Monophasic action potentials during induced hypothermia in hedgehog and guinea pig hearts

To evaluate mechanisms behind the difference in susceptibility to ventricular fibrillation (VF) between the guinea pig and hedgehog heart, the cardiac electrophysiology of the two species was studied at normal body temperature and at different hypothermic levels by simultaneous recording of the monophasic action potential (MAP) and the external electrocardiogram (ECG). At normal body temperature, the duration of the ventricular MAP was significantly shorter in the hedgehog (93 +/- 8.1 ms) than in the guinea pig (138 +/- 2.6 ms). There was a distinct plateau phase in the guinea pig, whereas no such phase could be detected in the hedgehog. During hypothermia, a similar increase in MAP duration at full repolarization was noticed for both species. However, the prolongation of the MAP at lower repolarization levels was much less in the hedgehog. Besides, hypothermia-induced slow conduction and dispersion of ventricular repolarization was much more apparent in the guinea pig heart compared with the hedgehog heart. These differences may be important factors in the resistance to VF in the hedgehog, at normal body temperature and during hypothermia.