Abstract
Objective:
Transcarotid artery revascularization (TCAR) has emerged as an alternative to transfemoral carotid artery stenting (tfCAS). We investigated the proportion of carotid arteries undergoing revascularization procedures that would be eligible for TCAR based on anatomic criteria, and how many arteries at high anatomic risk for tfCAS would be amenable for TCAR.
Methods:
We performed a retrospective review of consecutive patients who underwent carotid endarterectomy (CEA) or carotid stenting between 2012–2015. Patients were excluded if a CT angiogram (CTA) of the neck was not performed within 6 months of the procedure. We assessed TCAR eligibility based on the instructions for use (IFU) of the ENROUTE Transcarotid Neuroprotection System and high anatomic risk for tfCAS based on anatomic factors known to make carotid cannulation more difficult or hazardous.
Results:
Of the 118 patients and 236 carotid arteries identified, 12 carotid arteries were excluded for presence of an occluded ICA. Of the remaining 224 carotid arteries, 72% were eligible for TCAR based on IFU criteria; 100% had 4–9mm ICA diameters, 100% had ≥6mm CCA diameter, 75% had ≥5cm clavicle to carotid bifurcation, and 96% lacked significant CCA puncture-site plaque. Additionally, 7% of carotid arteries had bifurcation anatomy unfavorable for stenting; thus, of the entire cohort of arteries examined, 68% were eligible for TCAR. History of hyperlipidemia (OR 6.7 [1.7–26], P < .01), COPD (OR 3.5 [1.5–8.3], P < .01), and older age (OR 1.1 [1.0–1.1], P < .01) was independently associated with TCAR ineligibility, whereas white race (OR 0.2 [0.0–1.0], P = .048) and beta-blocker use (OR 0.3 [0.1–0.7], P < .01) was independently associated with TCAR eligibility. In addition, 24% of carotid arteries were considered high-risk for tfCAS based on presence of a type III aortic arch (7.6%), severe aortic calcification (3.3%), tandem CCA lesions (7.1%), moderate/severe stenosis at the carotid ostium (8.9%), and tortuous distal ICA precluding embolic-filter placement (4.5%). Active smoking (OR 4.4 [1.9–10], P < .01), hyperlipidemia (OR 4.0 [1.2–14], P = .03), and older age (OR 1.1 [1.0–1.1], P = .02) were independently associated with tfCAS ineligibility, whereas preoperative aspirin (OR 0.1 [0.0–0.4], P < .001) or Plavix (OR 0.3 [0.1–0.8], P = .01) use was associated with tfCAS eligibility. Of the arteries that were considered high-risk for tfCAS, 69% were eligible for TCAR.
Conclusions:
The majority of carotid arteries in individuals selected for revascularization meet TCAR eligibility, making TCAR a viable treatment option for many patients.
Keywords: carotid artery, transcarotid artery revascularization, eligibility
Table of Contents Summary
This retrospective, single-center study of 118 patients and 224 carotid arteries found that 68% of all carotid arteries are anatomically eligible for TCAR. Therefore, TCAR is a viable treatment approach for many patients despite its anatomic device restrictions.
INTRODUCTION
Surgical management of carotid artery stenosis using carotid endarterectomy (CEA) and transfemoral carotid artery stenting (tfCAS) has mitigated the risk of stroke and stroke-related deaths in patients with carotid artery stenosis.1–3 However, while tfCAS has been shown to be more minimally invasive compared to CEA and has similar efficacy in reducing long-term stroke rates in certain populations, it has failed to become accepted as an equivalent alternative to its more invasive counterpart.4–6 This reality, in part, is due to higher rates of peri-procedural stroke associated with tfCAS.7–10 One explanation for the increased stroke risk is likely suboptimal embolic protection during aortic manipulation, lesion crossing, and angioplasty/stenting.11.
In recent years, transcarotid artery revascularization (TCAR) has emerged as a novel technique for carotid revascularization. This hybrid technology allows surgeons to directly access the common carotid artery (CCA) and initiate temporary dynamic flow reversal to protect against embolic stroke during stent deployment.12 In the initial multicenter ROADSTER trial, use of the ENROUTE Transcarotid Neuroprotection System (Silk Road Medical, Sunnyvale, CA) resulted in a 30-day stroke rate of 1.4% and stroke/death of 2.8% in patients at high risk for CEA.13,14 These results compared favorably to both CEA and CAS outcomes in standard-risk patients seen in the CREST trials, which revealed a 30-day stroke rate of 2.3% and stroke/death rate of 2.6% following CEA, and a 30-day stroke rate of 4.1% and stroke/death rate of 4.8% following tfCAS.7 Subsequent data from the PROOF study demonstrated excellent procedural success with TCAR as there was no incidence of major stroke, myocardial infarction, or death at 30-days.15 Together, these trials suggest that TCAR may be a safe, effective surgical option for patients with carotid artery disease.
Despite the promise that TCAR holds as an alternative to standard carotid interventions, the applicability of TCAR to the general population is unknown. According to instructions for use (IFU) of the ENROUTE Transcarotid Neuroprotection System, patients must meet several criteria for TCAR based on anatomical requirements. While past studies have demonstrated that TCAR can successfully treat both asymptomatic and symptomatic patients with carotid disease who are at high-risk for CEA,14,15 no investigations have been made to determine the proportion of patients who meet anatomic requirements. We sought to assess the percentage of carotid arteries that meet anatomic criteria for TCAR and determine TCAR eligibility in those at high anatomic risk for tfCAS.
METHODS
Dataset
We retrospectively identified 478 consecutive patients undergoing carotid revascularization by CEA, tfCAS, and TCAR at our institution from 2012–2015. Patients without preoperative computed tomography angiography (CTA) imaging of the neck <6 months of procedure were excluded from analysis (n = 360, 75%), resulting in 118 patients and 236 carotid arteries; carotid arteries with internal carotid artery (ICA) occlusion were also excluded (n = 12, 5.1%) (Figure 1). Carotid measurements, utilizing internal program tools, were then performed for each patient regardless of intervention side (Figure 2). Subanalyses evaluating only diseased carotid arteries with stentable bifurcation anatomy and with stenosis >50% were performed to confirm eligibility findings, with the latter performed to focus on the carotid artery subset with a disease burden for which operative intervention would be considered. Patients were not counted twice if they had more than one carotid intervention during the study period.
Figure 1:
Inclusion and exclusion criteria for evaluating TCAR and tfCAS eligibility
Figure 2:
Measurements performed for transcarotid artery revascularization. Cla-Bi, clavicle-bifurcation distance; cm, centimeters; LCCA, left common carotid artery.
Baseline patient demographics and anatomic characteristics were obtained via chart review. Symptomatic status was defined as having an ipsilateral TIA, amaurosis fugax, or prior stroke within 6 months. Pre-operative renal insufficiency was calculated by the CKD-EPI formula and defined as glomerular filtration rate (GFR, mL/min/1.73m2) <60. PL manually performed all imaging review, including carotid and aortic arch measurements as well as calcification and tortuosity grading, using the Conserus™ Enterprise Viewer platform (Change Healthcare, Nashville, TN). Images that generated any uncertainty were reviewed by MS.
Patient Cohorts
TCAR eligibility was determined by the ENROUTE Transcarotid Neuroprotection System IFU (Silk Road Medical, Sunnyvale, CA), which is summarized in Table I. Aside from patients with an occluded carotid artery, each patient had two carotid arteries available for evaluation and could therefore have both a TCAR-eligible and a TCAR-ineligible artery. We treated each carotid artery individually, keeping baseline patient characteristics associated with each artery. Additionally, we assessed TCAR eligibility in patients >80 years old, which has been defined as a Centers for Medicare and Medicaid services high-risk CEA variable.
Table I.
Summary of carotid arteries that meet anatomic and medical requirements for TCAR
| TCAR Criteria | Carotid Arteries (n=224) |
|---|---|
| Anatomic Criteria | |
| ICA diameter 4–9 | 224 (100%) |
| Clavicle-carotid bifurcation distance >5cm | 167 (75%) |
| CCA diameter >6mm | 224 (100%) |
| None to mild puncture site plaque | 214 (96%) |
| Medical Criteria | |
| No nickel allergy | 224 (100%) |
| No bleeding disorder | 224 (100%) |
| No contraindication to aspirin or plavix | 224 (100%) |
| No contraindication to anticoagulation | 224 (100%) |
| Overall eligibility for TCAR | 162 (72%) |
CCA, common carotid artery; ICA, internal carotid artery; TCAR, transcarotid revascularization
Although not specifically noted as a contraindication for TCAR based on the ENROUTE IFU, CCA depth above the clavicle is an important anatomic consideration due to the higher degree of difficulty obtaining CCA access in patients with deeper necks. A CCA depth >4cm was considered more challenging. In patients with >4cm CCA depths, we evaluated the presence of extra clavicle to bifurcation length given the angled trajectory needed to access the artery.
Since not all carotid bifurcations are suitable for stent placement, we further assessed the proportion of arteries with stentable carotid bifurcations that were anatomically eligible for TCAR. Ineligibility for carotid bifurcation stenting was determined by presence of heavy circumferential common to internal carotid calcification, and severe ICA tortuosity directly adjacent to the distal endpoint of a carotid lesion, which would result in ICA kinking after stent deployment.
Carotid Disease and Calcification Grading
Degree of ICA stenosis was calculated based on a ratio of the narrowest ICA diameter to the diameter of normal distal cervical ICA. CCA puncture-site disease was graded on the degree of calcification of the CCA just above the clavicle. We subjectively qualified the degree of calcification as none/minimal or moderate/severe. We considered moderate/severe CCA calcification at the puncture site to be a contraindication to TCAR.
Transfemoral Carotid Stent Risk Evaluation
TfCAS was deemed high risk based on anatomic factors known to make carotid cannulation more difficult or hazardous. This included Type III aortic arches, severe aortic arch calcification or mural thrombus/non-calcified plaque, moderate/severe CCA ostium plaque/calcification, severe distal ICA tortuosity, or ICA diameters near the base of the skull precluding embolic filter placement. Distal ICA diameter criteria of 2.5–7.0mm for filter placement was based on the Abbott Emboshield Nav6 Embolic Protection System (Abbott Laboratories, Lake Bluff, Illinois) IFU. With the exception of 7 patients (6.0%), all CTA neck imaging extended to the chest and head, thereby allowing complete aortic arch and full-length ICA evaluation. Aortic arch type was based on the distance between the takeoff of the innominate artery and the top of the aortic arch: <1cm for Type I arches, 1–2cm for Type II arches, and >2cm for Type III arches. Tandem CCA lesions included any CCA stenosis >50%. Degree of aortic arch calcification and CCA ostium calcification were subjectively scored as minimal, moderate, or severe.
Statistical Analysis
Continuous variables were presented as median and interquartile ranges.Categorical variables were presented as counts and percentages. Univariate differences between patients who were eligible and ineligible for TCAR were assessed using χ2 and Fisher’s exact tests for categorical variables, and Student’s t-test or rank-sum for continuous variables where appropriate. All tests were two-tailed and P < .05 was considered statistically significant. Multivariable logistic regression was utilized to identify independent associations between patient comorbidities and either TCAR or tfCAS eligibility. Purposeful selection was initially used to populate these models, which utilizes both univariate screen using a P < .25 cutoff and variables shown to be associated on prior analyses. Covariates were removed from and added to the model if they were not significant and not a confounder. The Hosmer-Lemeshow statistic for goodness of fit was used to assess the multivariable models. All analyses were performed with Stata/SE 15.0 (StatCorp, College Statin, TX). The Institutional Review Board at the Beth Israel Deaconess Medical Center approved this study. Informed consent was waived given the retrospective nature of the design.
RESULTS
Of the 118 patients who had CTA imaging performed <6 months prior to their procedures, 54 (46% of patients, 24% of all carotid arteries) were treated for symptomatic carotid stenosis. After exclusion of carotid arteries with ICA occlusion, a total of 224 carotid arteries remained for anatomic eligibility analysis, of which 176 (79%) had evidence of carotid disease. Sixty-six percent of arteries with carotid disease had stenosis > 50%, and 43% had stenosis >80%. No patients had severe concomitant ipsilateral intracranial occlusive disease. A total of 113 (50%) interventions met inclusion criteria; 88 CEA (78%), 3 eversion CEA (2.6%), 20 tfCAS (18%), and 2 TCAR (1.8%). During this same period, we performed a total of 419 CEA and 43 CAS.
TCAR Eligibility
Anatomic characteristics of the carotid arteries assessed in our study are summarized in Table II. Based on ENROUTE IFU anatomic requirements, 162 (72%) carotid arteries assessed were eligible for TCAR. All carotid arteries had a 4–9mm ICA diameter and a ≥6mm CCA diameter, 167 (75%) met the required ≥5cm clavicle-carotid bifurcation distance, and 214 (96%) had minimal to no CCA puncture-site plaques. There were no patients with nickel allergies, bleeding disorders, and/or contraindications to anticoagulation or antiplatelet therapy. Even for patients >80 years old, a high-risk CEA variable, 63% qualified for TCAR based on anatomic requirements.
Table II:
Summary of carotid artery and aortic arch anatomic characteristics
| Characteristic | N (%) |
|---|---|
| Carotid Artery Characteristics (N = 224) | |
| ICA diameter at target lesion (mm), median, [IQR] | 5.9 [5.2–6.6] |
| ICA diameter at skull base (mm), median, [IQR] | 4.8 [4.3–5.5] |
| Clavicle to carotid bifurcation (cm), median, [IQR] | 6.1 [5.1–7.1] |
| Depth of CCA above clavicle (cm), median, [IQR] | 3.2 [2.5–3.7] |
| CCA depth <4.0 cm | 196 (88%) |
| CCA depth ≥4.0 cm | 28 (13%) |
| CCA depth ≥4.5 cm | 6 (2.7%) |
| CCA puncture site plaque | |
| None/minimal | 214 (96%) |
| Moderate/severe | 10 (4.5%) |
| Location of CCA plaque | |
| None | 203 (91%) |
| Anterior | 12 (5.4%) |
| Posterior | 7 (3.1%) |
| Circumferential | 2 (0.9%) |
| Aortic Arch Characteristics (N = 210) | |
| Aortic arch type | |
| Type I | 155 (74%) |
| Type II | 39 (19%) |
| Type III | 16 (7.6%) |
| Aortic arch calcification | |
| None | 60 (28%) |
| Minimal | 101 (48%) |
| Moderate | 44 (21%) |
| Severe | 7 (3.3%) |
| CCA ostium calcification | |
| None | 146 (65%) |
| Minimal | 58 (26%) |
| Moderate | 13 (5.8%) |
| Severe | 7 (3.1%) |
| Tandem CCA stenosis | |
| Yes | 16 (7.1%) |
| No | 208 (93%) |
| Bovine arch | |
| Yes | 32 (15%) |
| No | 186 (85%) |
CCA, common carotid artery; ICA, internal carotid artery
Demographics and Comorbidities
Patients with carotid arteries ineligible for TCAR were more likely to be older (72.4 ± 7.3 vs 69.1 ± 9.3 years, P = .01) and white (97 vs 85%, P = .01) (Table III). They were also more likely to have hyperlipidemia (95 vs 82%, P = .01) and COPD (24 vs 9.3%, P < .01), but were less likely to be on a beta-blocker (48 vs 65%, P = 0.02). Hyperlipidemia (OR 6.7 [1.7–26], P < .01), COPD (OR 3.5 [1.5–8.3], P < .01) and older age (OR 1.1 [1.0–1.1], P < .01) were independently associated with TCAR ineligibility, whereas white ethnicity (OR 0.2 [0.0–1.0], P =.048) and beta-blocker use (OR 0.3 [0.1–0.7], P < .01) were independently associated with TCAR eligibility (Table IV).
Table III:
Baseline characteristics of patients with carotid arteries that were eligible or not eligible for TCAR
| Baseline Characteristics | |||||||
|---|---|---|---|---|---|---|---|
| TCAR |
tfCAS |
||||||
| Eligible (n = 162) |
Not Eligible (n = 62) |
P - value | Eligible (n = 171) |
Not Eligible (n = 53) |
P - value | ||
| Age, years, mean ± SD | 69.1 ± 9.3 | 72.4 ± 7.3 | .01 | 69.5 ± 9.1 | 71.5 ± 7.6 | .15 | |
| Male | 65% | 60% | .48 | 66% | 57% | .24 | |
| White | 85% | 97% | .01 | 88% | 87% | .77 | |
| Coronary artery disease | 49% | 58% | .25 | 57% | 36% | <.01 | |
| Prior MI | 36% | 42% | .45 | 39% | 34% | .49 | |
| Hypertension | 93% | 86% | .10 | 92% | 88% | .27 | |
| Congestive Heart Failure | 26% | 17% | .20 | 28% | 9.4% | <.01 | |
| Hyperlipidemia | 82% | 95% | .01 | 90% | 91% | .21 | |
| Diabetes Mellitus | 41% | 27% | .07 | 38% | 34% | .59 | |
| Renal Insufficiency | 19% | 21% | .68 | 23% | 7.6% | .01 | |
| COPD | 9.3% | 24% | <.01 | 11% | 21% | .07 | |
| PVD | 19% | 27% | .18 | 19% | 28% | .16 | |
| BMI, kg/m2, mean ± SD | 28.3 ± 5.5 | 28.8 ± 4.9 | .62 | 28.8 ± 5.6 | 27.2 ± 4.3 | .07 | |
| Former Smoker | 74% | 74% | .91 | 71% | 83% | .08 | |
| Active Smoker | 16% | 24% | .16 | 14% | 32% | <.01 | |
| Preoperative Medications | |||||||
| Aspirin | 92% | 97% | .20 | 97% | 83% | <.01 | |
| Plavix | 29% | 21% | .22 | 32% | 11% | <.01 | |
| Anticoagulation | 14% | 15% | .95 | 14% | 15% | .84 | |
| Statin | 88% | 90% | .66 | 88% | 93% | .34 | |
| Beta-blocker | 65% | 48% | .02 | 66% | 43% | <.01 | |
| ACE inhibitor | 36% | 45% | .23 | 37% | 43% | .44 | |
| ARB | 19% | 18% | .81 | 19% | 19% | .98 | |
| Symptomatic | 42% | 55% | .08 | 47% | 40% | .32 | |
ACE, angiotensin converting enzyme; ARB, angiotension II receptor blocker; BMI, body mass index; COPD, chronic obstructive pulmonary disease; MI, myocardial infarction; PVD, peripheral vascular disease; TCAR, transcarotid artery revascularization; tfCAS, transfemoral carotid artery stenting. Bolded values indicate statistical significance at p< 0.05.
Table IV:
Factors independently associated with anatomic ineligibility for TCAR
| Characteristic | |||
|---|---|---|---|
| OR | 95% CI | P-value | |
| Hyperlipidemia | 6.7 | 1.7–26 | <.01 |
| COPD | 3.5 | 1.5–8.3 | <.01 |
| Age | 1.1 | 1.0–1.1 | <.01 |
| White | 0.2 | 0.0–1.0 | .048 |
| Beta-blocker | 0.3 | 0.1–0.7 | <.01 |
CI, confidence interval; COPD, chronic obstructive pulmonary disease; OR, odds ratio.
CCA Access Site Depth
CCA depth above the clavicle is an important anatomic factor given the higher degree of difficulty obtaining CCA access in deeper arteries. The median CCA depth above the clavicle was 3.2cm [2.5–3.7cm], and the majority of arteries assessed (88%) had CCA depths <4cm – which was deemed low-risk for TCAR access. Of the carotid arteries with CCA depths <4cm, 74% were anatomically eligible for TCAR; of the carotid arteries with CCA depths ≥4cm, 64% met anatomic requirements for TCAR.
While 34 (13%) carotid arteries had a CCA depth ≥4.0cm, only 6 (2.7%) had a depth ≥4.5cm. Since a deeper carotid artery typically requires a more angled entry, a longer clavicle to carotid bifurcation distance would be needed. For patients with ≥4.0cm CCA depth, 39% had a ≥6cm clavicle-carotid bifurcation distance. For patients with ≥4.5cm CCA depth, 33% had a ≥6cm clavicle-carotid bifurcation distance.
Carotid Bifurcation Disease
Sixteen patients (7.1%) with carotid lesions that were not suitable for carotid stent placement were identified. Of these, 11 (4.9%) had heavy circumferential internal carotid calcification and five (2.2%) had severe ICA tortuosity directly adjacent to the distal endpoint of a carotid lesion. Of the entire population studied, 152 (68%) of patent carotid arteries had stentable bifurcation anatomy and were eligible for TCAR. Furthermore, by excluding arteries without clinically significant carotid stenosis >50%, we discovered that 108 of the remaining 147 carotid arteries (73%) were anatomically eligible for TCAR and 99 (67%) arteries both met TCAR eligibility and had stentable bifurcation anatomy.
Transfemoral CAS Eligibility
Excluding patients without adequate imaging for complete aortic arch grading, 159 (76%) of 210 carotid arteries in our cohort were considered eligible for tfCAS, and 51 (24%) were considered high-risk for the procedure. Aortic arch characteristics and the percentage of carotid arteries possessing each high-risk variation are summarized in Tables II and V. Of note, all ICA diameters fell within the 2.5–7.0mm requirement for distal ICA embolic filter placement.
Table V:
Summary of carotid arteries that did not meet anatomic eligibility for tfCAS
| High-risk anatomic criteria | Total Carotid Arteries (n=210) |
|---|---|
| Type III aortic arch | 16 (7.6%) |
| Severe aortic arch calcification | 7 (3.3%) |
| Moderate/severe CCA ostium plaque | 18 (8.5%) |
| Severe distal tortuosity | 10 (4.8%) |
| Tandem CCA stenosis | 15 (7.1%) |
| ICA diameter <2.5mm or >7.0mm | 0 (0.0%) |
| Overall ineligibility for tfCAS | 51 (24%) |
CCA, common carotid artery; ICA, internal carotid artery; tfCAS, transfemoral carotid artery stenting
Patients with anatomy that precluded tfCAS were more likely to be active smokers (32 vs 14%, P < .01), but less likely to have coronary artery disease (36 vs 57%, P < .01), congestive heart failure (9.4 vs 28%, P < .01), and renal insufficiency (7.6 vs 23%, P = .01) (Table III). They also blocker (43 vs 66%, P < .01) use. Active smoking (OR 4.4 [1.9–10], P < .01), hyperlipidemia (OR 4.0 [1.2–14], P = .03), and older age (OR 1.1 [1.0–1.1], P = .02) were all independently associated with tfCAS ineligibility; aspirin (OR 0.1 [0.0–0.4], P < .001) and Plavix (OR 0.3 [0.1–0.8], P = .01) use were independently associated with tfCAS eligibility (Table VI).
Table VI:
Factors independently associated with anatomic ineligibility for tfCAS
| Characteristic | |||
|---|---|---|---|
| OR | 95% CI | P-value | |
| Active Smoker | 4.4 | 1.9–10 | <.01 |
| Hyperlipidemia | 4.0 | 1.2–14 | .03 |
| Age | 1.1 | 1.0–1.1 | .02 |
| Aspirin | 0.1 | 0.0–0.4 | <.001 |
| Plavix | 0.3 | 0.1–0.8 | .01 |
CI, confidence interval; COPD, chronic obstructive pulmonary disease; OR, odds ratio.
Of all patent carotid arteries studied, 79% were eligible for tfCAS and had stentable bifurcation anatomy. Whereas, of all patent carotid arteries with >50% stenosis, 77% were eligible for tfCAS and had stentable bifurcation anatomy. Overall, 35 (69%) of the 51 carotid arteries deemed high-risk for tfCAS met anatomic criteria to undergo TCAR. On the other hand, of the 61 (29%) carotid arteries that were anatomically ineligible for TCAR, 45 (74%) were considered acceptable anatomic candidates for tfCAS. Evaluating only arteries with stentable bifurcation anatomy and >50% stenosis, 25 of 35 (71%) were high-risk for tfCAS and anatomically eligible for TCAR and 35 of 45 (78%) were ineligible for TCAR but normal-risk for tfCAS. Ten (7%) carotid arteries were both TCAR ineligible and high-risk for tfCAS.
DISCUSSION
Surgical management of carotid artery stenosis has primarily relied on the utility of CEA and tfCAS to provide long-term ipsilateral stroke prevention in affected patients. TfCAS offers a more minimally invasive approach and results in lower overall surgical morbidity; however, it has failed to become the predominant procedure for treatment of carotid disease given its higher rates of peri-procedural strokes.7,16,17 Recently, TCAR has emerged as an attractive alternative to tfCAS due to its minimally invasive nature and low peri-procedural stroke risk.13 In this study, we found that the majority of carotid arteries of patients who underwent carotid revascularization met anatomic criteria for TCAR.
Of note, while a CCA depth of ≥4 cm was not an absolute contraindication for TCAR based on the IFU of the ENROUTE Transcarotid Neuroprotection System, carotid arteries with extended CCA depths were characterized as more technically challenging for TCAR in our study. They may preclude easy access of the CCA, require higher CCA punctures above the clavicle, and potentially increase the risk of dissections or access site complications given the steeper angle at which the artery is entered. Alternatively, these deeper CCAs can be accessed through a separate skin puncture below the clavicle after removing the outer sheath stopper; however, this technique increases technical difficulty, especially for novice TCAR users. Fortunately, while a sizeable number of CCAs had depths ≥4cm, most of these arteries were only a few millimeters deeper than 4cm; moreover, many of these deeper arteries were found to have long clavicle-carotid bifurcation distances, which would allow for the interventional working distances needed after a higher CCA puncture. Increased consideration of CCA depth, as well as other anatomic variations not specified by the IFU, is critical to ensure the safety and success of TCAR.
We additionally sought to identify potential demographic and comorbidity characteristics that may predispose individuals to anatomic variants that were compatible or incompatible with TCAR. Carotid arteries that were anatomically ineligible for TCAR were more likely to be in patients of older age. This result may be attributable to the physical changes in body curvature and variations in vascular structure that arise with the aging process. For instance, patients are more likely to develop thoracic kyphosis as they age, which may subsequently compress anterolateral neck structures and decrease the clavicle-carotid bifurcation distance needed for TCAR.18.Older patients also have a greater likelihood of developing aberrancies in their carotid artery anatomy, which may affect the clavicle-carotid bifurcation distances and CCA depth.19,20 Despite these findings, 63% of patients >80 years old in our cohort were still eligible for TCAR, emphasizing the promise that this hybrid technology holds in expanding treatment options for these high-risk individuals. Older age is often associated with anatomic characteristics that also make tfCAS more challenging and dangerous. Given that these anatomic factors are thought to contribute to the increased stroke risk observed in octogenarians, it will be interesting to see whether TCAR has potential in mitigating these risks in appropriately-selected patients.4
Carotid arteries that did not meet anatomic criteria for TCAR were also independently associated with non-white patients, hyperlipidemia, COPD, and beta-blocker use. On one hand, these results may be secondary to the overrepresentation of older patients or a subgroup of patients with numerous preoperative comorbidities. Alternatively, these findings could be a result of anatomic changes that stem from large and small vessel plaque formation, or mass effect from lung overexpansion.21,22
For patients considered high risk for CEA, tfCAS initially emerged as viable and less-invasive alternative for carotid artery revascularization. Randomized trials and retrospective studies have suggested that long-term outcomes of tfCAS are not inferior to CEA in high-risk patients with carotid artery stenosis.3,10 However, tfCAS has considerable downfalls to take into consideration, including its higher peri-procedural stroke rate and the technical challenges it poses in patients with severe calcification and aortic arch variations.23–25 The safety and benefit of TCAR as an alternative to tfCAS is supported by novel results from the Society for Vascular Quality Initiative (VQI) TCAR Surveillance Project (TSP), which show similar odds of in-hospital stroke/death and decreased odds of TIA/stroke/death compared to tfCAS, despite the presence of more comorbidities in the TCAR cohort.26 Because the VQI represents different practice patterns across the country, this reflects the continued success of TCAR in real-world practice. Of all carotid arteries assessed, we found that approximately 24% were considered to be high-risk for tfCAS. Notably, 68% of these high-risk carotid arteries were anatomically eligible for TCAR.
The implications of our investigations extend beyond the capacity of TCAR to serve simply as an alternative to tfCAS, for it also has the potential to become a viable alternative to CEA. In our assessment, the majority of patients who received carotid artery interventions and were found to be anatomically eligible for TCAR underwent CEA. Recent findings using the VQI-TSP database not only demonstrate that TCAR and CEA have equivalent in-hospital rates of stroke/death and stroke/death/MI, but also show that patients undergoing TCAR experience decreased operative times, length of stays, and cranial nerve injuries.27
Together, these findings show that TCAR can serve as a viable treatment option for many patients undergoing traditional methods of carotid artery revascularization, including those at high risk for CEA. In current real-world practices, TCAR patient eligibility and insurance coverage is dependent not only on IFU anatomic criteria, but also on anatomic and medical risk profiles for conventional revascularization techniques. However, if further long-term data continue to support the benefits of TCAR over tfCAS and the equivalence or superiority of TCAR over CEA, it is possible that indications for TCAR may be expanded to eventually serve as the predominant modality for interventional management of carotid artery disease. Therefore, we believe that both current and future vascular surgeons should become well-versed in TCAR use in light of these promising findings. Nevertheless, given the current paucity of studies examining long-term TCAR outcomes, the decision to offer TCAR, tfCAS, and CEA – at this time – should be determined using a surgeon’s best clinical judgement with these new data in mind. This study must be interpreted in the context of its content and design. Since our data were collected from a tertiary academic center with the proclivity to care for high-risk patients, the patient population and vascular anatomy represented in our cohort may not be fully reflective of the general carotid disease population. Also, none of the patients during this study period had neck radiation or a tracheal stoma, which would make TCAR more technically challenging. There is a risk for selection bias because a proportion of patients had images obtained at an outside hospital and were not available for review. We also do not routinely obtain CTA neck imaging for asymptomatic patients undergoing CEA; however, the proportion of asymptomatic patients (53%) included this study correlates well with the proportion of patients treated for asymptomatic disease (47%) at our hospital.
The accuracy of the grading scales and measurements recorded are also limiting factors. The grading of carotid artery calcifications was conducted based on an arbitrary classification system; however, this evaluation inherently reflects real-world practice. Additionally, the ≥5cm working length described by the ENROUTE IFU is determined by ultrasound measurements and not by preoperative CTAs, which may underestimate clavicle-carotid bifurcation distances. Lastly, our conclusions regarding eligibility and risk profiles for TCAR are largely based on anatomic and medical guidelines outlined in the system’s IFU. More extensive research is needed to further define and identify what characteristics are associated with favorable or adverse outcomes following TCAR.
CONCLUSION
TCAR is a readily available treatment option for many individuals with carotid artery disease undergoing revascularization based on the IFU of the ENROUTE device. These results suggest that TCAR may continue to grow as an important surgical technique for the treatment of carotid artery stenosis.
ARTICLE HIGHLIGHTS.
Type of research:
Single-center retrospective cohort study
Key Finding:
Based on the ENROUTE Transcarotid (TCAR) Neuroprotection System Instructions for Use (IFU), 68% of the 224 carotid arteries studied were anatomically eligible for TCAR. Of the 24% of arteries that were considered high anatomic risk for transfemoral carotid artery stenting, 69% were eligible for TCAR.
Take Home Message:
TCAR is a viable treatment option for many patients despite its IFU anatomic restrictions.
Footnotes
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Disclosure: PL and TO are supported by the Harvard-Longwood Research Training in Vascular Surgery NIH T32 Grant 5T32HL007734–22
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