Therapeutic hypothermia-induced electrocardiographic changes and relations to in-hospital mortality

Therapeutic hypothermia improves survival for selected patients who remain comatose after cardiac arrest. Hypothermia triggers changes in electrocardiographic (ECG) parameters; however, the association of these changes to in-hospital mortality remains unclear.

QT interval changes induced by therapeutic hypothermia are not associated with in-hospital mortality.

We retrospectively compared precooling ECG parameters to ECG parameters during hypothermia on all consecutive patients with available information who received hypothermia at our academic medical center between December 2006 and July 2012 (N = 101; 24% women). Paired 2-sample t test was used to compare precooling vs cooling ECG parameters. In-hospital mortality related to ECG parameter changes was compared using the Pearson χ(2) test.

Therapeutic hypothermia resulted in increases in PR and QTc intervals and decreases in heart rate and QRS intervals (P for all <0.02). During hospitalization, 45 of the 101 patients died. Survivors vs nonsurvivors did not differ in heart rate change (P = 0.74), PR change (P = 0.57), QRS change (P = 0.09), or QTc change (P = 0.67). Comparing patients who had reduced QTc intervals with hypothermia to those who had prolonged QTc with hypothermia, 14 out of 30 died in the former group, whereas 31 out of 71 died in the latter group (46.7% vs 43.7%, odds ratio [OR]: 1.13, 95% CI: 0.48-2.66). Patients presenting with right bundle branch block (RBBB) had a higher risk of in-hospital death compared to those without RBBB (72.2% vs 38.6%, OR: 4.14, 95% CI: 1.35-12.73).

Therapeutic hypothermia prolonged QTc interval with no association to in-hospital mortality. Presence of RBBB on initial presentation was related to increased mortality.