The impact of health maintenance organizations on improving cardiac surgery outcomes

California is one of a few states with mandatory reporting of mortality after coronary artery bypass graft (CABG) surgery. The Affordable Care Act restructured Medicaid, preferentially penalizing patients experiencing poverty because payments to hospitals for isolated surgical events overshadow payments to primary care clinicians. We propose outcomes are superior when hospital networks organize surgical episodes within the context of primary care inside that same network.

We listed factors impacting outcomes after CABG. CABG surgery outcome depends upon the integration of issues beginning years preoperatively and extending for decades. Therefore, we studied one health maintenance organization (HMO) from 2009 to 2020 compared to surrounding individual hospitals. We divided 58 hospitals in Northern California in 2009 according to income and population. To focus on changes introduced because of COVID-19, we compared a public database for the subset in 2009 for any relationship between poverty in a zip code and low volumes of CABG in that area to overall mortality in 2020. First, we defined low-income zip codes as those with a higher rate of poverty than the state average or with a lower per capita average income, per Census Bureau. Second, low volume was defined as a population under 165,000 because a hospital adjacent to a larger community can easily transfer care, sharing surgeons and processes. Third, we defined low volume as fewer than 180 CABG per year.

Our qualitative evidence synthesis reveals that informal communication and hospital HMO policies improve CABG outcomes. In our small pilot data, Chi-square analysis showed higher crude mortality rates in 1507 CABG in 17 low-income low-volume hospitals versus 8163 CABG in the other 41 Northern California hospitals (2.72% vs 1.69%, p = 0.0064). Low-income low-volume hospitals had a relative mortality risk of 1.61 (95% CI: 1.14-2.27). These hospitals had a mean mortality rate of 3.79%, readmission 11.12%, and stroke 1.84%. A patient undergoing CABG in a low-income low-volume hospital has a 61% higher chance of dying. The number needed to treat analysis shows that one life can potentially be saved for every 97 patients referred to another institution.

We describe features of an HMO that contribute to up to fourfold lower mortality rates.