Lindberg Lucas Alexander, Fuchs Boris, Evans Alina Lynn, Laske Timothy, Björkenheim Anna, Fröbert Ole, Gottlieb Lisa Amalie
Department of Biomedical Sciences, University of Copenhagen, Copenhagen, Denmark.
Department of Forestry and Wildlife Management, Faculty of Applied Ecology and Biotechnology, Inland Norway University of Applied Sciences, Koppang, Norway.
Physiol Rep. 2025 Sep;13(17):e70531. doi: 10.14814/phy2.70531.
In humans, hypothermia prolongs ventricular repolarization and associates with sustained ventricular tachyarrhythmias. In bears, body temperature drops during hibernation similar to moderate human hypothermia, yet they rarely face fatal outcomes during the winter. This suggests protective adaptations in bear electrophysiology. We studied seasonality in ursine ventricular repolarization by analyzing >1 year electrocardiogram (ECG) recordings from loop recorders implanted in 57 free-ranging Eurasian brown bears. In sinus rhythm, bears exhibited significantly longer RR, QT, and T-T intervals (2441 ± 470, 508 ± 50, and 53 ± 8 ms, respectively) during hibernation than in the active period (649 ± 323, 232 ± 39, and 29 ± 5 ms, respectively). Optimal heart rate correction of QT interval (QT/RR) demonstrated significant prolongation during hibernation. QT and T-T intervals remained longer during hibernation than in the active period, even when comparing ECGs with similar RR intervals in the two periods. Ventricular fibrillation occurred in four bears shot during licensed hunting in summer, which led to death. In conclusion, seasonal variations in ventricular repolarization in bears appear, at least partially, independently of heart rate. Compared to humans, ventricular repolarization is slower but more homogeneous. These findings, combined with the absence of fatalities during hibernation, support the theory of protective electrophysiological adaptations in bears. Insights into the underlying mechanisms have biomimetic potential for human therapy.
在人类中，体温过低会延长心室复极时间，并与持续性室性快速心律失常相关。在熊类中，冬眠期间体温下降，类似于人类的中度体温过低，但它们在冬季很少面临致命后果。这表明熊的电生理存在保护性适应机制。我们通过分析植入57只自由放养的欧亚棕熊体内的环形记录仪超过1年的心电图（ECG）记录，研究了熊类心室复极的季节性变化。在窦性心律下，熊在冬眠期间的RR、QT和T - T间期（分别为2441±470、508±50和53±8毫秒）显著长于活跃期（分别为649±323、232±39和29±5毫秒）。QT间期的最佳心率校正值（QT/RR）在冬眠期间显著延长。即使比较两个时期RR间期相似的心电图，QT和T - T间期在冬眠期间仍长于活跃期。在夏季合法狩猎中被射杀的4只熊发生了心室颤动，导致死亡。总之，熊类心室复极的季节性变化似乎至少部分独立于心率。与人类相比，心室复极较慢但更均匀。这些发现，再加上冬眠期间没有死亡情况，支持了熊类存在保护性电生理适应的理论。对潜在机制的深入了解具有用于人类治疗的仿生潜力。
