There are special features to bear in mind when stenting the carotid artery. It is particularly susceptible to incomplete stent deployment since heavy calcification resists complete stent expansion [16]. Furthermore, the internal carotid artery is not always uniform in diameter but is narrower distally and wider near its origin [17]. Stenting can also compromise the origin of the external carotid artery by compression, and recurrent stenosis following carotid endarterectomy may respond differently during stenting compared with a primary atherosclerotic lesion [18, 19]. The IVUS operator must appreciate these aspects and avoid dislodging embolic material or causing intimal dissection to the artery through overzealous instrumentation.

IVUS is a powerful tool in carotid stenting; however, the penalties are high if the disease is underestimated or the stent is badly deployed. We use IVUS more frequently now in carotid stenting since the introduction of cerebral protection devices. Immediately after deploying the protection device, IVUS can assess the lesion and take measurements to help stent and balloon sizing. We currently use the Eagle Eye Platinum catheter (Volcano Corporation, Rancho Cordova, CA), which is a low-profile 2.9F 20-MHz probe that configures with the 0.014-inch wire of most cerebral protection devices (Fig. 58.5). The IVUS probe is advanced into the distal internal carotid artery, and the pullback is begun. The distal internal carotid artery has a characteristic appearance on IVUS because it is so thin and usually spared of disease. The histologic layers are elegantly seen. Measurements can be taken just above the lesion to help size balloon and stent diameters, and the degree of stenosis can also be assessed to decide whether predilation is required or whether primary stent deployment can be performed [20]. While currently plaque morphology can be subjectively assessed by IVUS, the new advance of VH IVUS (Volcano Corporation, Rancho Cordova, CA) is promising since it will provide classified histologic plaque types.

Following stenting, the IVUS probe is introduced again and a pullback assesses the completeness of stent deployment. IVUS measurements of the minimum stent diameter can be made to decide whether further ballooning is required. Mid-stent waisting is a common finding. In general, a minimum stent diameter of more than 4 mm is recommended in the internal carotid artery to avoid residual hemodynamically significant stenosis [7]. The stent should be uniformly well expanded throughout its length following deployment. It should also appose completely to the artery wall with no space apparent between the stent and the vessel. It is important to make sure that the length of the lesion is covered by the expanded stent such that no proximal or distal disease is left untreated. A careful inspection for intimal dissection is also important.

Despite our enthusiasm for carotid IVUS, passing balloon catheters and the IVUS probes up and down the internal carotid artery is not without hazard even with protection devices. The decision to reballoon or deploy another stent needs to be made cautiously. The advantages must be weighed against the risks of possible complication for the patient. Sometimes it is best to accept a reasonable deployment rather than overpursue it.

Stenting the origin of the common carotid artery from a retrograde carotid approach poses a challenge to all endovascular specialists. The common carotid artery comes off the aortic arch or the innominate artery, and accurate stent location at the origin is difficult using aortography alone because of the natural curvature of the arch [20] (Fig. 58.6). Accurate placement is possible using IVUS by passing the IVUS probe down the common carotid artery from above. Fluoroscopy visualizes the radiopaque transducer as it passes down the vessel. Blood flow is displayed in color pulsing red with each cardiac cycle. When the probe passes from the stenosis into the aorta, there is a sudden change in the size of the luminal color. Together with fluoroscopy this technique pinpoints the origin of the vessel exactly for accurate device deployment. The same technique can also be used to stent the origin of all the supraaortic vessels.

In the thoracic aorta , a larger probe is required (8.2F) with more penetration (10 MHz), a larger diameter of 60 mm, and compatibility with a larger guidewire (0.035 in.). IVUS is useful in assessing and measuring the neck of a thoracic aneurysm being treated by endoluminal grafting. The exact origin of the subclavian artery can also be identified (Fig. 58.7). IVUS also defines the extent of thoracic dissection and greatly assists treatment of coarctation of the aorta [21].

Similarly in endoluminal grafting for abdominal aortic aneurysm , IVUS provides accurate measurements of neck diameters and assessment of the iliac arteries [3]. The IVUS catheter is advanced from the groin to a level just above the renal arteries. The proximal and then the distal necks of the aneurysm are measured together with the luminal length requiring grafting. The amount of calcification and mural thrombus is noted, and assessment of the shape of the proximal and distal necks can indicate how well the endoluminal graft will exclude the aneurysm. IVUS provides a greater understanding of the case than computed tomography (CT) alone (Fig. 58.8). Immediately following endoluminal graft deployment, it is difficult to obtain good IVUS images because of tiny pockets of air trapped in the endomaterial and because of the metal endoskeleton. These both cause bright reflection of ultrasound. Further technological advances with IVUS or the endoluminal grafts in this situation are necessary since color IVUS could potentially detect endoleak and its source in the operating room at the time of device implantation [4].