A new study from clinical researchers in London, Ontario, Canada, aimed at determining the true risk of stroke from occlusion of a carotid artery, revealed a surprising result: The risk of progression to carotid occlusion is well below the risk of carotid stenting or endarterectomy, and has decreased markedly with more intensive medical therapy.
The authors advise that "[P]reventing carotid occlusion may not be a valid indication for stenting" in their JAMA-Neurology paper, Risk of Stroke at the Time of Carotid Occlusion.
The approach to dealing with atheromatous (fatty) deposits in the main blood vessels feeding the brain the carotid arteries running from the aorta through the neck to supply the anterior cerebrum (most of the brain) has long been controversial. Vascular surgeons and neurosurgeons seem to prefer to operate on carotids with significant occlusive fatty deposits (atheroma), even if the patient has no symptoms of cerebrovascular insufficiency (e.g., stroke, transient ischemic attack or TIA). Meanwhile, internists and other non-surgical caregivers worry more about complications of such surgery, and how much benefit actually accrues from what amounts to prophylactic (preventive) surgery.
Surprisingly, cardiologists sometimes do the stenting procedures designed to keep partially- or completely-blocked vessels open, likely in the belief that the carotids are analogous to the coronary arteries and a blockage automatically leads to tissue damage: heart attack from a coronary blockage, stroke if the occlusion is in the carotid.
But that is not the case. In fact, the blood supply to the brain is far more complex than the coronary circulation. The "Circle of Willis" provides overlapping conduits to the anterior and posterior cerebrum, with the posteriorly-situated vertebro-basilar system working in concert with the common and internal carotids to make sure that the loss (occlusion) of one vessel is only an uncommon cause of a major stroke.
The current study involved 3,681 patients who had annual carotid ultrasonographic examinations during the study period, 1990-2012. Three-hundred sixteen (8.6%) were asymptomatic before an index occlusion that occurred during observation. Most of the new occlusions (254 of 316 [80.4%]) occurred before 2002, when medical therapy was less intensive. Only one patient (0.3%) had a stroke at the time of the occlusion, and only three patients (0.9%) had a stroke on the same side as the detected occlusion during follow-up and all four of those occurred before 2005.
Neither severity of stenosis nor occlusion on the opposite side predicted the risk of stroke or TIA on the same side, nor death from stroke, or death from unknown cause at a mean follow-up of 2 1/2 years. In fact, only age, sex, and carotid plaque burden significantly predicted risk of those events.
The authors emphasize that earlier in their study, they were not utilizing the same "intensive" medical therapy for those patients they did not choose to operate upon. Such therapy eventually included lifestyle modifications and medications, i.e., smoking cessation, a Mediterranean diet, daily exercise, maintaining a fit weight, moderate consumption of alcohol, effective control of blood pressure and diabetes, intensive treatment with lipid-lowering drugs and antiplatelet agents (including aspirin).
The key message: "So trying to prevent carotid occlusion by surgery or stenting, which both carry significant risks themselves, is not a valid approach," senior author Dr. J. David Spence told Medscape.
Among other things: Dr. Spence calls the practice of carotid stenting in asymptomatic patients "worse than unethical." But, he adds, "[i]t is hard to convince someone of something when their livelihood depends on not believing it." In case that wasn't clear enough, he went on, saying the situation in the United States is "deplorable. In the U.S., 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."
In the Medscape article, entitled Carotid Occlusion 'Not a Ticking Time Bomb,' Dr. Spence tempered his advice thusly: 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 added 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 one-year stroke risk of 15% in patients found to have microemboli compared with 1% in those who did not have microemboli.
"Doing a transcranial Doppler 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 the 10% of high-risk patients who would actually benefit from it."