Author + information
- Donald S. Likosky, PhD∗ (, )
- Devraj Sukul, MD, MSc,
- Milan Seth, MS,
- Chang He, MS,
- Hitinder S. Gurm, MD and
- Richard L. Prager, MD
- ↵∗Department of Cardiac Surgery, University of Michigan, 1500 East Medical Center Drive, Ann Arbor, Michigan 48109
Michigan is one of several states that expanded Medicaid coverage under the Affordable Care Act. The “Healthy Michigan Plan,” implemented in April 2014, provides coverage through Medicaid to adults with incomes up to 138% of the federal poverty level and requires a health risk assessment and cost sharing by enrollees.
Early results suggest that the Michigan Plan has been successful. Within 1 year of expansion, 600,000 new adults had enrolled (1). Primary care service utilization increased 6% following expansion, and participation in health risk assessments are more than double that of private health insurance plans (2). Less well known is the association between Medicaid expansion and the use and outcomes of cardiovascular revascularization.
We evaluated Michigan's Medicaid expansion as it relates to access and outcomes for 7,558 coronary artery bypass grafting (CABG) operations at 33 hospitals and 45,183 percutaneous coronary interventions (PCI) at 47 hospitals. We excluded patients ≥65 years of age and those with Medicare, non-Medicaid state or federal government coverage (e.g., military), or non-U.S. insurance. Clinical data from each institution’s participation in CABG and PCI collaboratives represent procedures performed between April 2012 and March 2014, as well as April 2014 and March 2016 (24 months before/after expansion).
We evaluated changes in access (i.e., number of procedures) by insurance type (private, Medicaid, uninsured) and used risk adjustment models for CABG (3) and PCI (4) to calculate adjusted mortality (CABG: operative mortality; PCI: during the index admission) before and after expansion. G-computation was used to estimate the relationship between Medicaid expansion and the number of patients presenting quarterly for revascularization within insurance coverage type (Medicaid, private, uninsured). A generalized estimating equation model using autoregressive covariance structure was fitted, including insurance type, calendar quarter, Medicaid expansion, and interaction terms (2- and 3-way interactions among quarter, Medicaid expansion, and insurance coverage type) as predictors.
The generalized estimating equation (Q) model was used to generate counterfactual (i.e., if Medicaid expansion had not occurred) predicted observations for the 8 quarters after expansion to estimate the causal effect of Medicaid expansion on access. Bootstrapping with 1,000 replicates drawn randomly with replacement from patient data was used to generate empirical 95% confidence intervals around causal effect estimates. We additionally assessed changes in procedural appropriateness, acute kidney injury, and length of stay across time and procedure.
We estimate a 103.8% (95% confidence interval [CI]: 45.8% to 182.5%), increase in Medicaid patients presenting for CABG following expansion, and a 59.6% (95% CI: 41.5% to 72.1%) decrease in uninsured patients, and 8.3% (95% CI: 0.2% to 20.1%) decrease in private insurance patients (Table 1). We estimate a 44.5% (95% CI: 24.6% to 69.9%) increase in Medicaid patients presenting for PCI following expansion, a 53.2% (95% CI: 46.1% to 59.3%) decrease in uninsured patients, and 16.3% (95% CI: 10.2% to 22.4%) decrease in patients with private insurance. Changes in CABG and PCI representation among the Medicaid and uninsured mostly occurred in the first quarter after expansion.
For both CABG and PCI, Medicaid expansion was not significantly associated with mortality, acute kidney injury, or length of stay, and there was no significant effect modification by insurance coverage (p > 0.05 for all main effect as well as interactions between Medicaid expansion and types of insurance). Mortality was similar before and after expansion for CABG (0.95% vs. 1.03%) and PCI (1.07% vs. 0.98%), including among Medicaid patients undergoing CABG (1.27% vs. 1.31%) and PCI (1.63% vs. 1.35%). Finally, expansion was not associated with significant changes in appropriateness for PCI (before: 88%; after: 91%) or CABG (before: 89%; after: 90%), and similar patterns were seen across payers.
This study, reflecting Michigan’s statewide experience, evaluates changes in access and outcomes for patients receiving cardiovascular revascularization. Similar to Davis and colleagues who evaluated insurance coverage following Michigan’s Medicaid expansion among hospitalized patients, most of the change in access to revascularization occurred within the first quarter following expansion (5). Michigan’s Medicaid expansion, which has been associated with reductions in predicted risk of morbidity and mortality among CABG patients, was associated with changes in the demographic of those using specialty cardiovascular services (i.e., reduction in uninsured patients undergoing coronary revascularization) absent increases in mortality.
Please note: The project was approved by the University of Michigan Institutional Review Board. Dr. Likosky received a grant from the Agency for Healthcare Research and Quality (R01HS022535). Support for the Michigan Society of Thoracic and Cardiovascular Surgeons Quality Collaborative and the Blue Cross Blue Shield of Michigan (BCBSM) Cardiovascular Consortium Percutaneous Coronary Intervention Quality Improvement Initiative is provided by the BCBSM and Blue Care Network as part of the BCBSM Value Partnerships program. This work was also supported by funding from the National Institute of Aging (grant no. P01-AG019783). Dr. Sukul was supported by the National Institutes of Health T32 postdoctoral research training grant (T32-HL007853). Dr. Gurm has a consulting role with Osprey Medical. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose.
- 2018 American College of Cardiology Foundation
- Tipirneni R.,
- Rhodes K.V.,
- Hayward R.A.,
- et al.
- ↵Udow-Phillips M, Lausch K, Shigekawa E, Hirth R, Ayanian J. The Medicaid expansion experience in Michigan. Available at: https://www.healthaffairs.org/do/10.1377/hblog20150828.050226/full/. August 28, 2015.
- ↵The Society of Cardvioascular Angiography and Interventions. PCI Risk Calculator. Available at: http://scaipciriskapp.org/pci_welcome. Accessed January 4, 2018.
- Davis M.M.,
- Gebremariam A.,
- Ayanian J.Z.