Carotid artery interventions
internal carotid narrowing with ulceation
What causes strokes?
There are four arteries that supply blood to the brain, two carotid arteries and two vertebral arteries. The carotid arteries supply blood mostly to the front part of the brain, while the vertebral arteries supply blood mostly to the back part of the brain. All four arteries connect with each other at the base of the brain, allowing these arteries to compensate for diminished flow in one or more of them. A stroke occurs when an area of the brain is damaged by lack of blood flow. There are several ways the blood supply to the brain can be compromised. One of the most common is when there is severe narrowing of the carotid artery by an atherosclerotic plaque, or hardening of the artery. This is called a carotid stenosis. This plaque builds up within the carotid artery over years and can rupture, occluding the carotid artery and/or releasing small fragments of atherosclerotic material that travel into the brain. There, depending on its size, the embolic atherosclerotic can lodge in arteries that supply specific parts of the brain. Those parts of the brain that are affected either die or are starved of oxygen from lack of blood flow. This causes the symptoms that are associated with transient ischemic attacks, in which the symptoms last less than one hour then completely resolve, or strokes, in which the symptoms are permanent. These symptoms include loss of vision in one eye, weakness and numbness on one side of the face of body, or difficulty speaking. Strokes can also be large enough to cause death. Therefore, it is of paramount importance that carotid stenoses be identified if they cause symptoms or if they are severe enough to potentially cause a major stroke in the near future.
How do you diagnose carotid stenosis?
There are several ways to identify carotid stenoses. Duplex ultrasound is a combination of ultrasound and Doppler measurements of blood speed as it travels through blood vessels. As blood travels through a narrowing, its speed increases. As the narrowing becomes more severe, the speed of the blood increases as well. Depending on the blood’s speed, the degree of narrowing of the blood vessel can be estimated. Duplex ultrasound is a readily available non-invasive test that has been proven to be very reliable in detecting carotid stenoses. However, the accuracy of the test is high dependent on the technologist that performs the study. In order to protect our patients from unnecessary interventions, we usually repeat the duplex scan at the hospital vascular laboratory. It is based on the information from the duplex scan that we base our treatment decisions.
Carotid angiography is an invasive test similar to cardiac catheterization in which a catheter is placed within the femoral artery in the groin and advanced into the carotid artery in the neck. Contrast dye is then injected through the catheter and xrays are done, creating images of the carotid artery and any narrowings it may have. Treatment decisions based on these images can then be made. Angiography is considered the gold standard for imaging of the carotid artery, but requires that the patient undergo an invasive procedure.
CAT and MRI scans are rapidly becoming acceptable imaging tests in evaluation of carotid stenoses. The improvements in the scanners and their software that have occurred in the last few years have made the images from these tests accurate and very useful. The risks of CAT scans include exposure to radiation and reactions to contrast dye. Despite the superb imaging that can now be obtained from CAT and MRI scans, they are still not as accurate compared to Duplex ultrasound and carotid angiography for certain degrees of stenoses. Therefore, at the mainstays for diagnosis of carotid stenoses remains Duplex ultrasound and carotid angiography.
When and how should a carotid stenosis be treated?
There are several ways to identify carotid stenoses. Duplex ultrasound is a combination of ultrasound and Doppler measurements of blood speed as it travels through blood vessels. As blood travels through a narrowing, its speed increases. As the narrowing becomes more severe, the speed of the blood increases as well. Depending on the blood’s speed, the degree of narrowing of the blood vessel can be estimated. Duplex ultrasound is a readily available non-invasive test that has been proven to be very reliable in detecting carotid stenoses. However, the accuracy of the test is high dependent on the technologist that performs the study. In order to protect our patients from unnecessary interventions, we usually repeat the duplex scan at the hospital vascular laboratory. It is based on the information from the duplex scan that we base our treatment decisions.
CAT and MRI scans have rapidly replaced formal angiography in evaluation of carotid stenoses. The improvements in the scanners and their software that have occurred in the last few years have made the images from these tests accurate and very useful. The risks of CAT scans include exposure to radiation and reactions to contrast dye. Despite the superb imaging that can now be obtained from CAT and MRI scans, they are still not as accurate compared to Duplex ultrasound and carotid angiography for certain degrees of stenoses. Therefore, at the mainstays for diagnosis of carotid stenoses remains Duplex ultrasound and carotid angiography.
Criteria for treatment of carotid stenoses was established in the early 1990s by large, multi-institutional studies. Surgery has been shown to reduce the risk of stroke in asymptomatic patients with stenoses greater than or equal to 60% or in symptomatic patients with stenoses greater than or equal to 50%. However, recommendations for treatment are individualized based on an assessment of the patient’s risk and expected benefit. Carotid endarterectomy is currently the safest treatment for appropriate symptomatic or asymptomatic stenoses. It is considered appropriate to operate if the risk of perioperative stroke is less then 3% in asymptomatic patients or less then 6% in symptomatic patients. Our current rate of stroke within 30 days of surgery is 0.3%, or around 1 in 300. Carotid endarterectomy is usually done under a general anesthetic. A 4-6 inch incision is made in the neck. The carotid artery is controlled with rubber loops before opening the vessel and inserting a tube to maintain blood flow to the brain. Once the artery is opened, the diseased layers of the vessel wall are gently removed. After a completely smooth surface is achieved, the artery is closed with a Dacron patch.
Most patients go to a regular room with the anesthetic has worn off and are discharged home the following morning. Carotid stenting is a relatively new method of treating carotid stenosis. In this procedure, a catheter is placed in the femoral artery in the groin and advanced into the carotid artery with the stenosis. Through this catheter, devices are placed within the carotid artery to safely dilate and stent it. A small filter is placed above the narrowing in the artery to catch any atherosclerotic debris that breaks off during carotid artery dilation and stent placement. The stent is a self-expanding, metal mesh cylinder that will line the inner surface of the carotid artery, preventing it from narrowing in the future. This entire procedure is done under local anesthesia while the patient is awake and very lightly sedated. Please refer to the section on carotid artery stenting for more information regarding the pros and cons of stenting.