Trends and outcomes of concurrent carotid revascularization and coronary bypass

Article Outline

• Abstract
• Methods
• Results
• Discussion
• Conclusions
• Author contributions
• Appendix (online only). 
• References
• Copyright

Background

The management of concurrent carotid and coronary artery disease is controversial. Although single-center observational studies have revealed acceptable outcomes of combined carotid endarterectomy (CEA) and coronary artery bypass grafting (CABG), community-based outcomes have been substantially inferior. Recently, carotid artery stenting (CAS) has been introduced for the management of high-risk patients with carotid stenosis, including those with severe coronary artery disease. This study was undertaken to evaluate the nationwide trends and outcomes of CAS before CABG vs combined CEA and CABG and to assess the risk for adverse events.

Methods

The Nationwide Inpatient Sample (NIS) was used to identify patients discharged after concurrent carotid and coronary revascularization procedures. All patients that underwent CAS before CABG and combined CEA-CABG during the years 2000 to 2004 were included. The type of revascularization and major adverse events (ie, in-hospital stroke and death rates) were determined by cross-tabulating discharge diagnostic and procedural codes. Risk stratification was performed using the Charlson Comorbidity Index. Weighted exact Cochrane-Armitage trend test and multivariate logistic regression were used to assess the association between types of revascularization, comorbidities, complications, and risk-adjusted mortality.

Results

During the 5-year period, 27,084 concurrent carotid revascularizations and CABG were done. Of these, 96.7% underwent CEA-CABG, whereas only 3.3% (887 patients) had CAS-CABG. From 2000 to 2004, the proportion of patients undergoing CAS-CABG vs CEA-CABG did not significantly changed (P = .27). Patients undergoing CAS-CABG had fewer major adverse events than those undergoing CEA-CABG. CAS-CABG patients had a lower incidence of postoperative stroke (2.4% vs 3.9%), and combined stroke and death (6.9% v. 8.6%) than the combined CEA-CABG group (P < .001), although in-hospital death rates were similar (5.2% vs 5.4%). After risk-stratification, CEA-CABG patients had a 62% increased risk of postoperative stroke compared with patients undergoing CAS before CABG (odds ratio [OR], 1.62; 95% confidence interval [CI], 1.1-2.5; P = .02). However, no differences in the risk of combined stroke and death were observed (OR, 1.26; 95% CI, 0.9-1.6; P = NS).

Conclusion

Although CAS may currently be performed for high-risk patients, it is still infrequently used in patients who require concurrent carotid and coronary interventions. In the United States, patients who undergo CAS-CABG have significantly decreased in-hospital stroke rates compared with patients undergoing CEA-CABG but similar in-hospital mortality. CAS may provide a safer carotid revascularization option for patients who require CABG.

The management of concurrent severe carotid and coronary artery disease is controversial. Although single-center observational studies have revealed acceptable outcomes of combined carotid endarterectomy (CEA) and coronary artery bypass grafting (CABG),¹, ², ³ community-based outcomes have been substantially inferior.⁴ Stroke remains the major noncardiac complication of open cardiac surgery, with an absolute incidence of 2%. Severe carotid artery disease has, however, been associated with a fourfold increased risk of perioperative stroke after CABG.², ⁵

Optimal timing and sequence of treatment of patients with combined coronary and carotid stenosis also remains unresolved, particularly for patients who require combined urgent reconstructions during the same hospitalization. Systematic reviews and meta-analyses of staged or simultaneous CEA and CABG revealed rates of perioperative major adverse events, such as combined stroke, myocardial infarction (MI), and death, in the 10% to 12% range.² No significant differences in outcomes between staged and simultaneous procedures were noted. Carotid revascularization may, however, reduce the stroke rates in patients with combined lesions, as suggested by reduced rates of post-CABG stroke in patients with a prior CEA.², ⁶, ⁷ To be beneficial in reducing stroke rates, carotid revascularization and CABG need to be performed with low cardiac and neurologic morbidity.

Carotid stenting with cerebral embolic protection is currently reserved primarily for high-risk patients with severe carotid stenosis, including those with severe coronary artery disease.⁸, ⁹ Recent observational studies have shown that CAS may be performed before CABG with acceptable stroke and death rates.¹⁰, ¹¹, ¹², ¹³ It is unknown to what extent CAS is currently used for the management of combined carotid and coronary artery disease. Although one potential advantage of CAS over CEA is a reduction in the rate of myocardial events in patients that need CABG because it is less invasive, the need of dual antiplatelet therapy and the potential adverse hemodynamic depression associated with CAS may limit its utility in patients with unstable coronary artery disease.

This study was undertaken to evaluate the nationwide trends and outcomes of carotid interventions performed in patients that undergo CABG in the United States (US). The objectives of this study were to compare the results of CAS vs CEA performed in conjunction with CABG during the same hospitalization and to assess the risk of stroke and death.

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Methods 

The Nationwide Inpatient Sample (NIS) from the Healthcare Cost and Utilization Project (HCUP) was used to identify all CAS and CEA procedures performed in conjunction with CABG from 2000 to 2004. The NIS, which is the largest all-payer inpatient database in the United States,¹⁴ represents a 20% stratified sample of inpatient admissions to US academic, community and acute care hospitals nationwide and includes about 1000 hospitals in 35 states (federal and prison hospitals were excluded). Typical discharge data collected include demographics, primary and 14 different secondary diagnoses, primary and 14 different secondary procedures per patient as identified by the International Classification of Diseases, 9th Revision, Clinical Modification (ICD-9-CM) codes, length of stay, charges, and outcomes (Appendix, online only). Sampling weights are provided for accurate calculations based on the complex survey design. The NIS core inpatient files were used for data extraction and analysis. Because NIS data are publicly available and contain no personal identifying information, this study was exempt from Institutional Review Board approval.

All CAS and CEA procedures performed in conjunction with CABG during the same hospitalization during the 5-year period were identified by linking the ICD-9-CM procedural codes for CEA and CAS and procedural codes for CABG. The ICD-9-CM coding system has had a specific code for CAS since 2004 (00.63). Before 2004, CAS procedures were coded using less specific procedural codes. To identify CAS patients before 2004, the NIS database was queried using a previously described method in which queries for the procedural codes for angioplasty of a noncoronary vessel (39.50) and insertion of a noncoronary artery stent (39.90) are linked to appropriate diagnostic codes for carotid artery stenosis.¹⁵, ¹⁶

Symptomatic status of patients with carotid stenosis was determined according to the ICD-9-CM discharge diagnosis. Patients were classified as symptomatic if the discharge diagnosis was “carotid artery stenosis with stroke” or if the diagnosis codes included transient ischemic attacks (TIA) or amaurosis fugax. Patients with a discharge diagnosis of “carotid artery stenosis without mention of stroke,” with no accompanying diagnoses for TIA or amaurosis fugax, were classified as asymptomatic.

The 15 diagnosis codes (ICD-9-CM) and the clinical classification software (CCS; Agency for Healthcare Research and Quality, Rockville, Md) coding system included in the data, which limits and prevents overcoding,¹⁷ were used to define comorbid medical conditions and further used to calculate a comorbidity score based on the modified Charlson Comorbidity Index (CCI).¹⁸ The CCI is a validated measure for use with administrative data that correlates with in-hospital morbidity and mortality after surgical procedures, including elective carotid interventions.¹⁹ Each of the indicated diagnoses is assigned a weight and summed to provide a patient's total score. The ability of CCI to predict in-hospital mortality was initially assessed. Once validated, the CCI was further used to define two groups based on surgical risk according to comorbidities (CCI ≤1 indicating low-risk vs CCI ≥2 indicating greatest comorbidity) for analyses.

The primary outcome end point of this cross-sectional population-based study was in-hospital stroke and death after combined carotid and coronary revascularization procedures; that is, stroke or deaths, or both, that occur after CEA or CAS performed during the same hospitalization as CABG. Postoperative stroke was defined as an ICD-9-CM secondary diagnostic code of “post-operative stroke (997.02).” Postoperative death was defined as any death occurring during the same hospitalization. Mortality data were available directly from the data set, which are entered as “died during hospitalization” and coded from disposition of the patient. HCUP quality control procedures are routinely performed to confirm that data values are valid, consistent, and reliable.²⁰ Weighted analyses for predictors of in-hospital stroke and death included demographic data, symptomatic status, preoperative comorbidities, risk stratification, which was based on the CCI, and hospital characteristics.

Descriptive statistics for categoric variables are presented as relative frequencies (percentages), which were compared with the χ² test (χ² for independent groups, two-tailed P value). Continuous variables were expressed as medians and interquartile ranges (IQR) and compared with nonparametric tests. In-hospital stroke and death rates were adjusted for patient age, sex, symptomatic status, and CCI for risk-stratification using multivariate stepwise logistic regression analyses. Findings were considered statistically significant for the primary end point of in-hospital stroke and death at P < .05. Multivariate odds ratios (OR) are reported with 95% confidence intervals (CI). Relative frequencies of the primary outcomes were calculated for each year. Weighted exact Cochrane-Armitage trend tests were used to determine if there were any trends in outcomes from 2000 to 2004. Because no significant changes in in-hospital stroke and death rates were evident, further statistical analyses included the whole data set using the revised trend sampling weights necessary for analyses that span multiple years to reflect increases in state participation. The data analyses were done with SAS 9.1 software (SAS Institute, Cary, NC).

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Results 

An estimated 27,084 concurrent carotid revascularizations and CABG were performed during the same hospitalization during the 5-year period, and 85.5% were elective combined procedures. Most patients (96.7%) underwent CEA-CABG, whereas CAS-CABG was only performed in 887 patients (3.3%). From 2001 to 2004, the proportion of patients undergoing CAS-CABG vs CEA-CABG did not significantly change (P = .16). CAS-CABG was performed in 2.5% of all combined procedures in 2001 and in 2.9% in 2004.

Patient characteristics and comorbidities according to type of carotid revascularization are listed in Table I. Most patients (96.4%) underwent treatment for asymptomatic carotid stenosis. Among patients with symptomatic stenosis, 12% had TIA and 88% had stroke listed as principal or secondary diagnoses.

Table I. Clinical characteristics of patients undergoing CAS-CABG and CEA-CABG

Characteristics	CAS-CABG	CEA-CABG	P
	(n = 887)	(n = 26,197)
Age, median (IQR) y	69(62-76)	72(62-77)	<.001a
Female sex, %	47.2	33.0	<.001b
Symptomatic carotid stenosis, %	2.8	3.6	.24
Comorbidities, %
Hypertension	68.9	63.0	<.001b
Diabetes mellitus	28.0	32.4	.005b
Chronic lung disease	28.5	26.9	.29
Acute myocardial infarction	29.7	20.4	<.001b
Congestive heart failure	2.3	2.7	.45
Renal failure	9.7	6.3	<.001b
CCI, median (IQR) score	1(1-3)	1(0-2)	<.001a
Teaching hospital, %	70.1	60.6	<.001b
Elective admission, %	42.6	52.3	<.001b

CABG, coronary artery bypass grafting; CAS, carotid artery stenting; CCI, Charlson comorbidity index; CEA, carotid endarterectomy; IQR, interquartile range.

Patients undergoing CAS-CABG had a significantly greater prevalence of acute MI, hypertension, and renal failure, whereas patients in the CEA-CABG group were older and had a greater prevalence of diabetes mellitus (Table I). Overall, CAS-CABG patients had a higher-surgical-risk profile according to the CCI (48.8% with CCI ≥2 vs 37.9% in the CEA-CABG group; P < .001). The percentage of octogenarians was significantly higher in the CEA-CABG group compared with the CAS-CABG group (14.4% vs 11.4%; P = .01). The length of stay of patients undergoing CAS-CABG (median, 11 days; IQR, 8-15 days) was significantly longer than that of patients undergoing CEA-CABG (median, 10 days; IQR, 7-15 days; P = .002). A higher proportion of CAS-CABG procedures were performed in teaching hospitals (70.1% vs 60.6%) as nonelective admissions (57.4% vs 47.7%) compared with CEA-CABG procedures.

Patients undergoing CAS-CABG had significantly lower rates of postoperative stroke (2.4% vs 3.9%; P < .001) and slightly lower rates of combined stroke and death (6.9% vs 8.6%; P = .1) compared with patients undergoing CEA-CABG, although in-hospital death rates were similar (5.2% vs 5.4%, respectively). Univariate analysis revealed that CEA-CABG patients had a 65% increased risk of postoperative stroke compared with patients undergoing CAS-CABG (odds ratio [OR], 1.65; 95% CI, 1.1-2.6; P = .02). However, no differences in the risk of combined stroke and death were observed (OR, 1.26; 95% CI, 0.9-1.6; P = NS).

Stratified analyses according to symptomatic status and type of carotid revascularization revealed that among 973 patients with symptomatic carotid stenosis, 96.4% underwent CEA-CABG, and postoperative stroke occurred in 14.2%. Only 25 patients with symptomatic carotid stenosis in this series underwent CAS-CABG, and postoperative stroke occurred in 11 (44%). Symptomatic patients undergoing CAS-CABG, therefore, had a fivefold increased risk of postoperative stroke compared with those undergoing CEA-CABG (OR, 4.7; 95% CI, 2.1-10.6; P < .001).

Multivariate logistic regression analysis revealed that patients undergoing CEA-CABG had a 66% increased risk of postoperative stroke compared with those undergoing CAS-CABG after adjusting for age, sex, symptomatic status, and comorbidities (OR, 1.66; 95% CI, 1.12-2.7; P = .015). Other independent predictors for postoperative stroke included increasing patient age, symptomatic carotid stenosis, and CCI (Table II). Alternative logistic regression models revealed that octogenarians had a 25% increased risk of postoperative stroke compared with patients aged <80 years (OR, 1.25, 95% CI, 1.06-1.5; P = .011), whereas high-risk patients (CCI >1) had a 70% increased risk of postoperative stroke compared with low-risk patients (CCI ≤1; OR, 1.7; 95% CI, 1.5-1.94; P < .001).

Table II. Independent predictors of postoperative stroke and death after combined carotid interventions and coronary bypass^a

CABG, Coronary artery bypass grafting; CEA, carotid endarterectomy; CAS, carotid artery stenting; CI, confidence interval; OR, odds ratio.

Increasing patient age, female sex, acute MI, renal failure, and elective admission were identified as independent predictors of in-hospital mortality by stepwise logistic regression (Table II). By separate analysis in which age was substituted by octogenarian status in the logistic regression model, octogenarians were found to have a threefold increased risk of in-hospital mortality (OR, 2.9; 95% CI, 2.6-3.3; P < .001).

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Discussion 

The results of this large population-based study indicate that asymptomatic patients who undergo CAS-CABG have significantly decreased stroke rates compared with those undergoing CEA-CABG but similar in-hospital mortality. US statistics also specifically demonstrate that nationwide, CAS is performed infrequently in patients who require concurrent treatment of carotid artery lesions and CABG. On the basis of these stroke and death figures, we conclude that CAS-CABG may be explored as alternative combined revascularization strategy in high-risk asymptomatic patients who require CABG. Our findings also indicate that further improvements are necessary to reduce in-hospital mortality, irrespective of carotid revascularization technique, in patients that require concurrent carotid intervention and CABG. The role of CAS-CABG in symptomatic patients remains undefined as, according to our series, it is very rarely performed.

Several observational studies have consistently reported that the risk of stroke associated with CABG is <2% in patients with no significant carotid disease and 3% in patients with asymptomatic severe carotid stenosis. These figures, however, increase to 5% in those with bilateral carotid stenosis and to 7% to 11% in patients with carotid occlusion²; therefore, stroke therefore remains the major noncardiac complication after CABG.

Optimal treatment of patients with concurrent carotid and coronary artery disease remains unresolved despite >110 publications during the last 30 years reporting results in >9000 patients.², ⁵, ²¹ Although only 40% to 50% of strokes after CABG are ipsilateral to an existing carotid lesion, carotid revascularization is one of the few available options to reduce the excessive stroke and death rates in patients with combined disease.

Systematic reviews and meta-analyses that have assessed perioperative outcomes of staged and simultaneous CEA and CABG demonstrate no significant differences in outcomes between the two strategies, albeit staged procedures have generally been associated with lower stroke and death rates than simultaneous ones.² Although CEA has not consistently reduced overall stroke and death rates in patients undergoing CABG, recent series demonstrate that adding CEA to CABG as a second operative procedure does not by itself result in an increased risk of stroke and death.³, ⁶ In fact, intrinsic risk factors may be responsible for the increased morbidity and mortality of combined CEA-CABG, as demonstrated in our study, in which several comorbidities were identified as independent predictors of postoperative stroke and death. Reduced rates of post-CABG stroke rates in certain high-risk patients who also undergo carotid interventions suggest, however, that carotid revascularization might be beneficial in reducing stroke rates if it could be performed with low stroke and MI rates.

CAS under cerebral protection is currently reserved in the United States for high-risk patients, including those with severe coronary artery disease.⁸, ²² Recent trials and “high-risk” registries revealed that CAS can be used in such patients with acceptable morbidity and mortality, particularly when patients are neurologically asymptomatic.²², ²³, ²⁴ Recent observational studies have also reported results of staged CAS, followed by CABG, with low periprocedural complication rates.¹⁰, ¹¹, ¹², ¹³, ²⁵, ²⁶ In most instances in which CAS and CEA before or concomitant with CABG have been compared, results tend to favor CAS. A recent observational study that assessed the safety and feasibility of staged CAS, followed by CABG, in asymptomatic patients revealed not only low periprocedural morbidity and mortality of 4.8% for death and stroke at 30 days but also long-term durable results of 71.4% freedom from all stroke and death at 5 years.²⁵ Our study confirms the safety and efficacy of staged CAS and CABG in terms of perioperative complications among asymptomatic patients and suggests that this approach may be a valuable, if not preferable, alternative to CEA-CABG.

Recent randomized clinical trials failed to demonstrate noninferiority of CAS compared with CEA among symptomatic low-risk patients.²⁷, ²⁸ Although CAS has been associated with an increased risk of stroke in symptomatic patients, a recent randomized trial revealed that such risk may be disproportionately higher among symptomatic patients undergoing CAS compared with CEA.²⁸ In our series, CAS-CABG was associated with a fivefold increased risk of postoperative stroke compared with CEA-CABG among symptomatic patients. This finding, however, needs to be interpreted with caution given the small number of symptomatic patients undergoing CAS-CABG in this series.

One possible explanation for the increased risk of stroke in the CAS-CABG symptomatic group may be related to the performance of CAS and CABG during the same hospitalization, which could have been performed under only aspirin and heparin therapy. Clopidogrel is frequently avoided under these circumstances to prevent its associated intrinsic increased risk of bleeding in patients undergoing CABG and is only started once mediastinal bleeding has been excluded. Although the reported experience with this approach is limited and has been restricted primarily to asymptomatic patients in whom no postoperative neurologic adverse events have occurred,¹³, ²⁹ its utility in symptomatic patients has not been determined. Our study suggests that when combined carotid and coronary interventions are required in patients with symptomatic carotid stenosis, CEA-CABG is probably a better option.

One potential advantage of CAS over CEA is related to its theoretic reduced invasiveness, which may prevent cardiac events in patients with significant and unstable coronary artery disease. Conversely, CAS-induced hemodynamic depression may result in worsening cardiac events.³⁰ It is unknown to what extent CAS may result in major adverse cardiac events in patients requiring CABG. Although postprocedural MI data is not available in the NIS data set, major postoperative cardiac complications did not occur after either CAS-CABG or CEA-CABG and in-hospital death rates were similar, thereby suggesting a similar incidence of major cardiac adverse events for both carotid revascularization techniques in patients requiring CABG.

One of the main limitations of the current study is the inclusion of combined CAS or CEA and CABG performed during the same hospitalization. This occurred because unique subject identifiers within the NIS data set prevent the identification of multiple admissions for the same patient. It is important, however, to emphasize that patients with such severe carotid and coronary artery disease that require treatment during the same hospitalization constitute the heart of the controversy regarding the best management of patients with combined vascular disease. In fact, nearly all patients with combined carotid and coronary artery stenosis have varying degrees of severity of their vascular diseases that allow them to safely undergo carotid interventions or CABG in different hospitalizations according to the clinical priority. In practice, therefore, only a few patients have such severe combined disease that a staged or simultaneous revascularization is required.² The current series focuses on such patients, those with severe combined disease who are more likely to undergo their combined reconstructions during the same hospitalization.

Although level I evidence would be ideal to determine the best treatment strategy for patients who require combined treatment of carotid and coronary arterial disease, the design and implementation of a multicenter randomized clinical trial has been proven impractical and unrealistic. The heterogeneity of patients with varying degrees of coronary and carotid artery disease and the preference of carotid intervention are the main limitations for such a trial. In this context, available evidence should focus on the outcomes of those patients with severe combined disease that required simultaneous or staged urgent procedures.

Although the present study is large, recent, and based on the entire spectrum of CAS-CABG and CEA-CABG experience in the United States, several important limitations should be acknowledged. First, miscoded and missing data can occur in large administrative data sets, such as the NIS; however, HCUP quality control procedures are routinely performed to confirm that NIS data values are valid, consistent, and reliable.²⁰ Moreover, potential misclassifications, if present, would have occurred without bias toward any of the two combined procedure groups.

Second, misidentification of CAS procedures may have occurred, because no specific ICD-9-CM procedural code for CAS existed before 2004. Linking and pairing angioplasty and stenting codes with diagnostic codes for carotid disease using primary and different levels of secondary codes, however, did not significantly change the results, which suggest that patients undergoing CAS-CABG were appropriately identified.

Third, the NIS data set only includes in-hospital stroke and death rates, which may erroneously be considered too low when compared with the usually reported 30-day rates of major adverse events after carotid interventions. Moreover, the inability to include as part of the primary end point the postprocedural MI rates, which are not reported in the NIS data set, would also suggest an apparently lower combined major adverse event rate in this series.

Fourth, the inability to perform an intention-to-treat analysis in patients undergoing staged procedures may bias the results against patients undergoing simultaneous CEA-CABG because patients who suffer a major complication or death associated with the carotid revascularization are unlikely to undergo subsequent CABG.

Finally, anatomic, procedural, and other patient characteristics that could be explored as possible predictors of adverse outcomes are not available in the NIS data set. Future studies assessing their effects on the outcomes of combined procedures as well as the influence of the severity and stability of both carotid and coronary conditions will probably alter the strategy and type of procedures used for the treatment of patients requiring concurrent carotid and coronary interventions. The effects of the degree of carotid stenosis and the presence of bilateral critical carotid stenosis in asymptomatic patients also needs further investigation, because most patients undergoing combined carotid and coronary interventions in the United States have asymptomatic carotid disease.

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Conclusions 

CAS is still infrequently used in patients in the United States who require concurrent carotid and coronary interventions. Patients with asymptomatic carotid stenosis undergoing CAS-CABG have significantly decreased stroke rates than those undergoing CEA-CABG but similar in-hospital mortality. CAS may be a safer carotid revascularization option for patients with asymptomatic carotid stenosis requiring CABG in terms of postoperative stroke prevention, but further improvements in in-hospital mortality are necessary. Conversely, in patients with symptomatic carotid stenosis, CEA-CABG is probably a better option. The best treatment approach for patients requiring combined carotid and coronary interventions is, however, still undefined and should be established by comparing the two strategies in the setting of a well-powered randomized clinical trial.

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Author contributions 

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Appendix (online only) 

Appendix (online only). International Classification of Diseases, 9th Revision, Clinical Modification (ICD-9-CM) diagnosis and procedural codes

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