Circ: Carotid imaging skyrockets across modalities

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CT images in 89-year-old woman with admission NIHSS score of 18 obtained 133 minutes after stroke.

Carotid imaging in a sample of Medicare beneficiaries rose by more than 25 percent between 2001 and 2006, with large variations occurring by geography and race, indicating a need for appropriate use guidelines, a study published online Oct. 12 in Circulation: Cardiovascular Quality and Outcomes concluded.

"Routine screening for carotid atherosclerosis is not recommended in asymptomatic patients because fewer than 1 percent are likely to have clinically important atherosclerosis. ... [T]he risk of complications outweighs the benefits," Lesley H. Curtis, PhD, of Duke University School of Medicine in Durham, N.C., and co-authors wrote. Curtis and colleagues sought to investigate recent trends in carotid imaging in Medicare beneficiaries, controlling for geography and race and specifically considering cost implications.

The authors looked at a nationwide sample of 5 percent of Medicare beneficiaries, ages 65 years and over, which totaled approximately 1.4 million individuals per year. The researchers investigated the incidence of carotid imaging using ultrasound, MR angiography (MRA) and X-ray angiography, as well carotid intervention rates, in the total sample and by geography, race and history of vascular disease.

Carotid imaging rates using ultrasound, MRA and x-ray angiography all increased during the study period, with a 27 percent cumulative growth in carotid imaging. MRA increased most rapidly over the period, growing by 66 percent, while carotid ultrasound remained the most common imaging modality with a rate of 124.3 per 1,000 person-years, which was calculated as the total days alive and enrolled in Medicare fee-for-service.

Despite these increases in carotid imaging, carotid intervention dropped by 13 percent over the same period. By 2006, the ratio of carotid interventions to carotid ultrasound had fallen from 1 in 24.7 in 2001 to 1 in 34.9, the authors observed. In the nearly half of beneficiaries with vascular disease, carotid imaging grew by 18 percent, from 193 per 1,000 person-years to 228 per 1,000 person-years. MRA grew by 56 percent in the vascular disease group.

The authors observed "substantial growth in carotid imaging in all geographic regions, but use of the three imaging modalities varied considerably by region." Ultrasound was the most common modality in all geographic regions; however, in 2006 its rate of use in the Middle Atlantic region (N.J, N.Y and Pa.) was 60 percent higher than in the Mountain and New England regions, the authors reported. The rate of carotid MRA in New England and the Middle Atlantic, on the other hand, was 64 percent higher than in the West North Central region (which includes six states).

Nationwide, black patients had 29 percent lower odds of receiving carotid ultrasound, 21 percent lower odds for MRA and 44 percent lower odds for undergoing x-ray angiography than nonwhites, the study revealed.

The authors postulated that more accessible and portable imaging devices were largely responsible for the increase in carotid imaging, while noting that imaging rates have increased dramatically outside of atherosclerosis testing. Curtis and colleagues also considered rising disease prevalence (vascular disease rose 9 percent in this sample) to contribute to increased imaging use, though they noted that there could exist a causal cycle of expanded imaging simply identifying more cases in addition to an actual growth in disease prevalence.

Commenting that the findings "support the possibility that carotid imaging has been underused in some groups of patients," particularly blacks, the authors concluded that "the observed geographic variation and increasing rates over time underscore the need for clear guidance regarding the appropriate use of carotid imaging."