Electrocardiographic changes during therapeutic hypothermia

Induced mild therapeutic hypothermia (MTH) is an effective treatment to improve outcome after out-of-hospital resuscitation. Adverse events are rare, but arrhythmias and bleeding complications have been reported. So far, only few data about electrocardiographic changes and associated events have been reported.

Between 6/2005 and 3/2011, 109 comatose survivors of out-of-hospital cardiac arrest admitted to our institution underwent MTH. In an observational single-center study, we analyzed preclinical course, electrocardiographic changes, arrhythmias, laboratory parameters and complication rates before, during and after MTH.

MTH led to a significant decrease of heart rate (85.0±23.3 min(-1) at admission; 59.1±20.5 min(-1) during, p<0.01 and 63.1±19.2 after hypothermia p<0.05) a significant prolongation of PR (0.17±0.04 s before, 0.18±0.05 s during, p<0.05; and 0.17±0.04 s after hypothermia, p<0.01) and QTc intervals (0.47±0.05 s before, 0.49±0.05 s during, p<0.01; and 0.46±0.05 s after hypothermia, p<0.01). Two patients developed ventricular fibrillation during hypothermia, both had an acute myocardial infarction. No significant MTH related changes in electrolytes or coagulation parameters were observed. Major bleeding complications occurred in four cases (3.7%) with a trend towards more bleedings after use of preclinical thrombolysis (21.4% with to 6.4% without thrombolysis, p=0.057). We did not find increased risk for bleeding complications in patients with double platelet inhibition after PCI (14.3% compared to 9.5% without PCI, p=0.63) compared to those without PCI.

Under strict clinical and laboratory parameter control, induced mild therapeutic hypothermia can be applied to most patients after out-of-hospital cardiac arrest with no increased risk for arrhythmias despite significant electrocardiographic changes.