Carotid Occlusion 'Not a Ticking Time Bomb'

September 22, 2015

New evidence suggesting that carotid occlusion is not actually associated with a high risk for stroke — with the inference that many carotid stenting or endarterectomy procedures for asymptomatic patients therefore may do more harm than good — has come from a new study.

"Carotid occlusion is not the catastrophe that it is widely perceived to be," senior author, J. David Spence, MD, Stroke Prevention & Atherosclerosis Research Centre, Western University, London, Ontario, Canada, commented to Medscape Medical News. "Since intensive medical therapy has been introduced, the risk of occlusion has dropped dramatically and even if it does occur, the stroke risk is very low.

"So trying to prevent carotid occlusion by surgery or stenting, which both carry significant risks themselves, is not a valid approach," Dr Spence concludes.

The findings were published online in JAMA Neurology on September 21.

For the study, researchers retroactively examined carotid duplex scans and clinical outcome data from 3681 patients with asymptomatic carotid stenosis seen in an atherosclerosis clinic during a 20-year period.

They found that the risk for progression to internal carotid artery occlusion fell over time, in line with the increasing use of more intensive medical therapy.

"The frequency of occlusion dropped dramatically in 2002/3, when intense medical therapy started to be used. In our study, 80% of the occlusions occurred before this time point," Dr Spence said.

The study also showed that of the 316 patients who progressed to carotid occlusion, only 1 patient (0.3%) had a stroke at the time of the occlusion, and only 3 patients (0.9%) had a stroke during an average 2.5-year follow-up.

The researchers point out that this risk for stroke is far lower than that associated with carotid stenting or endarterectomy. They cite data from the CREST trial, which showed a 30-day risk for stroke or death among asymptomatic patients of 2.5% for stenting and 1.4% for endarterectomy and a 4-year risk of 4.5% and 2.7%, respectively.

They note that real-world data show even higher risks, with a study in Medicare patients having reported a 1-year rate of stroke or death of 16.7% for stenting and 11.0% for endarterectomy.

These latest data add to concerns about the safety of carotid stenting for asymptomatic carotid stenosis. This practice that is particularly prevalent in the United States, where financial incentives encourage interventional procedures.

"Worse Than Unethical"

Dr Spence calls the practice of carotid stenting in asymptomatic patients "worse than unethical." But, he adds, "It is hard to convince someone of something when their livelihood depends on not believing it."

He describes the situation in the United States as "deplorable." He commented: "In the US, 90% of carotid intervention is for asymptomatic stenosis, but 90% of patients with asymptomatic stenosis would be at lower risk with intensive medical therapy than with intervention."

Dr Spence believes that part of the problem is that many carotid stenting procedures are performed by interventional cardiologists, who assume that a carotid occlusion, like a coronary occlusion, is a "ticking time bomb."

"Stenosis of the left main coronary is often called the 'widow maker,'" he explains. "However, cardiologists do not seem to understand that the brain is protected by the circle of Willis, which acts as a natural bypass. All the main arteries at the base of the brain are connected, so if one becomes blocked, blood can be delivered to that part of the brain by the other arteries."

But he does acknowledge that some patients (he estimates about 10%) do benefit from intervention, and the key is to correctly identify these patients.

"It is not the plaque burden that causes occlusion — the artery seems to enlarge to accommodate the plaque. Occlusion happens when the plaque ruptures," he said.

He said that the 10% of patients at high risk for plaque rupture can be identified by the presence of microemboli detected on transcranial Doppler ultrasonography. He cites a study that showed a 1-year stroke risk of 15% in patients found to have microemboli compared with 1% in those who did not have microemboli.

"A transcranial Doppler machine costs less than two stent procedures and the training can be done in a weekend," he adds. "There is no excuse for carotid stenting without identifying the10% of high-risk patients who would actually benefit from it."

"Fuel to the Fire"

In an accompanying editorial, Seemant Chaturvedi, MD, and Ralph L. Sacco, MD, University of Miami Miller School of Medicine, Florida, say the current study adds "some 'fuel to the fire' regarding the debate concerning the best treatment for asymptomatic carotid stenosis."

They point out that whether the improvements in aggressive medical therapy are sufficient to reduce the rationale for carotid stenting or endarterectomy in asymptomatic patients will need to be determined by contemporary randomized clinical trials.

They add that, fortunately, the National Institute of Neurological Disorders and Stroke has funded the CREST 2 trial, which includes two parallel studies: one comparing endarterectomy and aggressive medical management vs aggressive medical management alone and the other comparing carotid stenting plus aggressive medical management vs aggressive medical management alone.

The editorialists note that although CREST 1 evaluated carotid endarterectomy vs carotid stenting and included a sizeable number of asymptomatic patients, CREST 2 will be the first study to compare carotid stenting with medical therapy alone.

"Neurologists and other clinicians need to vigorously support enrollment in CREST 2 because our patients deserve to know whether carotid revascularization for asymptomatic stenosis is superior to contemporary medical therapies," they conclude.

The authors have disclosed no relevant financial relationships. Dr Chaturvedi is a member of the Executive Committee of the CREST 2 study. Dr Sacco received support from the National Institute of Neurological Disorders and Stroke for the Northern Manhattan Study.

JAMA Neurol. Published online September 21, 2015. Full text. Editorial

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