Arrhythmogenicity of hypothermia - a large animal model of hypothermia.
BACKGROUND
Therapeutic hypothermia (TH) is used to mitigate cerebral injury after an out of hospital cardiac arrest. There is a perceived risk of increased arrhythmias with temperatures lower than the current target of 32-34°C for TH. This study sought to develop and investigate the electrophysiological changes in a sheep model of systemic hypothermia regarding the susceptibility to ventricular arrhythmias.


METHODS
Ten sheep underwent systemic hypothermia using a venous-venous extra-corporeal circuit whilst instrumented with a 12 lead ECG. An epicardial sock recorded potentials to 30°C (N=10) or 26°C (N=6). Activation times (AT) and Activation Recovery Intervals (ARI) were calculated using custom software.


RESULTS
The AT and ARI were significantly prolonged with increased heterogeneity during hypothermia. This effect was most pronounced between normothermia and 34°C during sinus rhythm (SR). For ventricular pacing (VP) however heterogeneity continued to increase with progressive hypothermia.


CONCLUSIONS
Hypothermia causes a significant increase in the heterogeneity of depolarisation and repolarisation. There is evidence to suggest that SR is protective with most of the increase in heterogeneity occurring with cooling to 34°C. This raises the possibility that the current target temperatures for therapeutic hypothermia may be safely lowered to provide a gain in cerebral protection.
Cardiac Technology Centre, Kolling Institute of Medical Research, University of Sydney, Royal North Shore Hospital, St Leonards, NSW 2065, Australia; Faculty of Medicine, Royal Hobart Hospital Clinical School, University of Tasmania, Hobart, Tasmania 7000, Australia. Electronic address: levi.bassin@gmail.com.
Levi
L
Bassin
Faculty of Medicine, Royal Hobart Hospital Clinical School, University of Tasmania, Hobart, Tasmania 7000, Australia.
Ah Chot
AC
Yong
Faculty of Medicine, Royal Hobart Hospital Clinical School, University of Tasmania, Hobart, Tasmania 7000, Australia.
David
D
Kilpatrick
Cardiac Technology Centre, Kolling Institute of Medical Research, University of Sydney, Royal North Shore Hospital, St Leonards, NSW 2065, Australia.
Stephen Nicholas
SN
Hunyor
D000818:Animals; D001145:Arrhythmias, Cardiac / Q000209:etiology / Q000503:physiopathology; D004195:Disease Models, Animal; D004562:Electrocardiography; D006323:Heart Arrest / Q000209:etiology / Q000503:physiopathology; D007036:Hypothermia, Induced / Q000009:adverse effects*; D012756:Sheep
Cardiac arrhythmias; Cardiac electrophysiology; Hypothermia; Therapeutic hypothermia