Influence of ambient temperature and absolute humidity on sudden cardiac arrest in Singapore: a nationwide time-series study

Global warming is expected to increase the risk of cardiovascular morbidity and mortality. The effects of climate variability on sudden cardiac arrest (SCA) have not been studied in tropical climates. We aimed to study this in Singapore, a city-state with a tropical climate. We included all nationally reported SCA cases from 1 April 2010 to 31 December 2021. Using negative binomial regression adjusted for long-term trend, periodicity and public holidays, we estimated the temperature and absolute humidity effects on SCA risk within the Distributed Lag Non-Linear Model framework. We compared the seasonal trend components of SCA cases, temperature and absolute humidity. There were 27 209 cases. The majority were 65 years of age and above (62.3%), male (63.4%) and of Chinese ethnicity (68.4%). SCA risk increased by 13% (RR: 1.13, 95% CI: 1.07 to 1.20) at 29°C and by 33% (RR: 1.33, 95% CI: 1.04 to 1.70) at 24°C (relative to 27°C) when these temperatures sustained over 8 days. SCA risk increased by 78% (RR: 1.78, 95% CI: 1.34 to 2.37) when absolute humidity was sustained over 7 days at 18 g/m3 (relative to 25 g/m3). The cooler temperature effects on SCA risk were higher at lower levels of absolute humidity, suggesting effect modification. SCA had its highest peak in the first half of the calendar year, occurring concurrent to a seasonal trough in absolute humidity while its second peak was preceded by the seasonal peak in temperature. Temperature and absolute humidity were independently associated with SCA risk.