[Electrocardiographic studies of rabbits irradiated externally with various doses of ionizing radiation]

The investigations were carried out on rabbits irradiated with subletal (400R) and letal (800 and 1200R) doses of ionizing radiation. ECG was recorded prior to irradiation, 1 and 2hrs. after irradiation, and then every day at the same time for 10 days. The results of 312 electrocardiographic recordings and statistical analysis of some parameters are presented in graphs. They indicate that functional changes in the heart occur comparatively early after irradiation and are expressed by changes in the amplitude of the individual waves and by speeding-up of the rhythm of heart contractions and thus by shortening the duration of the individual waves, segments and intervals, the pacemaker rhythm being normal. No essential changes were found in cardiac vector deviation or in the configuration of the electrocardiographic curves. The intensity of these changes depended on the dosis of radiation and on the time which had elapsed since the moment of irradiation: in the rabbits which received 400R the changes were insignificant, and normal conditions returned after 24 hrs.; in those which received 800R the changes were more pronounced and the initial values returned after 8-10 days; with the dosis of 1200R the changes were the strongest and persisted until the death of the animal. The functional changes of the heart observed in the rabbits during 8-10 days were not permanent and had a compensative character, which indicates that the heart does not belong to the organs which are especially sensitive to radiation.