[Circadian rhythm and time variations in out-hospital sudden cardiac arrest].

OBJECTIVES To analyze the chronobiological and time variations of out- hospital cardiac arrest (OHCA). DESIGN A retrospective descriptive study was made. PATIENTS All cases of OHCA of cardiac origin registered over 18 months in the database of the emergency medical service (EMS) of the Autonomous Community of Castilla y León (Spain) were evaluated. VARIABLES ANALYZED: Age, sex, recovery of spontaneous circulation (ROSC), first monitored rhythm (amenable / not amenable to defibrillation), alert site [(home, public place, primary care (PC) center], alerting person (family, witness, law enforcement member, PC center staff), alert time (0-8; 8-16; 16-24), emergency team activation time, care time and day of the week. Univariate analysis (chi-squared), variance, and nonparametric tests comparing the variables in three periods of 8 hours. Chronobiological analysis by fast Fourier transform and Cosinor testing. RESULTS We studied 1286 cases reported between January 2007 and June 2008. Statistically significant differences were observed in terms of younger age, higher incidence in the victim's home, and greater frequency of family-cohabiting persons as witnesses in the period between 0 and 8 hours. Chronobiological analysis found daily rhythm (circadian) with acrophase at 11.16 h (p<0.001) and weekly rhythm (circaseptan) with acrophase on Wednesday (p<0.05). The median alert time-care time interval and emergency team activation time-care time were 11.7 min and 8.0 min, respectively, without differences between periods. CONCLUSIONS We have demonstrated the presence of a daily rhythm of emergence of OHCA with a morning peak and a weekly rhythm with a peak on Wednesdays. These results can guide the planning of resources and improvements in response in certain time periods.