Circadian rhythm in cardiac arrest: the Singapore experience

There appears to be a circadian rhythm in the timing of cardiovascular and neurovascular events. The majority of studies have been conducted in western populations. This is the first study to look at the peaks and distribution of out-of-hospital cardiac arrest (OHCA) patients in Singapore.

The Cardiac Arrest and Resuscitation Epidemiology Studies I and II were prospective observation studies on OHCA in Singapore from October 1, 2001 to October 14, 2004. This study analysed data for patients older than 16 years. All data was collected and recorded as per the Utstein style template. Analysis was done for each of the quadrants of the 24-hour clock: 0001-0600, 0601-1200, 1201-1800 and 1801-2400 hours.

Of the 2,428 cases, 2,167 OHCA patients qualified for the final analysis. Their mean ages were in the 60s for all the four quadrants, with a male predominance. The two peaks noted were at 0800 and 1900 hours for cardiac causes of death (n = 1,591), and at 0900 and 2000 hours for non-cardiac causes of death (n = 576). At all times of the day, the majority of OHCA occurred in residences and the bystander cardiopulmonary resuscitation rate ranged from 14.6 to 24.3 percent in the different quadrants of the day.

OHCA has a bimodal distribution in our local cohort of patients. The information obtained will be utilised for fine-tuning emergency medical services strategies, as we strive to improve our current survival rates for OHCA.