A correlation between the structure of myocardial cells and prolonged Q-T interval in young rats.

In the present study, we examined the electrocardiogram and the structure of myocardial cells in young rats at different postnatal ages. The offspring of rats were sacrificed on different postnatal days following electrocardiographical recordings, and sections of their hearts were examined microscopically. In a number of newborns, we observed definite prolongation of the Q-T interval in the electrocardiogram on the first day of life. Normal shortening of the Q-T interval with age was demonstrated in the majority of the offspring while, in some of them, the Q-T interval remained prolonged. In the "affected" offspring, which exhibit a typical pattern of Q-T prolongation with clear ST segment, definite retardation of histological differentiation of the myocardium was found at various ages. In these cases, there were large numbers of "myoblasts" scattered between normal myocytes in different parts of the ventricular walls and septum. These myoblasts were rarely identified in newborns and offspring with a normal Q-T interval. Our results clearly show a correlation between the ratio of persistence of undifferentiated myoblasts at any age and the typical prolonged Q-T pattern in the electrocardiogram (r = 0.9). Due to the possible clinical significance, the hearts of patients with prolonged Q-T syndrome should be examined so as to reach for abnormal differentiation of the myocytes.