Abstract
Objective: Hibernator heart is known to be resistant to ventricular fibrillation (VF) during hypothermia. We aimed to determine the role of different electrophysiological mechanisms in VF vulnerability during hypothermia in hibernating and non-hibernating mammals. Methods: Conduction velocity (CV), action potential duration (APD) and its dispersion, and functional refractory period (FRP) were mapped in ventricles of Langendorff-perfused hearts of winter hibernating (WH, n=6) and summer active (SA, n=6) ground squirrels, and rabbits (n=6) at temperatures from +37°C to +3°C using optical mapping and electrical stimulation. Resalts: In all animals, the temperature reduction from 37°C to 17°C resulted in significant slowing of CV, increasing FRP, APD and its dispersion. However, at all temperatures ground squirrels had more uniform patterns of ventricular activation and repolarization as compared to rabbits: APD dispersion more significantly (p<0.01) increased in rabbits, than in ground squirrels. Hypothermia increased probability of pacing-induced VF in rabbit and SA hearts from 20% to 60% and 0% to 17%, respectively. No VF was induced in WH hearts at any temperature. Conclusion: Hibernating species Cittelus undulatus is protected against VF during hypothermia by maintaining wavelength, conduction anisotropy ratio and homogeneity of repolarization. (Support: Stanley and Lucy Lopata Endowment, RFFI 05-04-483112)
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