Residential Greenness and Long-term Mortality Among Patients Who Underwent Coronary Artery Bypass Graft Surgery

Abstract

Background: Studies have reported inverse associations between exposure to residential greenness and mortality. Greenness has also been associated with better surgical recovery. However, studies have had small sample sizes and been restricted to clinical settings. We investigated the association between exposure to residential greenness and all-cause mortality among a cohort of cardiac patients who underwent coronary artery bypass graft (CABG) surgery. Methods: We studied this cohort of 3128 CABG patients between 2004 and 2009 at seven cardiothoracic departments in Israel and followed patients until death or May 1st 2021. We collected covariate information at time of surgery and calculated patient-level average Normalized Difference Vegetation Index (NDVI) over entire follow-up in a 300m buffer from the home address. We used Cox proportional hazards regression models to estimate associations between greenness and death, adjusting for age, sex, origin, socioeconomic status, type of hospital admission, peripherality, air pollution, and distance from the sea. Results: Mean age at surgery was 63.8 ± 10.6 for men and 69.5 ± 10.0 for women. During an average of 12.1 years of follow-up (37,912 person–years), 1,442 (46%) patients died. A fully adjusted Cox proportional hazards model estimated a 7% lower risk of mortality (HR: 0.93, 95%CI [0.85-1.00]) per 1 interquartile range width increase (0.04) in NDVI. Results were robust to use of different buffer sizes (100m-1,250m from the home) and to use of average NDVI exposure during the first vs last 2 years of follow-up. Conclusions: Residential greenness was associated with lower risk of mortality in CABG patients.