Benefit From Cooling Temps for Cardiac Arrest Does Not Differ in Randomized Trial

Ted Bosworth

May 25, 2021

The first randomized controlled trial to compare specific temperatures for therapeutic hypothermia in comatose survivors of out-of-hospital cardiac arrest showed no differences in major outcomes, according to a single-center, double-blind study.

In the CAPITAL-CHILL trial, cooling temperatures of 31 °C and 34 °C were compared to explore the hypothesis that a lower temperature would improve major outcomes, explained Michel Le May, MD.

No differences for the primary composite outcome of all-cause mortality or poor neurologic outcome at 180 days were observed, he reported at the annual scientific sessions of the American College of Cardiology.

The study was completed over a period of almost 7 years in patients presumed to have had an out-of-hospital cardiac arrest and who were unconscious when they reached a center affiliated with the Ottawa Heart Institute, where Le May directs the regional STEMI (ST-elevation myocardial infarction) program. The initial rhythm at the time of the cardiac arrest was not an entry criterion.

Of 389 patients enrolled, the intention-to-treat analysis included 184 randomized to a cooling temperature of 31 °C group and 183 to a temperature of 34 °C. The assigned target temperature, reached with an endovascular device, was known only by the managing nurses.

31 °C and 34 °C Are Equivalent

There was a small numerical disadvantage for the lower temperature assignment, but none reached statistical significance. This was true of the primary outcome (48.4% vs. 45.4% for the higher temperature) and its components of mortality (43.5% vs. 41.0%) and poor neurologic outcome (4.9% vs. 4.4%). Poor neurologic outcome was defined as a Disability Rating Scale score of greater than 5.

Deaths were most common in the early part of the 180-day follow-up in both arms. On a Kaplan-Meier survival graph, Le May showed curves that he characterized as "almost superimposable."

There were no significant differences for any subgroup stratifications, such as age 75 years or older versus younger, males versus females, presence versus absence or an initial shockable rhythm, percutaneous coronary intervention (PCI) within 24 hours versus later, and STEMI versus non-STEMI. In these analyses, the higher temperature was associated with a potential trend for benefit among females and those with a shockable rhythm.

There was no signal for a difference in neurologic outcomes on the Disability Rating Scale or the Modified Rankin Scale. On the latter, for example, 46% of those in the 31 °C group and 44% of these in the 34 °C group had a score of four or greater at the end of follow-up.

The baseline characteristics of the two groups were similar. About 80% were male; the average age was roughly 62 years. More than 80% of the cardiac arrests were witnessed with CPR being administered by bystanders in nearly 70%. Nearly 40% had a STEMI.

Interventions were similar. Almost all patients underwent coronary angiography, of which nearly 60% received a percutaneous coronary intervention. More than 50% received a stent. The time from arrest to randomization was slightly longer in the 31 °C group (228 vs. 204 minutes). The time to balloon inflation from arrival at the cardiac center was also slightly longer (73 vs. 60 minutes).

There was a trend for an increased rate of seizures in the 31 °C group (12.5% vs. 7.1%; = .08), but other secondary outcomes, including pneumonia (67.8% vs. 63.4%), renal replacement therapy (9.2% vs. 9.3%), and stroke (4.4% vs. 1.6%), were similar in the 31 °C and 34 °C groups, respectively.

Bleeding, whether measured by transfusion (19.6% vs. 22.4%) or TIMI major bleed (23.4% vs. 19.7%) were similar in the 31 °C and 34 °C groups, respectively. Thrombosis, whether measured by stent thrombosis (1.2% vs. 2.2%) or deep venous thrombosis (11.4% vs. 10.9%) were similar in these two groups, respectively.

The length of stay in the cardiac intensive care unit was significantly greater in the 31 °C group (10 vs. 7 days; = .004). Some of this increased length of stay can be attributed to the longer rewarming process required for the greater cooling, according to Le May, but he acknowledged that it is not clear this provides a full explanation.

More Trials Like CAPITAL-CHILL Needed

The validity of these findings is supported by several strengths of the methodology, according to Jeanne E. Poole, MD, director of the arrhythmia service and electrophysiology laboratory, University of Washington, Seattle. This includes the reliance of an endovascular device, which can accelerate the time to the target temperature and assure the precision with which it is reached and maintained.

Poole did note that many of the primary and secondary measures, including the rates of stroke, seizures, and major bleeds, even though not significantly different, favored the higher temperature. The slightly longer door-to-balloon times might have been a factor. For the higher rate of pneumonia in the 31 °C group, she questioned whether the longer period of ventilation linked to a longer period of rewarming might have been a factor.

However, Poole praised the CAPITAL-CHILL trial for drawing attention to a group of patients for whom survival rates remain "dismally low." She indicated that these types of high-level trials are needed to look for strategies to improve outcomes.

Le May and Poole report no potential conflicts of interest.

American College of Cardiology (ACC) 2021 Scientific Session

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