Informal Clinical Integration in Medicare Accountable Care Organizations and Mortality Following Coronary Artery Bypass Graft Surgery.

Background: Accountable care organizations' (ACOs') focus on formal clinical integration to improve outcomes overlooks actual patterns of provider interactions around shared patients.

Objective: To determine whether such informal clinical integration relates to a health system's performance in an ACO.

Research Design: We analyzed national Medicare data (2008-2014), identifying beneficiaries who underwent coronary artery bypass grafting (CABG).