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Carotid Stenting

Jiri J. Vitek*, MD, PhD; Gary S. Roubin, MD, PhD;
Gishel New, MBBS, PhD; Nadim Al-Mubarak, MD;
Sriram S. Iyer, MD

*Lenox Hill Heart and Vascular Institute of New York, New York, USA

INTRODUCTION
   Carotid artery stenting represents one of the final frontiers for percutaneous endoluminal intervention. In the United States, the first prospective, elective stenting trial of carotid bifurcation lesions was begun at the University of Alabama at Birmingham in March, 1994 by a multidisciplinary group consisting of cardiovascular, neurological, and neuroradiological specialists. From the beginning the group based its technique on the premise that combining angioplasty with elective intravascular stent placement would increase the reliability and safety of the procedure. The first series of patients to undergo stenting was reported in 1995. Since 1994 carotid angioplasty with stenting (CAS) has been investigated as an alternative treatment to carotid endarterectomy (CEA) at multiple centers. The purpose for CAS or CEA is the prevention of stroke related to the lesion in the carotid artery. In symptomatic patients, revascularization is indicated for lesions in 50% or more of men and in 60% or more of women if the revascularization can be achieved with a periprocedural stroke or death rate of 6% or less. Asymptomatic patients require > (greater then or equal to) 70% diameter narrowing if the complication rate is kept below 3%.

MATERIALS AND METHODS
   528 consecutive patients (604 vessels/hemispheres) underwent CAS. The mean age was 69 ± 10 years. Sixty-six (12.5%) patients were 80 years old or older and 172 (33%) were women. Forty-eight percent (290) were asymptomatic. Fifteen percent (91) had previously undergone ipsilateral CEA. Five percent (28) underwent previous neck surgery or radiation. Of the symptomatic hemispheres, 82% (257 of 314) were ineligible for the North American Symptomatic Carotid Endarterectomy Trial (NASCET) because of age, co-morbidities, previous CEA, neck surgery, or radiation.

   Patients were started on antiplatelet therapy, consisting of aspirin (325 mg daily) and clopidogrel (Plavix, Bristol-Myers Squibb, New York, NY)) 75 mg twice daily (currently, previously ticlopidine [Ticlid, Roche Laboratories, Nutley, NJ] was used), preferably for 4 days before the procedure. In all cases, patients received ticlopidin (total dose, 500 mg) or clopidogrel (total dose, 300 mg). Angiography and stenting were performed under local anesthesia. The neurological status of the patient was monitored after each step of the procedure.

Our current technical approach is illustrated in Figs 1 through 7 and can be separated into these steps:

1. Diagnostic angiography
2. Carotid sheath placement
3. Predilatation of the stenosis
4. Stent deployment
5. Postdilatation of the stent

Fig 1. (A) A 86-year old man had 90% stenosis in the ostium of the left internal carotid artery (ICA). Note the heavy posterior calcification. A 2.0 x40-mm Ranger and 4.0 x 40-mm Cobra 18 balloon (SciMed/Boston Scientific Corp.) were used for pre-dilatation.
(B) A 10 x 20-mm Wallstent (Schneider/Boston Scientific Corp.) had been deployed and with 5 x 20-mm Savvy balloon (Cordis Corp). The calcification prevented full expansion of the stent.
(C) Final angiographic image. Contrast within the ulceration is of no significance.

Diagnostic angiography
   The diagnostic angiography consists of visualization of the origins of the brachiocephalic arteries from the aortic arch (by selective injections), both carotid bifurcations in several projections, both vertebral arteries, and intracranial distribution of both carotid arteries and dominant vertebral artery.

Carotid Sheath Placement
   Once the diagnostic study is completed and the stenotic internal carotid artery is identified, the 5F diagnostic catheter is advanced by using 0.038-inch glide-wire (MediTech/Boston Scientific Corp, Watertown, MA) into the ipsilateral external carotid artery. The glide-wire is then withdrawn and replaced with an extra stiff 0.038-inch exchange wire. The 5F catheter is withdrawn and the 6/7F - 90 cm sheath (Shuttle Introducer, Cook Inc, Bloomington, IN.) is then advanced into the common carotid artery over the exchange wire anchored in the external carotid artery. If the diagnostic angiography has previously been performed, the stenting procedure is then begun by placing the 6/7F sheath, via the femoral approach, into the upper thoracic aorta. Then 125-cm, 5F catheter (VTK Thorocon NB, Cook Inc, Bloomington, IN.) is introduced into the 6/7F sheath. The common carotid artery is catheterized with the 5F catheter which ev. can be advanced into the external carotid artery. With the use of the appropriate guidewire within the 5F catheter, 6/7F sheath is slipped over the 5F catheter into the common carotid artery. If the advancement of the sheath over the 5F catheter is not smooth, the 5F catheter is removed, replaced with the sheath inner introducer, and the sheath then advanced into the common carotid artery (Figs 2B, 4B, 5B). One should be aware that by placing the 6/7F sheath in the common carotid artery occasionally displaces the bifurcation upward, which can create kinks in the internal carotid artery, especially if the artery is tortuous. These disappear once the sheath is withdrawn but can complicate the stenting procedure (Fig 4). As soon as the 6/7F sheath is placed into the arterial system, 4.000 - 5.000 U of heparin is given through the sheath to raise the activated clotting time (ACT) to approximately 200 seconds (Hemotec method).

Fig 2. (A) A 60-year-old man had 85% right ICA stenosis with large ulceration. Note long, diseased segment extended from the common carotid artery (CCA) to the ICA, and stenosis in the external carotid artery (ECA).
(B) Pre-dilatation with a 4 x 40-mm Cobra 18 balloon. Spasm has been caused by the 0.018-inch Roadrunner (Cook, Inc), placement of 10 x 20-mm Wallstent and post-dilatation with 5.0 x 20-mm Savvy balloon (Cordis Corp. Miami, FL).
(C) Final angiographic image. The previously seen spasm has resolved spontaneously after withdrawing the guide wire. There is no change in the ECA stenosis.

Fig 4. (A) A75-year-old man with symptomatic stenosis of 80%, which is visualized better in lateral projection. Oblique projection used for stenting, because it separates ICA from ECA. The angulation in the ICA is exaggerated by placement of the 6F sheath.
(B) First pre-dilatation was performed with 4 x 40 Ranger balloon (SciMed/Boston Scientific Corp). Spasm was produced by straightening of the ICA with support 0.014- inch Stabilizer Plus guide wire (Guidant Corp. Temacula, CA).
(C) A 10 x 20 Wallstent has been deployed and postdilated with a 5.0 x 20 Savvy balloon. The kink in the ICA has been displaced cephalad. Spasm still present.
(D) The 6F sheath has been withdrawn to the ostium of the CCA. Kink in the ICA have disappeared. Spasm treated with 100 mgr. of nitroglycerin.


Fig 5. (A) A 75-year old man with an ulcerated 90% stenosis of the left ICA. Note the 90° angle of the origin of the ICA.
(B) A 7F sheath is in the CCA. The stenosis was predilated with 2.0 x 40 and 4.0 x 40 Ranger balloons. The 0.014-inch soft guide wire was changed for 0.014-inch support wire. The straightening of the ICA caused spasm. Acculik stent (Guidant Corp. Temacula, CA) in position to be deployed. The 8.0 x 20-mm Acculink stent conforms better to the ICA tortuosity then a Wallstent.
(C) The stent was post-dilated with 5.0 x 20-mm Savvy balloon.

Pre-dilatation of the stenosis
   Arteriography is performed through the sheath, and the optimal angulation is found to perform the intervention. This projection is not necessarily the one that shows the maximum stenosis severity, but one that separates the internal and external carotid arteries and demonstrates bony landmarks (Fig 3A). The stenotic lesion is crossed with a maneuverable 0.014-inch guidewire. Selection of the wire depends on the severity, location, length, angulation and eccentricity of the stenosis and on the anatomy of the bifurcation. Predilatation is performed with 4.0-mm x 40-mm coronary angioplasty balloon. If the stenosis is preocclusive, we predilate in stages. First we predilate with 2-mm balloon, then with a 4-mm balloon (see Figs 1, 5, 6, 7). Four millimeter predilatation is usually sufficient to pass the stent smoothly, without encountering major resistance crossing the stenosis. After predilatation, the 0.014-inch wire is changed for an 0.018-inch exchange wire. The tip of both 0.014-inch and the 0.018-inch wires should be close to the skull base and passed beyond all the tortuosities of the cervical internal carotid artery. Before stent deployment, a control arteriogram is performed.

Fig 3. (A) Stenosis at the left CCA bifurcation in 60-year-old man. There is 50% stenosis of the CCA, 90% stenosis of the ICA, and 50% stenosis of the ECA. In the oblique projection, the stenoses are more pronounced. For stenting, the lateral projection is most advantageous. Note tortuosity of the ICA.
(B) Pre-dilatation was performed with 4.0 x 40-mm Cobra 18 balloon over an 0.018"-inch Roadrunner. A 10 x 20-mm Smart Stent (Cordis Corp., Miami Lakes,FL) has been carefully positioned proximally to the ICA tortuosity and post-dilated with a 5.0 x 20- mm Savvy balloon. The tortuosity on the ICA is maintained.

Fig 6. (A) A 76-year-old man with 90% stenosis in distal left CCA, a long 80% stenosis of the ICA (narrowed distally because of the lack of flow), and flow arrest in the ECA (with supply from the left vertebral artery).
(B) The stenoses were crossed with an 0.014-inch Balance guide wire (Advanced Cardiovascular Systems, Temecula, CA), predilated with 2.0 x 40-mm Ranger and 4.0 x 40-mm Cobra 18 balloons. The Balance wire was changed for an 0.018-inch Roadrunner guide wire. A 10 x 40-mm Smart stent was placed in the ICA, overlapping proximally with a 10 x 20-mm Smart stent in the distal CCA. No Postdilatation was performed. Flow re-established in the ECA.

Fig 7. (A) A 70-year-old man with restenosis after endarterectomy. There is 95% stenosis in the proximal ICA. The ECA is occluded.
(B) The stenosis was predilated with 2.0 x 20-mm Ranger and 4.0 x 40-mm Cobra 18 balloons. A 7 x 20-mm Smart stent was deployed and postdilated with 5.0 x 20-mm Savvy balloon.

Stent Deployment
   A self-expanding stent is deployed, with the vertebral bodies used as landmarks. The stent is never forced across the stenosis. If distal advancement is not achieved, the stent is withdrawn and additional predilatation is performed with 5 mm balloon. If this is not sufficient, a short balloon expandable stent is deployed, and the definitive self-expanding stent is placed through this stent. We oversize the self-expanding stents, using 8- or 10-mm width stents when the proximal end is placed in the common carotid artery and 7- or 8-mm width stents when they are placed entirely in the internal carotid artery. The stent is deployed from within the healthy segment of the internal carotid artery; it is not important where the proximal end of the stent is located in the common carotid artery.

Postdilatation
   The self-expandable stent is postdilated with either 5.0-mm, 5.5-mm or 6.0-mm x 20-mm balloon (Fig 1B), depending on the size of the internal carotid artery. In most cases, the stent will be placed across the external carotid artery. If the external carotid artery becomes significantly stenosed with or occluded after postdilatation of the stent, this vessel can be approached through the stent mesh and reopened. An 0.014-inch wire is used to enter the external carotid artery; a 2-mm balloon is used to predilate, and a 4-mm balloon is used for final dilatation.

RESULTS
   Technical success, defined as the ability to access the carotid artery and successfully stent the lesion, was 98.6%. Complications (Table 1) included all strokes and deaths occurring within 30 days, whether or not they were related to the procedure. Major stroke was defined as an increase in the National Institutes of Health Stroke Scale (NIHSS) of > 3 that did not resolve within 30 days. Minor stroke was defined as an increase in the NIHSS score of < (less then or equal to) 3. All data were collected prospectively. Neurological outcome was based on pre- and postprocedural (24 hours) examination by a board-certified neurologist.

   The results of carotid stenting are operator-dependent, and therefore there exists a significant learning curve. Table 2 shows the results of our series annualized over the last 5 years of experience. The incidence of procedure-related major neurological complications has been low throughout the experience. The majority of these complications were isolated events directly related to decision-making based on the use of non-dedicated equipment availability and the operators' inexperience concerning patient selection factors. We have learned that these problems can be avoided by meticulous technique.

DISCUSSION
   Over the last four years we have repeatedly analyzed our outcomes to examine the risk of complications in a variety of patient subsets. The results have provided guidance for patient selection, but are confounded by the dynamic learning curve, changing technique, evolving patient selection process and a small numbers of patients in some subsets.

   The first subset that clearly benefited from the CAS was composed of patients suffering restenosis after prior endarterectomy. In our initial group of 25 vessels, one patient had a minor stroke for a complication rate of 4%. We have now treated 83 such vessels with one major stroke (1.2%) and a non-disabling stroke rate of 3.6% (3 of 83).

   Importantly, no patients have had cranial nerve palsies and anaesthetic complications. The second group comprises patients with contralateral internal carotid artery occlusion. In our series of 26 patients, only one patient had a minor stroke (3.8%). In the minority of patients in our series, who would have been eligible for inclusion in the NASCET study, we have had satisfactory results. In this subset of symptomatic patients younger than 80 year of age, with no severe cardiac or pulmonary comorbidity, we have observed a 30- day risk of stroke or death of 2.7% . We have also identified several factors associated with embolic stroke. These include hypertension, increased lesion severity, long or multiple stenosis, and advanced age > (greater then or equal to) 80 years. There was also a notable trend towards a higher rate of embolic events in more calcified, eccentric lesions and lesions with markedly irregular borders. Sex, presence or absence of neurological symptoms, presence of coronary artery disease, diabetes mellitus, hypercholesterolemia, smoking, presence of bilateral carotid lesions, and ulcerations did not significantly influence the incidence of neurological complications. In general, it should more systemic factors and comorbidities increase the risk of CEA, whereas local anatomical and lesion factors increase the risk of stenting.

   Important questions to be answered were the incidence of embolic events during healing phase after stent placement (the first 3 to 4 weeks) and the incidence of stent thrombosis. There was only one embolic event within the first 4 weeks after the procedure occurred only once (into the ipsilateral retinal artery). This low rate is thought to be a result of careful preprocedural administration of antiplatelet therapy. This is in contrast to CEA, in which 50% of embolic events are observed within 7 days after the procedure. Stent thrombosis has been remarkably rare. After stent placement in 604 vessels, we have seen only one perioperative thrombosis.

   The success of carotid stenting depends on the ability of the operator to minimize procedural complications. Performing carotid stenting through percutaneous access without the need for general anesthesia minimizes the variety of wound and anesthetic complications associated with CEA. The evolution of technique and the learning curve over the last 4 years have been associated with a variety of complications that were encountered once and subsequently avoided with modification of technique (Table 3).

   Carotid stenting should only be undertaken within an interventional (endovascular) program, in which personnel are familiar with efficient and safe arterial sheath removal with minimal patient discomfort. Adequate hydration and pretreatment with atropine can prevent and treat hypotension associated with a vasovagal response to sheath removal.

   An unexplained decrease in blood pressure may be caused by retroperitoneal bleeding. We have started to use a femoral artery suture devise (Perclose, Perclose Inc., Redwood City, CA) which enables us to discharge the patients the same day.

   The occurrence of spasm in the distal internal carotid artery is a common angiographic event, caused by the mechanical irritation of the vessel (Figs 2, 4, and 5). It usually resolves spontaneously after the catheter or guide wire has been removed. Use of 0.018-inch or 0.014-inch soft- tipped wires minimizes the occurrence of spasm. Injections of 100 to 200 ĩg of nitroglycerine through the carotid access sheath will hasten the resolution of spasm. Spasm must be differentiated from kinking of the internal carotid artery (Fig 4C).

   Bradycardia and episodes of transient asystole are common during dilatation of the carotid bifurcation. More prolonged hypotension and bradycardia were seen with balloon-expandable stents, which place more sustained pressure on the receptors. Asystole during balloon inflation is transient and responds to balloon deflation. We administer atropine to patients who exhibit marked bradycardia, but large doses of atropine should be avoided in elderly patients. Hypotension is not uncommon after carotid stenting and may last from hours to days, depending on the sensitivity of the baroreceptors, the type of stent used, and whether bilateral stents are placed. The degree of hypotension appears to be more pronounced in heavily calcified lesions. Usually, there are no clinical sequelae and the modest decrease in blood pressure requires no specific intervention.

   In some hypertensive patients, and in patients with critical [ > 90%] lesions, we have observed a transient postprocedural confusional state with headaches, occasionally associated with transient localizing symptoms, that is not associated with angiographic abnormalities. A computed tomography (CT) or magnetic resonance scan will often show mild hemispheric swelling with effacement of sulci, or suggest luxury perfusion. The symptoms usually resolve over 24 hours with good control of blood pressure.

   Contrast encephalopathy is a rare syndrome in which the hemisphere, on ipsilateral to the CAS is overloaded with contrast agent. Patients developed a profound neurological deficit associated with the hemisphere at risk. CT scan characteristically shows marked contrast staining in the basal ganglia and in the cortex. There are no angiographic abnormalities. Patients recover within 24 to 48 hours with good hydration and control of the blood pressure.

   Transient cerebral ischemia (TCI) is a syndrome of almost complete or complete deprivation of blood flow to the cerebral tissue at the time of occlusion of the carotid artery with the angioplasty balloon. Sudden loss of consciousness with ischemic pseudo-seizure and contralateral extremity weakness is common but completely reverses on prompt balloon deflation and reestablishment of blood flow. The same symptoms are seen with the presence contralateral internal carotid artery occlusion, in which the opposite hemisphere is supplied through the anterior communicating artery. In this situation the angioplasty balloon has to be inflated for the shortest period of time possible, both during the predilatation and postdilatation of the stent.

   Major complications resulting in severe clinical sequelae are rare when carotid stenting is performed with meticulous technique. Carotid dissection is a rare but significant complication of the procedure. The most serious dissection is in the internal carotid artery distal to the stent. This distal dissection may occur when attempting to stent a lesion that is adjacent to a severe distal kink or bend point, but can also develop when the post dilatation of the stent is performed across the distal end of the stent with high inflation pressure. Dissections can be also caused by trying to force stiff peripheral balloons or stiff-ended stent delivery systems through bend points while trying to position the balloon or stent in the lesion. Dissections also can be precipitated by attempting to deliver a stent over a guidewire that is too flexible and not supportive. Distal dissections are best treated by using flexible stents of appropriate size. To be able to treat distal dissection, it is essential to maintain the position of the guidewire up to the skull base throughout the procedure. The second, less common site for dissection is in the common carotid artery caused by the tip of the guiding sheath. This complication can be treated, if necessary, by using another stent in the common carotid artery.

   Carotid perforation is a rare event in our experience, only one case occurred in 604 vessels stented. This perforation occurred because of aggressive balloon sizing in a misguided attempt to optimize the luminal appearance of the stented segment. We now appreciate that luminal irregularities or pockets of contrast in residual ulcerations external to the stent are of no prognostic significance in terms of immediate or late results (see Fig 1C). Our approach is to size all balloons conservatively for stent postdilatation. Leakage of the contrast from the internal carotid artery can be sealed with prolonged soft balloon inflation after heparin is reversed with appropriate dose of protamine sulfate.

   Stent thrombosis is uncommon in CAS. The low rate of stent thrombosis is predicated on correct and compulsive use of appropriate doses of adjunctive antiplatelet therapy. Basic stenting techniques must be followed. These include the following: (1) only stenting in the presence of brisk flow without significant inflow or outflow obstruction; (2) stenting from normal segment to normal segment if possible; and (3) ensuring proper stent sizing (oversizing in the case of self-expanding stents) and careful opposition to the vessel wall. Cerebral hemorrhage is a devastating, occasionally fatal complication of carotid stenting. Cerebral hemorrhage has been associated with at least one, but usually a combination, of the following factors: (1) CAS on preocclusive or occluded artery; (2) excessive anticoagulation; (3) poorly controlled hypertension; (4) stenting in the presence of a recent ischemic stroke [ < 3 weeks]; and (5) presence of a vulnerable aneurysm. Anticoagulation should be monitored carefully with use of ACT measurements, which should not exceed 200 to 250 seconds. The control of hypertension is very important, especially in elderly patients and after stenting a preocclusive stenosis. If a cerebral hemorrhage is suspected, the procedure should be terminated. Anticoagulation should be reversed with protamine, and an emergency CT should be performed. Sudden loss of consciousness preceded by a headache, in the absence of intracranial vessel occlusion and presence of moderate mass effect, should alert the operator to this devastating event.

   Distal embolization is the important complication of carotid stenting. Careful patient and lesion selection and meticulous technique can minimize this complication. The future availability of distal neuroprotection devices will hopefully make this complication a very rare event. The potential causes of distal embolization are listed in Table 4.

   It is essential to monitor the neurological status after every step of the procedure. Any changes in neurological status should prompt the operator to optimize the blood pressure and hydration and clarify the status of the cervical and intracranial vasculature. The change in neurological status may be a result of slow flow from lesion recoil, guidewire induced spasm, or dissection. The stenting procedure should be quickly and efficiently completed including stent dilatation. If a change in neurological status does not resolve and there are no signs of embolism on intracranial angiography, a CT scan should be performed immediately to rule out intracerebral hemorrhage or hyperperfusion syndrome. If intracranial embolus is detected, appropriate steps are taken to recanalize the occluded vessel as soon as possible.

CONCLUSION
   CAS is effective treatment for carotid stenosis. It represents the natural progression towards a less invasive approach to solving the problem of critical carotid stenosis. The complication rate compares favorably with endarterectomy. Proper selection of patients and dedication to meticulous technique are essential to achieve satisfactory results. The long-term outcome is not yet established.

Summary
Carotid endarterectomy (CEA) is one of the most frequently performed surgeries in the United States. To offer to the patients less invasive means to achieve same goal, we investigated carotid angioplasty with stenting (CAS) as an alternative to CEA.
A total of 528 patients underwent CAS; 604 vessels /hemispheres treated. Mean age was 69±10; 172 patients (33%) were women. Of the patients treated 91 (15%) presented with post-CEA restenosis. Contralateral carotid occlusion was present in 61 patients (10%). CAS was performed by using a coaxial system with 6/7F - 90cm sheath, predilatation, stent placement and stent dilatation. Patients were pretreated with anti platelet therapy. Same-day admissions and 23-hour discharges were typical. Technical success rate was 98,6%. The 30-day mortality rate was 1.6% (3 [0.6%] neurological, 5 [1%] systemic). There were 6 [1%] major strokes (4 [0.6%] related to intervention) and 29 minor strokes (4.8%) Of the 29 minor strokes, 11 (38%) resulted in complete recovery. On an annualized basis, the incidence of minor stroke declined: 7.1% (1994 to 1995), 5.8% (1995 to 1996), 5.3% (1996 to 1997), 3.2% (1997 to 1998) and 3.1%(1998 to 1999). Restenosis <(bigger or equal) 50% was identified in 5.3% of cases. We conclude that CAS is an effective treatment for carotid stenosis. The complication rate compares favorably with endarterectomy.

 

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2nd Virtual Congress of Cardiology

Dr. Florencio Garófalo
Steering Committee
President
Dr. Raúl Bretal
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