Out-of-hospital cardiac arrest incidence was 9% higher on the first working day after holidays vs other weekdays in a nationwide South Korean cohort study published in JAMA Network Open.

Researchers analyzed 203,471 adult cases recorded between 2013 and 2023 in the Out-of-Hospital Cardiac Arrest Surveillance registry, which integrates emergency medical services and hospital data from more than 700 institutions.

The study compared events occurring on a “postholiday weekday,” defined as the first working day after a weekend, public holiday, or combined holiday period, with baseline weekdays.

Researchers identified 49,199 cardiac arrests on postholiday weekdays and 154,272 on baseline weekdays. Patients had a median age of 71 years, and approximately 64% were male.

Higher Incidence on First Postholiday Day

Postholiday weekdays were associated with a 9% higher incidence rate of out-of-hospital cardiac arrest vs baseline weekdays, corresponding to median daily counts of 88 vs 80 cases.

The increase was confined to the first day after holidays and did not extend to subsequent days.

Subgroup Findings

The association between postholiday timing and cardiac arrest incidence appeared across several demographic and clinical subgroups.

Higher incidence rate ratios were observed in:

• Patients older than 65 years
• Patients with cardiac causes of arrest
• Patients presenting with nonshockable rhythms

Subgroup analyses also showed consistent associations across sex, witness status, and residential area categories.

Effect of Holiday Duration

Researchers also evaluated whether the duration of preceding holidays influenced the postholiday pattern.

No significant increase in cardiac arrest incidence was observed after single-day holidays. However, higher incidence was observed following longer holiday periods:

• 2-day holidays
• 3-day holidays
• Holidays lasting 4 days or longer

These findings suggested a dose-response association between holiday duration and postholiday cardiac arrest incidence.

Postholiday weekdays occurring after weekends or mixed holiday periods were linked to higher out-of-hospital cardiac arrest incidence. No significant associations were observed after isolated public or temporary holidays.

Possible Behavioral and Physiologic Factors

The researchers suggested that the postholiday pattern may reflect behavioral and physiologic changes associated with transitions from rest periods to structured daily routines.

Holiday periods may involve sleep disruption, increased alcohol consumption, and delayed care seeking. Returning to regular work schedules may also increase physiologic stress, including sympathetic nervous system activation and myocardial oxygen demand.

“These biological and behavioral changes lead to an accumulated physiological debt, creating a vulnerable window that precipitates the observed surge in out-of-hospital cardiac arrest incidence,” the researchers wrote.

Study Limitations

The study’s observational design prevents causal inference, the researchers noted. In addition, unwitnessed cardiac arrests could introduce uncertainty regarding the exact timing of events.

Some variables, including bystander cardiopulmonary resuscitation and initial cardiac rhythm, had missing data that limited statistical power in certain subgroup analyses.

The researchers also could not account for personal vacations or leave taken outside the national holiday system, which could influence exposure classification.

Clinical and Public Health Implications

The researchers concluded that the first working day after holidays was associated with higher out-of-hospital cardiac arrest incidence, particularly among older adults and patients with cardiac causes of arrest.

“Future research should investigate factors associated with changes in postholiday out-of-hospital cardiac arrest incidence, including sleep pattern alterations, alcohol consumption, emotional stress, and medication adherence,” they wrote.

The researchers reported no conflicts of interest.

Source: JAMA Network Open