presents summary statistics for fee-for-service Medicare beneficiaries who were treated for AMI between January 1st 1997 and September 30th 2001. The table illustrates the construction of the deciles used in the analysis. The average Medicare AMI patient was treated in a hospital where 6.9 percent of the patients were African-American. The bottom “decile” accounted for 12.5 percent of the population who were admitted to 1369 hospitals (comprising 32 percent of all hospitals) that saw no African-American AMI patients over the duration of the study period. These hospitals constitute Decile 1 (the lowest decile) of percent African-American patients in the hospital. On the other end of the spectrum, 33.6 percent of patients in Decile 10 hospitals were African-American. Patients admitted to hospitals with the highest fraction of African-American patients were more likely to live in the South, and less likely to live in an urban setting. Differences across the deciles are significant statistically (p < .001).
Characteristics of AMI Patients and Hospitals, by the Average Percentage of African-American AMI Patients in the Admitting Hospital
There was large variation in ownership status and treatment intensity between hospitals based on the extent to which they treat the African-American population (). Relative to the hospital that the average AMI patient was treated at, hospitals that disproportionately treat African-Americans are more likely to be teaching hospitals, more likely to be government (non-federal), and less likely to be not for profit. These hospitals are similar in terms of CABG and PTCA intensity, but have lower AMI volume. All differences across the deciles are highly significant statistically (p < .001).
Hospital Ownership Characteristics and Hospital Treatment Characteristics, by the Average Percentage of African-American AMI Patients in the Admitting Hospital
With the exception of hospitals that treat no African-Americans, the distribution of comorbidities and severity of the AMI across hospitals (adjusted for age, race and sex) is similar (). In decile 2 hospitals (where only 0.3 percent of patients were African-American), the index of predicted 90-day mortality based solely on comorbidities and severity of the AMI was 22.2 percent (95% CI: 22.1–22.3%). It was 22.1 percent (95% CI: 22.0–22.2%) and 22.0 (95% CI: 21.9–22.1%) for hospitals in deciles 9 and 10 respectively. The noticeable exception to the similarity in comorbidities across deciles of percent African-American is seen for patients in Decile 1 hospitals. These patients, all of whom are white, have predicted 90-day mortality of 23.7% (95% CI: 23.6–23.8%), 7 percent higher than the expected mortality in the other deciles. While not reported in the table, the elevated mortality in decile 1 is attributable largely to the elevated prevalence of renal failure (2.9 percent in this decile compared to 2.2 percent for other deciles; p<0.001), and a lower likelihood of being diagnosed with a subendocardical infarction (39.0 versus 49.0 percent for other deciles; p<0.001).
Index of Comorbidity and AMI Severity by the Average Percentage of African-American AMI Patients Admitted to the Hospital
illustrates risk-adjusted 90-day mortality across hospital deciles. Hospitals that have a greater share of African-American AMI patients have substantially higher risk-adjusted mortality. Even though patients in decile 1 hospitals are the sickest (as measured by the index of comorbidities) they experience the lowest risk-adjusted mortality following AMI. presents results from two models. In the first, outcomes are adjusted for age, race, sex and comorbidities. In the second, we further adjusted for income, hospital ownership, region, and treatment characteristics. The two models yield similar results suggesting that the hospital characteristics and income are not significant explanatory variables once comorbidities have been adjusted for. The area under the Receiver Operator Curve (ROC) is 0.679 for the first model, and 0.681 for the second.
Risk-Adjusted 90-Day Mortality after AMI, by the Average Percentage of African-American AMI Patients Admitted to the Hospital
presents estimated adjusted mortality separately by race. Because of the small number of African-American AMI patients in deciles 2–6, these deciles were combined to improve statistical power in estimating race-specific adjusted mortality. Estimated mortality for African-Americans in decile 10 hospitals are significantly higher than for decile 2–6 hospitals (p = .04). The difference between black and white adjusted mortality rates is not significant within each hospital decile, but a joint test of significance rejects the null hypothesis of equality (p < 0.001). For the logistic regressions estimated separately for white and black AMI patients, the mortality gradient (by fraction of African-American admissions to the hospital) was significant for both white (p < .001) and black (p = .007) patients.
Risk-Adjusted 90-Day Mortality after AMI, by Race and Average Percentage of African-American AMI Patients Admitted to the Hospital
We obtained similar results regarding the association between hospital deciles and mortality using 30-day mortality. In these models, which also adjusted age, race, gender, comorbidities, hospital teaching status, region, ownership and treatment intensity, 30-day mortality in Decile 1 hospitals is 14.9% (95% CI: 14.6–15.2%), in Decile 2 15.6% (95% CI: 15.2–16.1%), and in Decile 10 17.6% (95% CI: 17.2–18.0%). Using these estimates, hospitals in decile 10 experienced 18 percent higher mortality relative to decile 1 hospitals. However, 30-day mortality within hospitals was not significantly higher among African-American patients.
Any potential burdens of higher mortality risk in hospitals that serve African-Americans is borne disproportionately by African-American patients, since a large fraction of this population is seen in the hospitals that comprise decile 9 and decile 10 hospitals. As shows, nearly half of African-Americans are seen in decile 10 hospitals, those with among the highest risk-adjusted mortality. Sixty-nine percent of African-American patients are seen in the 21 percent of hospitals that constitute decile 9 and 10 hospitals.
Distribution of African-American and White Patients, by the Average Percentage of African-American AMI Patients Admitted to the Hospital