Heart rate in newborns is associated with age, sex and maternal levothyroxine therapy.

To evaluate the definition and causes of neonatal bradycardias. This retrospective study included 135 term-born newborns referred for 24-hour Holter monitoring due to bradycardia. Bradycardia was defined as either a heart rate below 80 beats per minute (standard definition) or a heart rate below our recently published age-specific reference values for neonatal heart rate. The mean (SD) age was 6.1 (1.3) days. With standard definition, 107 newborns (79%) had bradycardia, whereas only 20 (15%) had a minimum heart rate lower than the age-specific reference. Younger newborns had lower heart rates. Each day increased the minimum, mean and maximum heart rate by 1.8 (95% CI: 1.0, 2.6), 4.2 (95% CI: 3.0, 5.3) and 2.1 beats per minute (95% CI: 0.3, 3.8), respectively. Male sex and maternal levothyroxine medication were negatively associated with the mean and maximum heart rate. None of the newborns had a cardiac cause for low heart rate. Among term newborns with bradycardias, younger age, male sex and maternal levothyroxine medication were associated with a lower heart rate on Holter monitoring. Given the age-related increase in heart rate, the 80 beats per minute limit as a universal threshold for abnormal heart rate in newborns appears inappropriate. © 2024 The Authors. Acta Paediatrica published by John Wiley & Sons Ltd on behalf of Foundation Acta Paediatrica.

Citation

Asta Uusitalo, Antti Tikkakoski, Pieta Lehtinen, Kaisa Ylänen, Tuija Poutanen, Päivi H Korhonen. Heart rate in newborns is associated with age, sex and maternal levothyroxine therapy. Acta paediatrica (Oslo, Norway : 1992). 2024 May;113(5):973-979

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PMID: 38305638

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