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Carotid Endarterectomy
Stroke Prevention

Stroke is diagnosed one half million times each year and consumes a tremendous amount of medical resources, costing over fifteen billion dollars a year. In the early 1990's several well-designed studies clearly demonstrated the advantage of carotid endarterectomy over medical therapy in selected patients. Success of this surgery depends not only on patient selection but surgeon selection since the advantage of surgery is present only if the surgeon has a low incidence of complications such as stroke.

Anatomy and Physiology

  • Blood leaving the heart enters the aorta, the main central artery of the body (Figure 1)
  • The first arterial branches off of the aorta are the innominate artery (also called the brachiocephalic trunk), left common carotid artery and the left subclavian artery
  • The innominate artery gives rise to the right common carotid and subclavian arteries. In the neck the common carotid arteries branch into the internal and external carotid arteries, the internal carotid arteries extending upwards in the front of the neck to feed the front of the brain including the frontal, parietal and temporal lobes (see Craniotomy). The vertebral arteries on each side pass upwards in the back of the neck to feed the back part of the brain
Figure 1 - Arteries leading from the aorta to the internal carotid arteries

Pathology

  • Arteries become narrowed (stenosis) by the formation of a plaque
  • The plaque is composed of a fatty material and occasionally contains calcium
  • It is sometimes coated with small pieces of clot
  • For some unknown reason a common place for a stenosis to occur is at the point where the internal carotid artery branches from the common carotid artery
  • When a plaque narrows the vessel lumen (inside of the vessel) by 60-70%, the chance of a major stroke is statistically less with surgery than with medication
  • The chance of a major stroke is also greater if the patient has had a previous small stroke than if he has not had a small stroke. The stroke may occur because
    1. The stenosis in the artery limits the flow of blood to the brain
    2. A blood clot forms in a brain artery (thrombosis)
    3. A small piece of blood clot or plaque breaks off and lodges in one of the arteries in the brain (embolus)
  • When an artery to a part of the brain is blocked, the region that the artery feeds dies (an infarct). This produces the symptoms of a stroke (Figure 2)
  • A hemorrhagic stroke occurs when there is also bleeding into the brain
Figure 2a - CT scan showing an area of dead brain (infarct) in the distribution of the right middle cerebral artery due to a strokeFigure 2b - MRI showing an infarct in the distribution of the right middle cerebral artery due to a stroke

History and Examination

  • There are various risk factors that heighten the incidence of stroke. They are:
    1. Increased age
    2. Male
    3. African-American
    4. Family history of stroke
    5. Diabetes mellitus
    6. High blood cholesterol
    7. Obesity
    8. Inactivity
    9. High blood pressure
    10. Smoking
    11. Being overweight
    12. Family history of stroke
    13. Heart disease
    14. Radiation therapy to the neck
  • A patient may or may not have symptoms of a small stroke (transient ischemic attack (TIA) or mini-stroke). The symptoms of a TIA include
    1. Sudden numbness or weakness of the face, arm or leg on one side of the body
    2. Loss of speech, trouble talking or trouble understanding speech
    3. Sudden dimness or loss of vision in one eye
  • Additional symptoms that may represent a stroke are:
    1. Unexplained dizziness, unsteadiness, or fall
    2. Severe, unexplained headache
    3. Double vision
    4. Drowsiness
    5. Nausea and vomiting
  • Using a stethoscope the doctor may hear a bruit (swishing sound synchronous with the heart pulse) over the carotid artery.
    1. The bruit usually means that there is a significant stenosis of the carotid artery
    2. When there are no associated symptoms, this is designated as an asymptomatic carotid stenosis
    3. The stenosis is designated as symptomatic when associated with symptoms of a stroke
  • There may be weakness of one side of the body (the side opposite the stenosis)
  • Speech may be garbled or not understood
  • There may be a loss of vision in one eye
  • The blood vessels of the retina of the eye may show tiny spots that are very small emboli
  • There may be confusion and difficulty in recalling recent events
    A stroke is also known as a BRAIN ATTACK. An individual having the symptoms of a brain attack should immediately go to the nearest hospital emergency room that is able to treat a brain attack or call 911. If seen in the emergency room within three hours, medication that dissolves the blood clot in the blocked artery can be given and the stroke reversed.

Tests

  • Doppler/Duplex Ultrasound- A sensor connected to a special computer and monitor is placed over the carotid artery in the neck and images the flow of blood in the artery. The presence and approximate degree of stenosis can be determined. (Figure 3A, 3B)
Figure 3a - Normal Doppler/Duplex Ultrasound. Common, internal and external carotid arteries are labeled. Figure 3b - Ultrasound demonstrating a high grade (> 70%) stenosis if the internal carotid artery.
  • Angiography
    1. A catheter introduced into the femoral artery in the groin is passed upwards through the aorta and then under fluoroscopic control into each common carotid artery
    2. A dye that shows up on X-ray is injected through the catheter. Serial X-ray films or angiograms are then obtained of the carotid artery circulation Review of the films demonstrates whether a stenosis is present and the degree of the stenosis (Figure 4A)
    3. An ulcer in the wall of the artery may also be found (Figure 4B)
    4. Furthermore, examination of the remainder of the circulation may show a second point of narrowing or the occlusion of a vessel in the brain. The review will also help in planning future surgery
Figure 4a - Carotid angiogram demonstrating a 70% stenosis of the internal carotid artery.Figure 4b - Carotid angiogram demonstrating a 50% carotid stenosis along with an ulceration in the plaque.

 

  • Computerized Tomography (CT) and Magnetic Resonance Imaging (MRI)- Both these exams produce images of the brain which may demonstrate evidence of present or past strokes or evidence of a blood clot. (Figure 2)
  • CT or MR Angiography (MRA)- These are special types of CT and MRI that produce angiograms without passing a catheter.
    1. MRA is more accurate than Duplex Ultrasound but not as accurate as the standard angiogram
    2. CT angiography may be equal to the standard angiogram

Indications

Who should be selected for surgery? This at times can be a difficult question for your surgeon to answer. Some indications are listed:

  • Surgery is most appropriate in a symptomatic patient with greater than a 70% carotid artery stenosis
  • Surgery is appropriate in a symptomatic or asymptomatic patient with greater than 60% stenosis, particularly if
  • The plaque is ulcerated
  • The patient remains symptomatic on aspirin
  • The opposite carotid artery is blocked
  • The degree of stenosis is greater, particularly if serial studies demonstrate progressive narrowing
  • Evidence on CT or MRI of a small stroke that did not produce symptoms
  • The patient is relatively young

Surgery is not indicated when:

  • The stenosis is less than 50% in a symptomatic patient
  • The stenosis is less than 60% in an asymptomatic patient
  • The patient has a recent large area of dead brain on studies
  • The patient is in poor medical condition
  • The surgeon's surgical incidence of stroke or death is greater than 3%

Procedure

  • The procedure may be carried out with the patient asleep under general anesthesia or awake under local anesthesia depending on the preference of the surgeon
  • An incision is made in the neck (Figure 5A)
  • The dissection is carried down to the carotid artery
  • Care is taken to not injure the jugular vein, vagus nerve (to the heart and bowel), the hypoglossal nerve (to the tongue), and the recurrent laryngeal nerve (to the vocal cords)
  • The common, external and internal carotid arteries are separated from the surrounding tissues
  • Heparin, a blood thinner, is injected to prevent blood clotting during surgery on the vessels
  • An elevated blood pressure is maintained to improve the flow of blood through other vessels going to the brain
  • The three carotid arteries are clamped with special vascular clamps and the status of the patient monitored (Figure 5B)
Figure 5a - Position of the incision for a carotid endarterectomy. Figure 5b - The carotid arteries are dissected from the surrounding tissues and vascular clamps applied. The line of incision in the vessels is shown.
  • Under local anesthesia, the patient is asked to follow simple command so as to determine if the patient develops weakness
  • Under general anesthesia, the patient may be monitored in several ways such as a. monitoring the brain waves (EEG)
    1. monitoring somatosensory evoked potentials (SSEP) in which a nerve in the arm is stimulated and the response to the stimulus is monitored by processing the EEG
    2. Under general anesthesia, the patient may be monitored in several ways such as
      • Monitoring the brain waves (EEG)
      • Monitoring somatosensory evoked potentials (SSEP) in which a nerve in the arm is stimulated and the response to the stimulus is monitored by processing the EEG
      • Monitoring brain oxygen through the skull using a special instrument (not commonly done)
  • The common carotid artery is opened below the plaque and carried upward into the internal carotid artery (Figure 5C)
  • Some surgeons:
    1. Always place a shunt between the common carotid artery below the plaque and the internal carotid artery above the plaque (Figure 7D)
    2. Only place a shunt when monitoring indicates an inadequate amount of blood is getting to the brain
Figure 5c - After opening the artery, the plaque is peeled from the wall of the artery. Figure 5d - A shunt may be used to bypass the area where the plaque is being removed thus maintaining blood flow to the brain.
  • The plaque is peeled out of the inside of the internal, external and common carotid arteries. (Figure 5C - above)
  • The artery is sutured with a fine suture. (Figure 5E)
  • Some surgeons always insert a patch graft into the vessel to make it wider while others only insert a patch graft when they believe it is necessary (Figure 5F)
  • The incision is closed after a drain is inserted to drain away any blood that may accumulate in the wound
Figure 5e - After removal of the plaque the artery is sutured. Figure 5f - Patch graft sutured into the incision in the artery to widen the artery.

Percutaneous Angioplasty with Stent (PAS)

  • In the last few years a technique borrowed from coronary artery therapy (see Coronary Catheterization) has been used in patients with carotid artery stenosis
  • PAS involves the introduction of a catheter into the femoral artery in the groin, which is manipulated up through the aorta and into the involved carotid artery under fluoroscopic control
  • The catheter has a small balloon at its tip that is positioned within the narrowed segment of the artery and inflated, causing the plaque to be compressed and the vessel lumen reopened
  • A stent keeps the plaque from expanding again. The stent is a cylindrical mesh inserted in a collapsed state and expanded against the compressed plaque by a balloon
  • PAS is not a substitute for carotid endarterectomy since the long-term results of the procedure are still unknown and, at this time, has a greater incidence of stroke as a complication
  • Indications for PAS are probably best limited to the following patients:
    1. Symptomatic disease in an elderly patient who is a prohibitive surgical risk
    2. Patient with recurrent stenosis
    3. Patients with radiation (X-ray therapy) induced stenosis
    4. Patients with a stroke in progress that are very ill and who may also need thrombolytic therapy (infusion of a drug that dissolves small clots)

Complications

  • A major complication of this procedure is a stroke, just the medical problem that the patient is trying to avoid by having the surgery. The stroke may be minor or major and can lead to death
  • Death is usually due to a heart attack because many of the patients having a carotid endarterectomy also have
  • Significant coronary artery disease
  • Blood clot in the neck causing difficulty with breathing
  • Injury to various nerves in the neck
    1. Hypoglossal nerve- weakness of the tongue
    1. Vagus nerve- may effect the heart or bowel
    2. Facial nerve- weakness of the face
    3. Accessory nerve- weakness in turning the head to the opposite side due to weakness of the sternomastoid muscle
    4. Recurrent laryngeal nerve- vocal cord paralysis
  • Infection

Post Operative Care

  • After surgery, the patient is placed in the Intensive Care Unit or other unit in which the patient can be closely monitored
  • In the unit the patient is closely monitored for any change in level of consciousness and for excessively high or low blood pressure
  • The drain is removed and the patient may be discharged on the first post-operative day if there are no medical or surgical problems

After Care

A change in life style reduces the risk of further problems in the arteries

  • Stop smoking
  • Begin a low fat diet
  • Check blood cholesterol at least twice per year
  • Control diabetes and high blood pressure
  • Have a regular exercise program
  • Follow up with your doctor at regular intervals