Abstract
Background:
As the US population ages and the burden of dementia increases, an increasing number of patients with dementia will be evaluated by surgeons for coronary artery bypass grafting. Currently, there is little evidence on how dementia changes preoperative risk stratification. This study aims to characterize baseline characteristics and outcomes in patients with dementia who underwent CABG.
Methods:
We used data from the National Inpatient Sample database from 2008 to 2018 for patients ≥18 years old who underwent coronary artery bypass grafting. Patients were divided into 2 groups on the basis of dementia diagnosis. A propensity-matched analysis was used to account for attributable risk of dementia. Our primary outcome was in-hospital mortality. Secondary outcomes included postoperative delirium, length of stay, and total charges submitted to payors.
Results:
Of 522,949 total patients who met inclusion criteria, 8,487 carried a preoperative diagnosis of dementia. There was not a significant difference in 30-day mortality when compared with patients without dementia who had a coronary artery bypass grafting (odds ratio, 0. 834; P = .17). Dementia patients had longer length of stay (estimated treatment effect = 0.522 days, P < .01) and greater total charges submitted to payors (estimated treatment effect = $8,371, P = .00135). They were also significantly more likely to experience postop delirium (OR, 3.9; P < .001) and were more likely to be discharged to a nursing facility after their index hospitalization (41% vs 17%, P < .01).
Conclusion:
Our study suggests that patients with dementia are at no greater risk for postoperative mortality but have significantly greater length of stay, costs, and risk of delirium. In carefully selected patients, dementia should not be a contraindication for coronary artery bypass grafting.
Introduction
As the American population ages, the burden of chronic diseases, including dementia, has increased. Dementia, which is a broad term encompassing several different diagnoses, places an increasingly large financial, psychosocial, and medical burden on the population. Concurrently, the number of surgical procedures performed on elderly patients is increasing and already represents a majority of surgical procedures performed in the United States.1,2 The convergence of these trends necessitates study into the impact of diagnoses of dementia on surgical outcomes. Given the invasive nature of cardiac surgery and the average cardiovascular health of patients undergoing these surgeries, the impact of dementia is becoming of particular importance to cardiac surgeons. Several studies have demonstrated that patients with dementia have an increased risk of mortality and other adverse outcomes after surgery, but no study to date has reported on the unique risks to patients undergoing coronary artery bypass grafting (CABG).3,4
A diagnosis of dementia may result from one of several etiologies. Although these causes of dementia vary significantly in their pathophysiology, natural histories, and treatment courses, they tend to share common systemic features relevant to questions of surgical intervention.5 Certain cardiovascular risk factors have been shown to be independently associated with increased risk for dementia, including hypertension, hypercholesterolemia, diabetes, obesity, and smoking. The goal of this study is to attempt to identify and quantify the risk attributable to dementia in patients undergoing CABG.6
Methods
Data source
We queried the National Inpatient Sample (NIS) from January 2008 through December 2018. The NIS, developed for the Healthcare Cost and Utilization Project, is the largest publicly available database of inpatient admissions in the United States containing 7 million yearly admissions representing a 20% sample of all inpatient admissions in the United States.7 This study was deemed exempt from institutional review board review.
Study population
We conducted a retrospective study of patients ≥18 years of age who underwent CABG. Patients with any neurologic disorders, aside from dementia, were excluded. CABG, dementia, and the exclusion criteria diagnoses were identified using International Classification of Diseases, Ninth Revision (ICD-9) and Tenth Revision (ICD-10) codes.8 In our study, a diagnosis of dementia was defined as either Alzheimer disease, Pick disease, frontotemporal dementia, Lewy body dementia, vascular dementia, cerebral or corticobasal degeneration, nervous system degeneration due to alcohol, senile degeneration of the brain, cognitive impairment, or unspecified dementia. Patient characteristics, including age, sex, hypertension, diabetes mellitus, heart failure, previous coronary artery disease, and previous myocardial infarction were collected and included in the model. Please see Supplementary Table S1 for a complete list of all ICD codes used and comorbid conditions queried.
Variables and outcomes
The primary outcome was in-hospital mortality after CABG. Secondary outcomes measured included length of stay, total charges during the admission, postoperative delirium, acute arrythmia, acute bleeding, postoperative pneumonia, acute limb ischemia, postoperative infection, acute kidney injury, and acute myocardial infarction. These complications were identified using ICD-9 and ICD-10 diagnostic codes as listed in Supplementary Table S1.
Statistical analysis
Analysis was performed using Stata, mersion 15 (StataCorp LLC, College Station, TX). The svy command was used to apply weights and make national estimates using methodology outlined by the Healthcare Cost and Utilization Project.9 Propensity score matching was used to adjust for demographic differences between the dementia and nondementia groups using the MatchIt package (version 4.5.5, Ho et al10) in R (R Core Team, Vienna, Austria11) implemented in RStudio (RStudio, Boston MA). Multivariable logistic regression models were used for binary outcomes by using matched cohorts. Confounding variables were carefully controlled for, and collinearity and overfitting were minimized. To avoid bias, model covariates were chosen a priori.12 All models were adjusted for age, smoking, anxiety, dyslipidemia, obesity, heart failure, hypertension, previous coronary artery disease, previous mesenteric ischemia, previous percutaneous coronary intervention, previous CABG, previous transient ischemic attack/stroke, atrial fibrillation, peripheral artery disease, anemia, chronic pulmonary diseases, liver disease, coagulopathy, fluid and electrolyte disorders, and cancer. We reported adjusted odds ratios (ORs) after multivariable regressions on matched samples and 95% confidence intervals for binary outcomes and aggregated treatment affects for continuous variables. Alpha level of significance (P) was set at .05.
Results
Population characteristics
A total of 522,948 patients met the inclusion criteria for this study with 1.6% (n = 8,487) having a diagnosis of dementia and 98.4% (n = 514,462) not having a dementia diagnosis. Patients with dementia had an average age of 76.9 years and 62.8% were male compared with an average age of 66.4 years, 68.1% of whom were male for patients without dementia. Patients with dementia were more likely to have heart failure, renal failure, anemia, anxiety, and coagulopathy. Table I shows all unmatched means and Table II shows the matched cohort means. Figure 1 graphically represents matched and unmatched cohorts mean differences demonstrating that there were no significant differences in the matched cohort.
Table I.
Unmatched population characteristics
| Variable | No dementia, n (%) | Dementia, n (%) |
|---|---|---|
|
| ||
| Total, n | 514,462 | 8,487 |
| Age <60 yr | 28,861 (5.6%) | 2,280 (26.9%) |
| Age 60—64 | 24,849 (4.8%) | 1,192 (14.0%) |
| Age 65—69 | 45,941 (8.9%) | 1,421 (16.7%) |
| Age 70—74 | 72,899 (14.2%) | 1,298 (15.3%) |
| Age 75—79 | 110,249 (21.4%) | 1,097 (12.9%) |
| Age 80—84 | 122,288 (23.8%) | 750 (8.8%) |
| Age 85—90 | 79,793 (15.5%) | 348 (4.1%) |
| History of smoking | 190,711 (37.1%) | 3,492 (41.2%) |
| Dyslipidemia | 342,323 (66.5%) | 5,580 (65.8%) |
| Syncope | 7,820 (1.5%) | 72 (0.8%) |
| Angina | 15,537 (3.0%) | 382 (4.5%) |
| Anxiety | 59,369 (11.5%) | 799 (9.4%) |
| Diabetes | 115,857 (22.5%) | 1,990 (23.4%) |
| Previous coronary artery disease | 114,468 (22.2%) | 1,463 (17.2%) |
| Obesity | 42,700 (8.3%) | 1,102 (13.0%) |
| Previous MI | 64,925 (12.6%) | 1,073 (12.6%) |
| Previous PCI | 46,147 (9.0%) | 732 (8.6%) |
| Previous TIA/stroke | 80,513 (15.6%) | 634 (7.5%) |
| Atrial Fib/flutter | 185,103 (36.0%) | 2,579 (30.4%) |
| Heart failure | 262,118 (50.9%) | 2,908 (34.3%) |
| History of cancer | 5,556 (1.1%) | 82 (1.0%) |
| Chronic pulmonary dysfunction | 197,605 (38.4%) | 2,574 (30.3%) |
| Renal failure | 73,722 (14.3%) | 860 (10.1%) |
| Rheumatic disease | 823 (0.2%) | 21 (0.2%) |
| Peripheral vascular disease | 69,607 (13.5%) | 866 (10.2%) |
| Anemia | 91,471 (17.8%) | 1,151 (13.6%) |
| Liver disease | 14,045 (2.7%) | 218 (2.6%) |
| Coagulopathy | 130,570 (25.4%) | 1,947 (22.9%) |
| Fluid and electrolyte disorders | 175,020 (34.0%) | 2,706 (31.9%) |
| Pulmonary circulation disorders | 238,916 (46.4%) | 3,654 (43.0%) |
MI, myocardial infarction; PCI, percutaneous coronary intervention; TIA, transient ischemic attack.
Table II.
Matched population characteristics
| Variable | No dementia | Dementia | Standard mean difference |
|---|---|---|---|
|
| |||
| Matched, n | 8,487 | 8,487 | |
| Age <60 yr | 476 (5.6%) | 459 (5.4%) | 0.008 |
| Age 60–64 | 409 (4.8%) | 416 (4.9%) | −0.004 |
| Age 65–69 | 757 (8.9%) | 730 (8.6%) | 0.011 |
| Age 70–74 | 1,202 (14.2%) | 1,189 (14.0%) | 0.005 |
| Age 75–79 | 1,818 (21.4%) | 1,834 (21.6%) | −0.004 |
| Age 80–84 | 2,017 (23.8%) | 2,045 (24.1%) | −0.008 |
| Age 85–90 | 1,316 (15.5%) | 1,334 (15.7%) | −0.006 |
| History of smoking | 3,146 (37.1%) | 3,176 (37.4%) | −0.008 |
| Dyslipidemia | 5,647 (66.5%) | 5,698 (67.1%) | −0.013 |
| Syncope | 129 (1.5%) | 105 (1.2%) | 0.023 |
| Angina | 256 (3.0%) | 222 (2.6%) | 0.023 |
| Anxiety | 979 (11.5%) | 919 (10.8%) | 0.022 |
| Diabetes | 1,911 (22.5%) | 1,834 (21.6%) | 0.022 |
| Previous coronary artery disease | 1,888 (22.2%) | 1,951 (23.0%) | −0.018 |
| Obesity | 704 (8.3%) | 689 (8.1%) | 0.006 |
| Previous MI | 1,071 (12.6%) | 988 (11.7%) | 0.029 |
| Previous PCI | 761 (9.0%) | 695 (8.2%) | 0.027 |
| Previous TIA/stroke | 1,328 (15.7%) | 1,295 (15.3%) | 0.011 |
| Atrial fibrillation/flutter | 3,053 (36.0%) | 3,023 (35.6%) | 0.008 |
| Heart failure | 4,324 (50.9%) | 4,393 (51.8%) | −0.017 |
| History of cancer | 91 (1.1%) | 63 (0.8%) | 0.032 |
| Chronic pulmonary dysfunction | 3,259 (38.4%) | 3,202 (37.7%) | 0.014 |
| Renal failure | 1,216 (14.3%) | 1,199 (14.1%) | 0.006 |
| Rheumatic disease | 13 (0.2%) | 5 (0.1%) | 0.023 |
| Peripheral vascular disease | 1,148 (13.5%) | 1,077 (12.7%) | 0.025 |
| Anemia | 1,508 (17.8%) | 1,436 (16.9%) | 0.023 |
| Liver disease | 231 (2.7%) | 201 (2.4%) | 0.022 |
| Coagulopathy | 2,154 (25.4%) | 2,075 (24.4%) | 0.021 |
| Fluid and electrolyte disorders | 2,887 (34.0%) | 2,837 (33.4%) | 0.012 |
| Pulmonary circulation disorders | 3,941 (46.4%) | 3,972 (46.8%) | −0.008 |
| Age <60 yr | 476 (5.6%) | 459 (5.4%) | 0.008 |
MI, myocardial infarction; PCI, percutaneous coronary intervention; TIA, transient ischemic attack.
Figure 1.
Matched and unmatched covariate means. Indicated in blue are the mean differences in covariate balance from the matched data set and indicated in red are those for the unmatched dataset. MI, myocardial infarction; PCI, percutaneous coronary intervention; TIA, transient ischemic attack.
Primary outcome
Patients with dementia who underwent CABG did not have significantly different odds of 30-day mortality compared with those without dementia (OR, 0. 834; [0.643–1.08], P = .17). Table III shows predicted treatment effects after matching for primary and secondary outcomes.
Table III.
Matched adjusted outcome estimates
| Primary outcome | Adjusted odds ratio (95% CI) | P value |
|---|---|---|
|
| ||
| Death | 0.834 (0.643–1.08) | .172 |
| Secondary outcomes | Estimate (95% CI) | |
| LOS, d | 0.522 (0.291–0.753) | <.001 |
| Cost, $ | 8,371 (3,252–13,490) | .00135 |
| Adjusted odds ratio (95% CI) | ||
| Postoperative infections | 0.99 (0.985–0.994) | <.001 |
| Acute arrythmia | 1 (0.944–1.06) | .984 |
| Acute bleeding | 0.544 (0.319–0.93) | .026 |
| Delirium | 3.9 (3.09–4.92) | <.001 |
| Acute limb ischemia | 0.801 (0.408–1.57) | .518 |
| Postop pneumonia | 1.18 (0.804–1.73) | .398 |
| Acute kidney injury | 0.989 (0.828–1.18) | .906 |
| Acute myocardial ischemia | 0.838 (0.226–3.11) | .791 |
| Cardiogenic shock postoperative | 0.925 (0.727–1.18) | .525 |
CI, confidence interval; LOS, length of stay.
Secondary outcomes
Patients undergoing CABG with a concurrent dementia diagnosis had significantly increased odds of postoperative delirium (OR, 3.9, [3.09–4.92], P < .001) and very slightly decreased risk of postoperative infections (OR, 0.99, [0.985–0.994], P < .001). Patients with dementia had significantly longer length of stay (estimated treatment effect = 0.522 days, [0.291–0.753], P < .01) and total charges submitted to payors (estimated treatment effect = $8,371, [$3,252–$13,490], P = .00135). There were no significant differences in rates of acute postoperative arrhythmia, acute bleeding, acute limb ischemia, postoperative pneumonia, acute kidney injury, acute myocardial ischemia, and postoperative cardiogenic shock (all P > .05) Table III shows predicted treatment effects after matching for primary and secondary outcomes. Table IV shows the unadjusted discharge disposition after index admission. Patients with dementia were much more likely to be discharged to a skilled or intermediate nursing facility as patients without dementia in nonadjusted terms (41% vs 17%, P < .01).
Table IV.
Discharge disposition from index hospitalization
| No dementia |
Dementia |
|
|---|---|---|
| N = 293,000 | N = 4,554 | |
|
| ||
| Discharge home | 133,302 (46%) | 1,259 (28%) |
| Transfer to short-term hospital | 1,614 (0.6%) | 32 (0.7%) |
| Transfer to short-term or intermediate care facility | 49,961 (17%) | 1,857 (41%) |
| Home with home health care | 102,330 (35%) | 1,292 (28%) |
| Left against medical advice | 177 (<0.1%) | 12 (0.3%) |
| Died in hospital | 5,439 (1.9%) | 97 (2.1%) |
| Discharge alive but unknown disposition | 18 (<0.1%) | 0 (0%) |
| Unknown | 159 | 5 |
χ2 goodness of fit P < .0001
Discussion
Our study found that, in a well-selected population, patients with dementia undergoing CABG did not have greater in-hospital mortality than matched peers. However, they were more likely to develop postoperative delirium and to be discharged to a nursing facility after their index hospitalization. Although this result highlights the importance of patient-centered decision making, weighing the palliation offered by surgical revascularization to the length and quality of life expected of patients, it should be interpreted with caution. In both general and vascular surgery, preoperative dementia has been associated with increased risk of in-hospital mortality with varying degrees of evidence. Kassahun,13 for example, found that in a matched cohort of German patients with and without dementia undergoing both elective and emergent general and vascular surgical cases, there was a trend toward increased in-hospital mortality, but this did not reach the predetermined threshold of significance. A retrospective review from Taiwan that adopted a similar analysis to this study of an administrative dataset with propensity matching found that in surgical patients at large, there was moderately increased risk of mortality with dementia after adjusting with multiple linear regressions.14 This same trend has been borne out in single retrospective center analyses as well.2
Concordant with those other studies, in several key secondary outcomes, we find that dementia does appear to confer increased risk. As in studies investigating other surgical conditions including cardiac surgery, patients with dementia were found to be significantly more likely to suffer postoperative delirium.15,16 Several studies, have indicated the postoperative delirium itself may portend poor outcomes. One single-center retrospective analysis offered an OR of 3.1 for 1 year mortality in patients who experienced postoperative delirium.17 That same analysis found that patients who experienced delirium were 13 times more likely to be diagnosed with dementia within a year, highlighting the complex relationship between the 2 conditions. It is important not to forget that cardiac disease in of itself confers risk of mortality which cannot be avoided when preoperatively risk stratifying.
Our findings of increased cost, greater length of stay, and increased chance of discharge to a nursing facility for patients with dementia are also in line with other studies and comport with the increased risk of delirium. One study of patients in a large health care system undergoing any type of elective surgery found more than $20,000 in index-hospitalization-related cost increases associated with dementia in Medicare patients.18 Although the magnitude of the effect found in our study in total charges at the index hospitalization is lower than that finding, cardiac surgery already carries with it amongst the highest charges for any surgical procedure and thus the magnitude of difference may be masked by the overall high cost of the procedure.19 The increased chance of discharge to a nursing facility also increases the cost to the medical system and this figure is not included in total charges submitted to the NIS. Discharge to a nursing facility was also associated with up to a 7% absolute increased in mortality in the first year after cardiac surgery in a single center analysis over the same period as this study.20 Although in-hospital mortality was similar between groups, long-term mortality effects may differ.
It is important to note that there are several key limitations to this study. Perhaps the largest is the inherent selection bias in which patients were offered and underwent CABG. These patients are likely to represent the mildest phenotypes of dementia or are otherwise the most medically optimized to undergo surgery. Because of the nature of this study selecting included patients on the basis of procedure code, we are unable to see patients who, if not for their dementia, would meet criteria for CABG. These patients may not have been offered surgery or surgery may not have accorded with goals of care. Thus, it is likely that our study underestimates the true risk of surgery for patients with dementia. Further research utilizing datasets that include longitudinal data and comprehensive treatment records is needed to address this gap.
The NIS as an administrative dataset is subject to limitation on the accuracy of the provided billing codes that may not be perfectly concordant to the issues at hand. In our analysis, we did not stratify by type of dementia. This broader view of our study population allowed us to study more generally the effects of decreased cognitive function on outcomes following CABG; however, an inquiry into different subtypes of dementia could reveal more about the pathophysiologic basis for our results. Furthermore, we were unable to stratify by dementia severity or severity of outcomes due to limited available data. This study also progresses over a period during which the reporting of certain procedure and diagnosis codes were changed, and although careful programming does allow to account for differences between ICD-9 and ICD-10, this does add another layer of potential inaccuracy. Further, as an administrative dataset, the NIS does not allow for detailed clinical variables that would be available in a single center study. All ICD codes used in our study are provided in an appendix, but particularly secondary outcomes not directly provided by the NIS should be taken with nuance as the temporality of clinical events is also limited by the cross-sectional nature of the NIS. Although the methodology employed does allow us to investigate the impact of dementia, several variables which may affect outcomes are not captured by the NIS such as surgical and anatomical considerations, surgeon skill and comfort, and types and doses of medications given. However, this study does remain the most thorough attempt to investigate the surgical risk associated with dementia in patients undergoing CABG to our knowledge.
In conclusion, carefully selected patients with dementia may be at little to no increased risk of postoperative mortality and increased risk of discharge to nursing home, increased length and cost of stay, and increased risk of postoperative delirium after CABG as compared with a matched cohort of patients without dementia. A balanced discussion of dementia-related risks in cardiac surgery patients must consider both disease severity and overall health. However, dementia should not be regarded as an absolute contraindication for surgery. Further research into surgical risks in this growing demographic are needed to better counsel patients and family before surgery.
Supplementary Material
Supplementary material associated with this article can be found, in the online version, at [https://doi.org/10.1016/j.surg.2025.109391].
Funding/Support
This research was funded by National Institutes of Health grants T32HL160517 (to D.D.H., M.B., C.S.); R01HL46716 and R01HL128831 (to F.W.S.); and Brown University Department of Surgery Versaci Scholarship (to M.K.).
Footnotes
Conflict of Interest/Disclosures
The authors have no conflicts of interest to report.
CRediT authorship contribution statement
Meghamsh Kanuparthy: Writing – review & editing, Writing – original draft, Software, Resources, Methodology, Investigation, Formal analysis, Conceptualization. Krishna Bellam: Writing – review & editing, Writing – original draft, Methodology, Investigation, Formal analysis, Conceptualization. Anthony Harwell: Software, Methodology, Investigation, Formal analysis, Data curation. Christopher Stone: Writing – review & editing, Validation, Methodology, Conceptualization. Dwight D. Harris: Writing – review & editing, Validation, Methodology, Formal analysis, Conceptualization. Mark Broadwin: Writing – review & editing, Methodology, Investigation, Conceptualization. Frank W. Sellke: Writing – review & editing, Supervision, Resources, Project administration, Investigation.
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