As daily temperatures climb above 90 degrees Fahrenheit across the United States, the rate of out-of-hospital cardiac arrest (OHCA) admissions to hospital intensive care units (ICUs) rises sharply, according to new preliminary research presented at the American Heart Association's Resuscitation Science Symposium 2026. The findings, which are not yet peer-reviewed, highlight a growing strain on critical care resources as heat waves become more frequent and intense.
The study analyzed data from over 11,000 patients admitted to ICUs across 10 health systems between 2018 and 2024. Researchers found that compared with days reaching 85 degrees F, OHCA admissions were 45% higher at 91 degrees F and 102% higher at 98 degrees F. Women were admitted at a rate 33% higher on extreme heat days, and people aged 65 and older had a 48% higher admission rate at 90 degrees F compared to 67 degrees F. "Heatwaves are becoming more frequent and intense nationally, causing additional strain on communities and emergency services, as well as on hospitals," said Peter Graffy, Ph.D., M.P.H., a postdoctoral fellow at the University of Chicago and lead author of the study.
Cardiac arrest occurs when the heart's electrical system malfunctions, stopping blood flow to vital organs. Approximately 90% of people who experience OHCA do not survive, making it a severe cardiovascular emergency. While extreme heat has long been known to increase cardiac arrest risk, this study is among the first to examine its impact on ICU admissions and subsequent care. The research is particularly important because ICU beds, equipment, and staff are limited, and sudden spikes in critically ill patients can quickly overwhelm hospital resources.
Despite the increased need for interventions such as blood pressure support and continuous dialysis for kidney dysfunction, the study found no significant difference in overall survival or discharge outcomes for patients admitted during heat waves compared to cooler days. "We were surprised to find that outcomes were not that different between the two groups," Graffy said. "We think this is likely a testament to clinicians and care teams both in the emergency department and ICU to effectively stabilize these individuals."
However, the surge in admissions during heat waves has profound implications for health systems. "The health effects of extreme heat do not stop when an ambulance reaches the hospital," Graffy noted. "Our findings show that heat is associated with more cardiac arrest admissions and greater needs for advanced critical care interventions, which can strain already limited ICU capacity." The researchers suggest that hospitals could eventually use temperature forecasts to prepare ICU beds, staff, and resources in advance. For the public, experts emphasize the importance of taking heat warnings seriously, especially for older adults and those with chronic conditions. As Ashish Panchal, M.D., Ph.D., FAHA, chair of the American Heart Association's Emergency Cardiovascular Care Committee, stated, "Heat warnings should be taken seriously because extreme heat can have consequences that extend from the home all the way through to the ICU."
The study's findings are considered preliminary until published in a peer-reviewed journal. For more information on cardiac arrest, visit the American Heart Association's Cardiac Arrest page. The association also provides resources on Cardiac Arrest vs. Heart Attack and the Nation of Lifesavers initiative. Details about the symposium are available at About Resuscitation Science Symposium 2026. Additional heat-related cardiovascular risks are discussed in the association's news release, Extreme heat is rising – and so is the risk to your heart, and a scientific statement on Nonoptimal Temperature and Cardiovascular Health. The abstract is available via Link to abstract, and the full release can be viewed at www.newmediawire.com.
