Racial Differences in Incident Heart Failure among Young Adults

Study Cohort

The CARDIA study is a multicenter study designed to investigate the development of coronary disease in young adults. The CARDIA study began in 1985–1986 with the enrollment of 5115 blacks and whites of both sexes who were 18 to 30 years of age and were recruited in Birmingham, Alabama; Chicago; Minneapolis; and Oakland, California. The institutional review board at each of the study sites approved the study protocols, and written informed consent was obtained from all participants. The cohort is balanced with respect to race (52% of the participants are black), sex (55% are women), and educational level (40% have ≤12 years of education).⁷ Baseline measurements were repeated, and additional measurements performed, at years 2, 5, 7, 10, 15, and 20. The CARDIA study has had a high retention rate, with 87.5% of the original cohort completing the annual telephone interview for outcome ascertainment at year 20 and 71.8% completing the in-person examination at year 20.

Incident Heart Failure

During their scheduled study examinations and yearly telephone interviews, participants were asked about overnight hospitalizations, and records were requested in cases of suspected cardiovascular events. Deaths were reported to the field centers every 6 months, and records were requested after consent had been obtained from the next of kin. Two members of the end-points committee reviewed each record to determine the primary cause of hospitalization or death; disagreements were resolved by consensus. Hospitalization for heart failure was a prespecified study end point and required both that a final diagnosis of heart failure had been made by a physician and that medical treatment for heart failure had been administered during the hospitalization (administration of a diuretic and of either digitalis or an afterload-reducing agent, such as nitroglycerin, hydralazine, an angiotensin-converting–enzyme [ACE] inhibitor, or an angiotensin-receptor blocker). Heart failure was not a prespecified category for the primary cause of death; a death was considered to be due to heart failure if the adjudicated cause was cardiovascular and if an International Classification of Diseases, Ninth Revision (ICD-9) code for heart failure (428) or cardiomyopathy (425) was noted as a contributory cause. We also reviewed hospital and death records for coexisting conditions at the time of the participant's presentation with heart failure; these data were not used in the analyses but are described below.

Clinical Antecedents Measured at Each Examination

Race was reported by the study participants. We used the average of the second and third of three blood-pressure measurements (performed at 1-minute intervals after the participant had been sitting quietly for 5 minutes) and considered hypertension to be present when the systolic blood pressure was 140 mm Hg or higher, the diastolic blood pressure was 90 mm Hg or higher, or the person was taking antihypertensive medications. Weight, in kilograms, was measured with the use of a standard balance-beam scale, with the participant wearing light clothing, and the body-mass index was calculated as the weight in kilograms divided by the square of the height in meters. Diabetes was considered to be present if the person had a fasting blood glucose level of 126 mg per deciliter (7 mmol per liter) or more or was taking medication for diabetes. Total cholesterol and high-density lipoprotein (HDL) cholesterol were measured, and low-density lipoprotein cholesterol was calculated with the use of the Friedewald equation.⁸ The creatinine level was measured at years 0, 10, 15, and 20; the glomerular filtration rate (GFR) was estimated with the use of the Modification of Diet in Renal Disease equation,⁹ and chronic kidney disease was considered to be present when the GFR was less than 60 ml per minute. Educational level, family history of premature coronary disease, and the use of tobacco, alcohol, and illicit drugs were determined by self-report at each examination. Consumption of more than 14 drinks per week in the case of men or more than 7 in the case of women was considered to be alcohol use above a safe level¹⁰; illicit-drug use was defined as the use of cocaine, amphetamines, or heroin at any time in the participant's life.

Echocardiographic Antecedents

As part of the examination in year 5, CARDIA participants underwent two-dimensional, guided M-mode echocardiography and Doppler study of transmitral flow velocities performed on an Acuson cardiac ultrasound machine (Siemens).¹¹ All studies were recorded and read at a reading center at the University of California, Irvine. Systolic function was assessed as a continuous measure of ejection fraction (expressed as a percentage) in 1893 participants and as a qualitative ejection-fraction rating in the rest of the participants; we categorized systolic function as abnormal (ejection fraction of <40%, or qualitative rating of abnormal), borderline (ejection fraction of 40 to 60%, or qualitative rating of borderline), or normal. Left ventricular mass (in grams) was derived from the formula of Devereux et al.,¹² and the left-ventricular-mass index was calculated as grams per meter^2.7.¹³ Left ventricular hypertrophy was considered to be present if the left-ventricular-mass index was 51 g per meter^2.7 or more, a cutoff point that has previously been validated for both blacks and whites.¹⁴ Among the 4351 participants who were available for the echocardiographic examination, variables for either ejection fraction or left ventricular hypertrophy were missing for 121, leaving data from 4230 participants for this analysis.

Statistical Analysis

Using t-tests, chi-square tests, and Fisher's exact tests, as appropriate, we compared baseline risk factors in participants in whom heart failure developed with those in participants in whom heart failure did not develop. We used Cox proportional-hazards models to analyze associations between candidate risk factors and heart failure among blacks in unadjusted analyses. We developed two multivariate models, the first including baseline predictors only and the second including time-varying covariates, with predictor values updated at the time of each study visit. Because of the small number of outcomes, we used the forward-selection method to choose predictors for the adjusted analyses, retaining potential risk factors if they remained associated with heart failure at a P value of less than 0.05, and we reported hazard ratios per 1 SD for continuous variables. Finally, we explored the association of systolic dysfunction and left ventricular hypertrophy, as assessed on the echocardiogram obtained in year 5, with the risk of subsequent heart failure in bivariate and multivariate analyses.

Figure 1. Figure 1. Incident Heart Failure among the White and Black Men and Women in the CARDIA Study.

Kaplan–Meier curves are shown for incident heart failure over the course of 20 years of follow-up in the CARDIA study. P=0.001 for the comparison between black participants and white participants.

During 20 years of follow-up of the 5115 study participants, incident heart failure occurred in 27 men and women and was more common than myocardial infarction (which occurred in 16 participants). With the exception of one white woman, all of the participants in whom heart failure developed were black (P=0.001) (Figure 1). The cumulative incidence of heart failure in black women was 1.1% (95% confidence interval [CI], 0.6 to 1.7) and the cumulative incidence in black men was 0.9% (95% CI, 0.5 to 1.4), with a mean (±SD) age at onset of 39±6 years. The cumulative incidence of heart failure among white women was 0.08% (95% CI, 0 to 0.5), and the cumulative incidence among white men was 0% (95% CI, 0 to 0.4). Heart failure resulted in death in the case of three black men (accounting for 4.5% of all deaths among black men) and two black women (7.7% of all deaths among black women).

Table 1. Table 1. Characteristics of Study Participants, According to Subsequent Development of Heart Failure.

The baseline characteristics (assessed when participants were 18 to 30 years of age) differed between blacks in whom heart failure subsequently developed and white and black participants in whom heart failure did not develop (Table 1). As compared with all those in whom heart failure did not develop, blacks in whom heart failure subsequently developed had higher baseline systolic and diastolic blood pressures and were more likely to have hypertension. They were also more likely to be obese, to have diabetes, or to have chronic kidney disease. Alcohol and drug use did not differ significantly between blacks in whom heart failure subsequently developed and participants in whom it did not. Blacks in whom heart failure subsequently developed were more likely to have borderline or abnormal systolic function or left ventricular hypertrophy.

Table 2. Table 2. Hazard Ratios for Subsequent Heart Failure According to Baseline Antecedents among 2637 Black Participants in the CARDIA Study.

Because heart failure occurred almost exclusively in blacks, we restricted the Cox regression analyses to data from black participants. In bivariate models of baseline predictors (Table 2), higher blood pressure, higher body-mass index, fewer years of education, lower HDL cholesterol, the presence of chronic kidney disease, and the presence of diabetes were all associated with the subsequent development of heart failure. In multivariate models, higher diastolic blood pressure, higher body-mass index, lower HDL cholesterol, and the presence of chronic kidney disease were each independently associated with the risk of heart failure. Each standard-deviation increase (10.0 mm Hg) in diastolic blood pressure among blacks at 18 to 30 years of age doubled the risk that heart failure would occur, on average, 15 years later.

Figure 2. Figure 2. Proportion of Blacks with Hypertension in the First 10 Years of the CARDIA Study, According to Status with Respect to the Subsequent Development of Heart Failure.

By examination year 10, among blacks in whom heart failure subsequently developed, 75% had hypertension, as compared with 12% of blacks in whom heart failure did not develop (P<0.001).

During the first 10 years of the CARDIA study, clinical hypertension was more common among black participants in whom heart failure subsequently developed than among blacks in whom it did not (Figure 2). By year 10, when participants were 28 to 40 years of age, 75% of those in whom heart failure subsequently developed had hypertension, as compared with 12% of those in whom heart failure did not develop (P<0.001). Most participants with hypertension were not being treated for the condition or were being treated but had poorly controlled blood pressure. At baseline, 75% of all black participants with hypertension (66 of 88) were not taking medication, and another 9% (8 of 88) had poorly controlled blood pressure even though they reported taking antihypertensive medications; all of the black participants with hypertension in whom heart failure subsequently developed had untreated or poorly controlled hypertension. By year 10, 57% of black participants with hypertension (137 of 239) were not taking antihypertensive medications, and 19% (45 of 239) had poorly controlled blood pressure; among those in whom heart failure subsequently developed, 87% had untreated or poorly controlled hypertension.

To examine antecedents more proximal to the onset of heart failure, we used data from each examination and time-varying covariates. Over the entire course of 20 years, the following variables were associated with heart failure in bivariate models: higher diastolic blood pressure (hazard ratio per 10.0 mm Hg, 1.8; 95% CI, 1.5 to 2.2; P<0.001), higher systolic blood pressure (hazard ratio per 10.9 mm Hg, 1.7; 95% CI, 1.4 to 2.0; P<0.001), higher body-mass index (hazard ratio per 5.7 units, 1.7; 95% CI, 1.3 to 2.1; P<0.001), presence of diabetes (hazard ratio, 5.5; 95% CI, 2.4 to 13; P<0.001), and presence of chronic kidney disease (hazard ratio, 7.7; 95% CI, 1.8 to 31.0; P=0.006). Neither alcohol use nor drug use was associated with the development of heart failure (hazard ratio for alcohol use, 1.0; 95% CI, 0.4 to 2.5; P=0.97; hazard ratio for drug use, 1.1; 95% CI, 0.5 to 2.4; P=0.82). In multivariate models, higher systolic blood pressure and the presence of diabetes each remained independently associated with the development of heart failure (hazard ratio per 10.9 mm Hg systolic blood pressure, 1.7; 95% CI, 1.4 to 2.0; P<0.001; hazard ratio for diabetes, 4.9; 95% CI, 2.1 to 12; P<0.001), as did higher diastolic blood pressure in models in which diastolic blood pressure was substituted for systolic blood pressure (hazard ratio per 10 mm Hg, 1.8; 95% CI, 1.5 to 2.2; P<0.001).

Table 3. Table 3. Hazard Ratios for the Subsequent Development of Heart Failure in Blacks According to Echocardiographic Measures at Year 5.

Systolic dysfunction and left ventricular hypertrophy as assessed on the study echocardiogram in year 5 were independently associated with the development of heart failure an average of 10 years later (Table 3). After additional adjustment for clinical variables, systolic dysfunction remained strongly associated with the subsequent development of heart failure, whereas the association of left ventricular hypertrophy with subsequent heart failure was markedly diminished and was not significant.

Table 4. Table 4. Characteristics of Study Participants Who Died from or Were Hospitalized for Incident Heart Failure.

Information in clinical records with respect to coexisting conditions that were present at the time the participant presented with heart failure (Table 4) was consistent with study measurements of clinical antecedents (Table 1, Table 2, and Table 3). Hypertension, chronic kidney disease, and diabetes were commonly noted in the records of hospitalizations for heart failure among blacks; of 22 black participants hospitalized for heart failure, 17 were recorded as having hypertension, 9 as having chronic kidney disease, and 5 as having diabetes. Coronary disease was uncommon; none of the hospital or death records noted concurrent or previous myocardial infarction, and most of the cardiac-catheterization reports and autopsy records (eight of nine) noted mild or absent coronary disease. Although alcohol use above a safe level was noted in 3 of 10 cases of heart failure in men and cocaine use in 1 of the 10, none of the 16 records that documented the presence of heart failure in black women commented on these factors. We had information on systolic function from the hospital records of 17 participants; an ejection fraction of less than 50% was recorded for 14 of these participants. Evidence of dilated cardiomyopathy was noted on the autopsy records of 4 of the participants who died (an autopsy was not performed on the fifth participant who died).

In this large cohort of white and black young adults, incident heart failure was substantially more common among blacks. Heart failure developed before the age of 50 years in 1 of 100 black men and black women in the CARDIA study, a rate that was 20 times the incidence in whites. Heart failure occurred in blacks when they were 39 years of age, on average, and was predicted by the presence of hypertension, obesity, chronic kidney disease, and depressed systolic function 10 to 15 years earlier. These findings have important implications for efforts aimed at preventing heart failure in this high-risk population.

Previous research on the epidemiology of heart failure has focused on older adults.^2,3,15 Several recent studies showed that the incidence of heart failure was up to two times as high in blacks as in whites^16-18; the populations in these studies were largely elderly, with a mean age at the start of observation that ranged from 55 to 74 years. The one large cohort that included younger adults and that had low rates of incident heart failure before 50 years of age was predominantly white^1,3; the low rate of heart failure that we saw in white participants in the CARDIA study is consistent with the estimates from this cohort. National data have been used to compare the prevalence of heart failure across various demographic groups over the entire age spectrum,^2,4 although prevalence estimates may understate the burden of disease, given the high rate of death associated with heart failure (5 of the 26 cases of heart failure among black participants in the CARDIA study resulted in death). Our findings are consistent with those from these previous reports and extend them by making the additional observation of substantial rates of incident heart failure among black men and women early in adulthood.

We identified potentially modifiable antecedents of heart failure in blacks that were present more than a decade before the onset of clinical heart failure. Each increase of 10 mm Hg in diastolic blood pressure among blacks who were in their 20s doubled the likelihood that heart failure would develop when they were in their 40s, and three quarters of those in whom heart failure developed had hypertension early in adulthood. Obesity also contributes to the risk of heart failure, either directly¹⁹ or through the associated rise in blood pressure and the development of type 2 diabetes. This latter observation is consistent with our finding that an increased body-mass index was an early independent risk factor for heart failure, with diabetes confounding or, more likely, mediating this association when findings from the entire 20 years of follow-up were considered. Low HDL cholesterol in young adulthood may play a role in cardiac remodeling, particularly in patients with hypertensive disease.^20,21 Chronic kidney disease is a strong predictor of heart failure, and black men are disproportionately affected by declining kidney function in young adulthood.²² Our finding that clinical factors increased the risk of heart failure even many years later is consistent with observations in older cohorts^23-26 and suggests that these factors may be targets for the prevention of heart failure in young adults.

We found that blacks in whom heart failure subsequently developed were more likely than those in whom it did not develop to have systolic dysfunction and left ventricular hypertrophy in young adulthood, 10 years before the onset of clinical heart failure. These structural and functional cardiac changes may be the consequence of underlying clinical factors such as hypertension and obesity and may mediate the association between these factors and heart failure.^27,28 Systolic dysfunction remained a strong risk factor for heart failure independently of the other clinical risk factors, including blood pressure. Several studies have identified polymorphisms that appear to be linked to heart failure and systolic dysfunction in blacks, and some studies have shown that the risk associated with these polymorphisms is greatest among blacks with hypertension.^4,5,29,30 Most of these studies are limited by the small numbers of black participants and the lack of longitudinal data to determine how clinical and genetic factors may interact in the development of this disease. This is an important area for further study.

Our results with respect to systolic dysfunction have implications for the identification of persons who are at high risk for the development of heart failure and also have implications for the prevention of this disease. Current guidelines recommend initiating treatment for asymptomatic systolic dysfunction with ACE inhibitors and beta-blockers before the onset of symptoms of heart failure.^4,31-33 Although screening for systolic dysfunction in the general population has several limitations,³⁴ screening high-risk groups (e.g., persons with hypertension) in order to target therapies may be an important tool for the prevention of heart failure.^35,36 Young adults have not been included in clinical trials of preventive therapies or screening strategies, and the benefits and risks of these approaches in a young at-risk population are not known. However, the high rate of borderline or abnormal systolic function that we observed in both white and black participants (9% among whites and 13% among blacks), and its strong association with the subsequent development of clinical heart failure before the age of 50 years among blacks, underscore the importance of this area of investigation.

Our study also highlights the potential for preventing heart failure through interventions that decrease the prevalence of obesity and high blood pressure. Obesity was common among black participants in the CARDIA study, particularly black women,^37,38 and it is possible that preventing obesity in this population may reduce the subsequent incidence of heart failure. Recent national data suggest that young adults with hypertension are much less likely than their middle-aged counterparts to be aware of this diagnosis or to be receiving treatment.^39,40 The reasons for low rates of treatment for hypertension among young adults may include barriers in access to medical care.^41,42 It has been suggested that blood-pressure control may be more difficult to achieve among black patients, although a consensus statement on treating hypertension in blacks concluded that the failure of health professionals to initiate therapy early in accordance with established guidelines was the major obstacle to achieving effective blood-pressure control.^43,44 When they receive treatment according to the guidelines, blacks and whites appear to have similar rates of control.⁴⁵

Physicians may be reluctant to treat younger patients with hypertension because of the perceived large number needed to treat to prevent cardiovascular outcomes that are still rare and often far in the future. In the course of 20 years of follow-up in the CARDIA study, the cumulative incidence of heart failure among blacks who had hypertension at baseline (when their average age was 24 years) was 5.6%, as compared with 0.8% among those who did not have hypertension at baseline. Most of the persons with hypertension at baseline were not receiving antihypertensive treatment. A trial of antihypertensive therapy in older participants, including blacks, showed that diuretic therapy, in particular, was associated with considerable reductions in the risk of heart failure.⁴⁶ Thus, although treatment for hypertension and reduction of the risk of heart failure have not been studied in this age group, our data suggest that the number of young, black patients with hypertension that would need to be treated to prevent one case of heart failure before 50 years of age could be as low as 21.

Because we observed only a single heart-failure event among white participants, we are limited in our ability to assess whether racial differences in risk factors account for the racial differences in the incidence of heart failure. The fact that blacks and whites in the CARDIA study actually had similar mean levels of blood pressure and ejection fraction in young adulthood (Table 1) is worthy of comment. More black participants were obese at baseline, and hypertension developed more often in blacks than in whites when the participants were in their 20s and 30s,³⁷ but whether these observations explain the substantially higher rates of heart failure in blacks than in whites warrants further investigation. The small number of outcomes in our study limits the precision of our descriptive observations, as well as our ability to explore a broader range of clinical antecedents and mediators. Because we defined incident heart failure on the basis of hospitalization for or death from heart failure, heart failure that was identified in the outpatient setting was missed in these analyses. Another limitation of the study was that the retention rate for outcome ascertainment was 87.5% by year 20; since black men are the demographic group most likely to be lost to follow-up, we may have underestimated the incidence of heart failure, particularly in this group.

Despite these limitations, the clear strength of this study is the large, well-characterized cohort of white and black young adults for whom we had rich longitudinal clinical and echocardiographic data and adjudicated heart-failure outcomes. Heart failure occurs at a disproportionately high rate among young and middle-aged blacks as compared with whites, and it is not a rare condition. Elevated blood pressure, obesity, chronic kidney disease, and systolic dysfunction early in adulthood are important antecedents that could become targets for screening and interventions aimed at the prevention of heart failure. Studies are needed to examine the benefits and risks of these early approaches to preventing this serious disease in black young adults.