A recent study by Dr. Khan and his colleagues, published in the American Heart Journal, has shown that the application of post-resuscitation targeted temperature management (TTM) or hypothermia protocol was associated with increased mortality in patients with non-shockable associated sudden cardiac arrest (SCA). Additionally, TTM utilization was recognized as an independent predictor of mortality in this specific group after multivariate regression analysis.
Post-resuscitative hypothermia protocol also known as TTM has been associated with significant improvement in neurologically intact survival of sudden cardiac arrest (SCA) patients in whom, SCA was a result of shockable rhythm. However, the application of this protocol in patients with SCA due to non-shockable rhythms has shown conflicting data. The most recent trial (HYPERION trial) on 514 patients with non-shockable rhythm associated SCA showed some benefits of TTM application, however, the overall mortality was not different among those undergoing this protocol versus those without this treatment. Given the high prevalence of non-shockable rhythm in SCA patients, it seems reasonable to study the outcomes and effects of hypothermia management in this population.
A retrospective population-based cohort study was done from January 2006 to December 2013 using the National Inpatient Sample (NIS) data. A total of 1,185,479 CA patients due to non-shockable rhythm were included in the study using the International Classification of Diseases, 9th Revision, Clinical Modification (ICD-9-CM) codes. Patients characteristics and hospital outcomes, as well as TTM trend utilization, were assessed. Among study participants, 11,657 patients received TTM treatment. Patients receiving TTM tend to be younger, male, and white Americans. Mortality was higher in those receiving TTM treatment compared to those who did not receive this protocol (73.5% versus 69%). The result remained the same even after propensity-matched analysis (72.9% vs. 68.7%, p < 0.01). TTM treatment was also associated with significantly higher mortality in out-of-hospital non-shockable SCA (72.4% vs. 62.6%, p < 0.01) while no difference in mortality was observed in-hospital SCA patients with non-shockable rhythm who received TTM (75.3% vs. 75.3%, p = 0.97).
Current American Heart Association (AHA) guidelines recommended class I indication for the application of TTM in SCA patients due to non-shockable rhythm, which is based on previous observational studies done in this era. Also, the data from the previous trial (HYPERION) have shown promising results regarding TTM utilization in this population of patients. In contrast, this national cohort demonstrated that TTM utilization increased the mortality among SCA patients due to non-shockable rhythm. Also, this study showed an underutilization of TTM among the female population with SCA due to non-shockable rhythm that may provide evidence for gender-based disparities in caring for post-SCA patients.
There are some limitations to consider when interpreting the results of this study. First, NIS collects data of the same patients as an independent event, and patients are not followed longitudinally. Therefore, long-term outcomes of the patients are subject to errors. Second, some of the patient’s outcomes such as neurological status after the discharge could not be obtained using this dataset. Also, detailed data on the TTM protocol and its methodology is not recorded in this database. Despite all these limitations, if confirmed in a large randomized trial, the result of this study may have important clinical implications in medical practice.