Outcomes after carotid endarterectomy among elderly dual Medicare-Medicaid-eligible patients

Abstract

Objective: To determine whether patients who are dual eligible for Medicare and Medicaid benefits have outcomes after carotid endarterectomy (CEA) that are comparable to the outcomes of those eligible for Medicare alone.

Methods: The study cohort included fee-for-service Medicare beneficiaries ≥65 years of age who underwent CEA (ICD-9-CM code 38.12) between 2003 and 2010. Beneficiaries with ≥1 month of Medicaid coverage were considered dual eligible. We fit mixed models to assess the relationship between coverage (dual eligible vs Medicare only) and outcomes over time after adjustment for demographic and clinical characteristics.

Results: There were 53,773 dual-eligible and 452,182 Medicare-only beneficiaries hospitalized for CEA. The percentage of dual-eligible patients receiving CEA increased from 10.1% in 2003 to 11.5% in 2010, with no change in geographic distribution across the country. In adjusted analyses, dual-eligible vs Medicare-only beneficiaries had a higher rate of 30-day ischemic stroke or death; higher in-hospital, 30-day, and 1-year all-cause mortality; and higher 30-day all-cause readmission. Relative annual reductions in outcomes from 2003 to 2010 ranged from 2% to 5%, but there was no significant interaction between dual-eligible status and time.

Conclusions: Dual-eligible beneficiaries had worse outcomes than those eligible for Medicare alone. Additional work is necessary to understand the reasons for this difference.

Figure 1. County-level risk-standardized percentage of dual eligible among Medicare beneficiaries in 2003 and 2010

Spatial mixed models with county-specific random intercepts and adjustment for age, sex, and race-ethnicity were fit to calculate and map the smoothed risk–standardized percentage of beneficiaries who were dual eligible for each county in 2003 and 2010. The risk-standardized percentage of dual-eligible individuals in US counties ranged from 1.3% to 61.8%. The counties were grouped into 25 equal quantiles based on the data and shaded according to a gradient from green (lowest percentage of dual eligible) to red (highest percentage of dual eligible). Areas shaded white indicate insufficient data that precluded calculations (not calculable).

Figure 2. Adjusted association between dual-eligible status and outcomes

Longitudinal mixed models with a logit link function and hospital-specific random intercepts were used to model in-hospital, 30-day, and 1-year mortality as a function of dual-eligible status, an interval time variable representing annual change in outcome, and the interaction between dual-eligible status and time. Cox proportional hazards models were used to model the 30-day ischemic stroke or death composite outcome and 30-day all-cause readmission. All models were adjusted for patient demographics (age, sex, and race) and clinical characteristics (symptomatic carotid stenosis, congestive heart failure, prior myocardial infarction, unstable angina, chronic atherosclerosis, hypertension, diabetes mellitus, peripheral vascular disease, prior stroke, cerebrovascular disease, renal failure, chronic obstructive pulmonary disease, asthma, pneumonia, cardiopulmonary respiratory failure, dementia, Parkinson or Huntington disease, trauma, anemia, functional disability, protein-calorie malnutrition, depression, and other psychiatric disorder). ^aOdds ratios were calculated for in-hospital, 30-day, and 1-year mortality. ^bHazard ratios were calculated for 30-day ischemic stroke or death and 30-day all-cause readmission.