Heart rate dependence of the RT interval in the first month of life.

Computer analysis of more than 100 000 RT and RR intervals obtained from 70 babies spanning the age range 2-75 d indicates that the RR-RT relation cannot be characterised by any general formula during the first month of life. The babies included 22 sudden infant death syndrome (SIDS), 22 matched controls and 26 normal infants. RT intervals were corrected for RR variation for each baby using linear regression analysis. The corrected RT interval was observed to increase sharply during the first month of life for each group of babies. The similarity in the results for all three groups suggest that an investigation of the RT interval will contribute very little, if anything, to a SIDS investigation.