Remember hyppthermia slows everything down ! Depolarization and repolarization of the heart also slows down in hypothermia, therefore explaining a lot of ECG changes.
IGURE 1 | Temporal correlation between action potential duration and the QT interval on the surface ECG.
FROM THE FOLLOWING ARTICLE:
The impact of drug-induced QT interval prolongation on drug discovery and development
Bernard Fermini & Anthony A. Fossa
Nature Reviews Drug Discovery 2, 439-447 (June 2003)
Mild hypothermia (32-35 celcius)
- Prolongation of all intervals (PR, RR and QT)
- Sinus bradycardia, varying degrees of AV block, idioventricular junctional rhythm
Moderate hypothermia (30-32 celcius)
- Osbourne wave becomes apparent
- Due to bradycardia, ectopic atrial foci start to discharge, eventually leading to Atrial Fibrillation with slow ventricular response.
Severe hypothermia (<30 celcius)
- Progressive QRS widening can predispose to Ventricular fibrillation.