# Incidence of Out-of-Hospital Cardiac Arrest on a Postholiday Weekday

## TL;DR

In South Korea, the first weekday after holidays sees a 9% increase in out-of-hospital cardiac arrests, especially in older adults and those with heart conditions.

## Contribution

This study identifies a postholiday weekday as a period of increased cardiovascular risk, offering new insights into emergency preparedness.

## Key findings

- Postholiday weekdays had a 9% higher cardiac arrest incidence compared to baseline weekdays.
- The risk was higher after 2 or more consecutive holidays and among older adults and those with cardiac causes.
- Weekend and mixed holidays showed stronger associations than public or temporary holidays.

## Abstract

Is a postholiday weekday associated with a higher out-of-hospital cardiac arrest incidence vs baseline weekdays in South Korea?

In this cohort study of 203 471 adult cases over 11 years, a postholiday weekday was associated with a 9% higher out-of-hospital cardiac arrest incidence than baseline weekdays. This phenomenon was particularly pronounced among older adults, individuals with cardiac cause, and after 2 or more consecutive holidays.

These findings suggest that the postholiday transition represents a period of increased cardiovascular vulnerability, underscoring the need for enhanced emergency medical preparedness during those times.

This cohort study examines the incidence of out-of-hospital cardiac arrest on a postholiday weekday vs baseline weekdays in South Korea.

Although increased cardiovascular risk during holidays has been documented, whether this elevated risk persists into the postholiday transition period remains unclear.

To quantify the incidence of out-of-hospital cardiac arrest on a postholiday weekday in South Korea.

This nationwide cohort study analyzed data from the Out-of-Hospital Cardiac Arrest Surveillance database between January 1, 2013, and December 31, 2023. Adult out-of-hospital cardiac arrest cases occurring on weekdays were included, excluding those on holidays.

A postholiday weekday, defined as the first working day following any weekend or holiday period, compared with baseline weekdays (all other weekdays).

The primary outcome was the out-of-hospital cardiac arrest incidence rate ratio (IRR) comparing a postholiday weekday with baseline weekdays, estimated using negative binomial regression. Subgroup analyses examined demographic and clinical factors, and additional analyses assessed dose-response associations according to the duration and type of preceding holidays.

Among the 203 471 adult participants (median [IQR] age, 71 [56-81] years; 130 348 [64.1%] male), 49 199 cases occurred on a postholiday weekday and 154 272 occurred on baseline weekdays. The daily out-of-hospital cardiac arrest incidence was significantly higher on a postholiday weekday than on baseline weekdays (median [IQR], 88 [78-98] vs 80 [71-89] cases), representing a 9% higher incidence (IRR, 1.09; 95% CI, 1.08-1.11; P < .001). Subgroup analysis revealed increased vulnerability among adults older than 65 years (IRR, 1.03; 95% CI, 1.02-1.04; P < .001), individuals with cardiac cause (IRR, 1.02; 95% CI, 1.01-1.04; P < .001), and those presenting with nonshockable rhythms (IRR, 1.03; 95% CI, 1.01-1.04; P < .001). A clear dose-response association was observed. Significant associations were observed after 2-day holidays (IRR, 1.10; 95% CI, 1.08-1.11; P < .001), 3-day holidays (IRR, 1.09; 95% CI, 1.03-1.15; P = .003), and holidays of 4 days or more (IRR, 1.10; 95% CI, 1.03-1.18; P = .007) but not after single-day holidays (IRR, 1.03; 95% CI, 0.98-1.08; P = .25). Weekend (IRR, 1.09; 95% CI, 1.07-1.11; P < .001) and mixed (IRR, 1.10; 95% CI, 1.06-1.14; P < .001) holidays were associated with a higher out-of-hospital cardiac arrest incidence, whereas public (IRR, 1.03; 95% CI, 0.97-1.09; P = .24) and temporary (IRR, 1.01; 95% CI, 0.89-1.13; P = .86) holidays were not.

In this nationwide cohort study, a postholiday weekday was associated with a significantly elevated out-of-hospital cardiac arrest incidence in South Korea, particularly after consecutive rest days and among vulnerable populations. These findings support enhanced emergency medical services preparedness, targeted public health messaging during holiday periods, and evaluation of preventive interventions for high-risk populations during postholiday transitions.