In-Hospital Cardiac Arrest Risk Highest in Winter

Pauline Anderson

June 23, 2023


The incidence of in-hospital cardiac arrest (IHCA) varies markedly by season among both men and women, in middle-age and older populations, and across different geographic regions of the United States, a new study shows.


  • The study included adults with IHCA, mean age 66 years and 44% female, identified using 2005-2019 data from the National Inpatient Sample (NIS).

  • Covariates included demographic variables, hospital characteristics (bed size, teaching status, region), and comorbidities.

  • Researchers evaluated the overall, sex-based, age-based, and region-based seasonal trends in the incidence of IHCA per 100,000 hospitalizations and evaluated the most common causes of admission for patients with IHCA overall and in subgroups of shockable and nonshockable IHCA.


  • There was consistent seasonal variation, primarily driven by nonshockable IHCA, in the incidence of IHCA per 100,000 from 2005 to 2019, with the highest rates in the winter and lowest in the summer (adjusted odds ratio of IHCA in winter vs summer, 1.08; 95% CI, 1.005-1.15)

  • Seasonal variability was seen in male and female patients, in different US regions, and in middle-aged and older patients but not in younger people (age 18-44 years)

  • The overall incidence of IHCA was consistently highest in the West from 2012 and lowest in the Midwest from 2012 to 2013 but lowest in the Northeast after that.

  • The most common causes for hospitalization were sepsis, acute hypoxic respiratory failure, ST-segment elevation myocardial infarction (STEMI), non-STEMI, and heart failure, but causes differed in those with shockable vs nonshockable rhythm.

  • There was no significant seasonal variation in in-hospital mortality.


The study findings "suggest that more resources may be needed in the winter to manage susceptible patients to prevent IHCA" write the authors, adding that high-risk patients can be triaged and closely monitored during hospitalization for early warning signs of impending cardiopulmonary collapse.


The study was carried out by Muddasir Ashraf, MD, Aurora Cardiovascular and Thoracic Services, Aurora Sinai/Aurora St. Luke's Medical Centers, Advocate Aurora Health, Milwaukee, and colleagues. It was published online in the Journal of the American College of Cardiology (JACC): Clinical Electrophysiology.


Because the NIS is an administrative database, coding errors can occur, leading to misclassification bias, and residual confounding is possible given the database's retrospective nature. The database also does not include information on long-term outcomes or on laboratory tests and medications, which may affect in-hospital outcomes.


The authors have no relevant conflicts of interest.

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