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Cardiac conduction and resistance to ventricular fibrillation in Siberian hibernator ground squirrel Citellus undulatus

, : Cardiac conduction and resistance to ventricular fibrillation in Siberian hibernator ground squirrel Citellus undulatus. Biological Papers of the University of Alaska, 27: 543-555

Most nonhibernating mammals experience cardiac arrest during hypothermia (15-27deg. C) due to ventricular fibrillation (VF) or full conduction block. In contrast, hibernators maintain cardiac output even at -2deg. C to +8deg. C. Our goal was to assess safety of conduction in the hibernator heart during extreme hypothermia. We imaged electrical conduction in intact isolated hearts of summer active (n = 5) and winter hibernating (n = 4) ground squirrels Citellus undulatus from Siberia at different temperatures varying from +37deg. C to +2deg. C. Electrical activity was mapped during normal sinus rhythm and ventricular pacing using CCD camera (500 frames/sec) and voltage-sensitive dye di-4-ANEPPS. No spontaneous VF was observed in all nine hearts at any temperature. Hearts were able to maintain spontaneous sinus rhythm and normal pattern of epicardial excitation throughout the whole range of studied temperatures. Despite responsiveness to pacing in all hearts, the ventricular conduction velocity was significantly reduced at low temperatures 2-7deg. C from 80 plus or minus 4 cm/sec to 11 plus or minus 1 cm/sec. Our data provides the first direct demonstration that the isolated heart of the ground squirrel Citellus undulatus developed ability to maintain normal excitation pattern and protection against spontaneous hypothermia-induced VF in a range of temperatures from +37deg. C to +2deg. C.


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