Clinical paperOut-of-hospital cardiac arrest frequency and survival: Evidence for temporal variability☆
Introduction
Out-of-hospital cardiac arrest (OHCA) is a significant public health problem, with the North American incidence of EMS-treated cardiac arrest estimated to be 52.1 per 100,000 people.1 Understanding the chronobiology of OHCA is important to clarify the immediate precipitants of sudden cardiac death, develop preventative strategies, and to optimize resource planning for the prehospital and in-hospital response to cardiac arrest.
Several potential triggers for cardiac arrest have demonstrated circadian variability. Examples include physical activity, psychological stress, increases in heart rate, blood pressure and sympathetic tone, reduced fibrinolytic activity, and increased platelet aggregation.2 Epidemiological reports support underlying chronobiological mechanisms for cardiac arrest, demonstrating circadian,3, 4, 5, 6, 7, 8, 9, 10 circaseptan8, 9, 11 and circannual8, 9 variability in the frequency of OHCA. However, few studies have used a geographically diverse, population-based prospective registry of EMS-attended cardiac arrest as the basis for reporting. Furthermore, few studies have investigated whether survival from OHCA varies according to time of day, day of week or month of year. Patient characteristics, arrest circumstances, and treatment could vary according to time period and could in turn influence the likelihood of survival.12
The objective of this investigation was to evaluate temporal variability in the frequency and outcome of OHCA in a large, heterogeneous and unselected population.
Section snippets
Methods
Ethics approval for this study was obtained from 74 US Institutional Review Boards and 34 Canadian Research Ethics Boards as well as 26 EMS Services Institutional Review Boards.
Description of the cohort
There were 23,313 OHCAs occurring within the 9 participating ROC sites from December 1, 2005 to February 28 2007. Four hundred fifty cases (1.9%) were excluded for missing data. Only 57.5% of these patients were treated by EMS. Nine thousand six hundred sixty-seven patients met criteria for inclusion in the study (Fig. 1). Overall survival to hospital discharge was 8.3%.
Demographics, cardiac arrest characteristics and EMS response characteristics by time block are shown in Table 1. The initial
Discussion
In this large, population-based, multisite study using data from the Resuscitation Outcomes Consortium Epistry—Cardiac Arrest, we observed temporal variability in OHCA occurrence and outcome. These temporal observations provide a framework to advance our understanding of the triggers of OHCA. Such a framework can potentially improve resuscitation care through EMS resource planning and cardiac arrest research which incorporates this phenomenon as a potential variable affecting the risk for
Conclusion
In the Resuscitation Outcomes Consortium Epistry database, there is evidence for circadian variability in OHCA frequency with a daytime excess of out-of-hospital cardiac arrests an overnight nadir. Although OHCA frequency also varies significantly by day of week and month of year with most occurring on Saturdays and during December, there are no clear trends with respect to weekday versus weekend or across seasons of the year. Survival to hospital discharge varies by hour of day and is least
Conflict of interest statement
Steven Brooks, Robert Schmicker, Thomas Rea, Laurie Morrison, Ritu Sahni, Denise Griffiths, Scott Emerson and George Sopko have no disclosures relevant to this manuscript.
Tom P. Aufderheide is a paid consultant for Medtronics Inc. and JoLife. He sits on the Board of Directors for Take Heart America. He has received honoraria from EMS Today.
Daniel P. Davis has received an unrestricted research grant from Zoll Medical for an investigator-initiated study. He is a paid consultant to Cardinal Health.
Acknowledgements
The Resuscitation Outcome Consortium (ROC) is supported by a series of cooperative agreements to 10 regional clinical centers and one data Coordinating Center (5U01 HL077863, HL077881, HL077871 HL077872, HL077866, HL077908, HL077867, HL077885, HL077885, HL077863) from the National Heart, Lung and Blood Institute in partnership with the National Institute of Neurological Disorders and Stroke, The Canadian Institutes of Health Research (CIHR)—Institute of Circulatory and Respiratory Health,
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A Spanish translated version of the summary of this article appears as Appendix in the final online version at doi:10.1016/j.resuscitation.2009.10.021.