Impact of a nationwide COVID-19 lockdown on acute coronary syndrome referrals.

Since December 2019, the emergence of coronavirus disease 2019 (COVID-19) in Wuhan, China, has evolved towards a global pandemic stressing healthcare providers and local authorities all over the world [1]. While national coronavirus lockdowns have led to a deferral of elective procedures, the European Society of Cardiology (ESC), has issued guidance for the diagnosis and management of cardiovascular diseases during the COVID-19 pandemic, in particular acute coronary syndromes (ACS). However, reports recently published suggest a decline in primary percutaneous coronary intervention (PCI) volumes during the COVID-19 pandemic [2, 3]. In addition to these observations, we report the immediate impact of a nationwide lockdown during the COVID-19 outbreak on ACS referrals in a tertiary care center as well as data on death tolls in Switzerland during the observation period. Acute coronary syndrome patients and out of hospital cardiac arrests (OHCA) referred to the catheterization laboratories at the University Heart Center Zurich during the period 02/17-04/12/2020 were included. The number of ACS referrals reported 4 weeks before and after implementation of a nationwide lockdown on March 16 2020 was compared to the same period of time in 2019. Four weeks after March 16 2020 ACS referrals decreased by 42% (non-ST-segment elevation myocardial infarction: –49%, ST-segment elevation myocardial infarction: –56%, unstable angina: +37%) while OHCA referrals declined by 57% (Fig. 1A). An initial decrease in ACS referrals was observed following the first report of a COVID-19 case in Switzerland on February 25 (–2 weeks) and was precipitated by the implementation of a nationwide lockdown on March 16 (Fig. 1C). Numbers of ACS and OHCA referrals remained stable for the same observation period in 2019 (Fig. 1B, D). The decline in ACS referrals observed from March 16 2020 on was paralleled by an increase in weekly reported deaths in the population of persons aged 65 and over in Switzerland (Fig. 1E) while death numbers remained unchanged in 2019. Exposure to air pollutants is associated with an increased risk of near-term myocardial infarctions [4]. To assess the effect of restrictive actions following implementation of a lockdown on urban air quality, the time evolution of atmospheric pollutants recorded at a traffic air quality monitoring station were analyzed. Temperature monitoring revealed a significant increase in local temperature following the lockdown in 2020 (+2.2°, p = 0.02, Fig. 2A). As compared to 2019 an overall reduction in nitric oxides, pollutants mainly related to traffic emissions (Fig. 2B) could be observed during the COVID-19 pandemic. However, no significant difference in nitric oxides levels was observed before or after March 16. On the other hand, an increase in atmospheric particulates (PM10, Fig. 2C) was be registered for both years following March 16 which is most probably related to the prevailing secondary origin of fine aerosols as well as seasonal Sahara dust contributions. The present study supports previous observations and demonstrates a dramatic drop in ACS referrals within a few weeks during the COVID-19 pandemic in a tertiary care center in Switzerland which was precipitated by the implementation of a nationwide lockdown. Despite the potential