Multiarterial Grafting and Survival After Coronary Artery Bypass Grafting: An Instrumental Variable Analysis

This retrospective Medicare analysis assessed whether multiarterial grafting (MAG) improves survival after coronary artery bypass grafting (CABG) compared with single arterial grafting (SAG), accounting for unmeasured confounding using surgeon MAG rate as an instrumental variable. Among 1,275,606 beneficiaries undergoing isolated CABG from 2001 to 2019, 143,865 (11.3 percent) received MAG and 1,131,741 (88.7 percent) received SAG. In conventional adjusted analysis, MAG showed modestly longer median survival than SAG (10.74 vs 10.33 years; difference 0.41 years). However, in the instrumental variable model, median survival was identical (10.38 vs 10.38 years; difference 0.01 years). The authors conclude that observational studies may overestimate the MAG survival benefit due to unmeasured patient-selection and surgeon-decision confounding.