Perioperative strokes following combined coronary artery bypass grafting and carotid endarterectomy: A nationwide perspective
Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/0028-3886.222849
Source of Support: None, Conflict of Interest: None
Keywords: Carotid endarterectomy, coronary artery bypass grafting, in-hospital mortality, morbidity, perioperative strokes
Carotid endarterectomy (CEA) is increasingly been done in combination with coronary artery bypass grafting (CABG+CEA) for secondary prevention of ischemic strokes. However, secondary CEA procedures have also been reported to increase in-hospital mortality six-fold (6.1–0.9%). Carotid artery stenting (CAS) with CABG has been proposed as a safer alternative to CABG+CEA procedures; however, few randomized studies have been performed comparing the two and fewer with a large cohort size., While more research into the mechanism behind the difference in mortality and morbidity is needed, it is suggested that the high rates of perioperative stroke associated with combined CABG+CEA procedures account for this relatively higher mortality rates.
A perioperative stroke, defined as neurological deficits occurring within the first 30 days of surgery, represents a significant complication following CABG with an incidence rate of 3–5%.,, Neurological complications following CABG have been shown to increase the short and long-term mortality and are the leading causes of postoperative morbidity after CABG., While the overall rate of complications after CABG has decreased, the perioperative stroke rate has remained relatively the same. Intraoperative cerebral hypoperfusion, impaired cerebral autoregulation, and embolization potentiated by carotid stenosis have been attributed to the etiology of perioperative cerebral ischemia following CABG.,,, Examining the relationship between perioperative strokes and early postoperative outcomes following combined CABG+CEA would give us the impetus to investigate therapeutic and preventive strategies such as intensive medical management and neurophysiological monitoring.,
The primary aim of this study was to investigate the role of perioperative stroke on in-hospital mortality and mortality following combined CABG+CEA using the National Inpatient Sample (NIS) database. We also evaluated the trends in perioperative stroke, morbidity, and mortality following CEA and CABG over the 10-year period from 1999–2011.
Data from the Nationwide Inpatient Sample(NIS) was analyzed. Patients who underwent CABG with simultaneous CEA procedures were included in our study and were identified using the ICD-9 (International Classification of Diseases, Ninth Revision-Clinical Modification) diagnosis and procedure codes [Table 1] and [Supplemental Table 1]. Combined procedures were identified as CEA and CABG procedures that happened on the same day. Patients under the age of 18 and over the age of 100 years were excluded from the study. The following baseline characteristics of patients were available for analysis: age (categorized as <65, 65–74, 75–84, 85+), gender, race/ethnicity, admission status, transfer status, Elixhauser comorbidities, and other additional covariates including aortic atherosclerosis, left ventricular dysfunction and cardiac failure, prior cardiac surgery, previous myocardial infarction (MI), history of thromboembolic events, previous history of cerebrovascular disease (stroke/TIA), perioperative stroke, and cardiac arrest. A list of 29 Elixhauser comorbidities with their respective ICD-9 codes provided in the NIS database was used for the analysis. A complete list of covariates and their ICD-9 codes can be found in Supplemental [Table 1].
The primary outcome studied was in-hospital mortality, and the secondary outcome examined was postoperative morbidity, characterized by a long length of postoperative stay (i.e., >14 days) or discharge to a place other than home. The independent variable analyzed was perioperative stroke.
We performed our initial data extraction using SAS version 9.3 (SAS Institute, Inc., Cary, NC). We merged the Hospital Weight Files provided by the NIS database into each individual year's dataset to ensure that each hospital was accounted for at least once. We then stacked our datasets from 1999 to 2011. SAS was used to create the Elixhauser comorbidity index and to generate van Walraven (VWR) score. The Elixhauser comorbidity index was created using the comorbidity software available at the Health Care Utilization Project (HCUP) website.,, We created the VWR score using the macro created by the Cleveland Clinic's van Walraven macro. All subsequent analyses (both univariate and multivariate) were performed using Stata version 14 (StataCorp, College Station, TX). Analyses were performed using the survey command, grouping by hospital identity (ID), weighed with the discharge weights provided by HCUP, and stratified using the strata variable provided by HCUP. We performed our univariate analyses using unpaired t-test for continuous variables and a survey-adjusted Wald test for all variables that were categorical in nature. We ran several multivariable logistic regression models for the binary outcomes of mortality and morbidity [Table 2], [Table 3], [Table 4]. We chose to report one model in this manuscript in [Table 5] and elected not to include individual comorbidities as many of them had too few members in the group to be statistically significant and reporting them would risk overloading the model and deviate from the primary outcome.
Demographic data was obtained from a total population of 8457 patients who underwent combined CABG and CEA from 1999 to 2011 [Table 1]. The average age of the patient population was 69.98 ± 11.9. The study population had a male majority (68.05%) with a large proportion of the patients between 65 and 74 years of age. An in-hospital mortality of 4.96% (421 patients) and morbidity of 66.35% were observed in this cohort. A total of 6.17% (n = 521) of our study patients developed perioperative stroke following combined CABG and CEA. A total of 28.82% (n = 2437) of the study patients developed postoperative myocardial infarction, which is a noteworthy finding following the combined CABG and CEA. Risk stratification was done using the VWR score, which is a weighted numerical representation of Elixhauser comorbidities. The average VWR score observed for the patient cohort was 3.18 ± 7.40. Although majority (66.02%) of study patients were categorized as low risk (VWR <5), significant increases in the adverse outcomes were observed in patients with higher scores.
Predictors of in-hospital mortality and morbidity
Univariate analysis of predictors for in-hospital mortality and morbidity with the unadjusted odds ratios (OR) are reported in [Table 2], [Table 3], [Table 4]. Our multivariate analysis showed perioperative stroke to be one of the strongest independent risk factors for in-hospital mortality following combined CABG and CEA with an OR of 4.12 (95% confidence intervals [CI]: 3.1–5.4). Other noteworthy predictors of mortality include age (OR 1.04, 95%CI: 1.03–1.06; P = 0.000), female gender (OR 1.56, 95%CI: 1.27–1.93; P< 0.000) and medium-to-high risk van Walraven category. The medium risk group had an OR of 1.97 (95%CI: 1.58–2.46; P = 0.000), and the high risk group had an OR of 2.48 (95%CI: 1.38–4.44; P< 0.002). Previous cardiac intervention, coronary artery disease [CAD]/angina, left ventricular disease and heart failure, and post-operative myocardial infarction were found to be significant predictors of in-hospital mortality as well [Table 5].
Our analysis showed that the perioperative strokes increase postoperative morbidity with an OR of 3.69 (95%CI: 2.99–5.16; P< 0.000). Other independent predictors of morbidity include age (OR: 1.05,95%CI: 1.05–1.06; P< 0.000), female gender (OR: 1.38, 95%CI: 1.24–1.53; P< 0.000), and van Walraven category (medium risk OR: 1.77,95%CI: 1.57–2; P< 0.000 and high risk OR: 4.07,95%CI: 2.34–7.07; P< 0.000). This model was also adjusted for comorbidities such as previous cardiac intervention, CAD/angina, left ventricular disease and heart failure, and postoperative myocardial infarction [Table 5].
Trend analysis (1999–2011)
A trend analysis for the period of 1999 to 2011 was performed to study the average age of patients who underwent combined CABG and CEA, average VWR score, incidence of perioperative strokes and in-hospital mortality and morbidity rates [Table 6]. The average age of the patient cohort gradually decreased from 69.8 in 1999 to 67.9 in 2011, whereas the average VWR score increased from 2.7 to 4.5 over the years. In-hospital mortality rates decreased from 7.1% in 1999 to 3.2% in 2011. In comparison, postoperative morbidity rates increased from 61.1% in 1999 to 72.4% in 2011. Perioperative stroke rates remained relatively unchanged throughout the years (6.9% in 1999 and 6.3% in 2011).
Our study evaluates the in-hospital mortality and morbidity of combined CEA and CABG procedures conducted in over 8000 patients from the NIS database. The study found that in-hospital morbidity increased over the last 10 years for both the procedures. Meanwhile, mortality slightly decreased. Better surgical techniques and diagnostic tools explain the decrease in the average age of the patient population and in-hospital mortality rates over time. Overall, majority of the study cohort was between 65 and 74 years of age, with a mean age of approximately 69. Both in-hospital mortality and morbidity have shown a statistically significant increase with advancing age as with other cardiac procedures. This study cohort was predominantly white and male. However, female patients and African Americans showed a relatively higher risk for in-hospital mortality and morbidity. Previous studies have shown that female patients historically have a greater risk of adverse outcomes following CABG due to late onset of CAD, higher number of comorbidities, few bypass grafts and a low frequency of internal mammary artery utilization., Studies have attributed the adverse outcomes in African American patients to socioeconomic factors leading to more operations being performed in poor-quality hospitals. This relative difference in race disappears in single medical center studies.
In our study, multivariate logistic regression showed that perioperative stroke had a strong association with in-hospital mortality and morbidity following CABG and CEA. Studies have found that strokes following CABG are caused by intraoperative cerebral hypoperfusion, impaired autoregulation, and embolization of atheromatous debris potentiated by carotid stenosis.,,, Symptomatic or asymptomatic carotid stenosis (CS), vertebral, basilar arterial stenosis, and intracranial stenosis , have all been reported to contribute to perioperative ischemic strokes but are not routinely evaluated preoperatively.CEA procedures are thought to mitigate the high stroke rate of 3–5% post-CABG;,, however, our study found the combined procedures showed a similar percentage of perioperative strokes, undercutting the effectiveness of combined CEA and CABG. Due to the devastating effects of ischemic strokes, many hospitals identify and assess patients using tests such as the Face Arm Speech Time (FAST), Los Angeles Pre-hospital Stroke Screen (LAPSS), Melbourne Ambulance Stroke Screen (MASS), and Recognition of Stroke in the Emergency Room (ROSIER). In addition, different methods used to prevent postoperative strokes such as anticoagulant and antiplatelet medication, intraoperative blood pressure management, and blood transfusions need further investigation. Many hospitals employ stroke care pathways with regular imaging, admission to in-hospital stroke units, adequate thrombolysis, and physical therapy, which have been shown to improve perioperative patient recovery and reduce stroke-related mortality.,, Intraoperative neurophysiological monitoring with somatosensory evoked potential (SSEP) and electroencephalography (EEG) have shown to predict the occurence of postoperative neurovascular accidents early and can also be considered to predict strokes.
Our analysis also shows that in-hospital mortality and morbidity were two times more likely to occur in patients with preoperative LVD for combined procedures. LVD and HF have been known to increase the risk of stroke due to associated coronary hemodynamic abnormalities. Other factors identified through univariate analysis such as paralysis, renal failure, coagulopathy, weight loss, and fluid and electrolyte disturbances were also more likely to result in in-hospital mortality in combined procedures. While weight loss was only seen in 2.13% of the patients, it had a 90% morbidity rate. Recent studies have shown that postoperative weight loss may lead to disability as it is usually a decrease in muscle mass requiring longer monitoring signs for physical deficits. Preoperative risk stratification would allow for identifying patients with severe LVD and congestive heart failure (CHF) and other comorbidities to help with better patient selection. Once identified, the use of drugs, delaying surgery to correct coexisting anemia, and better control of ventricular rates in patients with atrial fibrillation can be used to decrease surgical risks.
Despite a modest population size, our study presents a comprehensive analysis of preoperative and perioperative variables contributing to in-hospital mortality and morbidity following combined CABG and CEA operations. A few limitations are to be addressed in our study. Our data did not determine the significance in the differences between the data. Our stroke and death data is limited to in-hospital occurrences due to the NIS database being a discharge-level database. In addition, differences in hospital postoperative care and availability of resources may also influence the outcomes rates. While the incidence of adverse perioperative events is recorded, the NIS database does not provide vital details regarding stroke timing and postoperative neurological evaluation and management. These factors could have influenced the in-hospital mortality and morbidity rates in our study.
Analysis of 8457 patients who underwent combined CABG and CEA over a period of 10 years (1999–2011) indicate perioperative stroke to be a strong postoperative predicator of in-hospital mortality and morbidity. Other factors including CHF, LVD and HF, post-operative myocardial infarction, weight loss, and gender should also be considered when determining patient risk. Further investigative studies on combined CABG and CEA procedures are needed to assess risk-stratification for better patient selection and examine other preventative strategies to minimize the risk of ischemic strokes.
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Conflicts of interest
There are no conflicts of interest.
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]