Abstract 12127: The Effect of Daylight Savings Time Transitions on the Incidence of Out-of-Hospital Cardiac Arrest: An Interrupted Time Series Analysis

Abstract

Introduction: Many studies have reported increases in the risk of acute cardiovascular events following daylight savings time (DST) transitions. We sought to investigate the effect of DST transitions on the incidence of out-of-hospital cardiac arrest (OHCA) in Victoria, Australia. Methods: Between January 2000 and December 2020, we performed an interrupted time series analysis of the daily number of OHCA cases of medical etiology from the Victorian Ambulance Cardiac Arrest Registry. The effect of DST transition on OHCA incidence was estimated using negative binomial models and reported as either ‘immediate’ or ‘cumulative’ effects. Immediate effects were the average effects observed on the day of DST transition or each of the 6 days after DST transition. Cumulative effects were the sum of the average effects up to 6 days after the day of DST transition. Models were adjusted for population growth, temporal trends, and public holidays. Results: A total of 89,409 adult OHCA of medical etiology were included. Following the spring DST transition (i.e. shorter day), there was an immediate 13% (IRR 1.13, 95% CI: 1.02, 1.25; p=0.02) increased risk of OHCA on the day of transition (Sunday) and the cumulative risk of OHCA remained higher over the first 2 days (IRR 1.17, 95% CI: 1.02, 1.34; p=0.03) compared to non-transitional days. Following the autumn (fall) DST transition (i.e. longer day), there was a significant lagged effect on the Tuesday following transition, with a 12% (IRR 0.88, 95% CI: 0.77, 0.99; p=0.04) reduced risk of OHCA. The autumn (fall) DST transition also showed a cumulative effect on OHCA incidence, with a 30% (IRR 0.70, 95% CI: 0.51, 0.96; p=0.03) reduction in the incidence of OHCA by the end of the transitional week. Subgroups aged > 65 years and cases with initial non-shockable rhythms were most vulnerable to DST transitions. Conclusions: This study showed that there is a modest increased risk of OHCA in the 2 days following the spring DST transition and a decreased risk of OHCA in the week following the autumn DST transition. These findings should promote further research exploring strategies to reduce the risk of OHCA in vulnerable populations.