Importance: Cardiovascular disease is the leading primary diagnosis among all hospital discharges, and insurance status is associated with patient outcomes. The association of state-level policy decisions regarding the Affordable Care Act (ACA) Medicaid expansion with rates of uninsured hospitalizations for major cardiovascular events and in-hospital mortality has not been investigated to date. Objective: To investigate whether the rates of uninsured hospitalizations for major cardiovascular events and in-hospital mortality varied by state-level policy on ACA Medicaid expansion. Design, Setting, and Participants: For this cohort study, difference-in-differences analysis of data from the Healthcare Cost and Utilization Project State Inpatient Databases of 30 US states on 524 848 non-Medicare hospitalizations in 2014 and a mean of 516 811 non-Medicare hospitalizations per year from 2009 to 2013 was performed for major cardiovascular events (defined as a composite of acute myocardial infarction, stroke, and heart failure) from January 1, 2009, through December 31, 2014. Analyses were completed September 1, 2017. Exposure: State Medicaid expansion as of January 1, 2014. Main Outcomes and Measures: Comparison of mean payer mix proportions (uninsured, Medicaid, and privately insured) and in-hospital mortality between expansion and nonexpansion states for the years preceding the ACA Medicaid expansion (2009-2013) and the year after the ACA Medicaid expansion (2014). Results: Of the 801 819 hospitalizations in the 17 expansion states in 2014, 428 503 (53.4%) patients were men, 514 036 (64.1%) were white, and 365 797 (45.6%) were aged 65 to 84 years. Of 719 459 hospitalizations in the 13 nonexpansion states in 2014, 383 311 (53.3%) patients were men, 492 136 (68.4%) were white, and 335 781 (46.7%) were aged 65 to 84 years. There were 281 184 non-Medicare hospitalizations for major cardiovascular events in the 17 expansion states and 243 664 non-Medicare hospitalizations in the 13 nonexpansion states in 2014. In multivariable regression analyses, the expansion states had a significant 5.8-percentage point decrease in the proportion of uninsured hospitalizations after Medicaid expansion relative to the nonexpansion states (adjusted difference-in-differences estimate, -0.058; 95% CI, -0.075 to -0.042; P < .001). The expansion states also had a significant 8.4-percentage point increase in the Medicaid share after Medicaid expansion relative to the nonexpansion states (adjusted difference-in-differences estimate, 0.084; 95% CI, 0.065 to 0.102; P < .001). In-hospital mortality did not change significantly after Medicaid expansion in either the expansion states (before ACA, 3.8% vs after ACA, 3.7%) or the nonexpansion states (4.0% vs 4.0%). Conclusions and Relevance: States that expanded Medicaid during the ACA implementation had a significantly greater reduction in the proportion of uninsured hospitalizations for major cardiovascular events compared with the nonexpansion states. This study suggests that expansion status was not associated with in-hospital mortality rates in the first year after ACA implementation.
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