The Aortic Arch: Markers, Imaging, and Procedure Planning for Carotid Intervention
- Volume 6 - Issue 1 - Jan/Feb 2009
- Posted on: 1/14/09
- 1 Comments
- 22530 reads
Brachiocephalic vessel configuration (branches’ number and position) are equally important to the arch elongation type. In the usual configuration, the innominate artery, the left CCA, and the left subclavian artery have separate origins.3 Aortic arch anomalies are not infrequent in the population. The most common anomaly of the aortic arch is the bovine variety (Figure 2), which occurs in about 27% of the population: the innominate artery and the left CCA have a common origin (20%), or the left CCA is a separate branch of the innominate artery (7%). Less frequent variations include a common origin of left CCA and left subclavian artery (1%) or a left vertebral artery originating from the arch (0.5%).8
Arch calcification. The higher reported embolization rates during CAS, compared with surgery, have been attributed to emboli dislodged to the brain during the passage of the aorta.9,10
Aortic arch calcification is a predictor of neurologic events in non-surgical patients11 and in patients undergoing coronary artery bypass grafting.12,13 It seems that a similar risk exists in carotid angioplasty and stenting. Severe aortic calcification is not only a marker of cerebral arteriosclerosis, which is less tolerant to hypoperfusion and hypoxia, but mainly provides a treacherous intravascular operating field, with a fragile intraluminal surface prone to ulceration and disruption by catheter and guidewire manipulations.3,4 Extensive maneuvers can produce emboli or disrupt aortic plaques with subsequent delayed dislodgment and, therefore, thrombus can form and dissections can occur.3
When carotid angioplasty and stenting are considered, aortic arch calcification can be categorized as favorable if there is no calcium shadowing or if there is a trace, and unfavorable if there is luminal irregularity or diffuse calcification.5 In the latter case, the vascular interventionalist should be cautious with catheter manipulation.
Arch vessel origin stenosis. When carotid angioplasty and stenting are considered, the aortic arch vessel origin stenosis < 50% can be categorized as favorable and > 50% as unfavorable.5 When a severe proximal CCA lesion is present, stenting (under filter protection, if possible) is required before further continuation of the procedure.3
The aortic arch of elderly people. Patients in their 80s and 90s who are fit enough to be managed interventionally upon indication are common. Arch characteristics tend to change over time with age and prolonged hypertension. Also, aortic calcification, arch vessel origin stenosis, arch vessel tortuosity, and aortic arch elongation and distortion emerge.4,5,11–15 The ascending aorta and transverse arch elongate, pushing the aortic valve and the origins of innominate and left CCA inferiorly. The locations of the origins of these major arch branches become harder to reach. These factors make carotid angioplasty and stenting technically difficult, leading to a higher risk of thromboembolic complications. Thus, carotid angioplasty and stenting in elderly patients (> 80 years old) have been associated with higher rates of stroke and death.16,17
Imaging of the aortic arch. While Doppler ultrasound is usually efficient when carotid endarterectomy is considered, it is definitely not enough for CAS. Several anatomic considerations are particularly crucial for CAS planning. Arch anatomy and lesions, vessel rigidity, the presence of ostial plaques, and underestimated tortuosities can be a source of unexpected technical challenge and thus, should be meticulously evaluated, before intervention (Table 1). A complete study that includes the aortic arch and the origins of the brachiocephalic trunks is essential. Imaging should be performed with arteriography, magnetic resonance angiography (MRA), or computerized tomographic angiography (CTA). However, while MRA and CTA have been validated to assess severity of stenosis, neither has yet been validated to assess disease of the arch or great vessel origins. For most patients, arch angiography remains the gold standard and can be achieved by a left anterior oblique angle visualization to open up the arch to the exact amount varying on the patient’s anatomy, but commonly at least 30 degrees. A 15 to 20 X 30 rate of injection (power injector), meaning a rate of 15 mL/s to 20 mL/s for a total volume of 30 mL is usually enough.18
The most important aortic arch issue to address is its configuration, followed by the extent of calcification and the originating vessel’s stenosis.3 Digital subtraction, CTA, or MRA will allow careful evaluation of the aortic arch and brachiocephalic origins, which is imperative in determining the ease or difficulty of CCA access, an absolute key to procedural success. (Figure 3) Such information will the influence the choice of catheters and the interventional strategy.
Aortic calcification and/or branch stenosis can be visualized angiographically (digital subtraction angiography, CT angiography). In many cases, MR angiography is not sufficient for the evaluation of the presence of calcification.
Transoesophageal echocardiography may be more accurate but is of less (or no) clinical significance. Plain chest radiography has been recently advocated as a useful, widely available, and inexpensive diagnostic tool in detecting aortic calcification.19
Intravascular ultrasound could be utilized for both quantitative and qualitative measurements of aortic plaque, though not of arch vessel origin during angiography.3
Selective Carotid Catheterization by Arch Type
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