Moderate but not severe hypothermia causes pro-arrhythmic changes in cardiac electrophysiology

Dietrichs, E. S., McGlynn, K., Allan, A., Connolly, A., Bishop, M., Burton, F., Kettlewell, S., Myles, R. , Tveita, T. and Smith, G. L. (2020) Moderate but not severe hypothermia causes pro-arrhythmic changes in cardiac electrophysiology. Cardiovascular Research, 116(13), pp. 2081-2090. (doi: 10.1093/cvr/cvz309) (PMID:32031595) (PMCID:PMC7584464)

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Aims: Treatment of arrhythmias evoked by hypothermia/rewarming remains challenging, and the underlying mechanisms are unclear. This in vitro experimental study assessed cardiac electrophysiology in isolated rabbit hearts at temperatures occurring in therapeutic and accidental hypothermia. Methods and results: Detailed ECG, surface electrogram, and panoramic optical mapping were performed in isolated rabbit hearts cooled to moderate (31°C) and severe (17°C) hypothermia. Ventricular activation was unchanged at 31°C while action potential duration (APD) was significantly prolonged (176.9 ± 4.2 ms vs. 241.0 ± 2.9 ms, P < 0.05), as was ventricular repolarization. At 17°C, there were proportionally similar delays in both activation and repolarization. These changes were reflected in the QRS and QT intervals of ECG recordings. Ventricular fibrillation threshold was significantly reduced at 31°C (16.3 ± 3.1 vs. 35 ± 3.5 mA, P < 0.05) but increased at 17°C (64.2 ± 9.9, P < 0.05). At 31°C, transverse conduction was relatively unchanged by cooling compared to longitudinal conduction, but at 17°C both transverse and longitudinal conduction were proportionately reduced to a similar extent. The gap junction uncoupler heptanol had a larger relative effect on transverse than longitudinal conduction and was able to restore the transverse/longitudinal conduction ratio, returning ventricular fibrillation threshold to baseline values (16.3 ± 3.1 vs. 36.3 ± 4.3 mA, P < 0.05) at 31°C. Rewarming to 37°C restored the majority of the electrophysiological parameters. Conclusions: Moderate hypothermia does not significantly change ventricular conduction time but prolongs repolarization and is pro-arrhythmic. Further cooling to severe hypothermia causes parallel changes in ventricular activation and repolarization, changes which are anti-arrhythmic. Therefore, relative changes in QRS and QT intervals (QR/QTc) emerge as an ECG-biomarker of pro-arrhythmic activity. Risk for ventricular fibrillation appears to be linked to the relatively low temperature sensitivity of ventricular transmural conduction, a conclusion supported by the anti-arrhythmic effect of heptanol at 31°C.

Item Type:Articles
Additional Information:This work was supported by a British Heart Foundation PhD scholarship [18909-01 to KMc] and a grant from the Northern Norwegian Health Authority [HNF1337-17 to ESD].
Glasgow Author(s) Enlighten ID:Smith, Professor Godfrey and Myles, Dr Rachel and Mcglynn, Miss Karen and Kettlewell, Dr Sarah and Burton, Dr Francis and Allan, Mr Andrew and Dietrichs, Mr Erik
Authors: Dietrichs, E. S., McGlynn, K., Allan, A., Connolly, A., Bishop, M., Burton, F., Kettlewell, S., Myles, R., Tveita, T., and Smith, G. L.
College/School:College of Medical Veterinary and Life Sciences > School of Cardiovascular & Metabolic Health
Journal Name:Cardiovascular Research
Publisher:Oxford University Press
ISSN (Online):1755-3245
Published Online:07 February 2020
Copyright Holders:Copyright © 2020 The Authors
First Published:First published in Cardiovascular Research 116(13): 2081-2090
Publisher Policy:Reproduced under a Creative Commons Licence

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
164725BHF 4 Year PhD Programme. 2nd Intake 2010 : Students C Livie A Allan A Campbell & C FattahAnna DominiczakBritish Heart Foundation (BHF)FS/10/50/28676Institute of Cardiovascular & Medical Sciences
165617BHF 4 Year PhD Programme FS/11/79/29329Anna DominiczakBritish Heart Foundation (BHF)FS/11/79/29329Institute of Cardiovascular & Medical Sciences