[Changes of the heart conduction system after exposure to fluorouracil]

Using 20 male rats the electron microscopic study of conducting system of the heart was performed to assess the effect of fluorouracil--an antineoplastic drug belonging to antimetabolite group. A daily dose of 15 mg/kg of fluorouracil was injected intraperitoneally for 5 days; three courses of injections with the intervals of three weeks were performed. Toxic effect of fluorouracil is demonstrated after the first course of injections and is revealed as a predominant injury of pacemaker cells in sinoatrial and atrioventricular nodes. Latent pacemaker myocytes and Purkinje fibers undergo "calcium injury" during the second and the third courses of fluorouracil injections. The irreversible damage of contractile and specialized myocytes results in fibrosis which develops predominantly in the areas of atrioventricular bundle and its branches.