An Algorithmic Approach to Carotid Access

A review of the techniques and possible complications associated with accessing this difficult anatomy.

By Subbarao Myla, MD, FACC, FSCAI
 

Safe carotid access with a guide catheter or sheath is the first step (and one of the most important) in successful embolism-free carotid stenting. Knowledge of anatomy and arch type, awareness of pitfalls posed by tortuosity, and the ability to modify the technique in special situations are essential cognitive and technical skills with a steep learning curve. Proper mentoring techniques are necessary to help disseminate these procedural skills to the community at large.

DIAGNOSTIC VERSUS INTERVENTIONAL CAROTID ACCESS
An interesting paradigm is the necessity of basic diagnostic carotid angiography skills as a stepping stone for safe interventional access (Table 1). Although diagnostic catheters are soft, low-profile 4- to 5-F flexible devices, the interventional access devices are typically stiffer, higherprofile 6- to 10-F devices that need deep common carotid placement. The starting point for these diagnostic carotid angiography skills is cognitive awareness of the type of aortic arch and the presence or absence of arch disease.

NONINVASIVE EVALUATION OF AORTIC ARCH
Computed tomographic and magnetic resonance angiography may help provide a road map of the aortic arch, defining the type and identifying the extent of ostial bifurcation external carotid artery (ECA) disease as well as tortuosity. Significant arch disease may dictate switching to a brachial or radial technique, avoiding the femoral route. Tortuosity alone may render device transit more difficult, along with the development of distal kinks and spasm. Aggressive manipulation may lead to scraping the vessel walls, dissection, embolization, and even vessel perforation. Knowledge of the anatomical layout even before angiography may assist the operator in technique and equipment selection (Figure 1).

AORTIC ARCH ANALYSIS
We originally described aortic arch classification in 1996 based on aortic arch curvature in relation to common carotid diameters and the extent of deep seating; 1,2 we have modified this technique by simplifying the measurements. Typical arch anatomy is seen in 70% of cases. Minor variations in the origin of the great vessels are common, but major variations are rare. Shared origin of the brachiocephalic trunk (BCT) and left common carotid artery (CCA) is seen in 15% of cases; bovine arch is seen in 8% to 10% of cases. With increasing age, hypertension, and disease of the aortic valve, the arch sinks deeper and elongates into the thoracic cavity while pulling the origins of the great vessels along with it. This creates difficulties in not only cannulating the great vessels but also in directing coaxial transfer of energy during catheter exchanges. Using the origin of the left subclavian artery as a landmark, the arch curvature can be classified into three levels of difficulty (Figure 2).

Aortic Arch Types
In a type I arch, the origins of the great vessels are at or near the superior arch line drawn at the origin of the left subclavian artery. In a type II arch, the great vessels arise between the superior arch line and inferior arch line drawn at the fulcrum point of the junction of the lower border of the arch and descending thoracic aorta. The fulcrum point provides a crucial landmark for the femoral approach, because all femorally advanced catheters hinge on this point, and if they had to bend into the arch below this level, it sets the stage for catheter prolapse.

In a type III arch, the great vessels arise below the inferior arch line, thereby making access very difficult. Refer to Carotid Anatomical Analysis sidebar for additional factors for determining access.

CAROTID ACCESS TECHNIQUES
Basic Technique/Telescopic Method
Applicable for type I and II arches; assumes the ECA is patent. After achieving groin access, the 7- to 9-F guide sheath is advanced over the 0.035-inch wire into the descending thoracic aorta (Tables 2 and 3). The 5-F diagnostic catheter is loaded into the sheath after the dilator is removed. After angiography of the target vessel is performed, the angled Glidewire (Terumo Interventional Systems, Somerset, NJ) is advanced through the diagnostic catheter into the ECA, and the catheter is advanced over the angled Glidewire into the ECA. Using the wire and diagnostic catheter as coaxial rails, the guide sheath is advanced into the CCA over the diagnostic catheter. If excessive tortuosity is present in the proximal CCA or if abnormal and deep angulation takeoff of the CCA is present, the sheath is advanced over an Amplatz super stiff guidewire (Boston Scientific Corporation, Natick, vessel needing to be cannulated, the guidewire is pulled back, reshaping the diagnostic catheter first. After engaging the great vessel, the guidewire is advanced, and the guide catheter is slowly advanced to the ostium; once this is reached, the wire is left in place, and the diagnostic catheter is withdrawn, allowing the guide catheter to resume its curve, hooking the ostium. The wire is left behind, removing the diagnostic catheter. If this is chosen, we recommend leaving the wire until an over-the-wire filter is placed in the high distal ICA to provide anchorage and to leave the guide opening without scraping the vessel wall (Figure 3).

SPECIAL SITUATIONS
Subclavian Anchor
For type III arch situations (although type II strategies can be used), serial stiffening methods are more likely to be associated with prolapse of the guide sheath/catheter into the ascending aorta. Although operators have used the bare-wire method of stenting across a bare guidewire (abandoning the guide sheath/catheter), more often, this was not successful either due to lack of support or lack of landmarks for precise placement of nitinol stents (Figure 4).5,6 We have developed a method by using the subclavian artery as an anchor for right CCA access. This involves placing a 6-F sheath in the right brachial artery.

After the diagnostic catheter, usually a SM2 catheter is placed in the BCT, an angled Glidewire is advanced into the right subclavian artery through the SM2 catheter. The angled Glidecath (Terumo Interventional Systems) is then advanced through the right brachial sheath and brought outside. By now, we have firm control of the wire from the brachial and femoral routes. The 8-F Arrow sheath is then advanced over this wire into the right BCT using traction control of the Glidewire from both ends. It is important to remember that the sheath cannot be advanced into the CCA without giving up the anchor wire in the subclavian artery. After the guide sheath with its dilator is advanced into the BCT, the dilator is removed. A 0.018-inch Steelcore wire (Abbott Vascular) is advanced into the ICA through the guide sheath placed in the BCT. Carotid predilatation and stent deployment are then carried out from this position. Due to the ability to leave the Glidewire through the guide sheath and anchoring it at both ends, there is enough wire purchase and support to complete the case. Excessive tension on the Glidewire is avoided to minimize trauma to the subclavian artery.

Ostial Stenosis of the CCA and BCT
Cannulate the involved artery with a diagnostic catheter and advance the 0.018-inch Steelcore wire into the ECA. A 4-mm coronary balloon is advanced across the ostial lesion and predilated to approximately 10 atm. The coronary balloon is removed, and a 6- to 8-mm balloon is advanced and dilated across the stenosis over the Steelcore wire. The Steelcore wire is removed, and a 0.035-inch wire is advanced into the ECA through the larger peripheral balloon placed across the ostial lesion. The peripheral balloon is then removed, and the guide sheath is backloaded with its dilator. The sheath and dilator are then advanced through the ostium as one seamless unit. The dilator is removed after positioning the sheath in the CCA. The ICA lesion is treated in the standard fashion by reintroducing the Steelcore wire, this time through the ICA lesion. On the way out, the CCA is stented by withdrawing the guide sheath, baring the stent. The guide sheath at the ostium can be used to take final images without removing the Steelcore wire (Figure 5).

Total Occlusion of the ECA
After placing the diagnostic catheter and recording images, make a tight pigtail loop to the Amplatz super stiff guidewire and advance it into the distal CCA without reaching the origin of the ICA. The super stiff wire can be used to advance the guide sheath assembly into the CCA after removing the diagnostic catheter.

The alternative approach is to advance a 0.018-inch Steelcore wire or tapered attenuation diameter wire (TAD) (0.018–0.035 inch) through the diagnostic catheter and into the lesion, placing it distally in the ICA. The diagnostic catheter is exchanged for the guide sheath assembly and coaxially advanced into the CCA. The TAD wire provides decent (but not superb) wire support that works well for type I and II arches. For a type III arch and total occlusion of the ECA, a 0.038-inch-diameter Amplatz super stiff wire is needed.

Distal Common Carotid Stenosis
Similar to the situation with total occlusion of the ECA, this situation also entails modifying the standard technique. Because the diagnostic catheter could not be dottered into the ECA through the stenosis at the distal CCA, we suggest the following alternative: After the proximal CCA is cannulated with the diagnostic catheter, advance an Amplatz super stiff wire with its tip tightly wound up as a pigtail through the diagnostic catheter into the distal CCA just below the stenosis. This usually gives sufficient traction and support for the guide sheath assembly to be advanced into the mid-CCA. Alternatively, a TAD wire can be used with its 0.018-inch tip advanced through the lesion in the distal ICA, while the 0.035-inch wire shaft provides adequate support for guide sheath advancement.

Anomalous Origin of the Left CCA (Bovine Arch)
We find a 5-F VTK catheter is best suited for this anomaly. If the angle of origin is not too steep, we can apply the level 2 techniques of backloading the sheath. If the origin has a steep right angle, we recommend an 8- to 9-F Amplatz left2,3 coronary guiding catheter to be placed over a 6-F multipurpose diagnostic catheter as a dilator into the origin of the left CCA. The multipurpose catheter is removed, and the procedure is completed in its entirety from the CCA origin without advancing the guiding catheter into the mid-CCA (Figure 2C).

COMPLICATIONS
Besides embolism, several complications can occur during carotid access, including dissection of the carotid arteries caused by the ledge effect due to unopposed space between a larger guide catheter (7–9 F) and a smaller diagnostic catheter and guidewire-related ECA branch arterial perforations (Figure 6). The small branch perforations can be deadly, with rapid development of retropharyngeal bleeding and airway compromise in an anticoagulated patient. Rapid diagnosis, prompt coil embolization, external pressure, and securing the airway are mandatory. The most dreaded complication to look for during the remote guide catheter access method is guide catheter prolapse, with the carotid filter getting entangled in the stent and detaching or embolizing. Keeping a vigil on the guide catheter position is extremely crucial. Choosing an over-the-wire filter also provides a long wire purchase and an increase in guide catheter stability. Cerebral embolism during carotid access is a stark reminder that not all parts of carotid stenting can be protected.7-10

CONCLUSION
Carotid anatomical analysis and an algorithm-based approach to carotid access can streamline a procedure and help achieve safe and embolism-free access in most situations. Aborting a progressively difficult and challenging access is far better than dealing with atheromatous embolism for which there is no effective recourse. Future technology should address an unmet need by developing a morphing catheter suitable for carotid access.

Subbarao Myla, MD, FACC, FSCAI, is Medical Director of Cardiovascular Research and Endovascular Therapy at Hoag Memorial Hospital Presbyterian in Newport Beach, CA. He has disclosed that he receives research grants from Abbott Vascular, Boston Scientific Corporation, and ev3 Inc., and that he is a consultant to and an advisory board member for Abbott Vascular and Boston Scientific Corporation. He further disclosed that he has equity in Boston Scientific Corporation. Dr. Myla may be reached at (949) 722-2411; subbaraomyla@yahoo.com.

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  10. Diethrich EB, Ndiaye M, Reid DB. Stenting in the carotid artery: initial experience in 100 patients. J Endovasc Surg. 1996;3:42-62.
 

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