the presence of a bruit in the symptomatic patients may not matter since you are most likely going to do a noninvasive test for a carotid stenosis, no matter what. >> Is there anything else you would like to tell our listeners about the clinical examination for carotid bruits? >> Well, yes. It's important to recognize that the diagnostic value of a bruit increases as the prior probability of a stenosis decreases. Now, that may seem counterintuitive at first.
But in mathematical terms, that means the positive likelihood ratio is higher in the low probability setting than it is in the high probability setting. So, one might infer that we should be listening for carotid bruits in the low-risk older patients. However, in a 2007 update to screening for a carotid stenosis, the U.S. Preventive Services Task Force reviewed carotid ultrasound in asymptomatic patients, or a low-risk population group, and they recommended against screening the general population for carotid artery stenosis.
Now, since ultrasound is certainly more sensitive and specific for significant carotid stenosis than the physical examination finding of a bruit. It stands to reason that the Preventive Services Task Force would also recommend that we stop listening for bruits in asymptomatic patients. Now, for many physicians, that can be a hard habit to break, and bruits will continue to be detected for a variety of reasons. I should note that there is uncertainty about what to do on finding a bruit because the studies used in current reviews were done before less invasive approaches to stenosis repair.
So, we will need to wait for studies that evaluate carotid stents to know if auscultating for bruits plays an important role in current approaches to the patient. Now, another thing that is interesting is that for those who have followed developments in evidence-based medicine, this clinical topic of carotid bruits is a really important one for the emergence of diagnostic effectiveness studies. And it highlights that just because we have tests that may identify patients more likely to have a condition, it doesn't mean we should necessarily use that test, in this case, auscultation for a carotid bruit.
For now, there seems to be some continuing gaps in our knowledge to know whether screening asymptomatic patients provides an important clinical benefit. >> Thank you, Dr. Simel, for this helpful look at carotid bruits. For additional information about this topic, JAMAevidence subscribers can consult Chapter 9 of the Rational Clinical Exam. This has been Joan Stephenson of JAMA, talking with Dr. David Simel for JAMAevidence.
