Should We Take Gestational Age Into Consideration When Assessing an ECG?

Abstract

Introduction: The electrocardiogram (ECG), a simple, low-cost test widely used in neonatal intensive care units, still has to have its normal range of parameters for the neonatal period defined, particularly regarding gestational age influence on ECG interpretation. Previous studies did not include echocardiographic evaluation of all participants, not ensuring anatomically normal hearts. This study compared ECG findings of term and late preterm (LPT) babies with proven normal hearts on echocardiogram. Methods: Thirty-two babies in their first seven days of life, with anatomically normal hearts on echocardiogram and normal in-hospital evolution, all born in a tertiary neonatal unit, were studied. Gestational age (GA) split them into two groups: Term [37­—41 6/7 weeks (n=16)]; and Late preterm (LPT) [34—36 6/7 weeks (n=16). Twelve-lead ECGs were performed and analyzed in all babies by a single not blinded investigator, assessing the parameters heart rate, frontal plane QRS axis, P wave amplitude, and P-R interval, Q, R, and S waves amplitudes, R/S ratio, QRS and T wave duration in all 12 leads. Comparison used unpaired T test and chi square test, p<0·05 considered significant. Findings: Our term population was similar to current parameters of normality: mean heart rate (122 vs 123bpm), QRS axis (134o vs 134o), PR interval (103 vs 110ms), QRS duration (49 vs 50ms), SV1+RV6 (21 vs 29mm). Compared to term, LPT babies had (mean±SD) significantly lower PR interval (103·8±15·0 vs 92·5±14·4s; p=0·0384), QRS duration in V2 (51·3±10·2 vs 41·3±5·0; p=0·015), and Q wave amplitude (3·40±2·2 vs 1·8±1·5; p=0·0247). Interpretation: The ECG of late preterm newborns differs from the term ECG, and gestational age should be considered for interpretation. Considering its low cost and easy performance, better knowledge of normal parameters of late preterm ECGs could be really useful in daily NICUs practice, especially in secondary units and in developing countries. Funding Statement: This research project received no funding for its conduction. Declaration of Interests: The authors have no financial relationships and have no conflicts of interest relevant to this article to disclose. Ethics Approval Statement: The research project was approved by the Institutional Ethics Review Board of Hospital das Clinicas–FMUSP under #14.742, SDC/COP/059/17. The Ethics Commission waived the need for a patient’s Consent Form since the electrocardiogram and echocardiogram examinations are routine at the neonatal unit.