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(Circulation. 1995;92:85-91.)
© 1995 American Heart Association, Inc.

Articles

Outcomes of Coronary Artery Bypass Graft Surgery in 24 461 Patients Aged 80 Years or Older

Eric D. Peterson, MD, MPH; Patricia A. Cowper, PHD; James G. Jollis, MD; Judith D. Bebchuk, MS; Elizabeth R. DeLong, PHD; Lawrence H. Muhlbaier, PHD; Daniel B. Mark, MD, MPH; David B. Pryor, MD

From the Division of Cardiology, Department of Medicine, and the Division of Biometry, Department of Community and Family Medicine, Duke University Medical Center, Durham, NC.

Correspondence to Eric D. Peterson, MD, MPH, Box 3236, Duke University Medical Center, Durham, NC 27708-3236.

	Abstract

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Background Coronary artery bypass graft surgery is increasingly common in patients of age 80 years. Single-institution reviews have cited a wide range of mortality results after bypass surgery in this age group, in part because of limited sample sizes. Using claims data, we examined recent national trends in the use and outcomes of bypass surgery in the very elderly.

Methods and Results From an examination of Medicare data from 1987 through 1990, we identified 24 461 patients of age 80 years who underwent bypass surgery. We compared surgical outcomes in these patients with those in Medicare patients of age 65 to 70 years. We found that the national use of bypass surgery in patients of age 80 years increased 67% between 1987 and 1990. Compared with patients of age 65 to 70 years, the very elderly had significantly longer postoperative hospital stays (mean, 14.3 versus 10.4 days), higher charges (mean, $48 200 versus $38 000), and greater costs (mean, $27 200 versus $21 700). In-hospital (11.5% versus 4.4%), 1-year (19.3% versus 7.9%), and 3-year mortality rates (28.8% versus 13.1%) after bypass surgery were also significantly higher in patients of age 80 years compared with younger patients. Although their initial surgical risk was high, octogenarians who underwent bypass surgery had a long-term survival rate similar to that of the general US octogenarian population.

Conclusions The use of bypass surgery in patients of age 80 years is increasing. These very elderly patients face high surgical risks and accumulate significant hospital expenses. Further research is indicated to determine whether the long-term benefits from bypass surgery in the very elderly outweigh the increased procedural risks.

Key Words: aging • survival • cardiopulmonary bypass • revascularization

	Introduction

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In the United States in 1990, there were 6.9 million persons of age 80 years, and there will be nearly 25 million by 2050. Currently, 1 in 35 Americans is of age 80 years; by 2050, this proportion will be 1 in 12.¹ Life expectancy at age 80 in the United States exceeds 8 years; however, surveys suggest that more than 25% of octogenarians have significant functional limitations secondary to cardiovascular disease.^{2 3} Many of these patients have disease refractory to medical therapy and may be potential candidates for coronary artery bypass graft surgery (CABG).

The results of CABG in patients of age 80 years have been reported only in single-institution case series.^{4 5 6 7 8 9 10 11 12 13 14 15} These reviews have generally reported higher surgical risk in octogenarians compared with younger patients. In-hospital mortality estimates for patients of age 80 years undergoing CABG, however, have ranged from 5.6% to almost 25% (Table 1). This variation in outcome results in part from differences in the mix of surgical patients at these institutions and from random variation in estimates due to the limited sample size at any single institution. Moreover, although previous studies have reported patient outcomes, they have not defined the resource costs associated with performing bypass surgery in patients of age 80 years.

View this table: [in this window] [in a new window]   Table 1. Literature on Bypass Surgery in Octogenarians

Our study examined the use and outcomes of bypass surgery in patients of age 80 years within the national Medicare database. Because Medicare provides insurance for the vast majority of America's elderly, these results are representative of the national outcomes of bypass surgery in the very elderly. To reflect recent cardiovascular practice, this study also included surgical cases performed from 1987 through 1990. Outcomes examined include postoperative length of stay, in-patient charges and costs, and mortality for up to 3 years after bypass surgery. Also, we compared the outcomes of bypass surgery in patients of age 80 years with those in Medicare patients of age 65 to 70 years. Finally, given the anticipated changes in US age demographics, we projected how the use of bypass surgery in octogenarians may have an impact on the nation's healthcare resource expenditures.

	Methods

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Data Sources
Data were obtained from the Medicare Provider Analysis and Review file provided by the Health Care Financing Administration for Medicare Part A enrollees who received coronary artery bypass graft surgery from 1987 through 1990. This file contains demographic and limited clinical information on all hospitalizations that are billed to Medicare, including the enrollee's health insurance claim number, age, sex, race, discharge status (including death), and up to five discharge diagnoses and three procedures as identified by International Classification of Diseases (ICD-9-CM) codes.¹⁶ In-patient hospital and department charges exclusive of professional fees were also obtained from the Medicare records. Departmental cost-to-charge ratios were taken from the Health Care Resource Information Systems (HCRIS) computer files (1987 through 1991). Mortality data through September 1993 came from Medicare records and date-of-death files. Using individual patient identifiers, we linked subsequent hospital admissions and procedures to form a longitudinal record of a patient's hospital care and costs for 1987 through 1990.

Patient Populations
The study population consisted of all patients of age 80 years in the Medicare files who underwent bypass surgery (ICD-9-CM codes 36.10 through 36.19) between 1987 and 1990. For the purposes of this report and consistent with previous literature, the term "octogenarian" was used in reference to patients of age 80 years. As noted in our results, patients between the ages of 80 and 89 years constituted 99% of our cohort. We contrasted surgical outcomes in this age group with those in a cohort of younger Medicare patients, of age 65 to 70 years, who received bypass surgery during the same time period. Within the timeframe of study, we could be sure that no patient was represented in both cohorts. Patients who underwent multiple bypass surgery procedures during the study period were included only once, identified by their initial bypass surgery.

We initially identified 202 488 patients of age 80 years or of age 65 to 70 years who received bypass surgery between 1987 and 1990. Patients were excluded for any of three reasons, with some patients meeting more than one of the following exclusion criteria:

Medicare eligibility and follow-up data. We excluded patients who received Medicare benefits as part of the Railroad Retirement Board (1.4%) and patients who had end-stage renal disease (0.2%) as a reason for Medicare eligibility. We excluded patients who were enrolled in health maintenance organizations because Medicare does not have continuous, reliable data on these patients (4.0%). Patients who were admitted to non-US hospitals or federal hospitals were also excluded for this reason (0.5%).

Failed coronary angioplasty. We excluded patients who received percutaneous transluminal coronary angioplasty (ICD-9-CM code 36.01, 36.02, or 36.05) during the same hospitalization as the bypass surgery to avoid attributing mortality from failed angioplasty cases to bypass surgery outcomes (2.4%).

Combined open-heart procedures. We wished to focus on outcomes after isolated bypass surgery in the elderly. Patients were therefore excluded who underwent concomitant cardiac valve replacement (ICD-9-CM codes 35.2 or 35.3), papillary muscle or chordae tendineae repair (ICD-9-CM codes 35.31 or 35.32), ventricular septal repair (ICD-9-CM 35.53, 35.62, or 35.72), and/or implantation of an automatic cardioverter-defibrillator system (ICD-9-CM 37.94 or 35.95) (7.2%).

Statistical Analysis
We determined the frequencies of demographic and clinical characteristics for the 65- to 70- year-old and 80-year-old bypass surgery cohorts. Patients were considered to have been admitted for an acute myocardial infarction if their primary diagnosis was ICD-9-CM code 410.xx and their total length of stay was 3 days (after linking interhospital transfers) for patients discharged alive.¹⁷ The frequencies of coded comorbid diseases (eg, congestive heart failure or pulmonary disease) were determined with previously developed ICD-9-CM mapping strategies applied to discharge abstract information.^{18 19}

Procedure utilization rates were calculated by dividing the number of initial procedures performed during a given year by the number of Medicare-eligible patients for that year. The denominators for these rates were derived from Medicare's enrollment database after applying patient exclusions as previously listed. Total and postoperative lengths of stay were calculated from admission date and procedure date, respectively, to date of discharge.

To estimate the cost of the hospital stay for bypass surgery, we converted hospital charges, exclusive of professional fees, that were billed to Medicare to costs with the use of department cost-to-charge ratios available from national Health Care Resource Information Systems files. The total adjusted cost for each admission was the sum of the adjusted department costs. Costs were then aggregated into inpatient episodes, which were defined as hospitalizations preceding or following the bypass surgery hospitalization by 1 day. Finally, all charge and cost data were standardized to 1990 dollars by use of the Consumer Price Index for hospital services.²⁰ It should be noted that although no gold standard exists for estimating the actual "cost" for a given procedure, cost-to-charge ratios have been used in previous investigations^{21 22} and in one study yielded equal bypass surgery cost estimates when compared with a detailed microcost accounting system (Transition System 1).²³

Survival after bypass surgery was calculated from the procedure date forward. The procedure date was missing in fewer than 0.1% of the records, and the admission date was substituted in these cases. Because we had complete survival follow-up without censoring through September 1993, we calculated unadjusted Kaplan-Meier survival rates²⁴ up to 3 years after bypass surgery for patients of age 65 to 70 years and for those of age 80 years. Long-term survival rates in octogenarians undergoing bypass surgery were also compared with survival estimates for US citizens of similar ages, which were available from vital statistics data prepared by the US Bureau of the Census.²

Independent clinical predictors of 30-day mortality in octogenarians receiving bypass surgery were estimated with a multivariate logistic regression model. Similarly, independent predictors of 3-year mortality were estimated with a Cox survival model.²⁵ Variables entered into these models were selected based on their univariate association with bypass surgery mortality (P<.01) or their clinical relevance. The final regression models simultaneously adjusted for patient age, race, sex, and presence of preoperative acute myocardial infarction, congestive heart failure, peripheral vascular disease, cerebral vascular disease, chronic renal failure, pulmonary disease, and diabetes mellitus with sequelae. From the variable parameter estimates and standard errors produced by these models, we calculated odds ratios (ORs) for mortality and the 95% confidence intervals surrounding these estimates for each clinical predictor.

	Results

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Demographics
Between 1987 and 1990, we identified 24 461 patients of age 80 years covered by Medicare who met study criteria and underwent coronary artery bypass graft surgery. A total of 83% of these patients were of age 80 to 85 years, 13% were of age 86 to 90 years, and 1% were of age 90 years. Baseline characteristics for these very elderly patients were compared with those for patients of age 65 to 70 years who received bypass surgery (Table 2). Octogenarians were significantly more likely to be female and white and to have been admitted for an acute myocardial infarction before receiving bypass surgery. Octogenarians receiving bypass surgery were also more likely to be coded as having congestive heart failure or cerebral vascular disease but less likely to have pulmonary disease or diabetes mellitus than were patients of age 65 to 70 years.

View this table: [in this window] [in a new window]   Table 2. Baseline Characteristics of Bypass Surgery Patients

We also examined temporal trends in the use of bypass surgery in these two age categories. The national rate of bypass surgery performed per year in octogenarians increased by 67% during the 4 years of this study, from 7.2 per 10 000 in 1987 to 12.0 per 10 000 in 1990. This rate significantly exceeded that of patients of age 65 to 70 years, whose rate increased by 10.3% during this same time period, from 38.1 per 10 000 to 42.1 per 10 000.

Mortality After Bypass Surgery
Unadjusted survival rates after bypass surgery in patients of age 80 compared with patients of age 65 to 70 years are given in Table 3. Overall 30-day, in-hospital, 1-year, and 3-year mortality rates for octogenarians were 10.5%, 11.5%, 19.2%, and 28.8%, respectively. These values were more than twice as high as those in patients of age 65 to 70 years: 4.3%, 4.4%, 7.9%, and 13.1%, respectively.

View this table: [in this window] [in a new window]   Table 3. Mortality After Bypass Surgery by Age Group

Mortality rates are generally higher in octogenarians than in younger patients regardless of whether they receive bypass surgery. To provide a perspective for evaluating long-term outcomes after bypass surgery in patients of 80 years, we compared 3-year mortality rates in these patients with mortality estimates for the general US octogenarian population (Fig 1). Although octogenarians receiving bypass surgery face high procedural risks, their 3-year mortality rate after the procedure was nearly equal to that of similarly aged US citizens: 28.8% versus 26.6%.

View larger version (11K): [in this window] [in a new window]   Figure 1. Plot of 3-year survival estimates in octogenarians who undergo bypass surgery ([CABG] solid line) compared with those in the general US octogenarian population (dashed line).

Independent clinical predictors of 30-day and 3-year mortality after bypass surgery in octogenarians are given in Table 4. Age was a significant predictor of both 30-day and 3-year mortality. For example, an 85-year-old patient undergoing bypass surgery would have nearly 40% higher odds for mortality at 30 days than a similar patient of age 80 years. Women and nonwhite patients had slightly worse procedural and long-term outcomes than did men and white patients. Measures of acute coronary disease, such as acute myocardial infarction before bypass surgery and congestive heart failure, also predicted higher procedural and long-term mortality rates. Finally, comorbid illnesses such as peripheral vascular disease and chronic renal disease were highly predictive of 30-day and 3-year mortality.

View this table: [in this window] [in a new window]   Table 4. Independent Predictors of 30-d and 3-y Mortality After Bypass Surgery in US Octogenarians

Resource Use
Postoperative hospital stays after bypass surgery were significantly longer in octogenarians than in patients of age 65 to 70 years (mean, 14.2 days [25th to 75th percentile, 8 to 15 days] versus 10.8 days [7 to 11 days], respectively; Table 5). These longer stays by the very elderly were reflected in increased total hospital charges (exclusive of professional fees) for the bypass surgery admissions in octogenarians (mean charges, $48 200 [$28 000 to $53 000] versus $38 000 [$24 000 to $42 000] for patients of age 65 to 70 years). Calculated hospital costs for the bypass surgery were also higher in those of 80 years (mean cost, $27 200 [$17 000 to $30 000] versus $21 700 [$14 000 to $23 000]).

View this table: [in this window] [in a new window]   Table 5. Resource Use After Bypass Surgery by Age Group

Longer postoperative length of stay by the very elderly was only a partial explanation for their higher relative costs. The intensity of medical services delivered per day was also increased in octogenarians after bypass surgery, as reflected in their higher cost per hospital day ($1567 versus $1472 per day). Finally, although the mean values for hospital stay, charge, and cost data were skewed in both age strata by high outlier patients with multiple postoperative complications, the median values for these resource measures remained 38%, 22%, and 21% higher, respectively, in octogenarians than in younger patients.

	Discussion

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Coronary artery bypass graft surgery in the very elderly is becoming increasingly common. During a 4-year period between 1987 and 1990, the national rate of bypass surgery in patients of age 80 years increased by 67%. Our data demonstrate, however, that the performance of bypass surgery in the very elderly is associated with substantially higher short- and long-term mortality rates and that they consume significantly more healthcare resources per procedure than do younger patients.

Previous studies have reported that increasing age is a risk factor for in-hospital and long-term mortality after bypass surgery.^{4 26 27 28 29 30} Specific mortality estimates in the very elderly, however, have varied widely, as noted in Table 1. Given that procedural mortality appears to be declining in the elderly,³¹ part of these differences in surgical outcome may be explained by the inclusion of cases from more than 15 years ago. Also, these institutional reviews contained patients with varying severity of illness and comorbidity. Because of the relatively small sample sizes available in these case series, minor differences in patient risk may have had large impacts on overall procedural mortality rates. Finally, the limited number of patients in these reports result in wide confidence intervals surrounding the estimates of procedural mortality rates. Thus, the "play of statistical chance" may also have contributed significantly to the variation in reported estimates.

By combining the results from published reports, one can examine an average or composite mortality estimate from these series. Composite estimates of bypass surgery mortality outcomes based on 1035 cases in the literature are similar to our results based on Medicare patients (in-hospital mortality, 10.4% versus 11.4%; 1-year mortality, 17.5% versus 19.3%; 3-year mortality, 28.7% versus 28.8%, respectively). The slightly lower mortality results from the published case series may reflect the higher efficacy of bypass surgery performed on octogenarians at major academic centers and/or the impact of reporting bias on published mortality estimates.

Predictors of Mortality
Literature regarding clinical predictors of mortality after bypass surgery in the very elderly has been extremely limited. The largest reported clinical series from the Mayo Clinic (159 patients) was able to identify only depressed left ventricular function as an independent predictor of bypass surgery mortality in octogenarians.⁷ Weintraub and colleagues⁹ also noted that the combination of left ventricular dysfunction and diabetes mellitus identified octogenarians at higher risk for in-hospital and long-term mortality. Congestive heart failure and the urgency of surgery have also been predictive of surgical mortality.^{11 13} Although other clinical factors such as peripheral vascular, pulmonary, and renal disease appear to increase surgical risk in octogenarians in many of these studies, no series has been large enough to confirm these trends.

Using national Medicare data, we had access to the results for more than 24000 patients from which to identify predictors of short- and long-term mortality in octogenarians undergoing bypass surgery (Table 4). We found that increasing age, female sex, and measures of disease acuity (preoperative acute myocardial infarction or congestive heart failure) identified octogenarians with significantly higher 30-day and 3-year mortality rates after bypass surgery. Comorbid illnesses such as chronic renal disease, peripheral vascular disease, and cerebral vascular disease also independently predicted patients with higher 30-day and 3-year mortality rates. Interestingly, diabetes mellitus and pulmonary disease were not predictive of 30-day mortality but did predict worse long-term outcomes.

Given that these mortality prediction models are based on claims data, they must be considered with caution. Claims data have previously been demonstrated to undercode comorbid disease processes.^{32 33 34} Although the specificity of claims coding for comorbid illness appears high, less severe conditions tend not to be coded.³² This selective undercoding of comorbidity could have led to an overestimate of the predictive power of these conditions. Also, it is often difficult to separate preoperative comorbid illnesses from postoperative complications. For example, the coding of cerebral vascular disease may indicate a previous stroke or a postoperative event. For certain conditions, such as myocardial infarction, we were able to identify preoperative events by identifying only those cases where the principal reason for hospital admission was acute myocardial infarction. Finally, Medicare claims data allow for the coding of no more than five disease processes. This limitation may lead to an undercoding of chronic conditions, such as pulmonary disease, in patients with multiple acute disease processes and complications. Because these patients also have increased mortality rates, this can lead to an apparent, albeit incorrect, assumption that the chronic condition is actually "protective."^{33 34} Despite these limitations, the predictors of increased surgical risk in octogenarians found in the present study are in general consistent with trends reported in previous smaller institutional series and with clinical expectations. Further confirmation of these findings will be required in large, multicenter clinical studies.

Cost Issues
Previous studies have not examined hospital costs in octogenarians undergoing bypass surgery. Compared with patients of age 65 to 70 years, octogenarians had significantly longer mean postprocedural lengths of stay and higher hospital costs. Although some of this increased mean expense in octogenarians may be attributable to high "outlier" patients who have multiple postoperative complications, the median values for postoperative hospital stays and hospital costs remained 20% to 40% higher for octogenarians than for younger patients.

Given the expected growth in the number of US octogenarians over the next 50 years, the overall cost of bypass surgery in the very elderly begins to have major health policy implications. For example, the right axis of Fig 2 depicts the expected number of bypass surgery procedures that will be performed in US octogenarians over the next 60 years if we conservatively assume that the "rate" of bypass surgery (which has been increasing by more than 15% per year) will remain constant at 1990 levels. Despite this conservative assumption, given the dramatic demographic shifts in the US population, the number of bypass surgeries performed can be expected to increase from 8000 per year in 1990 to more than 30 000 procedures per year by 2050. The left axis of Fig 2 displays the expected in-hospital costs for these procedures, again conservatively assuming no temporal changes in the cost per procedure. By 2050, in-hospital costs for bypass surgery alone in octogenarians will exceed $1.2 billion (in 1990 dollars). Because these projections do not include professional fees, the total cost for these procedures will be substantially higher than these estimates.

View larger version (21K): [in this window] [in a new window]   Figure 2. Plot showing projected number of bypass surgery (CABG) procedures performed per year in octogenarians (left axis) and the corresponding projected costs for these procedures (in 1990 dollars) (right axis).

Risk Versus Benefit
Multiple randomized clinical trials have helped define which patients are most likely to benefit from bypass surgery.^{32 33 34} These clinical trials, however, were not performed on the very elderly. It is clear from the present study that expected risks and outcomes from bypass surgery in the "young elderly," those between 65 and 70 years of age, cannot be extrapolated to octogenarians. Octogenarians face significantly higher procedural risk and can be expected to have significantly poorer long-term outcomes than patients of age 65 to 70 years (see Table 3).

The unanswered question is whether octogenarians incur sufficient benefit from these procedures in terms of symptom relief and improved survival expectations to justify the surgical risk. Unfortunately, information comparing surgical intervention with conservative care in the very elderly with coronary disease is quite limited. In terms of symptom relief, Weintraub and colleagues⁹ found that 82% of patients with severe baseline angina who were alive at 3-year follow-up remained asymptomatic. Other clinical series have confirmed these findings, demonstrating long-term improvements in functional status and symptom relief with surgical therapy in the very elderly.^{7 15}

Whether bypass surgery improves survival expectations in octogenarians, however, remains unknown. Published randomized trials of bypass surgery versus medical therapy have excluded the very elderly.^{36 37} Ongoing randomized trials of revascularization therapy have not enrolled sufficient numbers of octogenarians to examine the efficacy of these procedures in this age group.^{38 39 40} Finally, published nonrandomized comparisons of therapeutic options in octogenarians with coronary disease have been severely limited in size, decreasing the ability of these studies to adjust for baseline patient differences among the various treatment strategies.^{12 41 42}

When a patient and physician discuss options for the optimal therapy in a given clinical situation, they must weigh the risks of the procedure against the long-term risks of foregoing the procedure. In general, those patients at highest risk from their disease process (ie, severe coronary disease and depressed ventricular function), although facing higher surgical risk, stand to benefit the most in terms of long-term survival from surgery.⁴³ Although administrative databases such as the one applied in the present study can supply accurate overall procedural mortality estimates, these data lack important clinical variables, such as left ventricular function and coronary anatomy, necessary for meaningful nonrandomized comparisons of outcomes in octogenarians with coronary disease. Large multicenter clinical databases, such as the ongoing Cooperative Cardiovascular Project, may in the future have a sufficiently large database of elderly patients to address these important issues.⁴⁴

In conclusion, the present study demonstrated that the use of bypass surgery in octogenarians is expanding rapidly. We also provide patients and physicians with national mortality rates after bypass surgery in the very elderly. These accurate estimates can provide a starting point for the dialogue between physicians and patients faced with the difficult decisions surrounding the treatment of coronary disease in the very elderly. It is clear that with the ongoing demographic changes in the United States, these decisions have growing implications for healthcare resource utilization and national health policy. Decisions concerning these expenditures should, in part, be made more easily with increased knowledge concerning the effectiveness of this intervention in the very elderly in general practice. Further clinical studies are therefore strongly indicated to determine whether the benefits from bypass surgery in the very elderly justify the substantially increased risks.

	Acknowledgments

 
This work was supported by research grants HS-06503 and HS-05635 from the Agency for Health Care Policy and Research, Rockville, MD; by research grant HL-17670 from the National Heart, Lung, and Blood Institute, Bethesda, MD; and a grant from the Robert Wood Johnson Foundation, Princeton, NJ.

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