Brachiocephalic and Vertebral Arteriography: Technical Considerations

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Submitted on Fri, 09/05/2008 - 16:36
Authors

Ali Amin, MD,

Introduction Despite technologic advances in noninvasive vascular imaging (CTA, MRA), arch and carotid arteriography continues to play an essential role in the planning of surgical and endovascular interventions, and still is the gold standard for brachiocephalic and vertebral imaging. Endovascular treatment of carotid artery stenosis has become an accepted modality in a sub-group of patients who are “high risk” for carotid endarterectomy. At some point in the future, this may become the standard of care. As carotid, subclavian and vertebral interventions are more widely utilized, the need for safe and expeditious access to the aortic arch and its branches becomes extremely important. Optimal use of carotid angiography in patients with carotid artery stenosis requires thorough knowledge of anatomy, modifiable factors that contribute to risks, advanced endovascular skills, and treatment plans for complications. The purpose of this article is to provide the reader with technical aspect of carotid angiography, pre- and post-procedural assessment skill, and strategies for minimizing adverse neurologic events. Pre-procedural Assessment 1. Patient evaluation: This includes complete history and physical examination noting past medical history of diabetes, peripheral vascular disease, hypertension, and renal insufficiency. Obtain a complete list of medications and allergies. It is important to know if the patient had prior exposure to contrast media and any adverse reaction to iodinated contrast agents. A complete physical exam with evaluation of peripheral pulses is essential. 2. Laboratory evaluation: Complete blood count, assessment of renal function (serum creatinine, preferably creatinine clearance) and coagulation profile. 3. Informed consent: Educating the patient about the procedure, risks and alternatives is an important step in obtaining an informed consent. The procedure should be explained to the patient in a step-by-step fashion so the patient is more relaxed and cooperative. This knowledge is especially important in brachiocephalic angiography as opposed to peripheral angiography, since the patient is less sedated and any movement by the patient during the procedure would lead to motion artifact or sub-optimal angiogram. A comfortable, compliant patient will lead to a superior angiographic result without repeated injections and multiple catheter manipulations. Risks of procedures should be thoroughly discussed with the patient and/or family members but not in such a way to frighten the patient. Most of the complications are related to common femoral artery cannulation and deficient hemostasis after the catheter has been removed.1 Acceptable incidence of complications (numbness, pseudoaneurysm, AV fistula) secondary to common femoral artery puncture should be less than 0.5% Neurologic complications such as stroke or transient ischemic attack, although uncommon, are a major concern during this procedure. A stroke rate of 1.0–1.2% was present during carotid angiography in ACAS (Asymptomatic Carotid Atherosclerosis Study and NASCET (North American Symptomatic Carotid Endarterectomy Trial) trials.2,3 Patient Preparation Pre-operative orders include NPO status, except medications with sips of water. Additionally, it is important to adjust diabetic medications accordingly. Patients should continue to take their antihypertensive medications in order to avoid severe hypertension during and after the procedure. Intravenous hydration with saline should be started at 80–100 cc/hr. Caution should be used in patients with congestive heart failure. In patients with diabetes or renal insufficiency, a bolus of 250–500 cc saline may be appropriate to hydrate the patient prior to contrast study. Additionally, in patients with renal insufficiency, the use of Acetylcysteine (Mucomyst®) 600 mg p.o. bid one day prior to arteriogram and another dose given on day of the procedure may decrease the risk of radiocontrast nephropathy.4 The patient is given 50 mg of Demerol IM on call with occasional use of 1 mg of Versed at the start of the procedure for both analgesic and possible sedative effect. However, the patient should be alert enough to follow instructions and respond to neurologic assessment during the procedure. Oxygen by nasal cannula is appropriate in patients with low oxygen saturation as well as continuous EKG monitoring. Use of antiplatelet therapy is important and cannot be overemphasized. The patient should be on daily aspirin therapy prior to angiogram. For maximal platelet inhibition, clopidogrel (Plavix®, Sanofi Pharmaceuticals) may be added to the regime. Although intravenous heparin is not routinely used during the procedure, a heparin bolus dose of 2,000–5,000 units is used by some angiographers. If the higher dose is given, it is usually reversed by protomine at the end of the case. Use of heparin is not a substitute for meticulous handling of wires and catheters during selective catheterization and injections. Equipment The angiographic unit must be able to produce good quality digital subtraction angiography (DSA) as well as roadmap imaging to help with selective catheterization. The use of bi-plane digital subtraction angiography provides additional advantage in superior imaging, if it is available in the institution. This is especially important when evaluating intracranial vasculatures. The new low osmolality nonionic contract agents have several advantages over the old, high osmolality ionic contrast. Additionally diluting the contrast by 50% will decrease the amount of dye used and the burning sensation without compromising the angiographic details. Vascular Access One percent Lidocaine is routinely used for local anesthesia. The common femoral artery is cannulated at the medial aspect of the femoral head, utilizing a 19 gauge, single wall, entry needle. This size needle produces a smaller hole than an 18 gauge and allows passage of a 0.035 wire. Use of micropuncture kit utilizing a 21 gauge needle and .018 wire has been advocated by some physicians. Although this produces less pain, it has a learning curve and is associated with higher cost. It is important to use the groin with the stronger femoral pulse for cannulation. Use of fluoroscopy is very important to spot femoral head location, especially in obese patients. This will avoid puncturing the superficial femoral artery or deep femoral artery. After arterial puncture is achieved, a 0.035 J tip wire (primary wire) is used to gain entry to the common femoral artery. Fluoroscopy should be used to visualize advancement of the wire into the thoracic aorta. If any resistance is felt, it would be investigated with use of contrast, prior to advancing the wire further. Hydrophilic wires, such as Glidewire® (Terumo/ Boston Scientific Corporation) should not be used as a primary wire through the needle. These wires can be damaged by manipulation through the needle or can advance under plaque and cause extensive dissection. These wires are used as a “secondary” wire for selective catheterization. After the J wire is inserted, a 4 Fr. sheath is placed and the side port is flushed with heparinized saline. The smaller 4 Fr. arterial sheath minimizes trauma to the femoral artery and allows the angiographer to exchange 4 Fr. catheters without difficulty. Advanced angiographers may perform sheathless angiography by placing and manipulating the catheter directly into the femoral artery, where as other angiographers may prefer the 5 Fr. system. Catheter and sheath hygiene is extremely important and it needs to be done frequently to remove any debris or clot. A simple rule to remember is to double flush the catheter every two minutes. A 90-100 cm pigtail catheter (Fig. 1) with radiopaque tip is inserted over the .035 J wire into the ascending thoracic aorta just above the aortic valve under fluoroscopy. Radiopacity of the catheter tip allows for the best visualization within the ascending aorta. Prior to the removal of the wire, the image intensifier is positioned between 30-45 degrees left anterior oblique (LAO) to show the best “opened” aortic arch (Fig. 2). At this point, the wire is removed. Every time a catheter is inserted within the aortic arch or branched vessel, it is flushed using a “double flush” technique. With this technique, a saline syringe is used to aspirate blood from the catheter, and a second heparinized saline syringe is used to flush the catheter. This technique will minimize risk of any embolization. At this point, the injector has already been filled with 50% contrast such as Visipaque® (Amersham Health, Princeton, NJ), and attached to the connecting tube. The injector should be tipped straight up so that all the air rises to the top of the injector syringe. The plunger of the injector is advanced manually until the contrast fills the tubing. The pigtail is attached to the connecting tube through a high pressure stopcock. The stopcock is closed to the patient to remove any air from the tubing and then closed to the injector to allow back bleeding from the catheter. Finally, the stopcock is placed in a neutral (open) position and injector syringe is manually, gently aspirated backward until contrast blood interface is visualized to make sure no air has been introduced during the connection process (Fig. 3). Blood should not be aspirated all the way back to the injector syringe, since it will form a clot over a period of time. Although these steps may look cumbersome, they are essential in performing safe carotid and peripheral angiography. In order to visualize the arch and its branches leading to the brain, the image intensifier is placed so the lower border of the transverse aortic arch is at the bottom of the monitor (screen) and the patient’s head is turned toward the right with the chin raised (Fig. 4). This will maximize the visualization of bilateral common carotid artery, bilateral vertebral artery, as well as carotid bifurcations. At times, the culprit carotid lesion can be seen on this study. It is very important to instruct the patient before each injection to hold his or her breath, and avoid swallowing, movement, or talking. An injection of 50% diluted dye is done at the rate of 15 cc per second for a total of 30 cc during the arch injection. Since the dye is diluted, only 15 cc of full contrast dye is used, producing a good cervical thoracic arch aortogram. A PA or right anterior oblique (RAO) view would allow better visualization of the innominate artery bifurcation or proximal subclavian artery. Special attention must be made to severe disease involving the origin of the great vessels. If there is significant disease at the origin, it is recommended to leave the pigtail catheter near the origin of these great vessels. If available, use of bi-plane angiography will improve bifurcation views. Selective Catheterization Once the aortic arch has been evaluated, then the appropriate catheter can be chosen based on arch anatomy (Fig. 5). I. Catheter: There are two types of selective catheters. One is a self-forming (simple curve) catheter and the other is a manual-forming (complex curve) catheter. The advantage of a self-forming catheter over a manual-forming catheter is its ease of use. It does not need to be reformed and is, therefore, less traumatic on the arch since it does not require frequent manipulation to form it. In an atherosclerotic arch, frequent manipulation could result in plaque disruption and embolization. Both types of catheters are available as braided or non-braided catheters. The non-braided catheter, such as GlideCath® (Terumo/Boston Scientific Corporation) has two disadvantages. First, the tip is not radiopaque so it does not visualize well under fluoroscopy. Second, the non-braided catheter has poor torqueability and maneuverability, making selective catheterization more difficult (Fig. 6). The decision to use self-forming versus manual-forming catheter is based on arch anatomy (Fig. 5). As a general rule, type I arch and most of the type II arches can be catheterized using a self-forming catheter. For some type II arches and most of the type III arches, use of a manual-forming catheter is necessary. A. Self-forming Catheters These include Vertebral or Berenstein and Headhunter catheters (Fig. 7). Once the catheter is placed in the arch over the wire, the tip of the catheter is facing downward. After the wire (secondary hydrophilic angle Glidewire) is pulled back approximately 2 inches, the tip of the catheter can be engaged into the selective innominate or carotid artery by applying torque to the shaft of the catheter while simultaneously pulling it back. Once the tip is engaged into the origin of the selected vessel, the Glidewire is passed into the proximal artery and the catheter is advanced over the wire. Finally, the wire is removed and double flushing of the catheter is done prior to injection (Fig. 8). B. Manual-forming Catheters These catheters are more difficult to use for a beginner since they need to be reformed (Simmons I, II, III) (Fig. 9). The best and least traumatic way to reform this catheter is to use the left subclavian artery. This method will avoid reforming the catheter in the arch, which can lead to atherosclerotic plaque disruption and embolization. First, the arch angiogram with the left subclavian artery picture is retrieved and placed on the monitor. If you have a double monitor system, the image should be displayed next to the (real-time) monitor. The image intensifier is placed in the same LAO view as the initial arch angiogram. The appropriate Simmons catheter is brought to the proximal descending thoracic aorta over a .035 angle Glidewire. Then the wire is passed into the left subclavian artery, utilizing the displayed arch angiogram as a guide. The wire is passed into the distal left subclavian artery. At this point, the Simmon catheter is advanced over the wire until the secondary curve of the catheter is just proximal to the ostium of the left subclavian artery. If the secondary curve is pushed past the ostium, catheter reforming will not occur. Finally, the wire is pulled back a few inches, removing the rigidity on the secondary curve, and the catheter is slowly pushed and rotated into the ascending aorta. Once the catheter is reformed, the catheter is gently pulled back, while the tip is pointed inferiorly or horizontally (toward you), until the tip is aligned with the target vessel. Then gentle torquing will engage the tip superiorly into the innominate or left common carotid artery. The wire is gently advanced two inches into the artery and the catheter is pulled back gently to engage the proximal portion of the artery (Fig. 10). One of the big disadvantages of these catheters is the inability to access the distal part of the vessel because of its curvature and stiffness. If access to distal part of the artery is needed, then a self-forming catheter should be inserted over an exchange length wire to avoid loss of access. Another way of reforming the catheter is bouncing the Glidewire off of the aortic valve and reforming the catheter in the ascending aorta. Caution should be taken in patients with significant plaque in the ascending aorta or aortic vegetations while using this technique.5–9 II. Selective catheterization and contrast injections: Once the cervicothoracic arch aortogram is completed, my next selective catheterization involves the left common carotid artery. This is because of the following reasons. The left common carotid artery is between the innominate artery and the left subclavian artery, and is the most difficult to cannulate depending on its angle and tortuosity. Usually the tip of the selective catheter goes into the innominate or the left subclavian artery during the manipulation of the catheter in the arch to gain access to the left common carotid artery. Selective catheterization of the left common carotid artery after performing arch angiogram can be done easily by following a few steps (Fig. 11): 1. Do not move the image intensifier after the arch angiogram is completed. 2. Have a technologist draw on the monitor with a black marker the location of the left common carotid artery, and/or use the saved image on the other monitor. 3. At this point, you have decided which selective catheter to use based on the arch anatomy. 4. Under fluoroscopy, access the left common carotid artery using the drawing on the screen. Although this may look primitive, it will prevent excessive manipulation of the wire and catheter as well as minimize dye injection to find the left common carotid artery. This maneuver will avoid complications from atheroembolism or use of excessive dye. Once the left common carotid artery is cannulated, the regular angle Glidewire (180 cm) is passed into the mid common carotid artery. The catheter is advanced over the wire and parked at the proximal one-third of the common carotid artery. Torquing of the wire can be done utilizing a 4x4 to dry the wire near the catheter hub. Neither the wire nor the catheter should be passed to the carotid bulb, avoiding manipulation of the carotid plaque. Since the majority of the atherosclerotic plaque involves the distal common carotid artery and the carotid bulb, avoiding any manipulation will significantly decrease the risk of atheroembolism. Once the catheter is in place, the wire is removed and double flushing of the catheter is done. At this point, initial PA view (image intensifier is posterior) angiogram is taken to include both the carotid bifurcation and intracranial vessels. The head is immobilized with a head rest and the image intensifier is placed at approximately 15–20? craniocaudal view. The superior orbital rim and the petrous regions are superimposed, allowing visualization of the bifurcation of the internal carotid artery into the anterior and middle cerebral arteries (Fig. 12). After the catheter is attached to the injector, 50% contrast is injected at the rate of 5 cc per second for a total of 10 cc with lower PSI. Delayed filming into the venous phase should be done to rule out other intracranial vascular abnormalities. If the carotid bifurcation is low and not well-visualized during this injection, the image intensifier is placed in the lower cervical area to evaluate carotid bifurcation pathology. Next, the image intensifier is placed at a 90? angle for a lateral image. The patient is asked to relax their shoulders, and to try and reach their feet. This opens up the area of the carotid bifurcation and the cervical common carotid for better imaging (Fig. 13). It is important to ask the patient to abstain from moving, swallowing, and talking during all injections. The same injection rate is used for all cervical and intracranial injections. In some cases, a third injection utilizing oblique view (45?) may be necessary to fully evaluate and better visualize carotid bifurcation disease. The PA projection allows the best visualization of the anterior cerebral artery, middle cerebral artery and anterior communicating artery. There is little superimposition of the two vessels since the anterior cerebral courses toward the midline and the middle cerebral extends laterally. In the lateral position, some superimposition of the two vessels obviously exists. Detailed discussion of intracranial anatomy is beyond the scope of this article. However, once an aneurysm is visualized, it is important to obtain angle views to visualize the origin as well as the mouth of the aneurysm. Selective catheterization of the right common carotid artery is easier because of the larger diameter of the innominate artery and its more proximal position to the arch. Again, the original arch angiogram is retrieved and displayed on the second monitor. Depending on the arch anatomy, a self-forming or manual-forming catheter is used. The Glidewire is passed into the proximal common carotid artery, avoiding advancement into the right subclavian artery, utilizing the arch angiogram as a guide. The catheter is then passed over the wire into the proximal common carotid artery. If a manual-forming catheter such as the Simmons is used, gentle pull after withdrawing the wire engages its tip into the proximal common carotid artery. Due to its stiff nature, it will not advance easily into the mid common carotid artery. Selective injections are the same as in the left common carotid artery. Sometimes there is tortuosity at the innominate bifurcation and there is difficulty in passing the wire into the right common carotid artery. At this point, the catheter is left in the innominate artery and a road mapping is done in a PA view. This technique will help you navigate the Glidewire into the right common carotid artery (Fig. 14). Vertebral Catheterization Evaluation of the vertebral artery may be necessary for vertebrobasilar insufficiency or assessing collateral circulation in patients with carotid artery disease (i.e. carotid artery occlusion). Usually a good view of the vertebral arteries is obtained during the arch injection. However a closer look at each of the vertebral arteries may be necessary in selected cases. Evaluation of the left vertebral artery is easier than the right by reason of the straightforward anatomy of the left subclavian artery. Again, the arch anatomy can be used as a guide to place the selective catheter and wire. A 4 Fr. Vertebral or Headhunter is placed into the mid subclavian artery over a Glidewire. The wire is removed, and after flushing the catheter, gentle hand injection is done while the catheter is slowly pulled back and the origin of the vertebral artery is identified. The catheter is then placed just proximal to the ostium of the vertebral artery. The image intensifier is placed so the tip of the catheter is at the bottom of the monitor where the entire course of the vertebral artery can be visualized. The catheter is attached to the injector and dye is injected at 4 cc per second for a total of 8 cc. This allows maximum visualization of the entire vertebral artery into the basilar artery without direct cannulation. It is important to avoid direct cannulation of the vertebral artery, since this may cause spasm, dissection, or plaque disruption. If an ostial lesion is suspected or poorly visualized on a routine study, then additional craniocaudal views may be taken, as well as other intracranial views (Fig. 15). Another trick is to park the catheter in the proximal subclavian artery and inflate a blood pressure cuff on the arm to get enough contrast for intracranial vertebral images. If femoral route is not possible, then right brachial approach can be utilized (4 Fr. system) to select left common carotid, right carotid and vertebral arteries. Catheter Removal and Compression It is important to remove the catheter, especially the manual-forming or complex ones, over the wire. This will not only straighten the catheter while being taken out, but also minimizes catheter contact with the aortic wall. If high-dose heparin was given, then it should be reversed with proper dose of protomine, or we will wait for the ACT to fall below 180. Direct manual compression for 10–15 minutes is usually adequate to achieve hemostasis at the puncture site with a 4 Fr. sheath. The patient is to remain on bed rest for approximately four hours. Post procedure assessments should include groin checks, neurologic status, and blood pressure monitoring. Becoming comfortable with a few catheter types, rather than trying to use all the catheters mentioned here, will improve your skills. Selective carotid and vertebral angiography must be done carefully and expeditiously. Proper techniques, including minimal manipulation of the catheter within the aortic arch and its branches, will prevent trauma, dissection, spasm, clot or emboli. It is important for the angiographer to master the angiographic skills and complete the examination with minimal morbidity. Ali Amin, MD, FACS, FACC, RVT can be contacted at ali@talon.net.