Stenosis of the internal carotid artery is responsible for 10–20% of all strokes or transient ischemic attacks. Percutaneous transluminal carotid artery stenting (CAS) is a promising new treatment option for carotid artery stenosis. These procedures are currently performed in high-risk patients and have demonstrated favorable outcomes.1,2
Advanced age, decreased cerebral reserve, excessive tortuosity and heavy calcification are four major risk factors that will increase the risk of a stroke after carotid stenting.3 Heavy calcification can obscure the vessel border even after digital subtraction. Heavy calcification, especially in combination with arterial tortuosity, causes difficulties in tracking devices, lesion dilatation, stent positioning and achieving adequate stent expansion. We describe the use of intravascular ultrasound (IVUS) to facilitate internal CAS in a patient with heavily calcified and ambiguous common carotid artery stenosis.
Case Report. The patient, a 72-year-old male with a past medical history of type 2 diabetes mellitus, dyslipidemia and transient ischemic attack (TIA) presented with a non ST-T elevation myocardial infarction. Coronary angiography revealed severe coronary artery disease with heavy calcification and stenosis of the left anterior descending artery (LAD) and right coronary artery (RCA). The patient had undergone successful rotational atherectomy and stent placement of the LAD and RCA. Magnetic resonance angiography (MRA) evaluation for a history of TIA demonstrated bilateral high-grade internal carotid artery (ICA) stenosis. Echocardiographic Doppler of the carotid artery was not done because both internal carotid arteries were evaluated by MRA. The patient was scheduled for a carotid artery angiogram and possible CAS.
Procedural details. An 8 Fr Radifocus sheath (Terumo Medical Corp., Tokyo, Japan) was introduced into the right common femoral artery. A 6 Fr pigtailed 110 cm catheter was advanced to the ascending thoracic aorta over a standard 0.035 inch guidewire and an aortic aortogram was performed under digital subtraction angiography (DSA). An aortic arch aor-togram revealed a type 2 arch. A 5 Fr VTK diagnostic catheter (Cook, Inc., Bloomington, Indiana) was used to engage the innominate artery. After angiographic road mapping, a 0.038 inch stiff angled Terumo 260 cm length wire (Terumo Medical Corp. distributed by Boston Scientific Corp., Natick, Massachusetts) was advanced into the external carotid artery. The VTK catheter was then advanced into the right common carotid artery, and the Terumo wire was changed to an Amplatzer super-stiff 0.035 inch, 300 cm length wire. The VTK catheter was exchanged for an 8 Fr Multipurpose guiding catheter, and guiding angiograms were obtained in the lateral, antero-posterior and right anterior oblique angulations. Ninety percent stenosis of the proximal right internal carotid artery with calcification was noted. Intracranial angiography of the internal carotid in the anteroposterior and lateral views revealed a patent right middle cerebral artery (MCA) and a right anterior communicating artery (ACA) with a collateral to the left ACA. Stenting was successfully performed on the right ICA prior to attempting to dilate the left ICA. Using the same technique described above, an 8 Fr multipurpose (MP) catheter was placed in the left common carotid artery.
Guiding angiograms, obtained in the lateral, antero-posterior and left anterior oblique angulations, revealed 50% stenosis with calcification of the middle part of the left common carotid artery (Figures 1 and 2), 90% stenosis of the proximal left internal carotid, patency in the left MCA, and occlusion in the right ACA. The AngioGuard wire (Cordis Corp., Miami, Florida) was then advanced into the distal ICA and deployed. The activated clotting time (ACT) was maintained at > 250 seconds with heparin. The left ICA stenosis was predilated with a 4 x 20 mm Monorail balloon (Cordis).
A 6 x 40 mm Precise self-expanding nitinol stent (Cordis) was advanced, but was not able to pass a 50% stenosis in the left CCA. A common carotid angiogram without DSA revealed heavy calcification at the 50% stenosis lesion (Figure 3). A common carotid angiogram in an additional view did not reveal an eccentricity or further degree of stenosis of the 50% stenosis. An 8 Fr Multipurpose guiding catheter was then advanced over an Amplatzer super-stiff wire, but was not able to pass the 50% stenosis. Significant pressure damping occurred.
Using a 4 Fr Multipurpose diagnosis catheter to cross the lesion and pullback pressure recording from the 50% stenosis of the mid CCA to the normal segment at the distal CCA, a gradient difference of 50 mmHg was observed (Figure 4). IVUS was performed with a Volcano system (Volcano Therapeutics, Inc., Rancho Cordova, California) using 2.9 Fr catheter with a 20 MHz ultrasound crystal at 14 mm depth. An IVUS catheter was advanced into the distal CCA and pullback was done to the 50% stenosis with calcification observed in the mid CCA.
IVUS of the left CCA revealed significant stenosis with superficial calcification (Figures 5 and 6). The minimum lumen area was 4.1 mm2. The referencelumen area was 30 mm2, and the lumen area stenosis was 87%. A 6 x 40 mm Ultrathin balloon (Boston Scientific) was used to predilate at the CCA lesion. Using a “buddy wire” technique, a 0.014 inch ACS Hi-Torque Extra S’port guidewire (Abbott Vascular, Abbott Park, Illinois) was advanced across the stenosis of the mid CCA parallel to the AngioGuard wire. A 6 x 40 mm Ultrathin balloon was used to predilate at the CCA lesion. A 6 x 40 mm Precise nitinol self-expanding stent was then successfully advanced across the stenosis at the mid CCA and was deployed across the left ICA. A Smart Control 8 x 60 mm self-expanding stent was deployed across the CCA. A 6 x 40 mm Ultrathin balloon was used for post-stent dilatation. IVUS of the ICA and CCA revealed stent malapposition in the CCA secondary to vessel calcification. An IVUS catheter was exchanged for a 7 x 40 mm Ultrathin balloon and inflated at 16 atm. The common carotid angiogram revealed < 20% residual stenosis and good flow. Intracerebral angiography was unchanged from the preintervention angiograms.
The AngioGuard wire was then retrieved. A 5 Fr MP diagnostic catheter was used for recording pullback across the stent in the CCA. No significant gradient remained (Figure 7).
Postprocedure, the patient developed hypotension which required a low dose infusion of dopamine (3 μg/kg) to maintain his blood pressure. He was weaned off dopamine overnight and was discharged home on aspirin and clopidogrel.
Discussion. The utility of IVUS for accurate assessment of angioplasty outcome and for quantitative assessment of luminal volume following intervention and stent placement was first described by Wilson et al.4 Clark and et al reported on the safety and utility of intravascular-guided carotid artery stenting.6 The procedural success rate was 97%, with a combined stroke or death rate at 30 days of 5.6%. IVUS evaluation at the target vessel site revealed that the minimum lumen diameter (MLD) was significantly smaller compared to quantitative coronary angiography (QCA). IVUS was helpful in evaluating the severity of superficial calcification of the ICA lesion segments. Carotid stenting at the arteries with superficial calcification had significantly increased the incidence of stroke in this study. IVUS provided an accurate assessment of stent dimensions, expansion, and apposition. Clark et al have subsequently reported the use of serial IVUS to determine the mechanisms and predictors of carotid artery restenosis after CAS. In this study, they found that although self-expandingcarotid stents generated considerable neointimal hyperplasia, the process was balanced by marked late stent enlargement. Small stent dimensions immediately postprocedure were associated with a higher risk of restenosis.6 Kamawata et al applied the IVUS catheter extravascularly to the cervical carotid arteries to obtain intraoperative ultrasound images during carotid endarterectomy. Extravascular application of an IVUS catheter is efficient for intraoperative evaluation of the distal end of the stenotic lesion, especially in cases with stenotic lesions at very high positions and cases in which preoperative angiograms did not clearly demonstrate the distal end.7
Heavy calcification can obscure the vessel border, even after digital subtraction. Angiographic data alone is often insufficient to provide accurate assessment of vessel geometry and the degree of stenosis in the presence of heavy calcification. IVUS provides images from within the vessel, has greater resolution, does not have to penetrate extravascular soft tissues and can assess the vessel in three dimensions. IVUS is also the most sensitive in vivo method for detection of calcium.8 In this case, we describe the value of IVUS to evaluate significant stenosis outside the target lesion site at the CCA that was preventing delivery of the stent into the ICA. Angiographic assessment of the CCA did not show a significant lesion. IVUS demonstrated a 90% stenosis with complex superficial calcification. A significant physiological obstruction was demonstrated with a significant pressure gradient obtained via pullback recording. Protrusion of the superficial calcification inside the CCA, which was demonstrated by IVUS, not only created difficulty to deliver the stent to the internal carotid artery, but also left the CCA lesion untreated, which is not likely to achieve the same clinical benefit of internal carotid stenting. IVUS helped identify significant stenosis by superficial calcification at the CCA which facilitated the treatment strategy for this patient.
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