• R K Thakur, R G Hoffmann, D W Olson, R Joshi, D D Tresch, T P Aufderheide, and J H Ip.
• Arrhythmia Service, Thoracic and Cardiovascular Institute, Michigan State University, Lansing, USA.
• Ann Emerg Med. 1996 Jan 1;27(1):29-34.

Study ObjectivePrevious studies based on data obtained from vital statistics records have demonstrated circadian variation in the occurrence of sudden cardiac death. The purpose of this study was to examine the effects of age, sex, and initial cardiac rhythm on circadian variability in sudden cardiac death.MethodsThis study employed a retrospective analysis of the records of adult patients with witnessed cardiac arrest who underwent resuscitation in an urban paramedic system during a 5-year period.ResultsThe records of 2,250 consecutive patients with witnessed cardiac arrest were reviewed. Spectral analysis was used to decompose the data into frequency components. A circadian variation in the occurrence of sudden cardiac death was demonstrated, with a low occurrence rate between midnight and 6 AM and a 2.4-fold increase between the rate at 6 AM and the rate at noon. The same circadian pattern was noted among both men and women, among both patients aged 18 to 70 and those older than 70 years, and among patients with various initial cardiac arrest rhythms (ventricular tachycardia or fibrillation, asystole, and electromechanical dissociation). However, the outcome of resuscitation in these patients (ie, the rate of successful resuscitation and the rate of survival) did not demonstrate circadian variation.ConclusionWitnessed out-of-hospital sudden cardiac death demonstrated circadian variation, and this variability was observed regardless of the patient's age, sex, or initial cardiac arrest rhythm. The outcome of resuscitation did not show circadian variability. These results suggest a common pathophysiologic mechanism leading to sudden cardiac death.

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