Intraoperative duplex scanning of carotid repairs is performed after restoration of ICA blood flow, using a “hockey stick” linear array 10–15 MHz ultrasound transducer enclosed in a sterile plastic sheath. Acoustic coupling for vessel imaging is achieved by ultrasound gel in the sheath and saline in the incision. Imaging is accomplished by placing the transducer over the artery and then slowly moving it along the repair, beginning in the common carotid artery and proceeding distally to the ICA. If a bovine or polyester patch was used for vessel closure, lumen imaging is still possible, but use of a polytetrafluoroethylene (PTFE) patch hampers imaging due to air trapped in the PTFE material. Vessel imaging and velocity spectra recordings can be obtained by orienting the transducer foot pad along the non-patched vessel circumference. With the assistance of a vascular technologist to optimize instrument setting for imaging and pulsed Doppler spectral analysis, the exam time is less than 10 min, including archiving images for the patient medical record. Typically in the transverse and longitudinal planes, examination is performed of the common carotid artery (CCA), carotid bulb, and internal carotid artery (ICA) with B-mode and color flow imaging. The external carotid artery (ECA) is sampled to document patency. Velocity recordings are taken at both proximal and distal surgical endpoints with additional velocity analysis being made of the outflow distal ICA beyond the repair site (Fig. 11.1). The criteria for an “abnormal” duplex scan depends on the site imaged (CCA, carotid bulb, ECA, ICA), focusing on the severity of the anatomic defect and associated alter flow hemodynamics.

Duplex scanning should begin at the proximal CCA to verify normal proximal endarterectomy endpoint. The site of proximal clamp occlusion should be imaged, since focal traumatic wall dissection or plaque injury could have occurred. Scanning then proceeds from proximal to distal to confirm a widely patent lumen and normal velocity spectra. Special attention should be paid to endarterectomy endpoints where residual plaque >2 mm in thickness is abnormal and should be repaired (Fig. 11.2). The normal endarterectomy site should be free of lumen defects and should have no suture stricture, and PSV should be <150 cm/s. Using transverse imaging, the diameter of the proximal ICA (bulb segment) should demonstrate homogenous color flow, and the diameter can be measured, which should be <1 cm, as larger diameter patched segments are prone to aneurysmal dilation and mural thrombus formation. The ECA is imaged to verify patency and presence of distal plaque dissection since the endarterectomy of this vessel is accomplished using an eversion technique for plaque removal. The ECA typically has a high-resistant waveform pattern, oftentimes with an inconsistent diastolic flow pattern based on collateral flow and downstream atherosclerosis. Although uncommon, ECA thrombosis can occur in a heavily diseased vessel. Most surgeons will re-explore the ECA if occlusion or a focal high-grade stenosis is identified, as acute ECA thrombosis presents potential risk for thrombus extension. The ICA should be scanned as far distal as possible, especially if a shunt was inserted. Normal ICA duplex characteristics include sloped, but sharp rise, to systole with a gradual decline through diastole, low-resistant waveform pattern with diastolic flow above the baseline, absent dicrotic notch, and preservation of the spectral width from proximal to distal with or without a clear acoustic window (Figs. 11.3 and 11.4). When a structural defect is identified in the ICA (plaque edge, suture narrowing, artery kinking), tracking the sample volume through the region allows assessment of changes in PSV. Decision for repair is based on the altered hemodynamics produced by the imaged abnormality, with lesions producing focal elevations of PSV > 150 cm/s considered for repair. Figure 11.5 provides a clinical pathway for intraoperative duplex assessment after CEA. Spasm of the ICA is identified by a narrow lumen on color or power Doppler and moderate elevations of PSV in the range of 150–200 cm/s. The finding of lumen thrombus or PSV > 300 cm/s usually indicates that platelet aggregation has developed and re-exploration is mandatory [9, 12]. Table 11.2 provides intraoperative criteria for residual stenosis after CEA. Some vascular surgeons may perform angiography when the duplex imaging is abnormal to confirm an anatomic defect prior to proceeding with endarterectomy site re-exploration.

On occasion, increased PSV ≥ 125–150 cm/s with minimal spectral broadening and normal artery imaging can be the result of vasospasm or compensatory collateral flow due to contralateral ICA occlusion. The presence of high diastolic flow in the ICA, i.e., more than 50% of the PSV, may indicate hyperperfusion syndrome with loss of normal intracranial arterial autoregulation. Appropriate therapy for this condition may include meticulous blood pressure control, steroids, and antiseizure drug administration.

The prevalence of endarterectomy site repair, based on duplex testing , is approximately 5% for CCA and ICA defects (Table 11.1) and an additional 3–5% if correction of ECA stenosis/occlusion is included. If the endarterectomy site has normal duplex imaging and velocity spectra findings, the likelihood of repair site thrombosis is extremely low (<1%), as is the detection of >50% DR stenosis within 3 months of the procedure. A 2011 report from the Vascular Study Group of New England indicated that only one-half of vascular surgeons routinely image carotid repairs, with duplex ultrasound being the preferred technique [7]. Routine imaging was not associated with a reduction in operative strokes, but the incidence of restenosis was significantly less.

The high-resolution (0.1 mm) vessel imaging achieved by the 20 MHz IVUS catheter imaging system has been shown to improve clinical outcomes when used to assess the technical result of peripheral angioplasty procedures [13]. IVUS imaging is used in combination with digital fluoroscopy for monitoring the carotid artery stent-angioplasty procedure. More specifically, IVUS defines vessel character and diameter with an assessment of the treatment zone, which aides in the procedural sizing of the stent and angioplasty balloon. With stent deployment, IVUS can then be employed to interrogate the region of stent angioplasty for residual stenosis or stent deformity. The goal of IVUS imaging is to confirm vessel patency, full stent deployment with an expanded lumen in the region of the atherosclerotic plaque, and no lumen anatomic abnormality [13–17].

The IVUS catheter is delivered to the extracranial carotid bifurcation over a 0.014 in. wire platform after a cerebral protection device is deployed in the distal ICA. While the market presents several catheter choices, all of which offer B-mode real-time imaging, the IVUS Eagle Eye^® Platinum catheter (Volcano Corporation, San Diego, CA) combines B-mode real-time imaging with virtual histology (VH^®). This technology provides a 360° color tissue map, which can provide volumetric measures and assess plaque composition. These features allow for a detailed assessment of the treatment zone (Fig. 11.6). This particular brand catheter now comes with radiopaque markers, which allows for a more exact length measure of treatment zones and offers accurate angiographic calibration, if needed. During a carotid stent-angioplasty procedure, IVUS imaging is used to aid the interventionist in estimating disease extent (stenosis length), select appropriate proximal and distal stent landing zones in normal or minimally diseased arteries, and provide accurate vessel diameter measurements of the ICA and CCA for appropriate stent selection. Following stent angioplasty, reinsertion of the IVUS catheter with pull-back imaging alerts the interventionist to abnormalities of stent expansion, which, if judged to be inadequate, allows immediate endovascular treatment. In addition, by utilizing IVUS with Chromaflo^® imaging, vessel patency can be confirmed, and dissection or other vessel injury can be excluded (Fig. 11.7). The application of IVUS imaging during the stent-angioplasty procedure provides unique anatomic information for arterial repair using less contrast and fewer angiogram runs without increasing morbidity or sacrificing technical accuracy. The technical success of carotid stent angioplasty has been generally determined by multiplanar digital subtraction angiography, with the goal to achieve <20% residual stenosis relative to the normal distal ICA diameter. Figure 11.8 outlines the University of South Florida’s IVUS-guided stent protocol for CAS. Our vascular group and others have adopted IVUS as a quality control assessment of “adequate” stent deployment and balloon angioplasty in the treatment of ICA atherosclerotic occlusive disease, analogous to the use of intraoperative duplex testing during CEA. Following stent angioplasty, real-time B-mode IVUS imaging is performed by positioning the IVUS catheter distal to the stent in the normal ICA and slowly withdrawing the catheter through the stent, visualizing changes in lumen diameter. This maneuver allows identification of regions of poor stent expansion with associated reduction in cross-sectional area (Fig. 11.9). The degree of stent deformation may not be readily apparent by angiography. When IVUS confirms improper stent expansion, defined by an irregular or elliptical stent shape with a residual cross-sectional area reduction of >20% compared to the distal stent, additional balloon angioplasty is performed, typically upsizing the angioplasty balloon 0.5–1.0 mm from the previous size or performing a more prolonged (10 s) balloon angioplasty to expand the carotid bifurcation. Incomplete circular stent expansion after balloon angioplasty is typically caused by calcified carotid bifurcation plaque.