Key result
Moderate hypothermia reduces VF threshold by ~53% vs normothermic baseline.
Why the study?
Treatment of arrhythmias evoked by hypothermia/rewarming remains challenging, and the underlying electrophysiological mechanisms are unclear.
Does moderate and severe hypothermia cause pro-arrhythmic electrophysiological changes in isolated rabbit hearts?
Does moderate and severe hypothermia cause pro-arrhythmic electrophysiological changes in isolated rabbit hearts?
Moderate hypothermia creates a pro-arrhythmic substrate by prolonging repolarization without altering transverse conduction, whereas severe hypothermia is anti-arrhythmic due to parallel delays in both.
Answers are grounded in this paper and cite their sources.
Moderate hypothermia may increase arrhythmia risk in this model; leaves open translation to in vivo or clinical settings.
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.
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Dietrichs et al. (2020) studied Hypothermia (n=36). Moderate (31°C) and severe (17°C) hypothermia vs. Normothermic (37°C) baseline was evaluated on Ventricular fibrillation threshold (p=<0.05). Moderate hypothermia (31°C) significantly reduced the ventricular fibrillation threshold to 16.3 mA compared to a 37°C baseline of 35.0 mA, indicating a pro-arrhythmic state.
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