Pediatric Cardiology

, Volume 15, Issue 6, pp 268–274 | Cite as

Adjustment of cardiac repolarization to changing cycle length in healthy infants

  • O. Robert Levine
Original Articles


This study describes the relation of cardiac repolarization (QT interval) to a changing heart rate (RR interval) in healthy infants, utilizing abbreviated electrocardiographic (ECG) recordings. A total of 105 limb lead ECG recordings were made in 53 infants of postconceptional age 30 to 52 weeks over a 5- to 15-minute period in order to obtain a heart rate variation of at least 20%. The QT and preceding RR intervals were measured during one cycle from each 3 second ECG segment (minimum 40 cycles) and the log QT-log RR relation was examined by linear regression statistics. Average RR was 387 ms (SD 42) and the average log QT/log RR slope 0.39 (SD 0.16). The slope correlated negatively with RR and was unassociated with age or sex. In 7 of the infants a single recording showed a QT-RR regression that failed to meet the 5% level of significance; 6 of these infants had additional tracings with a significant regression. When the log QT-log RR regression was studied in 20 continuous rhythm strips with spontaneous rate variation, the analysis of 9–32 consecutive cycles yielded an average slope of 0.13 (SD 0.07); in more than one-half of these strips the QT-RR relation in brief ECG recordings varies substantially in normal is concluded that: (1) the QT-RR relation in brief ECG recordings varies substantially in normal infants; (2) a substantial part of this variation may be due to nonrandomization of measurement error and to a statistical requirement for larger sample size when the slope calculation is based on measurement of fewer than 40 cycles; (3) normal infants occasionally manifest absence of QT adjustment to a changing RR; and (4) the adjustment of QT to a changing RR is not immediate, so consecutive cycle sampling during short periods of changing heart rate frequently fails to demonstrate a tracking of QT with RR.

Key Words

Cardiac repolarization QT-RR slope Sudden infant death syndrome 


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Copyright information

© Springer-Verlag New York Inc. 1994

Authors and Affiliations

  • O. Robert Levine
    • 1
  1. 1.New Jersey Medical School, Department of PediatricsUniversity of Medicine and Dentistry of New JerseyNewarkUSA

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