Background: Over 900 Accountable Care Organizations (ACOs) have been created since 2010, and projections estimate that ACOs will manage the care for about one third of Americans by 2025; however, the impact of the MSSP on quality of care and patient outcomes is unclear.

Objective: This study compared outcomes before and after MSSP implementation for patients who were either (1) discharged from hospitals that chose to participate (N = 273) versus not participate (N = 1490) in MSSP or (2) assigned by Centers for Medicare & Medicaid Services (CMS) to a MSSP ACO versus not. I hypothesized that MSSP ACO participation would be associated with reduced inpatient utilization and improved outcomes of care.

Methods: Using a difference-in-difference (DD) design, I evaluated outcomes associated with MSSP in a national inpatient stroke registry, Get With The Guidelines (GWTG)-Stroke, linked with Medicare claims for 2010--2015. Utilization outcomes of discharge to home, number of hospital admissions, and Days Alive and Out of Hospital (DAOH) were modeled using negative binomial models with a log link and offset. Outcomes of all-cause rehospitalization, recurrent stroke and all-cause mortality were modeled using Cox proportional hazards models. Outcomes of CMO or hospice enrollment within 2 weeks, hospice use within one year of hospitalization, hospice enrollment within 7 days of death, and live discharge from hospice were modeled using logistic regression. Except for discharge destination, all outcomes were followed for up to one year following discharge, with appropriate adjustment for death.

Key Findings: I found no evidence that hospital participation in the MSSP decreased inpatient utilization among stroke patients in the year following discharge; however, beneficiary ACO-alignment was associated with increases in subsequent admissions. Among patients most likely to benefit from palliative care, MSSP increased hospice enrollment and inpatient comfort measures, without increasing rates of live discharge.

Conclusion: Except for increased use of palliative care among stroke patients, current quality metrics and incentives in MSSP contracts may not be sufficient to generate changes in post-stroke care.