Comparison of QT intervals in small and large hibernators and non‐hibernators

During winter months, small hibernating animals experience many physiological cycles of deep hypothermia followed by rewarming and feeding. This is in sharp contrast to bears, which remain in winter dens for 4 to 7 months, experience a large reduction in heart rate, a small reduction in core temperature, move very little, and forgo food, water, urination, and defecation throughout hibernation. Here we consider the QT segment of the electrocardiogram (EKG) as a taxonomic clue to determine whether the electrophysiological behavior of the hearts of bears is more like non‐hibernators, such as humans, or more like the classic small animal hibernators. This was accomplished by comparing the EKGs of typical small hibernators, woodchucks (Marmota monax), with the EKGs of two species of bears—grizzly (Ursus arctos) and polar (Ursus maritimus)—and comparing both with humans. Animal data was obtained during various seasons and activity levels using implanted radio capsules. The EKG of non‐dormant small hibernators is characterized by a shortened QT interval; similarly, our grizzly and polar bears also showed a shortened QT interval (bears: 0.14–0.23 sec, marmota: 0.07–0.14 sec, as compared to humans: 0.39 sec). An additional finding of interest is that even when controlled for rate, the QT interval of both bears and smaller hibernators, when non‐dormant, is different in winter and summer. Supported by ONR and NSF.