Clinical results of carotid artery stenting compared with carotid endarterectomy

Article Outline

• Abstract
• Methods
  • Searching
  • Selection
  • Data abstraction
  • Statistical analysis
• Results
• Discussion
  • Meta-analysis
  • Heterogeneity
  • Subgroup analysis
  • Limitations
• Conclusions
• Author contributions
• References
• Copyright

Objectives

Carotid artery stenting (CAS) is an alternative to carotid endarterectomy (CEA) for treating carotid artery stenosis. We conducted a systematic review and meta-analysis of the clinical trials to date comparing these two procedures to determine their relative safety and efficacy.

Methods

Searches of the Cochrane Controlled Trials Register, MEDLINE, and EMBASE identified two cohort studies and eight randomized, controlled trials (RCTs) comparing CEA and CAS. Meta-analysis was performed for the primary outcome of 30-day stroke or death, using an intention-to-treat analysis. Between-trial heterogeneity was assessed using the χ² test, and fixed-effects models were used to pool estimates in the absence of heterogeneity. Meta-regression was conducted to investigate potential effect differences by patient, intervention, and trial characteristics. To evaluate the effect of study design and inclusion criteria, sensitivity and subgroup analyses were performed.

Results

Ten trials encompassing 3580 patients were analyzed. Patients who underwent CAS had a higher risk of 30-day stroke/death relative to patients who underwent CEA (risk ratio [RR], 1.30; 95% CI, 1.01-1.67). Meta-analysis and meta-regression demonstrated no between-trial heterogeneity. Sensitivity analysis of only RCTs showed similar higher risk for stroke/death (RR, 1.38; 95% CI, 1.06-1.79) in CAS patients. Subgroup analysis of trials enrolling only symptomatic patients showed higher risk of 30-day stroke/death (RR, 1.63; 95% CI, 1.18-2.25), but trials enrolling both symptomatic and asymptomatic patients showed no significant differences (RR, 0.89; 95% CI, 0.59-1.35).

Conclusions

Meta-analysis of trials to date shows CAS is associated with higher 30-day risk of stroke/death compared with CEA. Thus, for the patient at average surgical risk, the role of CAS is unproven, especially for symptomatic patients. And for the patient at high surgical risk, the role of any intervention is uncertain in the setting of competing comorbidities. The results of ongoing clinical trials in this area will likely provide additional evidence to support treatment choices for carotid artery stenosis.

Large, randomized clinical trials from the early 1990s have shown the superiority of carotid endarterectomy (CEA) and aspirin therapy in preventing stroke compared with aspirin therapy alone for both symptomatic¹, ², ³, ⁴, ⁵ and asymptomatic⁶, ⁷, ⁸ carotid artery stenosis. On the basis of these trials, the most recent American Heart Association (AHA) guidelines recommend CEA for symptomatic patients with a stenosis of 50% to 99% if the perioperative risk of stroke or death is <6%.⁹, ¹⁰ In asymptomatic patients, CEA is recommended for a stenosis of 60% 99% if the perioperative risk of stroke or death is <3%.⁹, ¹⁰

Endovascular techniques for treating carotid artery stenosis have recently come to the forefront as an alternative to CEA, primarily for patients who are high operative risk. Multiple carotid artery stent (CAS) registries, both where enrollment was voluntary¹¹, ¹², ¹³ or standardized,⁹, ¹⁴ have documented high levels of technical success with CAS. The 30-day end points from these registries showed that rates of stroke and death were 2.8% to 4.7%,¹¹, ¹², ¹³ and rates of stroke, death and myocardial infarction (MI) were 3.8% to 8.3%,¹⁴, ¹⁵ which were comparable with rates of complications seen in the earlier trials for CEA.¹, ², ³, ⁴, ⁵, ⁶, ⁷, ⁸ Carotid artery stenting has the added benefit of being a less-invasive procedure, potentially minimizing the risks of wound complications and cranial nerve injury. In addition, this may translate to shorter length of hospitalization and less resource utilization.

Given the potential safety advantages of CAS in high-risk surgical patients, it is important to determine if it is equivalent to the gold standard of CEA. Although several clinical trials have been conducted to compare these two procedures, there has been no clear consensus among them of whether one is superior or if they are equivalent. To further evaluate this, we conducted a systematic review and meta-analysis of the clinical trials to date comparing CAS and CEA. Our objectives were to determine the end points of 30-day any stroke or death, and 30-day any stroke as measures to compare the safety and efficacy between CAS and CEA.

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Methods 

Searching 

Searches were conducted using the Cochrane Controlled Trials Register, MEDLINE, and EMBASE to identify trials comparing CEA and CAS. Relevant clinical trials in the Cochrane Controlled Trials Register were identified with the key words carotid stenting. For both MEDLINE and EMBASE, a combination of key words and MeSH terms were used including carotid, endarterectomy, stenting, clinical trial, and randomized, limited to humans. A few background articles and studies were also selected using hand-search methods.

The search was conducted in February 2007, and 347 references were found: 86 clinical trials were identified through the Cochrane Controlled Trials Register, 147 citations through MEDLINE, and 114 citations through EMBASE. The first round of eliminations was based on five criteria: (1) articles were unrelated to the topic of interest, (2) review articles, (3) articles in languages other than English, (4) articles focused only on the CAS procedure, (5) articles duplicating those found in other databases. The second round of eliminations covered studies that only discussed the design of a trial or if a trial measured outcomes other than the ones of interest.

Selection 

We selected both randomized, controlled clinical trials (RCTs) and cohort studies that evaluated the outcomes of CAS as compared with CEA. These trials included all patients with symptomatic and asymptomatic internal carotid stenoses who underwent CEA or CAS, including with or without embolic protection device (EPD). The primary outcome of interest was to assess postprocedural rates of any stroke and death ≤30 days of the intervention. The secondary outcome of interest was postprocedural rates of any stroke ≤30 days of the intervention. Any disputes were settled by discussion among the coauthors.

Data abstraction 

Relevant information was abstracted from the 10 selected studies. Study design information included the type of trial, duration of follow-up, randomization and allocation methods, and whether a trial was stopped (Table I). Patient characteristics consisted of inclusion criteria, baseline demographics (mean age, sex), and the numbers of patients in each treatment arm (based on an intention-to-treat analysis; Table II). Intervention characteristics included type of stent and whether an EPD was used for CAS (Table III). The 30-day end points of any stroke and any stroke/death were also extracted from all trials (Table IV).

Table I. Study design

Trial	Design	Allocation	Follow-up Duration	Trial Stopped
Naylor, 199818	Prospective, randomized, single-center trial	Sequentially numbered, sealed envelopes with random tx methods enclosed	≤30days	Trial suspended: highly significant risk of adverse outcome
Brooks, 200119	Prospective, randomized, single-center trial	NK	≤30days	No
Wallstent, 200120	Prospective, randomized, multicenter trial non-inferiority trial	Computerized random number generator; assignment by sequentially numbered sealed envelopes	1yr	Trial stopped early due to much higher rates of complications in CAS group; based on futility analysis
Cavatas, 200121	Prospective, randomized, multicenter trial	Randomization by computer minimization algorithm; pts. signed consent forms	>1yr	No
Madyoon, 200216	Prospective, single center trial	Physicians decided which procedure pt. receives	NK	NA
Brooks, 200422	Prospective, randomized, single-center trial	NK	≤30days	No
Sapphire, 200423	Prospective, randomized, multicenter non-inferiority trial	Randomization: pseudo-random-number generator; numbers distributed by an automated, centralized telephone device	1yr	Trial stopped early due to decreasing enrollment
Caress, 200517	Prospective, nonrandomized, multicenter, equivalence trial	Based on physician and patient preference	1yr	NA
Space, 200624	Prospective, randomized, multicenter noninferiority trial	Randomization computer-generated; 8-patient block randomization design per center	≤30days	No
Eva-3S, 200625	Prospective, randomized, multicenter non-inferiority trial	Randomization by computer-generated sequence	≤6months	Trial stopped early due to safety; higher stroke rates in CAS group. After 30 d.

CARESS, Carotid Revascularization using Endarterectomy or Stenting Systems; CAVATAS, Carotid and Vertebral Artery Transluminal Angioplasty Study; EVA-3S, Endarterectomy Versus Angioplasty in Patients With Symptomatic Severe Carotid Stenosis; NA, not applicable; NK, not known; SAPPHIRE, Stenting and Angioplasty with Protection in Patients at High Risk for Endarterectomy; SPACE, Stent-Protected Percutaneous Angioplasty Versus Carotid Endarterectomy.

Table II. Patient characteristics

Trial	Inclusion Criteria	Treatment Arms (CEA/CAS = total)	Percent Male	Mean Age (yrs.)
Naylor, 199818	Sx: ipsilateral stenosis 70%-99% (by duplex)	12/11=23	9(52.9%)	71.3
Brooks, 200119	Sx: neuro events within 3 mo. of eval.; >70% stenosis	51/53=104	NK	68.0
Wallstent, 200120	Sx: TIA or stroke within 120 d. of randomization and ≥60% stenosis (by angio.)	112/107=219	140(64.0%)	68.3
Cavatas, 200121	Pt. has stenosis that is suitable for either CEA or CAS by CTA/MRA/duplex; both asx & sx included	253/251=504	352(69.8%)	67.0
Madyoon, 200216	Sx: ≥50% stenosis Asx ≥75% stenosis (by angio)	138/49=187	187(58.8%)	73.3
Brooks, 200422	Asx: >80% stenosis (by angio)	42/43=85	NK	68.3
Sapphire, 200423	Sx: ≥50% stenosis Asx: ≥80% stenosis (by duplex)	167/167=334	224(67.0%)	72.6
Caress, 200517	Asx: ≥75% stenosis Sx: ≥50% stenosis (by duplex)	254/143=397	247(62.2%)	71.3
Space, 200624	Sx: sxs in prior 180 d. & ipsilateral stenosis ≥ 70% (by duplex)	595/605=200	849(71.6%)	67.9
Eva-3S, 200625	Sx: TIA /CVA in ≤120 d. & ≥60%-99% stenosis in symptomatic side (by duplex & MRA, or by angio	262/265=527	189(35.9)	69.7

Asx, Asymptomatic; CARESS, Carotid Revascularization using Endarterectomy or Stenting Systems; CAS, coronary artery stenting; CAVATAS, Carotid and Vertebral Artery Transluminal Angioplasty Study; CEA, carotid endarterectomy; CTA, computed tomography angiography; CVA, cerebrovascular accident; DUS, duplex ultrasound; EVA-3S, Endarterectomy Versus Angioplasty in Patients With Symptomatic Severe Carotid Stenosis; MRA, magnetic resonance angiography; NK, not known; SAPPHIRE, Stenting and Angioplasty with Protection in Patients at High Risk for Endarterectomy; SPACE, Stent-Protected Percutaneous Angioplasty Versus Carotid Endarterectomy; Sx, symptomatic; TIA, transient ischemic attack.

Table III. Intervention characteristics

CARESS, Carotid Revascularization using Endarterectomy or Stenting Systems; CAVATAS, Carotid and Vertebral Artery Transluminal Angioplasty Study; EVA-3S, Endarterectomy Versus Angioplasty in Patients With Symptomatic Severe Carotid Stenosis; SAPPHIRE, Stenting and Angioplasty with Protection in Patients at High Risk for Endarterectomy; SPACE, Stent-Protected Percutaneous Angioplasty Versus Carotid Endarterectomy.

Table IV. Clinical outcomes at 30 days

CARESS, Carotid Revascularization using Endarterectomy or Stenting Systems; CAS, coronary artery stenting; CAVATAS, Carotid and Vertebral Artery Transluminal Angioplasty Study; CEA, carotid endarterectomy; EVA-3S, Endarterectomy Versus Angioplasty in Patients With Symptomatic Severe Carotid Stenosis; SAPPHIRE, Stenting and Angioplasty with Protection in Patients at High Risk for Endarterectomy; SPACE, Stent-Protected Percutaneous Angioplasty Versus Carotid Endarterectomy.

Statistical analysis 

A meta-analysis was performed on two cohort studies¹⁶, ¹⁷ and eight RCTs¹⁸, ¹⁹, ²⁰, ²¹, ²², ²³, ²⁴, ²⁵ to evaluate the end points of 30-day stroke/death and 30-day stroke between CAS and CEA. Comparisons were made using risk ratios (RR), and all RCTs were analyzed using an intention-to-treat principle because the original numbers of patients allocated to treatment and control groups were available. Between-trial heterogeneity was assessed using the χ² test, and a fixed-effects model was used to pool RRs in the absence of heterogeneity (P > .05). To evaluate the effect of study design (RCT vs cohort), a sensitivity analysis was conducted which included RCTs only.

As an additional check, meta-regression was also conducted for the end point of stroke/death to investigate for potential effect differences by patient, intervention, and trial characteristics. Variables included in the regression model were percentage of men, mean age, duration of postprocedural follow-up, type of stent deployed, whether a trial was stopped before completion, inclusion criteria (symptomatic patients only, asymptomatic patients only, or both symptomatic and asymptomatic patients), and if an EPD was used. An additional subgroup analysis compared both end points between trials that enrolled only symptomatic patients and trials that enrolled both symptomatic and asymptomatic patients. A subgroup analysis on asymptomatic patients alone could not be conducted because only one trial was defined by this inclusion criterion.

Publication bias was evaluated for using the Begg test. A continuity correction was used to adjust for trials with sparse outcomes. An α = 0.05, corresponding to P = .05, and 95% confidence intervals (CI) were used define statistical significance. Analysis was performed using Stata 9 software (StataCorp, College Station, Tex).

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Results 

Ten trials encompassing 3580 patients were analyzed. The meta-analysis showed that patients who underwent CAS had a higher risk of 30-day stroke/death relative to patients who underwent CEA (RR, 1.30; 95% CI, 1.01-1.67; Fig 1) and that the 30-day risk of stroke was not significantly different between patients who underwent CAS vs CEA (RR, 1.27; 95% CI, 0.96-1.69; Fig 2). Sensitivity analysis, which only included RCTs, corroborated that patients who underwent CAS had a higher risk of 30-day stroke/death relative to CEA patients (RR, 1.38; 95% CI, 1.06-1.79; Fig 3). In addition, it showed that CAS patients had a higher 30-day stroke risk compared with CEA patients (RR, 1.37; 95% CI, 1.02-1.84; Fig 4).

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• Fig 1. 

  Thirty-day stroke/death in all trials. CI, Confidence interval.

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• Fig 2. 

  Thirty-day stroke in all trials. CI, Confidence interval.

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• Fig 3. 

  Thirty-day stroke/death in randomized, controlled trials only. CI, Confidence interval.

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• Fig 4. 

  Thirty-day stroke in randomized, controlled trials only. CI, Confidence interval.

Meta-analysis showed no evidence of between-trial heterogeneity in either the full analysis or RCT analysis for either end point. This finding was confirmed with meta-regression, where important factors such as percentage of men, mean age, duration of follow-up, type of stent deployed, completion of trial, inclusion criteria, and use of an EPD were found not to contribute to between-trial heterogeneity.

Subgroup analysis of trials enrolling only symptomatic patients showed a higher risk of 30-day stroke/death (RR, 1.63; 95% CI, 1.18-2.25; Fig 5) and 30-day stroke (RR, 1.62; 95% CI, 1.13-2.31; Fig 6) in CAS patients. Trials enrolling both symptomatic and asymptomatic patients, however, showed no significant differences in 30-day stroke/death rates (RR, 0.89; 95% CI, 0.59-1.35) or 30-day stroke rates (RR, 0.84; 95% CI, 0.53-1.35) between both procedures.

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• Fig 5. 

  Thirty-day stroke/death in trials with only symptomatic patients. CI, Confidence interval.

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• Fig 6. 

  Thirty-day stroke in trials with only symptomatic patients.

There was no evidence of publication bias according to the Begg test (P = .929). The corresponding funnel plot showed a symmetric distribution of individual trials, confirming the statistical analysis.

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Discussion 

Meta-analysis 

Until recently, results from completed CAS registries¹¹, ¹², ¹³, ¹⁴, ¹⁵ had been the strongest and most abundant evidence available in favor of CAS as an alternate treatment for carotid artery stenosis. As mentioned previously, these observational studies demonstrated a high level of technical success and 30-day end points of stroke/death and stroke/death/MI of 2.8% to 8.3%.¹¹, ¹², ¹³, ¹⁴, ¹⁵ Although informative, these results have to be interpreted with caution given that the subjects for these registries were not randomized, and the studies may suffer from inclusion bias for lower-risk patients, which would have artificially decreased the complication rate for CAS. More recent data from a meta-analysis of six RCTs by Coward et al²⁶ concluded that CAS was equivalent to CEA.

The meta-analysis for our study, however, found that 30-day stroke/death across all studies was slightly higher after CAS than after CEA. For the end point of 30-day stroke, the two procedures were found to be statistically equivalent, though trending toward being higher after CAS. The addition of the results from the two latest RCTs, Stent-Protected Angioplasty versus Carotid Endarterectomy (SPACE)²⁴ and Endarterectomy Versus Angioplasty in Patients With Symptomatic Severe Carotid Stenosis (EVA-3S),²⁵ partly explains why our results differ from those of the previous meta-analysis. The SPACE study showed that CEA trended towards better outcomes for both stroke/death and stroke, though this difference was not of statistical significance between procedures. In the EVA-3S trial, CAS patients had significantly higher rates of both outcomes relative to CEA patients, resulting in early termination of the trial.

Arguably, improvements in technology, technique, experience, and the use of EPD over time may give greater significance to more recent trials. However, analysis of the trial results in chronologic order does not indicate a time-related trend for outcomes. In fact, the latest trials have demonstrated poorer outcomes for CAS, indicating that technology and experience alone may not be a determinant for the safety and efficacy of CAS.

Although our primary analysis included RCTs and two cohort studies, we conducted a sensitivity analysis for RCTs alone to test if study design affected outcome. The results confirmed that 30-day stroke/death was higher in CAS patients and showed that 30-day stroke was also higher in CAS patients. The magnitudes of the RRs were also slightly larger for both end points in this analysis, indicating that the cohort studies may have diminished the effect of the original estimates in the pooled analysis. Because subjects were not randomized to CAS and CEA in the cohort studies, a greater number of low-risk patients may have selected CAS, improving the results in this group and lowering the overall estimate for both end points. A recently published meta-analysis using only RCTs also showed increased risk of 30-day death/stroke.²⁷

Heterogeneity 

The χ² test in meta-analysis showed no evidence of heterogeneity in all trials or in RCTs alone. Despite these results, potential effect differences by clinically relevant factors were further investigated to ensure a thorough analysis of heterogeneity. Meta-regression corroborated the absence of between-trial heterogeneity due to sex, mean age, duration of follow-up, type of stent deployed, completion of trial, inclusion criteria, or use of an EPD. These results demonstrate that our pooled estimate from the meta-analysis is fairly reliable because all trials were statistically similar across patient, trial, and intervention characteristics.

Subgroup analysis 

According to guidelines established by the AHA/ASA (American Stroke Association), symptomatic patients who have a low operative risk with either moderate (50%-69%) or severe (70%-99%) stenosis are recommended to undergo CEA, whereas patients who are symptomatic with severe stenosis (>70%) and who are high risk for CEA are recommended to undergo CAS.¹⁰ The findings from our subgroup analysis of trials enrolling only symptomatic patients, with a threshold stenosis of ≥60%, were not consistent with the AHA/ASA recommendations. We found that the 30-day risks for both any stroke/death and stroke were significantly higher in CAS patients, making it a suboptimal choice for symptomatic patients with moderate to severe stenosis. Many of the trials included in this meta-analysis were not performed on patients with high surgical risk, however; therefore, we cannot conclude whether CAS or CEA is better for the truly high-risk surgical patient.

Guidelines for management of asymptomatic carotid stenosis, on the contrary, are currently not well defined. For the asymptomatic patient who has a low operative risk, two areas of controversy exist: first, is intervention needed in these patients; and second, if recommending intervention, what should be the threshold stenosis to intervene?¹⁵ The AHA recommends CEA for these patients with stenosis of 60% to 99%, and a perioperative risk of stroke or death that is <3%.⁹, ¹⁰ The role for CAS in the patient with asymptomatic severe carotid stenosis is less clear. Although it would seem to be an appropriate intervention for patients who have high operative risk, no level I data are currently available to support this.

Our second subgroup analysis looked at trials enrolling both symptomatic and asymptomatic patients. Although isolated analysis of asymptomatic trials would have been more helpful, this was not possible owing to the small number of trials with this inclusion criterion. Our analysis of these combined trials showed that CAS trended toward a better outcome for both end points (RR <1), but this difference was not statistically significant. Because results from (only) symptomatic patients statistically favor CEA over CAS, it is tempting to speculate that analysis of only asymptomatic patients would favor CAS.

Limitations 

Several potential limitations are inherent in an analysis of this nature. Although meta-analysis and meta-regression showed no evidence of between-trial heterogeneity, there may have been other potential sources of heterogeneity that could not be measured. One example was the disparity between trials in criteria used to assess the qualifications of an interventionalist. Certain trials provided clear definitions of their criteria, but others were not as explicit; therefore, we could not assess if the differential training between interventionalists was a true source of heterogeneity. This ultimately affects our confidence in the pooled estimate from meta-analysis.

A second limitation was that most trials did not stratify their patients by level of operative risk. As mentioned previously, the AHA guidelines for CEA are based on three criteria: whether the patient is symptomatic or asymptomatic, whether the patient is considered high or low risk for an operation, and the degree of stenosis. Although we could evaluate the outcomes of CAS in symptomatic patients, we did not have information about whether they were considered high or low risk for surgery. Furthermore, there is no widely accepted consensus on the definition of high risk in CEA patients other than anatomic high risk. Because patients in RCTs must be eligible to receive both CEA and CAS, we can assume that these patients do not have a prohibitive risk for CEA. Nevertheless, operative risk has gradation, and we believe that more efforts to define and characterize operative risk in future trials may help answer the question of whether CAS is beneficial in truly high risk CEA patients.

Finally, this meta-analysis builds on the findings of previous analyses by including two contemporary RCTs. And although meta-analyses can be a useful tool in summarizing the results of several trials, the meta-analysis can only reflect the currently available data. With the completion of ongoing and potentially future trials, the conclusions about CAS vs CEA in the treatment of cerebrovascular disease may be changing.

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Conclusions 

Meta-analysis of trials to date shows CAS is associated with a higher 30-day risk of stroke/death compared with CEA. Thus, the role of CAS is unproven for the patient at average surgical risk, especially for symptomatic patients. And for the patient at high surgical risk, the role of any intervention is uncertain in the setting of competing comorbidities. The results of ongoing clinical trials in this area will likely provide additional evidence to support treatment choices for carotid artery stenosis.

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Author contributions 

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