CIRCADIAN VARIATION IN SUDDEN CARDIAC DEATH - EFFECTS OF AGE, SEX, AND INITIAL CARDIAC-RHYTHM

Study objective: Previous studies based on data obtained from vital st atistics records have demonstrated circadian variation in the occurren ce of sudden cardiac death. The purpose of this study was to examine t he effects of age, sex, and initial cardiac rhythm on circadian variab ility in sudden cardiac death. Methods: This study employed a retrospe ctive analysis of the records of adult patients with witnessed cardiac arrest who underwent resuscitation in an urban paramedic system durin g a 5-year period. Results: The records of 2,250 consecutive patients with witnessed cardiac arrest were reviewed. Spectral analysis was use d to decompose the data into frequency components. A circadian variati on 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 patt ern 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 ini tial cardiac arrest rhythms (ventricular tachycardia or fibrillation, asystole, and electromechanical dissociation). However, the outcome of resuscitation in these patients (ie, the rate of successful resuscita tion and the rate of survival) did not demonstrate circadian variation . Conclusion: Witnessed out-of-hospital sudden cardiac death demonstra ted circadian variation, and this variability was observed regardless of the patient's age, sex, or initial cardiac arrest rhythm. The outco me of resuscitation did not show circadian variability. These results suggest a common pathophysiologic mechanism leading to sudden cardiac death.