Postnatal evolution of electrocardiographic parameters in preterm infants: a prospective longitudinal cohort study

Electrocardiography (ECG), an indispensable bedside tool in neonatal intensive care, complements echocardiography by providing assessment of cardiac rhythm and conduction, and when advanced imaging is unavailable, serves as a screening tool. Preterm birth alters cardiac and autonomic maturation. Applying term-based ECG norms may misclassify physiological findings in preterm. We aimed to characterise serial ECG maturation in preterms from birth to term-equivalent age and define gestational- and postnatal-age-specific patterns relevant to clinical interpretation. In this prospective cohort, infants between 28⁰/₇ and 36⁶/₇ weeks' gestation without congenital heart disease underwent serial 11-lead ECG recording within 24 h of birth, on day 7, day 28 and at term-equivalent age. Postnatal and gestation-based differences in ECG parameters were analysed and centile charts were generated. Among 249 infants (mean gestation-33⁴/₇ weeks), 213 completed follow-up until term-equivalent age. ECG parameters demonstrated consistent maturation across time points. The mean QRS axis shifted leftward from 117° at birth to 82° at term-equivalent age (p < 0.001). PR-interval, QRS and P-wave duration remained stable across all time points. Mean QTc showed minimal overall change. Transient QTc prolongation occurred in 8.1% of infants and resolved by term-equivalent age. Right precordial R-wave amplitudes declined over time, whereas left precordial amplitudes increased. At term-equivalent age, very preterm infants exhibited a more leftward QRS axis compared with late preterm infants. Infants with bronchopulmonary dysplasia showed trends toward right ventricular dominance.

Preterm ECG findings are dynamic, gestation-dependent markers of cardiovascular transition. This study characterises longitudinal ECG maturation in preterms and provides reference values, supporting improved decision-making in preterm care.

• Electrocardiographic reference nomograms used in neonatal practice are primarily based on paediatric cohorts or cross-sectional studies of term infants. These references provide limited information on longitudinal electrophysiologic maturation in preterm neonates.

• In a cohort of 249 preterm infants, serial ECG measurements demonstrated changes in axes, QTc, and precordial voltages from birth to term-equivalent age. • These gestation and age-specific trajectories support cautious interpretation of preterm ECGs using term-derived standards.