Abstract Introduction The circadian pattern of occurrence of cardiovascular events is an evolving field of research. Sympathetic signaling can increase risk of fatal arrhythmias in patients with cardiovascular disease. Circadian rhythm regulated peak secretion of cortisol, a key modulator in sympathetic signaling, occurs at 07:00 to 08:00. Our study aims to identify incidence of in-hospital cardiorespiratory arrests and evaluate for associations with timing. Methods Patients age 18 who had cardiac arrest in three campuses of Geisinger Health System between January and June of 2025, documented in the Geisinger Code Blue Dashboard, were included. This encompassed in- hospital events and out of hospital arrests that continued in the emergency department. Retrospective review evaluated age, gender, clinical history (obstructive sleep apnea, heart failure, hypertension, coronary artery disease), and timing of arrest. At least twenty minutes was required between events to count as separate events in the same individual. The timing of cardiorespiratory events was the primary outcome. Results 162 patients were identified for preliminary analysis. The average age was 60.7 years (range 43-77). 59.3% (n= 96) were male. 18.52% had OSA (n= 30 patients), 67.28% (n = 109 patients) had hypertension, 45.06% (n = 73 patients) had CAD, 32.72% (n = 53 patients) had heart failure. Of 176 recorded events, 47.7% (n= 84) occurred prior to noon and 59.7% (n= 92) occurred after noon. 29.5% of events occurred between window of 08:00 and 13:00 (n = 52) with peak of 10:00 (n = 14). Peak codes in males occurred between 10:00 and 17:00, whereas in females occurred between 08:00 and 14:00. Conclusion Our data indicates occurrence of cardiorespiratory arrests between 08:00 and 13:00 in the general population which aligns with timing of circadian related changes such as peak cortisol, inflammatory and thrombotic marker levels. While sex differences in timing of out-of-hospital events were previously attributed to emergency services activation, our data suggests that sex differences in timing of in-hospital events also exist. A confounding factor may be type of cardiac disease prior to onset of arrest. Further data is needed to explore the pathophysiological reasons for these sex differences and implications on in-hospital arrests. Support (if any)
Mudigonda et al. (2026) studied this question.