CAPITAL-CHILL: No Improvement in Outcomes After OHCA With Moderate Therapeutic Hypothermia

In patients who suffered an out-of-hospital cardiac arrest (OHCA), moderate therapeutic hypothermia below 31 degrees Celsius for 24 hours, compared with guideline-recommended mild hypothermia (below 34 degrees Celsius), was not associated with an improvement in outcomes at six months, based on results from the CAPITAL-CHILL study presented May 17 during ACC.21.

The investigator-led trial enrolled 367 patients treated at the University of Ottawa Heart Institute between 2013-2020. All patients had been successfully resuscitated, as indicated by a return of blood pressure, but remained comatose. Participants were cooled with an endovascular device that uses temperature-controlled saline-filled balloons inserted near the heart via a vein to alter a patient's body temperature. For half of the patients, the endovascular device was set to cool the body to 31 C and for the other half the device was set to 34 C. Once the target temperature was achieved, the temperature was maintained for 24 hours before the patient was warmed up to normal body temperature at a rate of 0.25 degrees per hour.

The trial is the first to use a randomized, double-blind approach for testing different target temperatures for therapeutic hypothermia. Blinding for physicians was achieved with a shield over the temperature display; nurses were unblinded and maintained separate charts.

The study's primary endpoint, a composite of death or poor neurological outcome at six months, occurred in 48% of those cooled to 31 C and 45% of those cooled to 34 C, a difference that was not statistically significant. There was also no significant difference between groups in terms of the rate of death or the rate of poor neurological outcome when these outcomes were assessed individually.

The researchers examined outcomes by sex, age and other variables but found no significant differences in any subgroups analyzed. Patients cooled to 31 C on average had a longer stay in the cardiac intensive care unit, which researchers said may reflect the fact that both the cool-down and warm-up periods lasted longer for these patients due to the lower target temperature.

No differences were seen between the strategies for secondary outcomes of pneumonia, renal replacement therapy, seizure and stroke.

Moving forward, the researchers suggested brain monitoring approaches could be used to inform which strategies may be best suited for each patient's particular situation. Previous studies examining different strategies for temperature and duration also have not shown an improvement over current guideline recommendations.

"It may be useful to pool all these studies together and try to figure out if there is a particular temperature that's more suitable in particular cases," said Michel R. Le May, MD, FACC, the study's lead author. "We also have to find better, noninvasive tools to assess the brain and perhaps turn our attention toward a more personalized way of treating these patients. This would allow us to select the protocol that optimizes the benefit for a particular patient."

Clinical Topics: Arrhythmias and Clinical EP, Geriatric Cardiology, SCD/Ventricular Arrhythmias

Keywords: ACC Annual Scientific Session, ACC21, Geriatrics, Out-of-Hospital Cardiac Arrest

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