Heart rate pattern during sleep in an infant with congenital prolongation of the Q-T interval (Romano-Ward syndrome).

Heart rate and the variability of the heart rate, indices of autonomic control, were studied during sleep in an infant with prolonged Q-T interval (Romano-Ward syndrome) and were compared to the heart rate and variability of heart rate in 18 normal infants studied at monthly intervals during the first four months of life. The overall variability and beat-to-beat variability in the infant with Romano-Ward syndrome were significantly below the median in the normal infants at each age and sleep state. This decrease in overall and beat-to-beat variability persisted after normalization by the absolute heart rate; however, the heart rate in the infant with Romano-Ward syndrome was not different from those in normal infants. These data suggest that the presence of a normal heart rate does not exclude abnormal autonomic activity; and in certain clinical situations, the variability of heart rate may be a more sensitive index of abnormal autonomic function than the heart rate itself.