Wide geographic variation was found in two procedures to prevent stroke from diseased carotid arteries, according to a government report.

In a study published last week and commissioned by the Agency for Healthcare Research and Quality (AHRQ), researchers examined all claims filed for Medicare beneficiaries who underwent the procedures, carotid endarterectomy and carotid stenting, between 2003 and 2006.

In carotid endarterectomy, doctors surgically remove plaque from diseased carotid arteries, the blood vessels that carry blood to the brain. Stenting involves inserting a wire mesh into the arteries to keep the blood flowing, and is used in patients deemed unfit for the other procedure, the report said. Stenting was approved by Medicare, only for high-risk patients, in 2004.

In the report, widespread regional variation with the procedures was found, with parts of the South and Midwest having the highest rates.

"The New England, Mountain, and Pacific regions tended to have the lowest rates of both procedures, whereas the East South Central, West South Central, East North Central, and West North Central regions tended to have higher rates of revascularization," said the report, led by Dr. Manesh R. Patel and based on Duke University research.

According to the report, there was nearly a sevenfold difference in carotid endarterectomy rates in the most recent years studied, 2005 and 2006, between the lowest rate and highest rate regions. Beaumont, Texas, with 5.5 per 1,000 person-years, was the highest, and Honolulu, Hawaii, with 0.8 per 1,000 person-years, was the lowest.

Variation also applied to the diagnostic imaging modality chosen by doctors to help diagnose blocked carotid arteries.

Prior to carotid endarterectomies, most patients, about one-third, had the procedure preceded by ultrasound and x-ray angiography, while 27 percent had ultrasound and magnetic resonance angiography.

Controversially, another 27 percent had the procedure done based on ultrasound alone. For stenting, about 10 percent had only ultrasound, the report said.

Relying only on ultrasound scans is tricky, the report said, as previous research has suggested it can misclassify up to 28 percent of patients.

Nonetheless, a recent survey of Canadian surgeons found one out of ten neurosurgeons, and about half of vascular surgeons, said ultrasound alone was sufficient for diagnosis.

"Our findings highlight the need for consensus regarding diagnostic imaging criteria for the identification and management of carotid artery disease," the authors write.

Other findings

Endarterectomy rates fell from 3.2 per 1,000 person-years in 2003 to 2.6 per 1,000 person-years in 2006, while stenting rates rose about a tenth of a percent, from 0.3 in 2005 to 0.4 in 2006.

Previously the estimated rate of carotid stenting, in 2003 and 2004 before Medicare coverage began, was 0.3 per 1,000, the report said.

"The similarly low rate of carotid stenting we observed is likely related to the fact that the CMS national coverage decision for carotid stenting was limited to patients at high surgical risk," the authors wrote.

Unsurprisingly, prior diagnosis of diseased arteries and having previous procedures increased the likelihood of getting treatment, the study found. More than two-thirds of those getting endarterectomy had a prior diagnosis of coronary artery disease, while 37 percent had peripheral vascular disease. About half had cerebrovascular disease. For stenting, two-thirds had a prior diagnosis of coronary artery disease; nearly half had a prior diagnosis of peripheral vascular disease, and 61 percent had cerebrovascualr disease. They were also likely to have had a previous endarterectomy.

Also unsurprising, the reports said, stenting was linked with higher morality rates.

For carotid endarterectomies, 1 percent died within a month, and 7 percent within 1 year, for the most recent year, 2005. But for stenting, 2 percent died within a month and almost one out of ten died within a year. The higher mortality for stenting is likely because patients getting stents are sicker; as noted, Medicare only covers the procedure for high-risk patients.

"The differences likely reflect the differential selection of high-risk patients into the carotid stenting cohort, consistent with the CMS national coverage decision," the report said.

Of note, the mortality rates for both procedures were higher than those reported in the clinical studies that led to regulatory approval of the procedures, the report said. While mortality rates for the endarterectomy in 2005 declined almost 50 to 100 percent from some reported death rates in the mid-1990s, they were substantially higher than those in the regulatory-granting studies of 0.5 to 0.8 percent, according to the report.

But this was also not entirely surprising, the report said.

"Because this analysis was limited to elderly Medicare beneficiaries, the differences between the mortality rates we observed and those reported in clinical trials are not unexpected," concluded the report.