Technique of carotid angioplasty with stenting

Vitek J.J.

New York Heart and Vascular Institute at Lenox Hill Hospital

Carotid artery stenting (CAS) is currently being investigated as an alternative treatment to carotid endarterectomy (CEA). The goal of both procedures is the prevention of stroke from extra-cranial carotid artery occlusive disease. Carotid stenting, in comparison with surgery offers patients a less invasive and less traumatic mean of achieving this goal.

Clinical Protocol:

Patients are admitted the day of the procedure and consented for brachiocephalic angiography and possible stent placement, should the lesion prove to be of significant severity and is anatomically suitable. All patients are referred for neurological examination to document the pre-procedural clinical neurological status. All patients have a National Institute of Health stroke scale completed by a neurologist. Symptomatic patients or patients with history of stroke or TIAs and those with abnormal neurological examination have a CT or MRI-scan (if not recently done) to document pre-procedural pathological changes. Before stenting, all patients undergo brachio-cephalic angiography (if not recently done). Patients are informed that CAS is considered an investigational procedure, and that in spite of favorable medium-term (2 year) outcome, long-term data are not yet available. Patients are started on antiplatelet therapy; aspirin 325 mg daily in addition to Ticlopidin (Ticlid ®) 250-mg bid, presently Clopidogrel (Plavix ®) 75 mg bid for 2-4 days prior to the procedure. In all cases, patients should have received ticlopidin (total dose 500mg) or clopidogrel (total dose 300mg) prior to the intervention.

Procedural Considerations:

Angiography and stenting is performed under local anesthesia. Neurological status of the patient is monitored after each step of the procedure. Throughout the intervention continuous electrocardiogram with monitoring of the heart rate and blood pressure is done.

Current Technique:

Our current technique can best be discussed in terms of initial angiography, access sheath placement, pre-dilatation and stenting.

1. Initial angiography:

In the vast majority of elderly patients only one 5F catheter [VTK Thorocon 100 cm, (HNB5.0-38-100-P-NS-VTK)Cook Inc. Bloomington, IN.] is needed to catheterize all brachiocephalic arteries. With exceptions, in extremely dilated aortic arches, a side-winder curved catheter is used. (Simmons 3 curve). 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 study of both carotid arteries and dominant vertebral artery.

The initial brachiocephalic angiography has several advantages:

1. Remains the most reliable method for precise assessment of degree of carotid artery stenosis.

2. Demonstrates anatomical conditions which are unfavorable for carotid stenting or increase the difficulty of the procedure, e.g. dilated/extended arch, marked vessel tortuosity, heavily calcified stenosis, lesions with obvious filling defects.

3. Preprocedural knowledge of contra-lateral carotid stenosis or occlusion and the status of the intracranial circulation (isolated hemisphere, collateral supply) impacts the stenting technique (e.g. shorter balloon inflations, choice of future neuro-protection device, occlusion v/s filter).

4. Reliably demonstrates significant flow limiting distal and intracranial internal carotid artery stenosis. Although the bifurcation stenosis may be treatable, the ultimate benefit of stroke reduction may not accrue to the patient because of disease more cephalad.

5. In case of an intraprocedural neurological event, the post-procedure intracranial angiogram can be compared with the baseline pre-procedure study.Disadvantage of brachiocephalic angiography: The main risks relate to the use of contrast and the risk of a neurological event. With present techniques this risk is very small (0.1-0.2%).

2. Access sheath placement:

Once the diagnostic study is completed and the stenotic internal carotid artery is identified (Fig.11A,B), the 5F catheter (HNB5.0-38-100-P-NS-VTK,Cook Inc.Bloomington,IN.) is advanced, using the 0.038" glide wire, into the ipsilateral external carotid artery. The glide wire is then withdrawn and replaced with an extra stiff 0.038" exchange wire (0.038" Extra Stiff Amplatz a Wire-260 cm, Cook Inc., Bloomington, IN). The 5F catheter is withdrawn and the 6F or 7F - 90 cm guiding sheath (Shuttle ®, Cook Inc. Bloomington, IN.) is then advanced into the common carotid artery over the exchange Amplatz wire, anchored in the external carotid artery (Fig.11C-I) If the brachio-cephalic diagnostic angiography has previously been performed and target lesion identified, the stenting procedure begins by placing the Shuttle sheath, via the femoral approach, into the upper thoracic aorta. After withdrawing the inner dilator from the sheaths, the 125 cm 5F catheter (HNB5.0-38-125-P-NS-VTK, Cook Inc., Bloomington, IN) is introduced into the Shuttle sheath. Care must be taken not to advance the 90 cm sheath too close to the aortic arch because this will decrease the maneuverability of the 5F catheter. Then the common carotid artery is catheterized with the 125 cm 5F catheter and this catheter is advanced into the external carotid artery (road mapping is very useful). Using the appropriate guide wire (0.038" glide wire or extra stiff 0.038" Amplatz wire) depending on the arch extension and carotid artery tortuosity, the Shuttle sheath is advanced over the 5F catheter into the common carotid artery, just proximally to the stenosis. 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 then advanced into the common carotid artery. There are modifications of this technique, especially if the stenosis is located in mid or distal segments of the common carotid artery or if the external carotid artery cannot be catheterized. In these situations the 5F catheter – guide wire assembly, over which the Shuttle sheath is placed in the common carotid artery, is kept below the stenosis or bifurcation (Amplatz exchange J-wire is used). Exceptionally, in significant aortic arch elongation or common carotid artery tortuosity, the stenosis is traversed with a glide wire and 4F or 5F catheter. Then using an Amplatz wire the sheath is advanced proximally to the stenosis. The same technique is also used in ostial and very proximal carotid stenoses. One should be aware that by placing the 7F sheath in the common carotid artery, especially if the carotid artery is tortuous, the bifurcation is displaced upward and kinks can be created on the internal carotid artery (Fig.11I). These disappear once the sheath is withdrawn, but can complicate the stenting procedure. As soon as the guiding sheath is placed into the arterial system, 5.000 – 6.000 units of heparin are given through the sheath to raise the ACT to no more then 250 sec. (Hemotec Company method).

Advantages of the Co-axial Sheath Technique:

1. Permits continuous access to the common carotid artery. Once the sheath is in the common carotid below the bifurcation, unfavorable anatomy (elongated arch, tortuosity of the common carotid artery) is no longer an issue influencing technical success.

2. The sheath carries a large bore Tuohy-Borst valve seal, which permits unimpeded catheter or guide wire introduction. The side-arm allows intermittent or continuous flushing and contrast injection and also allows for continuous intra-arterial blood pressure monitoring.

3. The sheath can be also used as a reference for precise measurement of the internal and common carotid arteries dimensions. Disadvantages of the Co-axial System (Sheath or Guiding Catheter):

1. By placing the 7Fr sheath in the common carotid artery (especially if the carotid artery is tortuous), kinks can be created, existing tortuous loops can be exaggerated, and the tortuosity along with the carotid bifurcation is displaced cephalad. These disappear once the sheath is withdrawn, but the appearance of “pseudo-lesions” can complicate the stenting procedure .

2. On rare occasion, dissection of the innominate or common carotid artery may result.

3. There is always the possibility of embolization during sheath advancement, a part of the procedure that cannot be “neuroprotected.” Based on our experience, the risk of a clinically obvious embolic event during this phase of the procedure is quite small.

3. Pre – dilatation:

Arteriography through the sheath, in appropriate angulation, is performed to show the maximum tightness of the stenosis. QCA (quantitative carotid arteriography) is performed in this projection to measure the percent diameter of the stenosis and also the diameter of the common carotid artery. Then the optimal angulation is found to perform the intervention. This projection is not necessarily the one to show the maximum stenosis severity, but the one separating the internal and external carotid arteries and to show comfortably bony landmarks (Fig 11J-P). To continuously monitor neurological status and particularly strength of the contralateral upper extremity, a squeeze toy is placed in patient's hand. The stenotic lesion is crossed with a steerable 0.014" guide wire (Fig. 11J). The wire is guided with small contrast injections through the sheath rather then road-mapping, which is subject to misregistration (especially in tight stenosis) due to the patient’s breezing. Selection of the wire depends on the tightness, location, lengths, angulation and eccentricity of the stenosis and on the anatomy of the bifurcation. The tip of the 0.014" wire is shaped appropriately. A variety of 0.014" wires are available. We commonly use exchange-length 0.014" Balance® Wire (Guidant Inc., Temacula, CA) or 0.014" Choice PT® Wire (SciMed Inc., Maple Grove, MN). After crossing the stenosis, the tip of the wire is placed close to the skull base. If the internal carotid artery is kinked, presents coils or tortuosities, the wire is passed through, distally, to the level of skull base. For pre-dilatation of the stenosis we routinely use 0.018” compatible balloons, such as Cobra®, 4 mm x 40 mm coronary balloon (SciMed Inc., Maple Grove, MN), more recently Savvy® balloon 4 mm x 40 mm (Cordis Corp., Miami, FL). 40mm balloon length prevents the balloon to slide out from the stenosis. The pressure used for pre-dilatation is nominal for the balloon used. We use higher pressure (14-16 atm.) only in heavily calcified stenoses. The duration of the pre-dilatation depends on the appearance and behavior of the balloon. If the balloon immediately attains its full shape, the pre-dilatation time is shorter. If the balloon attains its full shape slowly, the pre-dilatation time is prolonged up to 120 sec., again especially in calcified lesions, which have tendency for recoiling. We routinely inflate the balloon only once and we vary the inflation time. If the stenosis is preocclusive, we use step-like predilatation method. First we predilated the stenosis with 2 mm x 40 mm balloon (Ranger® SciMed Inc., Maple Grove, MN). After this pre-dilatation, a second pre-dilatation, using the 4 mm balloon, follows. After the pre-dilatation, if needed, the 0,018” compatible balloon catheter is advanced distally into the internal carotid artery and the 0.014" wire is changed for 0.018" exchange wire (Roadrunner®, Cook Inc. Bloomington, IN) (Fig.11K). Again the tip of the 0.018" wire should be located close to the skull base and certainly must be passed through all kinks and tortuosities of the internal carotid artery. Occasionally, if the stenosis is not significantly irregular, ulcerated, if it is less the 80% in diameter and if the ICA is not tortuous, we traverse the stenosis directly with 0.018” Roadrunner. Very rarely, usually in heavily calcified lesions, if after pre-dilatation with 4 mm balloon the stent does not easily pass through the stenosis, a 5 mm balloon has to be used for additional pre-dilatation. All predilatation balloons are deflated very slowly. After the pre-dilatation and placement of the 0.018” guide wire, control arteriogram is performed (Fig.11L).

Why predilate ?

1. Experimental work has demonstrated that embolic debris is potentially released with “primary stenting” without predilatation and during lesion dilatation with large peripheral (0.035” compatible) balloons.

2. We do not practice “primary stenting” without pre-dilatation; it is our impression that later postdilatation of the constricted stent is associated with more “scissoring” of the stent wires on plaque with greater risk of embolization.

4. Stenting: stent deployment and post - dilatation:

Presently we are using only self expanding stents. In our early experience we worked with balloon expandable stents. This practice was abandoned (following observation of balloon expandable stents deformation) with three exceptions: 1) when the ostium of the common carotid artery is treated and the proximal end of the stent has to be placed with precision 2) when the most distal neck segment ( pre-petrous segment) of the internal carotid artery is treated. (Present delivery systems for self-expanding stent can cause dissections in petrous portion of the internal carotid artery, i.e. in any sharp bends of the internal carotid artery.) and 3) when the self expandable stent cannot be smoothly advanced through the stenosis after 5 mm balloon pre dilatation (usually in heavily calcified stenoses).

The self expanding stent is deployed using the vertebral bodies as landmarks. We oversize the stents, using 8 mm or 10 mm widths stents when the proximal end is placed in the common carotid artery (Fig.11M,N) and 7 mm or 8 mm widths stents when they are placed exclusively in the internal carotid artery. The self expandable stent is post-dilated with a 5 mm, 5.5mm or 6 mm x 20 mm balloon (Symmetry®, MediTech Watertown, MA; Savvy®, Cordis Inc., Miami, FL) over the 0.018" wire, depending on the size of the internal carotid artery (Fig.11O). Nominal pressure is used to fully expand the balloon and the stent. The balloon is again deflated slowly. High pressures are not used any more. Only in heavily calcified stenosis we post-dilate with Titan balloons (Cordis Inc., Miami, FL) which accept higher pressures. In majority of the cases the stent is placed across the bifurcation into the common carotid artery, crossing the origin of the external carotid artery. To cover the external carotid artery with the stent does not cause problems, our follow-up arteriograms showed external carotid artery to be patent with rare exceptions (Fig.1-9).

Stent Length and Positioning:

1. If a Wallstent of 10 mm x 20 mm is chosen and it expands to 10 mm, then the length would be 20 mm. Since there is a size differential between the internal and the common carotid arteries, the former being 5-6 mm and the latter 7-9 mm, the allstent does not expand to the full 10 mm and hence does not shorten to 20 mm.

Instead it ends up being 30-40 mm in length. In the case of the Nitinol stents ( we currently use 10 x 20, 30 or 40 mm long stents), when deployed, they maintain its length despite the size differential between the internal and the common carotid arteries.

2. Avoid placing the distal end of the stent into kinks and tortuosities of the internal carotid artery. These cannot be eliminated and are only displaced distally and can become more exaggerated.

3. The Nitinol stents are less rigid, conform more to the “curve” of the vessel and do not straighten the internal carotid artery as much as the Wallstent (Fig.8).

4. Since there is no appreciable foreshortening in Nitinol stent, they can be more precisely placed using the distal and proximal markers (Fig.6). An important technical point is to release 3 to 5 mm of the stent distally and wait for the stent to expand fully and stabilize against the vessel wall before releasing the reminder of the stent. These stents have the tendency to “jump” distally if released too fast.

5. If the external carotid artery becomes significantly stenosed with flow restriction or occluded after postdilatation of the stent (Fig 10), this vessel can be approached through the stent mesh and angioplasted using coronary balloon techniques. A 0.014" wire is used to enter the external carotid artery with 2 mm balloon, and 4 mm balloon is used for final dilatation. The goal is not to completely open the external carotid artery ostial stenosis, but to establish acceptable flow into the vessel.

Critical points in post-dilatation.

1. It is perhaps the time when the greatest amount of emboli are released and consequently the patient is at the greatest risk of stroke. To minimize the embolic load   we recommend:

a) using balloons that are no larger than 5.5 mm in diameter;

b) inflating to nominal, not very high pressures; deflate slowly,

c) accepting a 10-15% residual stenosis. This does not cause hemodynamic problems. The self expanding stents have the tendency for late, progressive expansion, especially if oversized and

d) restricting the postdilatation to a single postdilation effort .

2. In some cases, continued flow via the stent struts into an ulcer or bulbous of the ICA is seen (Fig.3,10). No attempt should be made to obliterate this communication by using larger balloons or higher pressures as this communication will seal off in the ensuing few weeks and is of no consequence.

Post procedural angiographic assessment:

  1. Lesion Site and Cervical ICA: Following stent postdilation, final angiograms are acquired in the “working” projection ( Fig.11P) and in the projection of maximum stenosis. Particular attention must be directed to the ICA immediately cephalad to the stent.It is not unusual to encounter spasm in this segment particularly if the ICA is tortuous. A small dose of intra-arterial nitroglycerine (100-200 m mg) and pulling back the Shuttle sheath to the carotid origin aids in relieving the spasm, relaxing the artery and helps the operator get a better idea of the status of the stented vessel. Distal dissections are unusual and when present can be remedied with an additional stent of appropriate size.

  2. Intracranial: We do not routinely acquire post CAS intracranial angiograms, reserving it for patients with poor prestenting intracranial blood supply (Fig.11Q)and for patients who experience intra-procedural neurological deficits. Several operators

  3. will do this as a routine, and all the current carotid stent investigational
  4. protocols call for repeat intracranial views.

Sheath removal an access site hemostasis

The Shuttle sheath is pulled back (over a wire) into the iliac artery and exchanged for a short sheath of appropriate size (usually 7Fr, sometimes 8Fr) which is removed when the ACT is <150sec. This takes usually 3-4 hours and it is important to inform the person pulling the sheath whether atropine and vasopressors were used intraproceduraly or not.The effect of these medications wears off in a few hours and typically coincides with the timing of sheath removal. This and the exaggerated vagal response that is not unusual in these patients can lead to profound hemodynamic perturbation for which anticipation and treatment preparation (e.g. ensuring good peripheral venous access, adequate hydration, holding antihypertensives prophylactic dosing with atropine, etc.) is extremely helpful..Although “low blood pressures” is not unusual in the immediate post procedure phase, it is worth emphasizing that other causes, e.g. retroperitoneal bleed related to access site problems, should be excluded as a cause of any unexplained persistent, disproportionate hypotension. At the present time in suitable patients, access site hemostasis is achieved at the end of the procedure using a suture closure device (Perclose, Perclose Inc; Redwood City CA). We prefer the 6Fr perclose device, and following diagnostic angiography, the 5Fr arterial sheath is exchanged for the 6F Perclose device. The sutures are brought out and left untied at which point the Perclose device is exchanged for the Shuttle sheath. At the end of the procedure, the Shuttle sheath is removed and the sutures are knotted. This approach is particularly valuable for those patients who are proposed to be discharged the same day (day case carotid stenting).

Discharge Protocol

1. Ambulate next day
2. NIH stroke scale before discharge
3. Carotid ultrasound (optional)
4. ASA 325mg PO qd indefinitely
5. Clopidogrel 75mg PO qd x 1 month
6. Clinical F/U: 1mo, 6mos, yearly
7. Ultrasound F/U: 6mos, yearly
8. Meticulous follow up records

Carotid artery stenting has rapidly evolved into a less invasive procedure that CEA to treat patients with symptomatic and significant asymptomatic carotid stenosis. With today's equipment and technique stenting mortality and morbidity from stroke related complications is in the range of 3%, similar or lower to comparable patient's population treated with traditional carotid endarterectomy. And there are no cranial nerve palsies. In both, percutaneous stenting and endarterectomy, embolic stroke events can occur. In each technique the incidence of ischemic or embolic stroke depends on meticulous procedural technique and expertise and is markedly dependent on the volume of cases performed. With availability of dedicated carotid stenting equipment (low profile stent delivery systems with variety of different stent designs, better access sheaths and specially designed wires and balloons) and carotid neuro-protective devices, current CAS results will likely be enhanced.

 

Illustrations:

Fig.1A. – Complex lesion in the right common carotid artery with tight stenosis and large ulcerations.
1B. – Post CAS with Wallstent 10 x 20.

Fig.2A. – Post. CEA with 90% restenosis in the right internal carotid artery.
2B. – Post CAS with Wallstent 10 x 20.

Fig.3A. – Complex lesion within the bifurcation of the left common carotid artery involving internal (90%) and external carotid arteries. Previously stented RICA.
3B. – Post CAS with Wallstent 10 x20.

Fig.4A. – Complex stenosis involving the left common and internal(99%) carotid arteries. Post angioplasty and stenting with Wallstent 10 x 20. Previously stented right internal carotid artery.
4B. – Post CAS with 10 20 Wallstent.

Fig.5A. – Post CEA 90% restenosis on the right internal carotid artery. Post CEA occlusion of the external carotid artery.
5B. - Post CAS with Wallstent 10 x 20.

Fig.6A. – Post CEA on the right carotid artery. Large venous patch with proximal and distal stenosis. Occlusion of the external carotid artery.
6B. – Post CAS with Smart stents. (proximal 7x40, distal 7x20)

Fig.7A. – 90% left internal carotid artery stenosis within the vessel kink.
7B. – Wallstent 10 x20
7C. – Post CAS. Moderate kink distally to the stent.

Fig.8A. – 90% stenosis in the right internal carotid artery with significant distal tortuosity
8B. – Post CAS with Smart stent 10 x 30.

Fig.9A.- 85% long, ulcerated stenosis on the left internal carotid artery.
9B. – Post predilatation. Spasm caused by placement of the 0.018” guide wire.
9C. – Post CAS with Wallstent 10 x 20.

Fig.10A – Left carotid bifurcation stenosis involving internal (85%) and external (70%) carotid arteries. Significant distal tortuosity of the internal carotid artery.
10B – Post CAS with Wallstent 10 x 20. Kinks distally to the stent. No flow in the external carotid artery.

10C – Angioplasty of the external carotid artery (Ranger 4 x 20) across the Wallstent.
10D – Stenosis in the external carotid artery with reestablished TIMI 3. flow.

Fig.11. - Technical steps in carotid angioplasty with stenting.
11A – 90% ulcerated stenosis in the right internal carotid artery.
11B - Antero-posterior intracranial view. Poor filling of the right middle cerebral artery. Right anterior cerebral artery is not opacified.
11C – Visualization of tortuous innominate artery with 5F catheter (HNB5.0-38-100 or 125-P-NS-VTK, Cook Inc.)
11D – Advancement of 0.038” glide wire into the right common carotid artery.

11E – Glide wire in the right external carotid artery. 5F catheter in the right common carotid artery on the way into the external carotid artery.
11F – 5F catheter in the right external carotid artery. Glide wire exchanged for stiff, 0.038” exchanged wire.
11G – Advancement of the 7F – 90 cm sheath through the aortic arch.
11H – 7F sheath in the right common carotid artery.

11 I – Lateral view of the bifurcation after placement of the 7F sheath. Bifurcation displaced superiorly with development of kink in the internal carotid artery.

11 J - 0.014” exchange wire placed across the internal carotid artery stenosis and distal kinks.
11K - 0.014” wire exchanged for 0.018” exchange wire. Predilatation balloon (Cobra 18. 4 x 40) within the stenosis.
11L – Control angiography after predilatation ( bony landmarks).
11M – Placement of the stent (Wallstent 10 x 20).

11N – Deployed stent.
11O – Postdilatation of the stent ( Savvy 5 x 20).
11P – Final post CAS control angiography.
11Q – Post CAS intracranial angiography. Improved intracranial blood supply.