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Heart rate and systolic time intervals in healthy newborn infants: longitudinal study
Insights
Heart rate significantly impacts neonatal systolic time intervals (STI), particularly the pre-ejection period to ejection time ratio (RPEP/RVET). High heart rates in newborns can mimic increased pulmonary vascular resistance, necessitating careful interpretation of these measurements.
Area of Science:
- Neonatal physiology
- Cardiovascular research
- Pediatric cardiology
Background:
- Systolic time intervals (STI) are crucial indicators of cardiac function.
- Understanding neonatal cardiovascular adaptation is vital for early diagnosis and management.
- Previous research on STI in neonates has established age-related changes.
Purpose of the Study:
- To investigate the influence of heart rate (HR) on systolic time intervals (STI) in healthy term newborn infants.
- To differentiate HR-related changes in STI from age-related changes.
- To assess the clinical implications of HR variations on STI interpretation in neonates.
Main Methods:
- Serial measurements of right ventricular (RVSTI) and left ventricular systolic time intervals (LVSTI) were performed on 30 healthy term neonates.
- Measurements were taken at multiple time points: 4-8 hours, 24-30 hours, 8 days, and 4 weeks of age.
- Right ventricular systolic time intervals (RVSTI) were specifically analyzed in relation to heart rate (HR) changes in a subset of infants.
Main Results:
- The pre-ejection period (RPEP) and left ventricular pre-ejection period (LPEP) significantly shortened with increasing age.
- Right ventricular ejection time (RVET) and left ventricular ejection time (LVET) were not significantly related to age.
- Increasing HR led to decreased RVET and increased RPEP/RVET ratio across all age groups, with a less pronounced effect at four weeks.
- Elevated RPEP/RVET values in neonates may be influenced by high HR and infant restlessness, potentially mimicking increased pulmonary vascular resistance.
Conclusions:
- Heart rate-related changes in neonatal RVSTI differ from those observed in older individuals.
- High heart rate and infant unrest can elevate the RPEP/RVET ratio, a finding that must be considered when assessing pulmonary vascular resistance in neonates.
- These findings highlight the importance of accounting for neonatal physiological states when interpreting cardiac function parameters.
Abstract:
To determine the influence of heart rate (HR) on systolic time intervals (STI) in neonates, serial measurements of right ventricular (RVSTI) and left ventricular systolic time intervals (LVSTI) were made on 30 healthy term newborn infants at age 4-8 h, 24-30 h, eight days, and four weeks. STI was related to HR and age. Age-related changes were similar to previously reported results. The preejection periods (RPEP and LPEP) significantly shortened with increasing age, whereas the right and left ventricular ejection times (RVET and LVET) were unrelated to age. RPEP was unrelated to HR, but tended to be prolonged in restless infants. With increasing HR, RVET decreased and RPEP/RVET increased in all age groups, but less at four weeks. A rise in HR of 50/min resulted in an increase of RPEP/RVET by 26% of the mean value at age 4-8 h and by 20% at four weeks. In 14 infants, RVSTI was recorded during a change in HR. In all these infants, RPEP and RPEP/RVET increased with increasing HR. We conclude that HR-related changes of RVSTI in neonates are different from those in older subjects. It should be considered that in neonates elevated values of RPEP/RVET, suggesting increased pulmonary vascular resistance, may be caused by high HR and unrest.