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Predictive Power of Duplex Ultrasonography in Asymptomatic Carotid Disease

Rosamund F. Lewis, MD, MSc; Michal Abrahamowicz, PhD; Robert Cote, MD; and Renaldo N. Battista, MD, ScD
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From McGill University and The Montreal General Hospital, Montreal, Quebec, Canada. Acknowledgment: The authors thank Xiaoming Tang, MSc, for assistance with data analysis. Grant Support: In part by grant OGP-0105521 from the Natural Sciences and Engineering Research Council of Canada. The Asymptomatic Carotid Bruit Study was funded by grant 6605-2761-52 from the National Health and Research Development Program. Requests for Reprints: Michal Abrahamowicz, PhD, Division of Clinical Epidemiology, The Montreal General Hospital, 1650 Cedar Avenue, Montreal, Quebec H3G 1A4, Canada. Current Author Addresses: Dr. Lewis: Epicentre, Groupe europeen d'expertise en epidemiologie pratique, 8, rue Saint Sabin, 75011 Paris, France.


Copyright ©2004 by the American College of Physicians


Ann Intern Med. 1997;127(1):13-20. doi:10.7326/0003-4819-127-1-199707010-00003
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Background: Duplex ultrasonography is considered a valid measure of stenosis of the carotid arteries, but the prognostic value of repeated ultrasonographic examinations is unknown.

Objective: To determine the ability of serial ultrasonographic measurements to predict cerebrovascular events in patients with asymptomatic carotid disease.

Design: Secondary analysis of data from a natural history study of asymptomatic carotid disease.

Patients: Asymptomatic patients with cervical bruits.

Measurements: Duplex ultrasonography of the carotid arteries was done at study enrollment and biannually thereafter. Multivariable Cox proportional-hazards models with fixed and time-dependent covariates were used for analysis.

Results: 61 transient ischemic attacks (TIAs) and 38 strokes occurred in 715 participants over a mean follow-up period of 3.2 years; 4 strokes were disabling, and no deaths from stroke occurred. Sixty percent of strokes occurred in persons who did not have severe stenosis. One fifth of participants had stenosis progression. Baseline carotid stenosis was a significant predictor of the outcome “TIA or stroke” (relative risk, 1.5 [95% CI, 1.2 to 1.7]) and retained its predictive ability for more than 3 years. Progression of stenosis to 80% or more significantly increased the risk for cerebrovascular events and death. The sensitivity and positive predictive value of progression as an independent predictor of TIA or stroke were low.

Conclusion: Severe carotid stenosis is associated with a higher risk for cerebrovascular events, but the power of repeated ultrasonography to predict ischemic events is limited by low incidence rates and low rates of progression. The evidence does not support the routine use of serial ultrasonography to determine the risk for stroke in unselected patients with asymptomatic carotid disease.

Figures

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Figure 1.
Probability of remaining free of transient ischemic attack (TIA) or stroke.

Univariate Kaplan-Meier estimates of the probability of remaining free of TIA or stroke for each of six categories of initial maximum stenosis are shown. Numbers below the x-axis are numbers of patients at risk in each category (category A = no occlusion; category B = stenosis of 1% to 15%; category C = stenosis of 16% to 49%; category D = stenosis of 50% to 79%; category E = stenosis of 80% to 99%; and category F = complete occlusion) in years 0, 1, 3, and 5.

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Figure 2.
Predictive ability of the initial stenosis category over time.

The solid curve (hazard ratio) is the estimated relative risk over time, adjusted for baseline risk factors (age, sex, heart disease, hypertension, hyperlipidemia, diabetes, claudication, smoking, and use of aspirin), for transient ischemic attack (TIA) or stroke associated with an increase in baseline stenosis by one category compared with other patients. Dotted curves indicate the 95% Cls for the relative risk. The dashed horizontal line represents a reiative risk of 1.0, corresponding to equal risk in all groups. Areas below this line represent risk reduction; areas above this line represent increases in risk.

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