Use of Cardiovascular Procedures among Black Persons and White Persons: A 7-Year Nationwide Study in Patients with Renal Disease

Coronary atherosclerotic disease remains the leading cause of death in the United States despite a considerable decrease in mortality rates since the 1980s (1). This decrease in the rate of death from ischemic heart disease is attributable in part to the now-established technologies of invasive cardiac procedures: cardiac catheterization, percutaneous transluminal coronary angioplasty, and coronary artery bypass grafting (2). Unfortunately, as with many health indicators and health services, improvements in both the mortality rate from coronary disease and rates of invasive cardiac procedures among black persons have lagged behind those of white persons (1, 3-10). Although previous work documented ethnic differences in use of cardiac procedures, the studies were limited by cross-sectional design, examination of a few selected practice settings, or exclusion of potentially confounding clinical and socioeconomic variables (11-24). Furthermore, previous research has not addressed whether or which factors can alter trends in use of cardiac procedures and thus narrow disparity among ethnic groups. We hypothesized that the large variation in use of cardiac procedures between black persons and white persons would decrease with acquisition of adequate health insurance when this occurs in conjunction with development of a serious illness. Increased use of cardiac procedures among black persons may follow attainment of health insurance or establishment of a regular source of medical care. Once serious illness occurs, avoidance of discretionary procedures because of increased risk for complications may lead to a relative decrease in use of procedures among white persons, especially if procedures were previously overused. End-stage renal disease (ESRD) is a significant illness in which patients are at high risk for cardiovascular disease; patients with ESRD almost always acquire Medicare health insurance and enter a comprehensive system of care. Cross-sectional research suggests that access to dialysis and physician visits improved after enactment of the Medicare program (25, 26). We used the progression of patients from chronic renal failure to ESRD as a natural experiment to examine whether ethnic differences in use of cardiovascular procedures narrow with initiation of long-term dialysis and coincident acquisition of insurance. Methods Study Design and Patients We performed a national longitudinal cohort study in patients with chronic renal failure and ascertained use of cardiovascular procedures before (baseline) and after (follow-up) development of ESRD. To be eligible for inclusion in the study, patients had to have new-onset ESRD in 1986 or 1987, be either black or white, and be at least 18 years of age. We followed patients for up to 7 years: until death, renal transplantation, or the end of the study on 31 December 1992. Data Collection We used data from the Case Mix Severity Study of the United States Renal Data System (USRDS). The USRDS is a national research organization created and funded by the National Institutes of Health to assemble information on ESRD incidence, prevalence, treatment, morbidity, and mortality. The primary purpose of the Case Mix Severity Study, conducted from 1989 to 1991, was to provide prevalence data on the frequency of various comorbid conditions that commonly occur in ESRD. The Case Mix Severity Study used a two-stage random sampling method of patients and dialysis units to obtain a 5% national random sample of patients with incident ESRD in 1986 to 1987 (27). Abstracters reviewed medical charts in dialysis units to identify patients' clinical and socioeconomic status by using a standardized instrument that recorded information obtained shortly before development of ESRD and initiation of dialysis. Variables included information about health insurance, education, marital status, employment status, type of employment, medical history of coronary disease, coronary risk factors, comorbid conditions, and physical examination and laboratory data. Data on medical evidence of ESRD, as part of the USRDS, provided baseline sociodemographic information on date of birth, sex, ethnic group, and date of ESRD onset. For data sources in the 7-year follow-up period after the onset of ESRD, we used Medicare hospitalization records that provided the date of admission, date of discharge, and procedure and diagnosis codes for each hospitalization. Medicare registry data provided the dates of renal transplant or death. Consequently, we could identify patient admissions at any acute care hospital in the United States over the course of the study and link medical record abstraction data to Medicare registry and hospitalization files. Medicare hospitalization and registry data were assembled 3 years after the end of follow-up to provide complete records. Outcome Measures For receipt of a cardiac procedure before onset of ESRD, we used evidence of cardiac catheterization, angioplasty, or coronary artery bypass grafting from medical record abstraction. For longitudinal outcomes after the onset of ESRD and initiation of dialysis, we used the first evidence of these cardiac procedures from hospitalization records. The following codes from the International Classification of Diseases, Ninth Revision, Clinical Modification [ICD-9-CM], were used: for cardiac catheterization, codes 37.21, 37.23, and 88.57 to 88.59; for angioplasty, codes 36.01, 36.02 and 36.05; and for coronary artery bypass grafting, codes 36.10 to 36.19 (28). In the primary longitudinal analysis, we did not examine patients who had already undergone a cardiac procedure at baseline because, by definition, they had already had access to a procedure. These patients were included in sensitivity analyses. For both baseline and follow-up analyses, we also separately examined receipt of diagnostic procedures (cardiac catheterization) and therapeutic procedures (angioplasty and coronary artery bypass grafting). Furthermore, as a follow-up outcome, we examined the specific case of receipt of a cardiac procedure within 90 days after admission for a primary diagnosis of coronary artery disease (ICD-9-CM codes 411.1, 411.81, 411.89, 410, 413, and 414) or acute myocardial infarction (ICD-9-CM codes 410.x) as a proxy measure of clinical appropriateness (12, 13, 29). Statistical Analyses Primary Analysis We performed bivariate analyses with the chi-square and Student t-tests to investigate differences in baseline socioeconomic and clinical characteristics between black persons and white persons and to examine the relations between individual clinical and socioeconomic characteristics and the outcomes of receipt of a cardiac procedure at baseline and at follow-up. We then developed a logistic regression model to examine whether receipt of a cardiovascular procedure at baseline varied by ethnic group while adjusting for explanatory or potentially confounding socioeconomic and clinical variables. We constructed the model with covariates that were significantly associated with receipt of a cardiac procedure in bivariate analyses or variables that were deemed clinically relevant for the analyses. Our explanatory demographic and socioeconomic variables were age, ethnic group, sex, type of health insurance at baseline (private, Medicaid, Medicare, or no insurance), education (high school graduate), type of employment (white collar, blue collar, or other), employment status (employed, retired or disabled, or unemployed), marital status (single, married, or previously married), and region of the United States (northeast, southeast, midwest, west, or southwest). Clinical variables were coronary artery disease (history of myocardial infarction or angina), hypertension (Fifth Joint National Committee on Hypertension criteria for hypertension steps 1 and above or history of hypertension), history of smoking, elevated cholesterol level (>5.2 mmol/L [>200 mg/dL]), elevated triglyceride level (>2.8 mmol/L [>2.5 g/L]), diabetes mellitus (history of diabetes or receiving medication for diabetes), obesity (body mass index>27.8 kg/m2 for men and>27.3 kg/m2 for women or nutritional status described as obese), cerebrovascular disease (history of stroke), congestive heart failure (history of congestive heart failure), history of a malignant condition, low serum albumin level (<30 g/L), and type of dialysis (hemodialysis or peritoneal dialysis) (30). To identify receipt of a cardiovascular procedure during follow-up, we constructed a similar logistic regression model. In this model, we included adjustment for the number of days at risk for having a cardiac procedure, because black persons who receive dialysis live longer than white persons who undergo this treatment (31-33). We also performed stratified subgroup analyses by year of follow-up and by insurance status at baseline; in these analyses, we modified the models to include key but fewer variables because of the smaller number of patients in each stratum. Adding variables to these models in separate analyses did not appreciably change the point estimates. Finally, we developed a Cox proportional-hazards model to examine time to receipt of a cardiovascular procedure during follow-up for white persons compared with black persons. In addition to the explanatory variables in the other models, we included time-dependent covariates for specific comorbid diseases during follow-up in this model so that we could account not only for baseline conditions but also for conditions that may have developed after the onset of ESRD and could have decreased or increased the likelihood of an invasive cardiac procedure. For time-dependent covariates, we used evidence of hospital admission for cerebrovascular disease (ICD-9-CM codes 430 to 438), malignant conditions (ICD-9-CM codes 140 to 172.9, 174 to 195.8, 196 to 199.1, and 200 to 208.9), and peripheral vascular disease (ICD-9-CM codes 440.2, 443.8 to 444.0, and 444.22 to 444.81). We also examin