Four arteries supply almost all of the blood flow to the brain. These are the right and left internal carotid arteries and the right and left vertebral arteries. There are cross connections between the four arteries at the base of the brain (the circle of Willis) so that if one artery is blocked, blood can flow through a cross-connection to supply blood to the part of the brain normally supplied by the blocked artery.
However, blockage of one of the main arteries can sometimes lead to an acute stroke and does lead to an increased risk of future stroke.
When an acute complete blockage of an internal carotid artery (one of the four main brain arteries) occurs it can cause a transient ischemic attack or an ischemic stroke at the time the blockage occurs.
And the risk of the patient having an ischemic stroke over the two years following the acute blockage is 10 to 15% on medical therapy.
That increased stroke risk from internal carotid artery occlusion lead to the Carotid Artery Occlusion Surgery Study. Surgery was performed to bypass the blocked internal carotid artery to bring more blood flow to the brain, and hopefully, reduce the risk of future stroke. A branch of the external carotid artery was sewn (connected) to a branch of the internal carotid artery in the brain beyond the blockage.
The results of the study were reported in today’s Journal of the American Medical Association article Extracranial-Intracranial Bypass Surgery for Stroke Prevention in Hemodynamic Cerebral Ischemia: The Carotid Occlusion Surgery Study Randomized Trial available on the internet at:
And the conclusion of the study is that “Among participants with recently symptomatic AICAO [atherosclerotic internal carotid artery occlusion] and hemodynamic cerebral ischemia, EC-IC bypass surgery plus medical therapy compared with medical therapy alone did not reduce the risk of recurrent ipsilateral ischemic stroke at 2 years.”
That is, the bypass surgery does not reduce the risk of stroke. I believe that most doctors, myself included, believed that the study would show that the surgery did reduce the risk of stroke. But it did not.
Even if a treatment (or medicine) seems to make a lot sense, like the EC-IC bypass surgery, we have test the treatment (or medicine) carefully to find out if it really helps. Over and over doctors have been surprised when careful studies have shown that treatments or medicines we strongly believed in did not help or even made things worse.
In an accompanying editorial in today’s JAMA, Doctors Broderick and Meyers draw some very important lessons from the Carotid Artery Occlusion Study.
They point out that there are many other treatment devices for stroke are used [by interventional radiologists] without any evidence that they reduce the risk of future stroke. These include devices to mechanically remove blood clots from brain arteries and include stents placed in brain arteries. The doctors who perform these procedures strongly believe that they are doing the patients good. But the writers of the editorial point out that we need to test the devices and procedures with careful randomized trials to be sure that they are helping. We’ve been wrong too many times before when we just relied on what seemed to make sense.
We all owe a debt of gratitude to the doctors of the Carotid Artery Occlusion Study for their careful scientific testing of EC-IC bypass surgery.