Transcarotid artery revascularization

INTRODUCTION — For patients with indications for carotid revascularization, the treatment options include carotid endarterectomy (CEA) and carotid artery stenting (CAS), which is commonly accomplished with stent delivery using a percutaneous transfemoral approach (ie, TF-CAS); percutaneous delivery of a stent through a transcervical approach has also been described. Transcarotid artery revascularization (TCAR) is a distinct hybrid approach to carotid stenting that requires surgical exposure of the common carotid artery at the base of the neck for stent deployment. TCAR uses dynamic flow reversal for cerebral protection. As with other approaches to carotid revascularization, the TCAR has advantages and disadvantages, and the patient's anatomy must meet specific anatomic requirements to undergo the procedure safely.

The technical aspects of TCAR and clinical outcomes are reviewed. The decision to proceed with carotid revascularization, and the general aspects of carotid stenting are reviewed separately. (See "Management of asymptomatic extracranial carotid atherosclerotic disease" and "Management of symptomatic carotid atherosclerotic disease" and "Overview of carotid artery stenting".)

TRANSCAROTID STENTING SYSTEM — TCAR is a hybrid procedure that requires an incision at the base of the neck and surgical exposure of the common carotid artery. TCAR uses a specialized arterial sheath through which the stent is deployed to treat the carotid stenosis [1,2]. The TCAR neuroprotection system consists of the arterial sheath, venous sheath, and a flow controller with a built-in filter [3].

An arterial sheath is placed directly into the common carotid artery through a small surgical incision. The sheath is connected to the flow controller, which is in turn connected to a venous sheath placed percutaneously into either of the common femoral veins. During the procedure, surgical occlusion of the common carotid artery proximal to the arterial sheath location creates a "reversal of flow," with blood flowing away from the brain through the neuroprotection system, returning the blood via the venous system. This reversed flow, which is driven by the differential pressure within the arterial system and the venous system, prevents distal embolization and stroke. Other devices for embolic protection are discussed separately. (See "Overview of carotid artery stenting" and "Percutaneous carotid artery stenting", section on 'Embolic protection devices'.)

One stent has been approved for use in the United States for TCAR (ie, ENROUTE stent). Since the stent was designed specifically for TCAR, it has a shorter delivery system (57 cm) compared with stent platforms used for percutaneous carotid artery stenting (CAS). [1,4,5]. This stent also has the smallest cell size among the available open-cell design stents on the market.

Alternative stents (ie, those typically used for a transfemoral approach) can be used for TCAR provided they fit within the arterial sheath for safe delivery. (See "Percutaneous carotid artery stenting", section on 'Carotid stent devices'.)

Learning curve for TCAR — As a hybrid procedure that draws upon experience from open carotid surgery as well as percutaneous CAS, there is much interest in knowing the learning curve associated with TCAR. A learning curve has been demonstrated for percutaneous CAS, with increasing experience with transfemoral CAS (TF-CAS) leading to significantly decreased complications [6]. Comparatively speaking, for TCAR, users achieve low complication rates (eg, stroke, death, myocardial infarction) early in their experience, even when the procedure is performed under general anesthesia. However, increasing experience does improve operative efficiency.

In a study looking at 188 consecutive patients treated at three large academic medical centers, the learning curve for TCAR was relatively short. After 15 cases, operators decreased procedural time (79 to 71 minutes) and duration of flow reversal (13 to 9 minutes). However, the low rate of stroke, death, and stroke/death was similar for the early and late experience, suggesting that this technique can be adopted quickly by vascular surgeons experienced with carotid intervention [7].

In a review of data from the TCAR Surveillance Project (TSP), clinician experience was divided into four levels: novice (cases 1 to 5), intermediate (cases 6 to 20), advanced (cases 20 to 30), and expert (cases >30) [8]. The study included 3456 procedures performed by 417 unique surgeons from 178 centers between September 2016 and December 2018. Procedures performed by operators at the novice experience level made up of the largest proportion (41 percent) of the registry, with only 18 (4.3 percent) physicians at the expert level. Cases performed at the higher experience levels were more likely to have United States Centers for Medicare and Medicaid Services high-risk factors and trended toward more symptomatic patients. Overall, the data showed low stroke and mortality rates, even among operators in the early stages of the learning curve. There were no significant differences in major in-hospital outcomes, including stroke, death, and stroke/death/myocardial infarction between groups. However, increased experience was associated with lower operative, fluoroscopy, and flow reversal times, and decreased bleeding.

In reviewing an international quality assurance database, the performances of 18,240 procedures by 1273 physicians were analyzed [9]. It was determined that a flow reversal target time of <13.1 minutes and skin-to-skin time of 81 minutes demonstrated proficiency to minimize adverse event rates.

CAROTID REVASCULARIZATION

TCAR for internal carotid lesions — Carotid artery stenosis most commonly results from atherosclerotic degeneration. Disease in the carotid arteries can lead to embolization or thrombosis, resulting in neurologic events (eg, transient ischemia attack, stroke). The treatment of carotid stenosis includes maximal medical therapy and carotid revascularization for patients with appropriate indications. The general indications for carotid revascularization for stenotic atherosclerotic lesions are the same, regardless of revascularization approach (carotid endarterectomy [CEA], transfemoral carotid artery stenting [TF-CAS], TCAR). Indications in patients with asymptomatic or symptomatic carotid artery stenosis, whether to proceed with CEA or CAS are reviewed separately. (See "Management of symptomatic carotid atherosclerotic disease", section on 'Patients likely to benefit' and "Management of asymptomatic extracranial carotid atherosclerotic disease", section on 'Our approach to patient selection'.)

In the United States, reimbursement for carotid artery stenting (both TF-CAS and TCAR) is determined by the National Coverage Decision (NCD) by the Centers for Medicare and Medicaid Services. The NCD was created in March 2005 and provides coverage for stent placement in symptomatic patients with ≥70 percent stenosis and at least one defined "high-risk" criteria for CEA. The creation of the TCAR Surveillance Project (TSP) in 2016 extends coverage to "high-risk" patients with either asymptomatic ≥80 percent stenosis or symptomatic ≥50 percent stenosis. The TSP is an open-ended registry intended to compare real-world patient outcomes for TCAR with alternative procedures. All patients enrolled in the TSP have clinical data entered in the Society for Vascular Surgery Vascular Quality Initiative (SVS-VQI) to provide indefinite interval monitoring of TCAR outcomes. Enrollment in the TSP requires the use of specific devices with "transcarotid" labeling. In June 2022, the TSP was expanded to include "standard-risk" patients with either asymptomatic ≥70 percent stenosis or symptomatic ≥50 percent stenosis. (See "Overview of carotid artery stenting", section on 'TCAR surveillance project'.)

Anatomic requirements and eligibility — Anatomic requirements must be met for TCAR to ensure that the arterial sheath can be safely inserted. These include:

●Distance between access site (at common carotid artery above clavicle) and the lesion >5 cm

●Diameter of common carotid artery >6 mm

●Common carotid artery access and carotid occlusion sites are free of significant disease (ie, no thrombus/calcification within 1 cm of either site)

Ultrasonography can usually determine if the patient's anatomy meets these anatomic constraints. The patient is evaluated in the intended surgical position (ie, head turned away from the side of the lesion with the shoulders elevated), similar to positioning for carotid endarterectomy.

Alternatively, computed tomography (CT) angiography can be used. In a retrospective review of CT angiography in 118 patients, 100 percent had adequate common carotid artery (CCA) diameter, 75 percent had the necessary >5 cm distance, and 96 percent had no significant CCA disease at the puncture site [10]. Based on these, 72 percent of carotid arteries are eligible for TCAR based on the criteria listed above. Another 7 percent of the carotid arteries had significant calcification/tortuosity that was felt to be unfavorable for stent placement. Overall, only 68 percent of the entire cohort was eligible for TCAR. In the same analysis, among the 24 percent of carotid arteries that were considered to be high risk for TF-CAS, 69 percent were eligible for TCAR. In a similar study evaluating CT angiography of 433 carotid arteries, overall 85 percent were eligible for TCAR [11].

However, use of straight-line CT angiography during preoperative planning when determining TCAR anatomic eligibility may underestimate the clavicle-to-carotid bifurcation length. In a small retrospective review of 46 patients, duplex US performed with extended-neck surgical positioning and center-line CT angiography provided similar and longer length measurements compared with CT angiography with straight-line measurements [12]. Among patients with tortuous common carotid arteries, duplex US and center-line CT added 1 cm more in length.

Contraindications — While TCAR is a relatively new procedure, it still relies on stent placement to treat the carotid lesion. As such, lesion characteristics not favorable for TF-CAS (eg, severe carotid calcification, severe carotid tortuosity, visible thrombus within lesion) remain contraindications for TCAR. The general contraindications for CAS are reviewed separately. (See "Overview of carotid artery stenting", section on 'Contraindications'.)

Several features of TCAR (compared with TF-CAS) merit discussion. By accessing the artery at the base of the neck, the presence of severe aortic arch calcification or arch tortuosity (especially type III arches) are not factors in TCAR. While aortic anatomy is almost not relevant in TCAR, the health of the common carotid artery is paramount to successful arterial sheath placement and procedural success. A history of radiation therapy to the neck and prior surgery are factors that must be considered for TCAR, since surgical exposure of the common carotid artery is required during this procedure (like CEA). However, the incision is small and often well away from the worst areas of radiation such that TCAR can be conducted safely.

Finally, TCAR requires placement of the stent through a sheath placed through an incision in the neck. As such, the presence of a tracheostomy with likely significant oropharyngeal bacterial colonization of the skin at the neck is considered a relative contraindication.

TCAR for supra-aortic lesions — The use of the TCAR neuroprotection system for treatment of supra-aortic lesions ("off-label" use) has also been described. In a series of 16 patients, endovascular stenting was used to treat 11 patients with single lesions of the supra-aortic arch vessels and five patients with tandem stenotic lesions. Eleven of these patients were symptomatic. A total of 21 lesions were treated, including seven innominate artery, one right common carotid artery, eight left common carotid artery, and five in the internal carotid artery. To treat the proximal lesions, the procedures were performed with the arterial sheath directed in a retrograde fashion, with clamping at the common carotid artery distal to the insertion site. Once the lesion was treated, the procedure was either terminated (for single lesions), or the sheath was then inserted in an antegrade fashion through a separate common carotid artery puncture as per standard TCAR (if there was a tandem lesion). Technical success was obtained in all cases, and there were no strokes or transient ischemia attacks during the 30 days after the procedure [13].

PATIENT PREPARATION — Much of the preparatory management for TCAR is similar to that of the patient undergoing transfemoral carotid artery stenting (TF-CAS). (See "Overview of carotid artery stenting", section on 'Medication management'.)

Dual antiplatelet therapy and statins — Dual antiplatelet (DAPT) using aspirin and clopidogrel and statin therapy are recommended for all patients prior to undergoing TCAR (algorithm 1). The efficacy of DAPT and statin therapy for CAS, in general, are reviewed separately. (See "Overview of carotid artery stenting", section on 'Dual antiplatelet therapy' and "Overview of carotid artery stenting", section on 'Statin therapy'.)

We use the regimen as reported in the Safety and Efficacy Study for Reverse Flow Used During Carotid Artery Stenting Procedure (ROADSTER [2]) trial, which was derived from the Carotid Revascularization Endarterectomy versus Stent (CREST) Trial [14], modified slightly, and consisting of:

●For those patients not on chronic aspirin therapy, we start aspirin (75 to 325 mg once daily) at least 72 hours before the procedure or, if within 72 hours of the procedure, we give a loading dose of at least 650 mg four or more hours before the procedure.

●For those patients not on chronic clopidogrel therapy, we start clopidogrel 75 mg once daily at least 72 hours before the procedure, or if within 72 hours of the procedure, we give a loading dose of clopidogrel 450 mg four or more hours before the procedure.

●For those patients not on chronic statin therapy, we start atorvastatin 40 mg daily for seven days before the procedure or we give a loading dose of 80 mg 12 hours before the procedure.

The timing of the loading dose depends on procedure scheduling. Daily aspirin, clopidogrel, and atorvastatin are subsequently provided until the time of the procedure. Following TCAR, DAPT with aspirin (75 to 325 mg once daily) plus clopidogrel (75 mg once daily) for 30 days is recommended. For patients with a history of neck irradiation, we continue DAPT indefinitely. For all other patients, after clopidogrel is discontinued, we continue aspirin 325 mg daily (range 75 to 325 mg) indefinitely.

In a study that reviewed over 31,000 CAS procedures (approximately 50/50 TCAR and TF-CAS), perioperative P2Y12 inhibitors markedly reduced the rate of perioperative neurologic events. Looking specifically at TCAR procedures, only 87.3 percent of patients appeared to be on P2Y12 inhibitors during the periprocedural period, suggesting room for significant improvement in real-world clinical practice [15].

For patients that cannot tolerate clopidogrel or have been shown to have clopidogrel resistance, the available data suggest that aspirin/ticagrelor may be a reasonable alternative to aspirin/clopidogrel [16]. We typically use ticagrelor 90 mg orally twice daily along with aspirin 81 mg orally daily. In cases when loading is necessary, we administer ticagrelor 180 mg orally and wait at least two hours prior to stent placement.

TECHNIQUES — TCAR can be performed in a dedicated angiography suite or in an operating room with a dedicated or mobile fluoroscopy unit.

Carotid artery access — TCAR requires a small cutdown over the proximal ipsilateral common carotid artery [1,4,5,17-32]. The carotid access used for TCAR eliminates the need to pass the catheters through a diseased or anatomically challenging aortic arch and is appealing in this regard.

A short (3 cm) longitudinal or transverse incision is made at the base of the neck just cephalad to the clavicle. The incision is centered between the clavicular and sternal heads of the sternocleidomastoid muscle. Careful dissection through the avascular plane between these two muscle heads will allow identification of the carotid sheath. Care is taken during dissection of the proximal common carotid artery to avoid injury to the vagus nerve and other nerve branches. A vascular loop or umbilical tape can be placed around the common carotid artery to aid with subsequent vascular control or clamping.

Anticoagulation — Before arterial sheath insertion, the patient should be anticoagulated with intravenous heparin to maintain a target activated clotting time (ACT) greater than 250 seconds. For patients with an allergy to heparin, alternative agents (eg, argatroban, bivalirudin) may be used. (See "Heparin and LMW heparin: Dosing and adverse effects" and "Direct oral anticoagulants (DOACs) and parenteral direct-acting anticoagulants: Dosing and adverse effects", section on 'Bivalirudin'.)

Once the procedure is completed, we recommend reversal of anticoagulation (eg, protamine sulfate to reverse heparin) to facilitate hemostasis. In a review of 944 matched pairs of patients undergoing TCAR who did and did not receive protamine, the use of protamine was associated with a significantly lower risk of bleeding complications (2.8 versus 8.3 percent), including bleeding that resulted in interventional treatment (1 versus 3.6 percent), and a lower rate of blood transfusion (1.1 versus 2 percent) [33]. There was no increased risk of thrombotic events with protamine use.

Arterial and venous sheath placement — For arterial access, a 5-0 polypropylene "U" or "Z" suture is first placed on the common carotid artery at the intended puncture site to aid with later puncture site closure and hemostasis. The common carotid artery is accessed at that site using a micropuncture access kit that includes appropriate length wires and a sheath. The initial angiography is performed to demonstrate the anatomy.

Over a stiff wire with a short, floppy tip, the arterial sheath is carefully inserted, taking care to ensure that the target lesion is not disturbed. The venous sheath is placed into the right or left common femoral vein in a standard fashion using ultrasound guidance. The arterial sheath is then connected to the venous sheath using the provided intervening flow controller device. Additional angiography is obtained to demonstrate the lesion and prepare for intervention.

Pretreatment to prevent hypotension — Prior to occlusion of the common carotid artery, the blood pressure is controlled (recommended systolic blood pressure 140 to 160 mmHg). All TCAR patients should also be pretreated with 0.2 mg of glycopyrrolate (antimuscarinic anticholinergic agent) to prevent hypotension and bradycardia that may occur during carotid angioplasty and stimulation of the baroreceptors. An additional dose of 0.2 mg can be given depending on the patient's response to the initial dose. Atropine should be available for use as needed if hemodynamic compromise occurs.

Establishing flow reversal and carotid stenting — The common carotid artery proximal to the arterial sheath location is occluded, either by tightening a vessel loop or using a vascular clamp. With the differential pressure between the arterial sheath (arterial pressure of the distal carotid from collateral circulation) and the venous sheath (central venous pressure), reversal of flow occurs with blood traveling away from the internal carotid into the venous system through the neuroprotection system. Flow reversal is confirmed by infusing saline into the external tubing of the venous sheath and demonstrating clearance of the saline with blood.

"Intolerance" to flow reversal is a rare occurrence during TCAR. In the Safety and Efficacy Study for Reverse Flow Used During Carotid Artery Stenting Procedure (ROADSTER)-1 study, there was one instance (0.7 percent) of intolerance to high-flow reversal [2]. In a review of 297 patients who underwent TCAR under local/regional anesthesia in the ROADSTER-1 and ROADSTER-2 clinical trials, eight (2.7 percent) had intolerance, though all cases were successfully managed, with four cases completed under low flow reversal, three were weaned from high to low over several minutes, and one required general anesthesia [34].

The mean flow reversal time was 13 minutes. With increasing experience, flow reversal times are shorter. In a review of the TCAR Surveillance Project, flow reversal time decreased from 12 minutes for novices (first five cases) to less than 10 minutes for experts (>30 cases) [8].

With reversal of flow established, the internal carotid artery stenosis is crossed with a 0.014-inch diameter wire. The lesion is predilated to the nominal internal carotid artery diameter to ensure luminal gain, and then the stent is deployed across it. Poststent ballooning appears to be safe without an increased risk for postoperative in-hospital stroke/death. However, the rate of transient ischemia attack may be increased [35]. As such, it is our practice to avoid poststent dilation unless there is significant residual stenosis >30 percent.

After allowing additional time (minimum two minutes) for clearance of any potential debris from manipulation of the lesion, completion arteriography is performed in at least two orthogonal views to ensure adequate stent lumen expansion and apposition to the arterial wall.

Completion — Once technical success has been verified, the wire is removed, and antegrade flow is restored in the common carotid artery. The flow controller is disconnected, the arterial sheath is removed, and hemostasis is obtained by tying down the previously placed suture. Anticoagulation is reversed. (See 'Anticoagulation' above.)

The venous sheath is removed, and manual pressure is used for hemostasis. The incision in the neck is closed in layers in the standard fashion.

POSTPROCEDURE CARE AND FOLLOW-UP — Postprocedure care following TCAR is similar to carotid endarterectomy (CEA) and other techniques for CAS. Following TCAR, the patient is transferred to a monitored setting for frequent blood pressure and neurologic assessment. The importance of tight blood pressure control cannot be overemphasized. Dual antiplatelet and statin therapy should be continued postprocedure. (See 'Dual antiplatelet therapy and statins' above.)

Routine duplex imaging is performed to identify restenosis. (See "Overview of carotid artery stenting", section on 'Postprocedure care and duplex surveillance'.)

COMPLICATIONS — Complications of TCAR include stroke, bleeding, hematoma, arterial dissection, and nerve injury. The most serious acute complication associated with TCAR is stroke, which can occur due to thromboembolism, hypoperfusion, hyperperfusion syndrome, or hemorrhage. Stroke rates for TCAR are overall low and compare favorably to those for carotid endarterectomy and transfemoral carotid artery stenting (TF-CAS). Other complications that are not specific to TCAR, including myocardial infarction, renal failure related to intravenous contrast, carotid thrombosis and restenosis, and stent fracture are reviewed separately. (See "Overview of carotid artery stenting", section on 'Complications'.)

Access-related issues are the most common complications following TCAR, occurring in 2 percent of all cases in one systematic review [36]. Arterial dissection related to placement of the arterial cannula occurred in 1 to 2 percent of cases. Overall, the incidence of cranial nerve injuries was very low (0.3 percent). Bleeding complications occurred in 2 percent of cases. In a comparative review, although the bleeding risk was similar between differing carotid artery revascularizations, the risk of access site complications resulting in interventional treatment was significantly higher for TCAR compared with TF-CAS (1.3 versus 0.8 percent) [37]. The use of protamine for reversal of heparin is associated with significantly less bleeding [33]. (See 'Anticoagulation' above.)

SUMMARY AND RECOMMENDATIONS

●Transcarotid artery revascularization (TCAR) is a hybrid procedure using a specialized carotid stenting system that combines surgical exposure of the common carotid artery (CCA) with stent placement to treat carotid artery stenosis. To prevent embolization during the procedure and resultant stroke, the cerebral vasculature is protected using flow reversal, with blood flow directed away from the internal carotid artery during the stenting procedure. (See 'Introduction' above and 'TCAR for internal carotid lesions' above.)

●In addition to the standard National Coverage Decision, the United States Centers for Medicare and Medicaid Services also allows coverage for TCAR in "high-risk" patients with either asymptomatic ≥80 percent stenosis or symptomatic ≥50 percent stenosis. There is a requirement for patient enrollment in the TCAR Surveillance Project (TSP) with data available within the Vascular Quality Initiative for outcome analysis. The TSP also requires use of stenting devices with "transcarotid" labeling. (See 'TCAR for internal carotid lesions' above.)

●TCAR has a short learning curve, with low rates of complications early in the user's experience. The available data show similar postoperative strokes rates compared with carotid endarterectomy, but with lower rates of myocardial infarction, shorter procedure time, and a lower incidence of cranial nerve injury. Outcomes for TCAR are also improved compared with transfemoral carotid angioplasty and stent placement (TF-CAS). (See 'Learning curve for TCAR' above and "Overview of carotid artery stenting", section on 'Approach to carotid artery stenting'.)

●For internal carotid stenting using TCAR, the patient's anatomy must meet specific anatomic criteria: (See 'Anatomic requirements and eligibility' above.)

•Distance between access site (at CCA above clavicle) and the lesion must be >5 cm

•Diameter of CCA >6 mm

•CCA access/occlusion sites free of significant disease (thrombus/calcification)

•Carotid lesion amenable to stent placement (thrombus/calcification)

●For patients in whom TCAR is scheduled or anticipated, dual antiplatelet therapy (DAPT) using aspirin and clopidogrel is recommended. Furthermore, periprocedural statin therapy is also recommended. (See 'Dual antiplatelet therapy and statins' above and "Overview of carotid artery stenting", section on 'Summary and recommendations'.)

Specifically, for TCAR this includes:

•For those patients not on chronic aspirin therapy, we start aspirin (75 to 325 mg once daily) at least 72 hours before the procedure or, if within 72 hours of the procedure, we give a loading dose of at least 650 mg four or more hours before the procedure.

•For those patients not on chronic clopidogrel therapy, we start clopidogrel 75 mg once daily at least 72 hours before the procedure, or if within 72 hours of the procedure, we give a loading dose of clopidogrel 450 mg four or more hours before the procedure).

•For those patients not on chronic statin therapy, we start atorvastatin 40 mg daily for five days before the procedure or we give a loading dose of 80 mg 12 hours before the procedure.

●Following TCAR, DAPT with aspirin (75 to 325 mg once daily) plus clopidogrel (75 mg once daily) for 30 days is recommended. For patients with a history of neck irradiation, we continue DAPT indefinitely. For all other patients, after clopidogrel is discontinued, we continue aspirin 325 mg daily indefinitely. (See 'Dual antiplatelet therapy and statins' above and "Overview of carotid artery stenting", section on 'Dual antiplatelet therapy'.)

●Following open access to the carotid artery and sheath placement, the patient is systemically anticoagulated, typically using heparin. At the completion of the procedure, we reverse heparin with protamine. Protamine reduces the risk for bleeding complications without any increased risk for thrombotic events. (See 'Anticoagulation' above.)

●The most serious acute complication associated with TCAR is stroke, which can occur due to thromboembolism, hypoperfusion, hyperperfusion syndrome, or hemorrhage. The overall stroke rate for TCAR is low at <1 to 2 percent. Other complications include access-related issues (eg, hematoma, bleeding), myocardial infarction, contrast-related renal failure, restenosis of the target lesion, and carotid stent fracture. (See 'Complications' above.)