General Description

Carotid artery revascularization is an effective method of stroke prevention in select patients with carotid stenosis. Carotid endarterectomy (CEA) has been performed routinely to achieve this goal. However, with the advancement of endovascular techniques protected carotid artery stenting (CAS) has become an excellent alternative to CEA.

There are two different types of embolic protection: distal and proximal (accomplished via flow arrest or flow reversal). There are a few reports of combined proximal and distal protection as well. Devices used for proximal protection include the MoMa embolic protection device (Medtronic), balloon guide catheters (not tested on a large scale for this indication), and the Gore Flow Reversal System (Gore). In this chapter, proximal protection with flow arrest with the MoMa device is discussed. Distal protection is addressed in Chapter 11. Proximal protection under flow reversal using the Gore device and balloon guide catheters is discussed in Chapter 13. Stabile et al ¹ presented the results of a large series of proximal endovascular occlusion in 1300 patients. The procedure was successful in 99.7% of patients. Perioperative complications included five deaths (0.38%), six major strokes (0.46%), five minor strokes (0.38%), and no acute myocardial infarction. At 30 days of follow-up, two additional patients died (0.15%), and one patient had a minor stroke (0.07%). The 30-day stroke and death incidence was 1.38% (n = 19). Symptomatic patients presented a higher 30-day stroke and death incidence when compared with asymptomatic patients (3.04% vs. 0.82%; p < 0.05). No significant difference in 30-day stroke and death rate was observed between patients at high (1.88%; n = 12) and average surgical risk (1.07; n = 7; p = NS). Independent predictors of adverse events included operator experience, symptomatic status, and hypertension.

Evidence-Based Outcomes

The proximal protection with the MoMa device during carotid stenting (ARMOUR) Trial had the lowest event rates of any independently adjudicated study. The trial reported a 0.9% major stroke rate in symptomatic patients at 30 days. Proximal protection devices have the benefit of being in place before the lesion is crossed with any device. The MoMa device is able to arrest flow while the atherosclerotic lesion is crossed, aiding in protection from distal emboli and stroke. Furthermore, the device can be utilized in conjunction with a distal protection device should there be a need because of irregular anatomy or lack of confirmed flow arrest.

Indications

CAS is indicated in patients with symptomatic internal carotid artery (ICA) stenosis > 70% or asymptomatic ICA stenosis > 80%. Other indications include the inability to tolerate general anesthesia during CEA, contralateral carotid occlusion or laryngeal nerve palsy, previous neck surgery or radiation therapy, restenosis after CEA, and poor neck mobility. CAS is also used for treatment of dissections and cases of acute stroke with tandem (extra- and intracranial vessel) occlusions.

Proximal protection is used for extremely stenotic lesions that may be difficult to pass through with a microcatheter for distal protection. Another indication for proximal protection is a tortuous ICA or the presence of a loop at the distal ICA with no adequate landing zone for a distal protection filter device. Brittle, symptomatic, or hemorrhagic plaque lesions should also be considered for proximal protection.

Proximal protection devices with flow arrest are contraindicated in patients with contralateral ICA occlusion or patients who have relatively small femoral arteries that do not accommodate a 9F sheath.

Neuroendovascular Anatomy

A brief overview of ICA anatomy is provided in Chapter 10. The anatomic considerations when using a MoMa device are somewhat more specific than those for other devices used for proximal protection (e.g., the Gore system or balloon guide catheters). The MoMa device relies on flow stagnation with occlusion of both the common carotid artery (CCA) and the external carotid artery (ECA). An inflated balloon in the CCA provides arrest of anterograde flow, while an inflated balloon in the ECA suspends retrograde flow. Therefore, any anatomic variant near the carotid bulb could theoretically result in loss of flow stagnation. For example, if the superior thyroid vessel extends from the CCA or very proximal ECA (between the balloons), this could result in backflow into the ICA and embolus. The spacing between the ECA and CCA balloons is fixed on the MoMa device and, therefore, anatomical variants must be identified. Overly tortuous carotid anatomy can make placement of the stiff MoMa device difficult. Extension of the carotid bulb plaque into the ECA can prevent safe passage of the device. It is important to identify aberrant anatomy because proatlantal persistent vessels could be disrupted during stenting or occlusion (flow arrest), resulting in posterior circulation stroke, especially if balloon occlusion is being utilized.

Periprocedural Medications

As with the use of distal protection, dual antiplatelet therapy with aspirin (325 mg daily) and clopidogrel (75 mg daily) is administered for the prevention of intraluminal thrombus during or after the stenting procedure under proximal protection. The regimen is started 5–7 days prior to the procedure for elective procedures. Otherwise, a loading dose of aspirin (650 mg) and clopidogrel (600 mg) should be given before the procedure, followed by daily doses of aspirin (325 mg) and clopidogrel (75 mg). Dual antiplatelet therapy should be continued for at least 1 month. Aspirin should be continued indefinitely. Aspirin and clopidogrel serum responses should be monitored and therapeutic. Some patients can be nonresponsive or allergic to clopidogrel. Ticagrelor (60 mg twice daily) can be give as an alternative.

Intraprocedural systemic heparinization is strongly recommended because of the ever-present risk of thrombus formation. An activated coagulation time between 250 and 300 seconds is the goal. Heparin administration prior to crossing the lesion may limit thrombus formation on devices positioned within the ICA.

Hemodynamic instability sometimes occurs during balloon inflation for proximal protection and during balloon angioplasty. Bradycardia, asystole, and hypotension are the most common types. Asking the patient to perform a Valsalva maneuver (cough) will usually reverse bradycardia. A good practice is to have a vasopressor (e.g., dopamine or phenylephrine) available, as well as atropine. We typically perform CAS with the patient awake for accurate neurological assessment. The neurosurgeon or interventionist should be familiar with the MoMa device to limit the time of balloon inflation and flow arrest.

Specific Technique and Key Steps

Several clinical trials have demonstrated the efficacy of embolic protection devices in preventing intraprocedural ischemic complications. When using a proximal embolic protection device (MoMa), the key steps for CAS are as follows ( Fig. 12.1–12.4, Video 12.1–12.4 ).

The MoMa device should be prepared before groin access:

1. 
   

   Remove packaging and set aside three filters/traps to be used at the conclusion of the procedure.

   
   
2. 
   

   Flush the working channel (center) and hollow mandrel with saline.

   
   
3. 
   

   Insert the hollow mandrel though the working channel while rotating the valve.

   
   
4. 
   

   Vacuum preparation of the ECA and CCA balloon channels are then completed with negative aspiration of air in an upright syringe containing 50:50 or 70:30 contrast material dilution.

   
   
5. 
   

   Connect the safety connectors and two-way valves to ports.

MoMa steps:

1. 
   

   A 9 French sheath is placed in the femoral artery.

   
   
2. 
   

   After the femoral angiogram has been performed, the diagnostic catheter (Simmons 2 or angled catheter, Terumo) surrounding the Glidewire (0.035-inch, Terumo) is advanced into the aorta under fluoroscopic guidance ( Video 12.1–12.4 ).

   
   
3. 
   

   Magnified working views of the carotid artery are obtained prior to entry into the ECA or exchange from the CCA. Measurements of the degree of stenosis, length of stenosis, and diameters of the CCA and distal ICA are obtained for proper stent sizing.

   
   
4. 
   

   Roadmap technique is used for navigation of the diagnostic catheter into the ECA. Once the diagnostic catheter is in the ECA or in one of its large branches (internal maxillary or occipital arteries), an exchange of catheters is performed.

   
   
5. 
   

   Under roadmap guidance and using an exchange-length (300 cm) stiff 0.035-inch wire (e.g., Supra Core 35, Abbott), the diagnostic catheter is exchanged for the MoMa catheter. Utmost care should be taken to prevent the wire, MoMa catheter, and diagnostic catheter, from crossing the stenotic lesion ( Video 12.1–12.4).

   
   
6. 
   

   The prepared MoMa proximal protection device is navigated through the arch up to the upper cervical ECA over the stiff exchange-length wire that is placed through the hollow mandrel. The distal balloon is placed in the ECA and the proximal balloon in the CCA. The hollow mandrel and the wire are removed ( Video 12.1–12.4 ).

   
   
7. 
   

   Selection of the stent:

   
   
   
   
   1. 
      

      Closed cell stent—Xact (Abbott Vascular) or Wallstent (Boston Scientific)—is used for acute symptomatic ICA stenosis or with other high-risk features (hemorrhage or plaque morphology).

      
      
   2. 
      

      Open-cell stent—Acculink (Abbott Vascular)—for tortuous anatomy.

      
      
   3. 
      

      High-radial-force stents for heavily calcified lesions.

      
      
   4. 
      

      Tapered stent when a large discrepancy between the diameters of the ICA and CCA is noticed.

   
   
8. 
   

   The stent or pre-angioplasty balloon (if needed) is brought into the guide catheter and up to the proximal balloon.

   
   
9. 
   

   The CCA and ECA balloons are then inflated with 50:50 or 70:30 contrast material under roadmap or fluoroscopy for ECA and CCA occlusion until flow arrest is obtained.

   
   
10. 
    

    Flow arrest should be confirmed before crossing the lesion with any device by injecting a small amount of contrast material that should stagnate in the ICA. The stent envelops a stiff 0.014-inch wire (e.g., Spartacore 14, Abbott) that is brought up through the MoMa device. It is then navigated out of the opening between the two ECA and CCA balloons into the ICA and past the stenosis under flow arrest. This process must be completed quickly but safely because the flow is arrested! ( Video 12.1–12.4 )

    
    
11. 
    

    Standard stent deployment is carried out under fluoroscopy.

    
    
12. 
    

    A noncompliant balloon is used to perform angioplasty poststent placement if needed.

    
    
13. 
    

    Intravascular ultrasound can be used to look for any residual stenosis or debris within the lumen and adequate stent apposition to the artery wall.

    
    
14. 
    

    At the conclusion of the stent placement, the stagnant blood in the ICA (presumably with atherosclerotic plaque within) is aspirated ×3 with a large 10 cc syringe and examined in the three filter/traps on the back table. There must be two clean traps prior to restoring flow via decompression of the balloons ( Video 12.1–12.4 ).

    
    
15. 
    

    Final angiographic runs are taken after the device has been removed. Hemostasis is established, and the femoral artery is closed with an AngioSeal device (Terumo) because of the large size (9F) of the femoral artery sheath ( Video 12.1–12.4 ).

Device Selection

In our practice, the following are common provisions and devices used for CAS with proximal protection under flow arrest.

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  9F sheath.

  
  
• 
  

  0.035-inch angled Glidewire.

  
  
• 
  

  5F diagnostic catheter (Simmons 2 or angle catheter).

  
  
• 
  

  0.035 Stiff exchange length wire (e.g., Supra Core 35).

  
  
• 
  

  0.014-inch exchange wire (e.g., Sparta Core 14).

  
  
• 
  

  MoMa guide catheter (MoMa system) ( Video 12.1–12.4 ).

  
  
• 
  

  Carotid stent (closed-cell Wallstent, Boston Scientific).

  
  
• 
  

  Noncompliant balloon.

  
  
• 
  

  Continuous heparinized flush.

Pearls

• 
  

  There are some caveats to proximal protection related to the MoMa device, including the need for a 9F sheath and additional setup time for preparation of the ECA and CCA balloons.

  
  
• 
  

  Some patients are unable to tolerate flow-arrest while awake. In those cases, the MoMa device cannot be utilized and the procedure has to be aborted.

  
  
• 
  

  Tortuous anatomy can make navigation of the MoMa device difficult. Extra purchase from the stiff wire can be acquired by looping it (i.e., the stiff wire) in an ECA vessel.

  
  
• 
  

  For crossing the lesion, a steerable 0.014-inch wire is used. Some angulation of the tip of the wire is recommended to ease the guidance of the wire through the area of stenosis and exit from the MoMa catheter.

  
  
• 
  

  In patients with tortuous anatomy or a looped ICA, navigation into the distal cervical ICA may be more difficult. The wire (0.0014 inch) on which the stent is mounted is passed to a point in the cervical ICA that enables passage of the stent safely beyond the stenosis. A stiffer wire might be required.

  
  
• 
  

  For stent placement, we recommend having an osseous landmark (cervical vertebrae) for a distal landing site of the stent because the roadmap may be unreliable because of vessel deformation with positioning of the stent or the guide catheter or because of patient movement.

  
  
• 
  

  If the stent is not easily passed through the lesion over the microwire, a pre-stent angioplasty is performed with an undersized balloon to prevent plaque rupture.

  
  
• 
  

  For closed-cell stents, a malpositioned stent may be recaptured if partially deployed (up to 80% for most closed-cell stents). Otherwise tandem stenting may be required.

  
  
• 
  

  Be careful when removing the MoMa guide catheter. The distal portion of the catheter containing the distal balloon can catch the proximal portion of the stent. Carefully pull the MoMa guide catheter into the CCA under fluoroscopy.

  
  
• 
  

  A final cerebral angiogram is always recommended to assess for smooth synchronized reperfusion and to identify any delayed capillary filling or large occlusions or dissections.