QT intervals compared in small and large hibernators and humans

Abstract

Small hibernating animals experience cycles of deep hypothermia followed by rewarming and feeding. This contrasts with bears, which remain in hibernation for four to seven months, experiencing large reductions in energy metabolism and heart rate, and small reductions in core temperature, and do not eat, drink, urinate, or defecate throughout. We measured the QT interval (QT) of the electrocardiogram (EKG) to determine whether the hearts of bears behave electrophysiologically more like classic hibernators or non-hibernators. We compared EKGs from grizzly and polar bears with small hibernators (marmots) and humans. Animal data were obtained using implanted radio capsules. EKGs of non-dormant marmots were characterized by a shortened QT (0.07–0.14 s); this held for grizzly and polar bears (0.14–0.23 s), but not for humans (0.39 s). Thus, the QT of bears resembles that of small hibernators. At the same heart rate, the QT of non-dormant bears and marmots differs in winter and summer.

Keywords:

• QT interval
• EKG
• cardiac electrophysiology
• hibernation

Acknowledgements

This research was partially supported by the Office of Naval Research under contract number N00014-75-C-0635, and by the Department of Molecular Physiology and Biophysics and the Department of Emergency Medicine of the University of Iowa College of Medicine. We also thank Dr. Max C. Brewer of the former Naval Arctic Research Laboratory for considerable assistance.