Outcomes of carotid artery stenting and endarterectomy in the United States

Article Outline

• Abstract
• Methods
  • Data source
  • Study population
  • Statistical analysis
• Results
• Discussion
• Author contributions
• References
• Copyright

Objectives

With the evolution of endovascular techniques, carotid artery stenting (CAS) has been compared to carotid endarterectomy (CEA). Several studies have reported inferior results with CAS in the elderly. The objective of this study was to evaluate national outcomes of CAS and CEA and to compare utilization and outcomes of these procedures in different age groups.

Methods

We evaluated the 2005 Nationwide Inpatient Sample for hospitalizations with a procedure of CAS or CEA within 2 days after admission at age 60 years and above. Procedures were analyzed with respect to patient demographics and associated complications.

Results

A total of 80,498 carotid interventions (73,929 CEA and 6,569 CAS) were identified. The overall incidence of stroke was 4.16% after CAS and 2.66% after CEA (P < .0001). CAS was more often utilized in octogenarians than in younger patients (8.55% in 80+ vs 7.92% in 60-69 years; P < .0002). Increased age was not associated with greater stroke rates after CAS or CEA (P = .19 and .06, respectively). Octogenarians, compared to younger patients, had greater cardiac, pulmonary, and renal complications after CEA (3.0% vs 1.9%, 1.9% vs 1.0%, and 1.4% vs 0.54%, respectively; P < .0001). When adjusted by age, gender, complications, and Elixhauser comorbidities, patients after CAS were 1.6 times as likely to have a stroke (confidence interval [CI] = 1.37-1.78) when compared to CEA. Significant predictors of postoperative hospital mortality were stroke (odds ratio [OR] = 29.0; 95% CI = 21.5-39.1), cardiac complications (OR = 6.4; 95% CI = 4.4-9.1), pulmonary complications (OR = 3.5; 95% CI = 2.31-5.19), and renal failure (OR = 2.5; 95% CI = 1.6-3.8). With increasing age, overall mortality steadily increased after CAS (from 0.23% to 0.67%; P = .0409) but remained stable after CEA.

Conclusion

Octogenarians did not have a higher risk of stroke after CAS when compared to younger patients. Stroke was the strongest predictor of hospital mortality. The increased utilization of CAS in the aged, which had significantly higher stroke rates in all age groups studied, may account for the greater hospital mortality seen after CAS in the elderly. Further studies focused on the aged are needed to define the best management strategies in the elderly.

Carotid endarterectomy (CEA) has been established as the gold standard for the management of carotid disease through large prospective randomized trials.¹, ², ³ However, as technology has evolved there has been the implementation of carotid artery stenting (CAS) for the management of carotid artery disease with reported noninferiority⁴, ⁵ as well as inferior results when compared to CEA.⁶ Studies including the 30-day lead-in results from the Carotid Revascularization Endarterectomy vs Stent Trial (CREST) and the 30-day results from the Stent-Supported Percutaneous Angioplasty of the Carotid Artery vs Endarterectomy (SPACE) trial have demonstrated adverse outcomes and increased stroke rate after CAS in the elderly.⁴, ⁵, ⁷, ⁸ Proposed explanations for inferior outcomes in the elderly include an increase in unfavorable anatomy with aging⁹ and increased numbers of pre-existing comorbidities.

It has been estimated that the number of persons aged 65 years and above in the United States will more than double between 2000 and 2030 and that the proportion of elderly in the total population will increase from 12.4% to 19.6%.¹⁰ With the elderly increasing the demand on health care, the best treatment of carotid disease is an important health concern for the future. Understanding that single institutions and trial data may not be generalizable to the population at large, we evaluated national outcomes of CAS with our focus on the elderly.

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Methods 

Data source 

The Nationwide Inpatient Sample (NIS) for the year of 2005 was used for this study. The NIS is the largest all-payer hospital database developed as part of the Healthcare Cost and Utilization Project (HCUP), sponsored by the Agency for Health Care Research and Quality (AHRQ).¹¹ This publicly available database contains data about approximately 8,000,000 hospital stays from more than 1,000 hospitals and represents a 20% sample of hospitals in the United States. The NIS sampling and weighting strategies provide researches with the opportunity to obtain national estimates with variances for the variables of interest.

Study population 

All adult patients aged 60 years and older who underwent CAS or CEA within 2 days after elective admission to the hospital were analyzed. We used the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) procedure code 00.63 in any of 15 procedure positions in the data to identify patients with CAS and procedure code 38.12 to select cases with CEA. Because the NIS database contains information about the number of days from admission to each procedure performed, we selected only those observations where CAS or CEA were carried out within 2 days after admission. This approach, in association with the elective type of admission, was employed to focus on the cohort of patients hospitalized primarily for performing the procedure. The NIS administrative data do not yet have an indicator that distinguishes between diagnoses presented at admission and those arising during hospitalization. We identified the following complications with the appropriate ICD-9-CM diagnosis codes for the secondary diagnoses: cardiac complications including myocardial infarction (MI) (997.1, 410.00-410.02, 410.10-410.12, 410.20-410.22, 410.30-410.32, 410.40-410.42, 410.50-410.52, 410.60-410.62, 410.70-410.72, 410.80-410.82, 410.90-410.92), pulmonary (997.3, 518.4, 518.5), and renal (997.5) complications. Identifying stroke as a complication, we utilized ICD-9 code 997.02 (postoperative stroke) and other appropriate codes for stroke. The ICD-9 descriptions and the distribution of stroke each code adds for patients after CAS and CEA is in Table I. Stroke is considered an acute code and by selecting elective carotid interventions patients should not have acute stroke codes in their administrative discharge data unless they occurred during that hospitalization in association with a carotid intervention. To identify symptomatic patients, we used the following ICD-9-CM diagnosis codes: 435 (transient cerebral ischemia) and all subcodes, 437.1 (other generalized ischemic cerebrovascular disease), 781.4 (transient paralysis of limb), 362.34 (transient arterial occlusion, amaurosis fugax), and 368.12 (transient visual loss). The Elixhauser Index¹², ¹³, ¹⁴ was employed to identify and adjust for comorbidities in the study cohort. NIS data includes 29 AHRQ comorbidity measures reported by Elixhauser et al.¹³ To identify these comorbidities we used the Comorbidity Software developed as part of the HCUP.¹⁵ The performance of the Elixhauser comorbidity measures in predicting patient outcomes are well validated and has been established in the prediction of in-hospital and 1 year mortality among patients with congestive heart failure (CHF), diabetes, chronic renal failure (CRF), stroke, and patients undergoing coronary artery bypass grafting (CABG).¹⁴ For the analysis of the age disparities, we divided all study population into three age categories: 60-69, 70-79, and 80 years and above.

Table I. Distribution of study population by ICD-9-CM stroke codes utilized

ICD-9-CM, International Classification of Diseases, Ninth Revision, Clinical Modification; CAS, carotid artery stenting; CEA, carotid endarterectomy.

Statistical analysis 

We used SAS 9.1 software (SAS Institute, Cary, NC) for the analysis of the database and all statistics. To test the difference between two groups, we utilized χ² analysis with calculating odds ratio (OR) and 95% confidence interval (CI) for categorical variables, t test or Wilcoxon rank-sum test for continuous variables (with normal and non-normal distribution, respectively), and calculated the z-ratio with P value for the significance of the difference between two independent proportions. The Cochran-Armitage trend test was employed to analyze procedure performance and changes in the postoperative complications with the patient's age. We employed multivariate logistic regression analysis to compare complications and mortality in patients after CAS and CEA adjusted by age, gender, and comorbidities. A P < .05 was considered significant.

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Results 

Using the weighting function, 80,498 carotid interventions were identified in hospitalized patients aged 60 years and older in the United States in 2005: 73,929 CEA (91.8% of all carotid interventions) and 6569 CAS (8.2%). Table I displays demographic and clinical characteristics of the study population.

The major complications after CAS and CEA in various age groups are shown in Table II. Stroke was the most common complication after carotid intervention. In our study group, the overall incidence of stroke was 4.16% after CAS and 2.66% after CEA (P < .0001), and the same phenomenon was noted in all age groups (P < .0002). Table III depicts the ICD-9 codes utilized and the percentage each added to the overall stroke rate. We did not find a significant positive trend in stroke rate with aging after either procedure. After adjustment by age, gender, and comorbidities, patients after CAS were still 1.6 times as likely to have a stroke (95% CI = 1.37-1.78) as patients after CEA. After CEA, cardiac, pulmonary, and renal complications in the elderly significantly increased with the advanced age of the patients. Among patients with CAS, pulmonary and renal complications developed more frequently in those who were older.

Table II. Demographic and clinical characteristics of study patients

Characteristic	CAS	CEA	P value
Number of patients	6569(8.2%)	73,929(91.8%)	<.0002
Age, year (mean ± SD)	73.4±7.53	73.2±7.33	.3664
Gender:
Men	4041(61.5%)	42,382(57.3%)	<.0002
Women	2528(38.5%)	31,537(42.7%)	<.0002
Missing	0	<11
Complications:
Stroke	273(4.16%)	1963(2.66%)	<.0002
Cardiac	139(2.12%)	1728(2.34%)	.2535
Pulmonary	25(0.38%)	1016(1.37%)	<.0002
Renal	30(0.46%)	661(0.89%)	.0002
Symptomatic patients	189(2.88%)	2048(2.77%)	.6136
Died	25(0.38%)	189(0.26%)	.0596

CAS, Carotid artery stenting; CEA, carotid endarterectomy; SD, standard deviation.

Table III. Postoperative complications (%) in different age groups

CAS, Carotid artery stenting; CEA, carotid endarterectomy.

A significant increase in the utilization of CAS was found with aging. Patients aged 60-69 years underwent CAS for 7.92% of all interventions. In patients aged 70-79 years CAS was utilized more often (8.15%). The greatest proportion of CAS was found in octogenarians 8.55%. On the contrary, a proportion of CEA steadily decreased with the age of patients from 92.08% in patients aged 60-69 years to 91.85% at 70-79 years and to 91.45% in octogenarians; P = .0277 utilizing the Cochran-Armitage trend-test.

Fifty-eight percent of study patients were men and their proportion among CAS patients (61.5%) was greater than among patients undergoing CEA (57.3%; P < .0002). A similar distribution was found in all the age groups. Overall, men were 1.2 times as likely as women to have CAS. Hospital charges for CAS were found to be significantly greater when compared to CEA ($29,171 vs $20,052, P < .001).

Overall mortality among elderly patients after CAS (0.38%) tended to be greater than in patients after CEA (0.26%; P = .056). In univariate analysis of the whole study population, men were 1.5 times as likely to die as women (95% CI = 1.15-2.04). When adjusting by age, gender, type of procedure, comorbidities, and complications in multivariate analysis, the difference remained significant (OR = 2.03; 95% CI = 1.028-4.027). It was also found that with increasing age, mortality steadily increased after CAS (from 0.23% to 0.67%; P = .0409) utilizing the Cochran-Armitage trend-test, but this trend was not noted after CEA (0.22% to 0.29%; P = .86). There were no significant differences in mortality rates between patients with CAS and CEA in age groups 60-69 and 70-79 years. However, octogenarians after CAS procedure were 2.3 times as likely to die as those after CEA (95% CI = 1.16-4.59).

In univariate analysis, there were no significant differences in stroke rates between men and women both after CAS and CEA. In the multivariate analysis, when adjusted by age, gender, comorbidities, and type of procedure (CAS or CEA), we did not find gender differences in stroke either. In both men and women the rate of stroke after CAS was greater than after CEA.

To adjust for confounding variables, multivariate logistic regression analysis was performed with postoperative hospital mortality or stroke as an outcome (Table IV, Table V) and age, gender, procedure (CAS or CEA), postoperative complications and Elixhauser comorbidities as the independent variables. The most significant predictor of postoperative hospital mortality was stroke (OR = 29.0; 95% CI = 21.54-39.08), followed by cardiac complications (OR = 6.4; 95% CI = 4.44-9.09), pulmonary complications (OR = 3.5; 95% CI = 2.31-5.19), and renal failure (OR = 2.5; 95% CI = 1.6-3.8). Women were found to be less likely to die compared to men (OR = 0.48; 95% CI = 0.35-0.66). After adjusting for comorbidities, patients after CAS were more likely to have a postoperative stroke after CAS (OR = 1.6; 95% CI = 1.4-1.8), as were patients with renal failure (OR = 2.0; 95% CI = 1.6-2.4), metastatic cancer (OR = 4.2; 95% CI = 2.4-7.5), and fluid and electrolyte disorders (OR = 1.9; 95% CI = 1.6-2.3).

Table IV. Risk factors for postoperative mortality

OR, Odd ratio; CI, confidence interval.

Table V. Risk factors for postoperative stroke

OR, Odd ratio; CI, confidence interval; CAS, carotid artery stenting.

We compared length of hospital stay (LOS) and hospital cost for patients with CAS and CEA. Mean LOS with standard deviation (SD) in patients with CAS was 1.8 ± 2.33 days whereas in patients with CEA it was 2.1 ± 2.69 days. In contrast to these findings, hospital cost for patients with CAS was $11,717 ± 6,242 while for patients with CEA it was $7,926 ± 7,320; we analyzed the differences in LOS and cost between patients with CAS and CEA with non-parametric Wilcoxon rank sum test and these differences were found to be significant (P < .0001 for both).

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Discussion 

As the proportion of older patients steadily increases, the best management of carotid disease in this population will become more germane. It is expected that the number of elderly with cardiovascular disease will produce a significant economic burden on the medical system.¹⁶ It has also been shown that as the population ages and requires more health care, a significant part of this is in surgical services.¹⁷ There is a generalized perception that a minimally invasive intervention such as CAS may be better tolerated over a surgical, open CEA, but the debate has continued to what constitutes the safest management for this group of patients. Considering the potential rise in utilization of CAS and the increased cost of CAS¹⁸ there remains controversy delineating the best management of carotid disease in the aged.

The NIS data for 2005, contrary to previously published trial and registry results, demonstrates similar stroke rates after CAS in all age groups examined. CAS was found to have a significantly higher risk of stroke overall. Previously published results showing higher stroke rates in octogenarians include the CREST 30-day lead-in phase study,⁷ the 30-day results of the SPACE trial,⁴ and the CAPTURE registry.⁴, ¹⁹ Data from the lead-in phase of the CREST trial evaluated 30-day stroke and death among 749 patients who had undergone carotid angioplasty and stenting for symptomatic carotid stenosis and found that octogenarians had an increased rate of 12.1%, which was significantly higher than the rates of patients aged 70-79 (5.3%), 60-69 (1.3%), and less than 60 years (1.7%).⁷

Multiple smaller series have shown no increased complications in the use of CAS in the elderly. Shawl et al²⁰ reported no difference in the 30-day stroke rate between octogenarians and younger patients in a cohort of 170 consecutive patients. Ahmadi et al²¹ as well found no significant difference in neurological complications at 30 days between patients above the age of 75 years and patients below age 75, and this series concluded that elective carotid stenting can be performed safely in older patients and age was not an independent risk factor for poor inferior outcomes after CAS. Finally, Kadkhodayan et al²² demonstrated no significant difference after CAS in the 30-day rate of stroke, transient ischemic attack (TIA), MI, or death between the elderly and younger patients.

We have demonstrated using national data that stroke rates are not greater in the elderly after CAS or CEA. We have demonstrated that CAS has a higher overall stroke rate compared to CEA and that CAS is more often utilized in the elderly. Overall, this creates inferior outcomes in the aged. Other studies have also demonstrated increased utilization of CAS in the elderly. The Arbeitsgemeinschaft Leitende Kardiologische Krankenhausarzte (ALKK) Carotid Artery Stent Registry studied 2,780 CAS procedures and noted a significant increase in the proportion of octogenarians between 1996 (5.9%) and 2005 (13.7%) undergoing CAS.²³ The higher percentage of patients over age 80 receiving CAS demonstrated from this study may represent more liberal use of the procedure in older patients, reluctance to perform CEA in the elderly, more stringent criteria for CEA, or provider bias based on perceived lower risk of CAS.

Of greatest importance is that these data demonstrate that the overall stroke rate is significantly greater after CAS (4.16%) when compared to CEA (2.66%). Previous studies have reported increased stroke rate after CAS, including the Endarterectomy vs Angioplasty in Patients with Symptomatic Severe Carotid Stenosis (EVA-3S) investigators.⁶ The EVA-3S investigators reported a 30-day incidence of stroke or death among patients who underwent stenting (9.6%), as compared with those who underwent surgery (3.9%). Inferior outcomes for CAS have also been reported by other authors using national discharge data.²⁴

The dissemination of new technology into the population at large may lead to different outcomes than reported from trial and registry data. Explanations for these differences may include variations in practice, experience of the operator, patient selection, the learning curve utilizing CAS, and the lack of regimented protocols mandated by studies. Mas et al⁶ referred to the “learning curve” for carotid stenting as a reason for the inferior results associated with CAS in this study. It has been established that the risk associated with carotid endarterectomy varies among surgeons and CAS likely has similar risks associated with the operator.

With regard to utilization for CAS, we found hospital charges for CAS to be significantly greater when compared to CEA, even though the LOS was found to be greater for CEA. Others have reported procedural costs of CAS are higher than those of CEA, primarily due to material costs and that cost-effectiveness and utilization of CAS primarily depends on major stroke rates which are greater after CAS.²⁵ As well, Kilaru et al²⁶ demonstrated CEA as cost saving compared with CAS due to the higher rate of stroke with CAS and the high cost of stents. Therefore, from a global utilization perspective for treatment of the elderly, CAS may demonstrate inferior cost-effectiveness.

Overall mortality among elderly patients after CAS was found to be greater than in patients after CEA. To adjust for comorbidities we utilized the validated Elixhauser¹³ method for administrative data and mortality still remained higher in the elderly. Explanations for inferior outcomes after CAS for octogenarians is primarily due to the increased stroke rates associated with CAS. Stroke was found to be the greatest predictor of mortality and carried a 29 times greater risk of death. Octogenarians were significantly more likely to receive CAS than other age groups and this may account for the increased mortality in the CAS group. As well, comorbidities including cardiac, pulmonary, and renal complications were associated with inferior outcomes after CAS. Renal failure and cancer were also associated with stroke in all patients. Men were found more likely to have postoperative mortality in the entire cohort when including CAS and CEA. These results are similar to other population-based studies of CEA using Medicare data showing higher mortality for men overall.²⁷

One of the major limitations of this study is the coding used for the diagnosis of stroke. The NIS is an administrative discharge dataset based on billing. The data contained in the NIS and other discharge datasets are limited by the coding schemes created by AHRQ and ICD-9 codes. It is possible that the definition of stroke and the way it is coded within the dataset may vary between institutions and hospital coders. Previous authors have reported extremely low stroke rates (0.88%) in the nation at large for CEA.²⁴ The stroke rate calculated by McPhee et al²⁴ utilized only the iatrogenic stroke code (997.02) which we believe to be an underutilized code based on the bias of the hospital coders. For this reason we expanded the stroke codes utilized with the rationale that stroke is an acute code and by selecting elective carotid intervention patients were unlikely to have acute stroke codes in their administrative discharge data unless they occurred during that hospitalization in association with a carotid intervention.

Other limitations are that the NIS database does not include patients in military hospitals or VA medical centers. The potential for inclusion bias based on limited coding schemes for the many clinical entities cannot be entirely excluded as well as confounding by indication of the procedures. Classification as elective vs non-elective was based on the HCUP variable for admission type. We acknowledge that there is a trade-off in using administrative data on thousands of patients and the use of smaller cohorts with more refined clinical information. While both types of studies have drawbacks and strengths, we feel that administrative data provides valuable population-based information on carotid procedure outcomes. Of course the CEA group of patients suffers these same limitations, thus supporting the differences between the CAS and the CEA groups.

In conclusion, this study suggests that the paradigm of utilizing CAS for management of carotid disease in the elderly may not offer improved outcomes and likely increases resource utilization. Octogenarians were significantly more likely to have received CAS than younger patients. The greatest predictor of mortality was found to be stroke and the highest stroke rates were associated with CAS. Due to increased utilization and poorer outcomes, mortality after CAS was found to be greater in octogenarians. Further prospective analysis with emphasis on the aged is needed to determine the best management as the percentage of elderly in the US population steadily grows over time.

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Author contributions 

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References 

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