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

Aim To evaluate the definition and causes of neonatal bradycardias. Methods 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 ra...

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Bibliographic Details
Published in:Acta Paediatrica 2024-05, Vol.113 (5), p.973-979
Main Authors: Uusitalo, Asta, Tikkakoski, Antti, Lehtinen, Pieta, Ylänen, Kaisa, Poutanen, Tuija, Korhonen, Päivi H.
Format: Article
Language:English
Subjects:
Age
Bradycardia
Bradycardia - chemically induced
Cardiac arrhythmia
Family
Heart rate
Heart Rate - physiology
Holter
Humans
Infant, Newborn
Male
neonatal
Neonates
Retrospective Studies
Sex
Thyroxine
Thyroxine - therapeutic use
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Summary:Aim To evaluate the definition and causes of neonatal bradycardias. Methods 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. Results 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. Conclusion 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.
ISSN:0803-5253
1651-2227
1651-2227
DOI:10.1111/apa.17140