Ann Thorac Surg 2003;76:S1370-S1376
© 2003 The Society of Thoracic Surgeons
Supplement: understanding disparities in cardiovascular and thoracic surgical outcomes in African-Americans
Impact of renal disease in cardiovascular surgery: emphasis on the African-American patient
William A. Cooper, MDa*,
William Brinkman, MDa,
Rebecca J. Petersen, RN, BAb,
Robert A. Guyton, MDa
a Emory University School of Medicine, Atlanta, GA, USA
b The Emory Clinic, Division of Cardiothoracic Surgery, Atlanta, Georgia, USA
* Address reprint requests to Dr Cooper, Department of Surgery, Division of Cardiothoracic Surgery, Emory University School of Medicine, 550 Peachtree St. NE, MOT 6th Floor, Atlanta, GA 30308, USA
e-mail: william_cooper{at}emoryhealthcare.org
Presented at the symposium on Understanding Disparities in Cardiovascular and Thoracic Surgical Outcomes in African Americans, San Diego, CA, Jan 30, 2003.
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Abstract
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Cardiovascular disease remains a significant source of morbidity and mortality for patients with kidney disease. Coincident with the development of chronic renal failure, patients typically manifest a systemic vasculopathy often involving the cardiovascular system. The renal failure patient is also plagued by multiple comorbid conditions that may adversely affect cardiovascular outcomes. Consistent with the national trend of increasing numbers of patients requiring renal replacement therapy (RRT), patients requiring invasive cardiovascular procedures are also on the incline. The morbidity and mortality related to these procedures has remained high despite significant advances in delivery and maintenance of care. Is the African-American patient with renal failure unique in terms of cardiovascular morbidity and mortality? Numerous studies have documented racial differences in access to invasive cardiovascular procedures, even after controlling for multiple physiologic risk factors and socioeconomic and sociocultural factors. Studies have also shown higher morbidity and lower survival for African-American patients after cardiac procedures. In this high-risk population these same issues perhaps would persist. The following paper will examine the current status of cardiovascular disease in the renal failure patient with emphasis on the African-American patient population.
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Introduction
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In the year 2000 there were more than 370,000 patients living with end-stage renal disease (ESRD) reported in the United States renal data system (USRDS) annual data report (ADR). This represents a 48% (199,951 vs 378,862) increase in the point prevalence rate of ESRD cases since 1991 [1]. African Americans (AA) represent approximately 32% (120,000) of the patients in this group. Over a 20-year period, from 1981 through 2000, the unadjusted incidence of new ESRD patients increased at a rate of 5% to 10% per year, as illustrated in Figure 1.
The rates are similar for black and white patients. However, the overall incidence is 35% higher in AAs (269 vs 777 cases per million population) [1].
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Fig 1. Trends in incident rates and annual percent change. Rates adjusted for age, gender, and race. The incidence of dialysis dependent renal failure has continued to increase over the past 20 years. The rate of new cases increased by 5% to 10% over this time period. The overall incidence is higher in the African American subgroup, however, new cases are similar to Caucasians. [Reprinted from U.S. Renal Data System, USRDS 2002 Annual Data Report: Atlas of End-Stage Renal Disease in the United States, National Institutes of Health, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD, 2002. The interpretation and reporting of these data are the responsibility of the author(s) and in no way should be seen as an official policy or interpretation of the U.S. government.]
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Cardiac surgery trends
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Renal failure (RF) patients undergoing coronary artery bypass (CAB) procedures increased during the last decade of the twentieth century. Nonwhite CAB patients increased by 82% (5.6% vs 10.2%) over this period [2]. At our own institution, we observed a 400% (10 vs 50 procedures) increase in dialysis patients requiring open heart surgery from 1994 through 2001 (Fig 2).
An STS database query including all CAB patients from May 1, 2000 through December 31, 2001 revealed 89% (6851 of 7644) of AA patients with mild to severe renal impairment based on calculated creatinine clearance (CCL) [3].
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Fig 2. Annual trend of dialysis-dependent open heart procedures from Crawford Long and Emory University Hospitals from 1994 through 2001.
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Demographics
Black ESRD patients requiring cardiovascular interventions (CAB, angioplasty, or coronary catheterization) have different baseline demographic variables relative to their white counterparts, which are illustrated in Tables 1 and 2.
Black patients are significantly younger (64 years old vs 57 years old) at the onset of renal replacement therapy (RRT). Only 50% of black men and 32% of black women have private insurance carriers, whereas almost 70% of white men and 65% of white women have private insurance at the onset of RRT. African-American patients are more likely to be uninsured and nonhigh school graduates (Tables 1 and 2) [4].
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Table 1. Demographic and Socioeconomic Characteristics at Baseline in Cohort of 4987 Patients With Chronic Kidney Disease
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Overall, 14% to 87% of patients undergoing CAB have some degree of renal impairment [3, 5]. High rates of comorbid risk factors exist in all ESRD patients. Hypertension, diabetes, and tobacco abuse dominate the comorbidities. African-American patients have higher rates of hypertension but not, as one might expect, cerebrovascular disease.
Economics
Coincident with the rise in ESRD, Medicare expenditures have also increased. In 1991, the monetary burden for ESRD was 1% of total Medicare expenditures (approximately 5 billion dollars). In 2000, the cost had more than doubled to more than 12 billion dollars in annual Medicare expenditures (Fig 3)
[1].
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Fig 3. Costs of the end-stage renal disease (ESRD) and Medicare program dollars in 2000 are inflated by 2% to account for costs incurred not reported. Medicare expenditures have increased coincident with the increasing number of patients requiring dialysis. Annual cost has more than doubled and the percent of expenditures allocated to dialysis programs have increased similarly (green line = total medicare dollars; red line = total dialysis dollars; blue bars = ESRD percent of medicare dollars). [Reprinted from U.S. Renal Data System, USRDS 2002 Annual Data Report: Atlas of End-Stage Renal Disease in the United States, National Institutes of Health, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD, 2002. The interpretation and reporting of these data are the responsibility of the author(s) and in no way should be seen as an official policy or interpretation of the U.S. government.]
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Cardiovascular surgical outcomes
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Survival
Numerous reports in the literature document the high morbidity and mortality related to surgical procedures in the ESRD population [5–11]. During the decision-making process of evaluating an ESRD patient for any surgical procedure, the following question might be asked: will a successful cardiac intervention make a reasonable difference in long-term survival for the patient? Cardiac disease accounts for 44% of deaths in ESRD patients [11]. Twenty percent of the cardiac-related deaths are attributed to acute myocardial infarction (AMI). The inhospital mortality is approximately 26% after AMI. The 2-year mortality in patients with AMI is 74% [12]. Relative to the probability of survival of ESRD patients and the survival of patients after coronary revascularization, it seems highly reasonable to assume that revascularization would offer some benefit in this patient population (Fig 4).
No studies to date have examined these outcomes versus medical therapy.
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Fig 4. All cause survival; results of invasive coronary artery procedures in dialysis patients could be of some inherent benefit. It remains to be demonstrated in a prospective fashion which procedures may have the most impact on patient long-term survival. (CAB = coronary artery bypass; IMA = internal mammary artery; PTCA = percutaneous transluminal coronary angioplasty.)
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Inhospital mortality for ESRD patients after CAB ranges from 7% to 30% [5–11, 13]. Five-year survival ranges from 20% to 70% [6, 7, 9]. When evaluated in large database systems, blacks have a higher overall 30-day mortality after CAB than whites [13–15]. These differences persist even after adjustment for baseline characteristics. In the Veterans Administration series reported by Rumsfeld and associates [14], the differences were even more striking in low-risk patients (odds ratio [OR] = 1.52, 95% confidence interval = 1.10–2.11).
It has been well documented that AA patients on RRT live an average of 12 months longer than whites, which is illustrated in Figure 5
[1, 4]. This survival difference persists in blacks with renal failure after CAB. Bridges and associates [13] reported a 30-day mortality of 7.61% for AA patients with renal failure versus 10.51% for Caucasians. In the same study, blacks on dialysis had a risk of death of 1.30 versus 1.77 for whites. Similarly, Herzog and coworkers [11] reported a 23% decrease in the risk of death for blacks versus whites undergoing coronary revascularization.
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Fig 5. Incident end-stage renal disease (ESRD) and survival probability adjusted for age, gender, race, and primary diagnosis. The incident cohorts and associated modalities are determined at the time of ESRD initiation with the 60-day stable modality rule and the 90-day rule. Age as of date of ESRD initiation. Unknown age, gender; other and unknown, and primary diagnosis are excluded. [Reprinted from U.S. Renal Data System, USRDS 2002 Annual Data Report: Atlas of End-Stage Renal Disease in the United States, National Institutes of Health, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD, 2002. The interpretation and reporting of these data are the responsibility of the author(s) and in no way should be seen as an official policy or interpretation of the U.S. government.]
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Morbidity
Coincident with the increased mortality in ESRD patients after revascularization, there is also an increase in major morbidity [5–11]. The majority of these studies have focused on the dialysis patient. However, the trend towards increasing morbidity begins with baseline dysfunction. Anderson and associates [5] reported the adverse outcomes associated with an increased serum creatinine following CAB in the Veterans Administration system. Seventeen percent of the patients in this study had a serum creatinine greater than 1.5. In addition to the increased mortality, this study found significant increased rates of prolonged ventilation (15% vs 8%), stroke (7% vs 2%), renal failure requiring dialysis (3% vs1%) and bleeding (8% vs 3%) in patients with a serum creatinine 1.5 to 3.0.
A recent STS database query [16] found similar increasing morbidity in CAB patients with mild to severe renal impairment. Based on calculated creatinine clearance (CCL), 87% of the patients in this study had some degree of renal impairment. The trend towards increasing morbidity and mortality began in those patients with only mild decrease in creatinine clearance. In fact, the CCL was the strongest predictor of adverse outcomes for both white and AA patients (Fig 6).
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Fig 6. Mortality by creatinine clearance from The Society of Thoracic Surgeons national adult cardiac registry of coronary artery bypass procedures, May 2000 through December 2001. Although African-American patients tend to live longer once dialysis is initiated, the impact of renal dysfunction on those undergoing coronary artery bypass procedures is profound. No appreciable ethnic differences exist in coronary artery bypass patients.
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Valve surgery outcomes
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Overview
For a number of years, clinicians and surgeons have recognized the similarities between atherosclerotic coronary artery disease and valvular calcification. Dystrophic valvular calcification can lead to valvular insufficiency with regurgitation or stenosis. Patients with these lesions are at risk for stroke and heart failure.
Cardiac valve calcification is increasingly prominent in the ESRD patient. Aortic valve calcification is 10 times more prevalent and mitral calcification 4.5 times more prevalent in the hemodialysis patient [17].
Consistent with the rise in CAB procedures, we have also observed a rise in valve procedures in ESRD patients at our institution (Fig 7).
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Fig 7. Annual trend of dialysis dependent coronary artery bypass (CAB) or valve procedures at Crawford Long and Emory University Hospitals from 1994 through 2001. (ESRD = end-stage renal disease.)
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Mortality and morbidity
Herzog and associates [18], reporting from the USRDS, found 20% mortality in dialysis patients undergoing valve replacement. Blacks comprised 31% of the patients studied with no racial differences in outcomes noted. Fifty-eight percent had aortic (3415 patients), 32% had mitral (1848 patients), and 10% had combined (562 patients) valve replacements. The 2-year survival in this study was approximately 40% [18]. Brinkman and associates [19] reported a 40% survival at two years in 72 dialysis patients. Similarly, Kaplon and associates [20] reported on 42 dialysis patients. The 3-year survival was 50% for mechanical valves and 33% for bioprosthetic valves.
Over the years, cardiac surgical teaching implored surgeons to favor mechanical valves over bioprosthetic valves in ESRD patients. This teaching was predicated on an assumption that bioprosthetic valves placed in dialysis-dependent patients would rapidly calcify and degenerate. All three studies cited above confirmed that there is no appreciable difference in mortality based on valve type [18–20]. Brinkman and coworkers [19] did find a sixfold increase in bleeding due to warfarin therapy in patients with mechanical valves. This observation might favor bioprosthetic valves for ESRD patients.
Valve location does have an impact on survival. Edwards and associates [21] reported operative mortality rates of 17.07%, 22.45%, and 24.59% for aortic, mitral, and combined valve replacements, respectively, in the ESRD patient. Again, no racial differences were noted.
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Access to cardiovascular procedures
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Racial differences in access to cardiovascular procedures have been well documented [4, 15, 22]. These differences persist even after controlling for base line clinical and socioeconomic factors [22].
Daumit and coworkers [4] examined the influence of race, sex and insurance on access to these procedures in the ESRD population. One will recall that black ESRD patients are more likely to be younger, uninsured, and nonhigh school graduates at the onset of RRT. Based on the well-documented differences in procedure rates in the overall population, it is no surprise that in this high-risk subset, the crude rates of cardiovascular interventions is higher in whites than blacks, Tables 3 and 4.
The vast majority of dialysis patients obtain Medicare coverage. The frequency of dialysis also places these patients in direct contact with healthcare providers on a consistent basis. During follow-up in the Daumit and coworkers report [4], most of the differences in procedure rates decreased. However, the procedure rates were still prominent when one takes into account the number of years a patient is at risk. At the onset of dialysis in this cohort, AAs lived 12 months longer than white patients.
It appears from this data that insurance coverage and frequent contact with the healthcare system may partially eliminate the racial differences in cardiovascular procedure rates.
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Conclusions
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Renal dysfunction has a tremendous impact on the cardiovascular patient and the healthcare system in the United States. Over the past 20 years, the incidence of new cases continues to rise. The economic burden of care is also a significant consideration for the continued vitality of the Medicare system. Because cardiac disease is the major cause of death in renal failure patients, the number of patients being considered for cardiovascular interventions continues to increase.
In an attempt to improve the cardiovascular outcomes of renal failure patients, invasive procedures carry an increased risk of death and major morbidity. Across the board, ESRD patients have higher rates of death and complications when compared with those patients without renal dysfunction. Although the focus of most investigations in this regard focuses on the patients on dialysis, the impact of renal dysfunction begins much sooner in the course of development of ESRD. Those with "normal" serum creatinine may in fact still be at increased risk.
Collectively, the AA subsets of ESRD patients tend to have a lower mortality after most cardiac interventions. The reasons behind this are unclear. We know that AA ESRD patients live longer. Are they somehow better adapted to the harsh consequences of dialysis? Despite a more favorable outcome for the black renal failure patient, why are blacks still less likely to undergo bypass or angioplasty? The answers to these and many other questions remain unanswered.
Clearly, many aspects of this disease have yet to be elucidated. The focus of future investigations in the ESRD patients should concentrate on specific causes of death and morbidity and ways to improve outcomes by risk modification.
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References
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- United States Renal Data System 2002 Annual Data Report, www.usrds.org, 2002
- Ferguson T.B., Jr, Hammill B.G., Peterson E.D., Delong E.R., Grover F.L. A decade of change-risk profiles, and outcomes for isolated coronary artery bypass grafting procedures 1999. A report from the STS National Database Committee and the Duke Clinical Research Institute: Society of Thoracic Surgeons. Ann Thorac Surg 2002;73:480-490.[Abstract/Free Full Text]
- A report from the STS National Database, and Duke Clinical Research Institute Committee. Coronary Artery Bypass Procedures May 2000–December 2001
- Daumit G.L., Powe N.R. Factors influencing access to cardiovascular procedures in patients with chronic kidney disease: race, sex, and insurance. Semin Nephrol 2001;21:367-376.[Medline]
- Anderson R.J., O’Brien M., MaWhinney S., et al. Renal failure predisposes patients to adverse outcome after coronary artery bypass surgery. VA Cooperative Study #5. Kidney Int 1999;55:1057-1062.[Medline]
- Franga D.L., Kratz J.M., Crumbley A.J., Zellner J.L., Stroud M.R., Crawford F.A. Early, and long-term results of coronary artery bypass grafting in dialysis patients. Ann Thorac Surg 2000;70:813-819.[Abstract/Free Full Text]
- Hosoda Y., Yamamoto T., Takazawa K., et al. Coronary artery bypass grafting in patients on chronic hemodialysis: surgical outcome in diabetic nephropathy versus nondiabetic nephropathy patients. Ann Thorac Surg 2001;71:543-548.[Abstract/Free Full Text]
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- Herzog C.A., Ma J.Z., Collins A.J. Comparative survival of dialysis patients in the United States after coronary angioplasty, coronary artery stenting, and coronary artery bypass surgery and impact of diabetes. Circulation 2002;106:2207-2211.[Abstract/Free Full Text]
- Herzog C.A., Ma J.Z., Collins A.J. Poor long-term survival after acute myocardial infarction among patients on long-term dialysis. N Engl J Med 1998;339:799-805.[Abstract/Free Full Text]
- Bridges C.R., Edwards F.H., Peterson E.D., Coombs L.P. The effect of race on coronary bypass operative mortality. J Am Coll Cardiol 2000;36:1870-1876.[Abstract/Free Full Text]
- Rumsfeld J.S., Plomondon M.E., Peterson E.D., et al. The impact of ethnicity on outcomes following coronary artery bypass graft surgery in the Veterans Health Administration. J Am Coll Cardiol 2002;40:1786-1793.[Abstract/Free Full Text]
- Peterson E.D., Shaw L.K., DeLong E.R., Pryor D.P., Califf R.M., Mark D.B. Racial variation in the use of coronary-revascularization procedures. Are the differences real? Do they matter?. N Engl J Med 1997;336:480-486.[Abstract/Free Full Text]
- STS National Database. 2001
- Christian R.C., Fitzpatrick L.A. Vascular calcification. Curr Opin Nephrol Hypertens 1999;8:443-448.[Medline]
- Herzog C.A., Ma J.Z., Collins A.J. Long-term survival of dialysis patients in the United States with prosthetic heart valves: should ACC/AHA practice guidelines on valve selection be modified?. Circulation 2002;105:1336-1341.[Abstract/Free Full Text]
- Brinkman W.T., Williams W.H., Guyton R.A., Jones E.L., Craver J.M. Valve replacement in patients on chronic renal dialysis: implications for valve prosthesis selection. Ann Thorac Surg 2002;74:37-42.[Abstract/Free Full Text]
- Kaplon R.J., Cosgrove D.M., Gillinov A.M., Lytle B.W., Blackstone E.H., Smedira N.G. Cardiac valve replacement in patients on dialysis: influence of prosthesis on survival. Ann Thorac Surg 2000;70:438-441.[Abstract/Free Full Text]
- Edwards F.H., Peterson E.D., Coombs L.P., et al. Prediction of operative mortality after valve replacement surgery. J Am Coll Cardiol 2001;37:885-892.[Abstract/Free Full Text]
- East MA, Peterson ED. Understanding racial differences in cardiovascular care and outcomes. Issues for the new millenium. Am Heart J 2000;139:764–766
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Abstract
Introduction
