Abstract 53: Evidence for Circadian Variability in the Frequency of Out-of-Hospital Cardiac Arrest
Introduction: Several sudden cardiac phenomena demonstrate circadian variability. It is not clear if there is also circadian variability in the frequency and outcome for out-of-hospital cardiac arrest (OHCA). The Resuscitation Outcomes Consortium (ROC) Epistry is a large prospective cohort of OHCA.
Hypothesis: The maximum frequency of OHCA occurs in the morning hours.
Methods: We included adult patients from all 11 North American emergency medical services (EMS) systems participating in the ROC with OHCA of presumed cardiac cause between 12/1/2005 and 11/30/2006. We excluded cases of unwitnessed, untreated OHCA. The relation between time block (4 arbitrary 6-hour blocks) and survival to hospital discharge was analyzed using multivariate logistic regression adjusting for age, sex, witness status, bystander CPR, time from 911 call to EMS arrival and initial rhythm.
Results: Of 15363 OHCAs occurring during the study period, 8297 were included. The figure⇓ shows circadian variation of OHCA frequency by witness status. The highest frequency was observed between 0601–1200 hrs and the lowest during 0001– 0600 hrs (p<0.001). This pattern was observed regardless of initial rhythm, witness status, gender or location of arrest. The adjusted odds ratio with 95% CI for survival to hospital discharge (patients in the 0001– 0600 time block as reference) was 1.00 (0.88, 1.15) for 0601–1200 hrs, 0.99 (0.91, 1.07) for 1201–1800 hrs, and 1.00 (0.91, 1.09) for 1801–2400 hrs.
Conclusions: OHCA shows circadian variability in frequency but not in survival to hospital discharge. OHCA occurs more frequently in the daytime as compared to night.