Should You Order a Repeat Carotid Duplex Ultrasound?
Yes, you should order a repeat carotid duplex ultrasound now, as it is reasonable to perform annual surveillance imaging for your patient with 55% carotid stenosis detected over a year ago. 1
Guideline-Based Surveillance Recommendations
The ACC/AHA/ASA guidelines provide clear Class IIa recommendations (meaning it is reasonable to perform) for your exact clinical scenario:
Annual duplex ultrasonography is reasonable for patients with atherosclerosis who have had stenosis greater than 50% detected previously. 1 This applies directly to your patient with 55% stenosis.
The surveillance should be performed by a qualified technologist in a certified laboratory to ensure accuracy. 1
The primary purpose is to assess progression or regression of disease and response to therapeutic interventions (such as statin therapy, antiplatelet agents, and blood pressure control). 1
When Surveillance Intervals Can Be Extended
The guidelines acknowledge that once stability has been established over an extended period, longer intervals or termination of surveillance may be appropriate. 1 However, your patient has only had one imaging study over a year ago, so stability has not yet been established. You need at least one follow-up study to determine the trajectory of disease.
Additionally, surveillance modification is appropriate if the patient's candidacy for further intervention has changed (for example, if they develop severe comorbidities that would preclude revascularization). 1
Clinical Rationale for Surveillance at This Stenosis Level
Moderate stenosis (50-69%) warrants annual ultrasound surveillance according to appropriateness criteria. 2, 3
Research demonstrates that approximately 7% of patients with <60% stenosis progress to 60-99% stenosis over a mean follow-up of 18 months, and this progression is often asymptomatic. 4
Patients with initial peak systolic velocities ≥175 cm/s have significantly higher progression rates (26% vs 4%) and may warrant even more frequent surveillance at 6-month intervals. 4
The risk of stroke ipsilateral to moderate stenosis exists, and detecting progression to severe stenosis (≥70%) would change management, as revascularization becomes more strongly indicated at that threshold. 2
What to Do With the Results
If the repeat duplex shows:
Progression to ≥70% stenosis: Consider referral for revascularization evaluation (carotid endarterectomy or stenting), particularly if the patient remains a surgical candidate. 2
Stable 50-69% stenosis: Continue annual surveillance and optimize medical therapy. 2, 3
Regression to <50% stenosis: You may consider extending surveillance intervals or discontinuing routine imaging, though continued medical management remains essential. 2, 3
Any new neurological symptoms: Immediate additional imaging (potentially CTA or MRA) and urgent neurovascular consultation are warranted. 1
Critical Pitfalls to Avoid
Do not assume stability without follow-up imaging. Nearly half of patients with ≥50% carotid stenosis receive no imaging follow-up in real-world practice, which represents a quality gap. 5
Ensure the patient is on optimal medical therapy regardless of imaging findings: high-intensity statin, antiplatelet therapy (typically aspirin), blood pressure control, and smoking cessation if applicable. 2 Patients without imaging follow-up are less likely to be on statins (85% vs 94%). 5
Do not order catheter angiography as your next test; duplex ultrasound is the appropriate surveillance modality. 3, 6
Coordinate with the neurology team to ensure they are aware of the surveillance plan and that medical management is optimized. 2