ECG Abnormalities Induced By Scorpion Venom Administration: The Effect And The Mechanism
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Intramuscular administration of scorpion (Leiurus quinquestriatus) lyophilized venom (100, 200 and 400 mg/kg) into rats produced drastic changes in the electrical activity of the cardiac muscle. These abnormalities were most significant after the injection of higher doses (200 and 400 mg/kg). Most of the ECG changes recorded in this study were in rhythmicity and conductivity. The changes in rhythmicity were in the form of sinus abnormalities and ectopic beats, while the toxic effects on the conduction system were recorded as varying degrees of heart block. Propranolol (an antiarrhythmic drug) was injected into another group of animals (1 mg/kg, i.p.) 20 min. prior to venom administration (400 mg/kg) to get a clear evidence about the role of catecholamines in producing such abnormalities. To study further the mechanism of the cardiotoxic effect of the venom, another technique was performed to examine the histopathological effects of the venom on the cardiac muscle. The results of this study revealed that the venom had a drastic effect on the electrophysiological responses of the cardiac muscle due to their exposure to an excessive venom-dependent released catecholamines. At the same time, the venom and its components have a direct histopathological effect on the heart in addition to their sympathomimetic action. On the other hand, propranolol pretreatment abolishes these abnormalities to a great extent. It is important to emphasize also, that the direct histopathological effect of this poison may affect the specialized fibers forming the conduction system of the heart and thereby induce the fatal recorded heart blocks.