Cardiac arrest ICU admissions rose with outdoor heat, especially in women, older adults

Research Highlights:

• The rate of cardiac arrest admissions to hospital intensive care units (ICUs) increased during times of extreme heat (90 degrees Fahrenheit (F) or above), leading to the need for more medical care and resources within the ICUs, according to new preliminary research.
• Researchers found that both the number of out-of-hospital cardiac arrest (OHCA) admissions and the proportion of OHCA among all ICU admissions increased as temperatures rose. Compared with days reaching 85 degrees F, OHCA admissions were 45% higher at 91 degrees F and 102% higher at 98 degrees F.
• Being admitted on days 90 degrees F and above did not appear to impact the status at discharge for people who experienced cardiac arrests. Also, deaths, discharges to hospice and lengths of hospital stays remained about the same for people admitted during heat waves compared to those who were admitted for cardiac arrests on days that reached 67 degrees F and below.
• Note: The study featured in this news release is a research abstract. Abstracts presented at American Heart Association's scientific meetings are not peer-reviewed, and the findings are considered preliminary until published as full manuscripts in a peer-reviewed scientific journal.

Embargoed until 4 a.m. CT/5 a.m. ET, Monday, Nov. 2, 2026

DALLAS, Nov. 2, 2026 - As daily temperatures climbed above 90 degrees Fahrenheit (F) across the U.S., so did the rate of out-of-hospital (OHCA) cardiac arrest admissions to hospitals intensive care units (ICUs); however, the heat didn't appear to impact the overall outcomes of people admitted for cardiac arrest during heat waves compared to other times, according to new, independent, preliminary research to be presented at the American Heart Association's Resuscitation Science Symposium 2026. The meeting will be held Nov. 7-8 in Chicago and will feature the most recent advances related to treating cardiopulmonary arrest and life-threatening traumatic injury.

Cardiac arrest occurs when the heart's electrical system abruptly malfunctions and stops the heart from pumping blood to the rest of the body, which results in loss of blood to the brain, lungs and other vital organs. Out-of-hospital cardiac arrest (OHCA) is a serious cardiovascular emergency, and approximately 90% of people who experience OHCA do not survive. Extreme heat has been known to increase the risk of cardiac arrest, although this has been historically measured using EMS calls or deaths, with those most vulnerable including older adults, people with disabilities and individuals who lack air conditioning or reliable transportation. As extreme heat events become more common globally, these researchers sought to better understand how heat exposure may affect people who experience OHCA, including their need for intensive care and their chances of recovery after arriving at the hospital.

"Heatwaves are becoming more frequent and intense nationally, causing additional strain on communities and emergency services, as well as on hospitals who must absorb the influx of climate-related illnesses. This is important because ICU beds, equipment and staff are limited, and sudden increases in critically ill patients can quickly overwhelm hospital resources if we are not ready," said Peter Graffy, Ph.D., M.P.H., a postdoctoral fellow in the section of pulmonary and critical care at the University of Chicago. "People who are resuscitated after out-of-hospital cardiac arrest are usually admitted to an intensive care unit because they are often unconscious and unable to breathe independently. They may require advanced life support for several days or weeks while patients' families wait to see if their loved one regains consciousness."

Researchers analyzed data from 10 health systems across the U.S. participating in the Common Longitudinal ICU Format Consortium (CLIF), a network that standardizes electronic health record data across hospitals for research. Daily temperatures near each hospital were itemized while also accounting for humidity and air pollution. These data were cross-analyzed to determine if hotter days were associated with more OHCA admissions to the ICU. They also tracked whether heat exposure was associated with an increase in the number of people who required organ-support, differences in laboratory markers or changes in outcomes such as survival and neurological recovery.

During the study period from 2018-2024, more than 11,000 patients with OHCA were admitted to an intensive care unit. About half of those were admitted during warm weather seasons, and 270 were admitted during a period of extreme heat (>90 degrees F).

What are the study's key findings:

• The researchers found that as temperatures climbed past 90 degrees F, so did the rate of OHCA admissions to the ICU when compared to days at or below 67 degrees F (the median reference temperature across all CLIF sites).
• When daytime temperatures reached 91 degrees F or higher, the daily rate of OHCA admissions to the ICU increased 45% when compared to the days with max temperature of 85 degrees F; 65% at 93 degrees F and 102% at 98 degrees F.
• People ages 65 and older had a 48% higher admission rate for OHCA at 90 degrees F versus 67 degrees F.
• Women were admitted for OHCA at a rate of 33% higher on days with extreme heat.
• When daytime temperatures reached 98 degrees F, there were approximately 1.5 additional OHCA ICU admissions across the 10 health systems compared to days with median temperature of 67 degrees F.

People admitted to the hospital after cardiac arrest on days with temperatures of 90 degrees F or warmer were more likely to require interventions for low blood pressure and, later in their ICU stay, continuous dialysis for kidney dysfunction. They also had markers for impaired circulation and metabolic stress while in the ICU. However, despite the requirement of different clinical interventions during the ICU stay, overall hospital discharge status and survival rate of these individuals were similar to people admitted after cardiac arrest during times when temperatures were closer to 70 degrees F. No significant differences were seen in rates of being discharged home, transferred to an acute care hospital or in-hospital death based on temperature at admission.

"We were surprised to find that outcomes were not that different between the two groups," Graffy said. "We had assumed that since extreme heat typically contributes to multi-organ system dysfunction that the rates of death would be higher among the people whose OHCA was potentially influenced by heat. But this was not the case, and we think this is likely a testament to clinicians and care teams both in the emergency department and ICU to effectively stabilize these individuals with OHCA upon admission to give them the best chance at recovery."

However, Graffy noted, the increase in ICU admissions during heat waves has a profound impact on health systems. "The health effects of extreme heat do not stop when an ambulance reaches the hospital. 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," he said. "Since OHCA can take days to weeks to resolve in the ICU, the eventual outcomes are not being attributed to heat despite it potentially being the primary reason for OHCA onset. As extreme heat becomes more common, healthcare systems must adapt and prepare for its growing impact. Our goal is that hospitals could one day use temperature forecasts in a data-driven way to adequately prepare ICU beds, staff, resources and coordination between emergency departments and intensive care units."

"For the public and caregivers, especially those supporting older or medically vulnerable adults, heat warnings should be taken seriously because extreme heat can have consequences that extend from the home all the way through to the ICU," said Ashish Panchal, M.D., Ph.D., FAHA, volunteer chair of the American Heart Association Emergency Cardiovascular Care Committee, physician and professor of emergency medicine at The Ohio State University. "We also know that about 70% of cardiac arrests that happen outside of a hospital happen at home, and people need to be prepared: at a minimum, everyone should learn the lifesaving skills of CPR and seek medical care as quickly as possible."

Statements and conclusions of studies that are presented at the American Heart Association's scientific meetings are solely those of the study authors and do not necessarily reflect the Association's policy or position. The Association makes no representation or guarantee as to their accuracy or reliability. Abstracts presented at the Association's scientific meetings are not peer-reviewed, rather, they are curated by independent review panels and are considered based on the potential to add to the diversity of scientific issues and views discussed at the meeting. The findings are considered preliminary until published as a full manuscript in a peer-reviewed scientific journal.

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Additional Resources:

• Multimedia is available on the right column of the release link.
• Link to abstract; and the American Heart Association's Resuscitation Science Symposium 2026 Online Program Planner
• American Heart Association news release: Extreme heat is rising - and so is the risk to your heart (July 2026)
• American Heart Association Scientific Statement: Nonoptimal Temperature and Cardiovascular Health (March 2026)
• American Heart Association health information: Cardiac Arrest vs. Heart Attack
• Join the American Heart Association Nation of Lifesavers
• About Resuscitation Science Symposium 2026
• For more news at the American Heart Association's Resuscitation Science Symposium 2026, follow us on X @HeartNews, #ReSS26

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