The Evolution of the Neonatal QRS Axis during the First Four Weeks of Life

Abstract

Background: The QRS axis represents the sum and orientation of the ventricular depolarization. Accurate interpretation of abnormalities in the QRS axis may facilitate early diagnosis of heart disease in newborns. We aimed at describing the evolution of the QRS axis during the first 4 weeks of life and provide reference values from healthy newborns. Methods: The Copenhagen Baby Heart Study is a prospective general population study that offered cardiac evaluation during the first month of life to all newborns delivered in the Copenhagen area. Results: Electrocardiograms from 12,317 newborns (52% boys; mean age 12 days) with normal echocardiograms were included. The median QRS axis was 119° at the ages 0–7 days and shifted leftward to 102° at the ages 22–28 days (p < 0.001). We found that girls had a significantly less pronounced right-shifted axis than boys (p < 0.001) and that increasing gestational age (GA) was associated with a more pronounced right-shifted axis (p < 0.05). Infant size did not affect the axis (p > 0.05). Only 0.5% had an axis within the interval 0 to −90° and 1.1% in the interval +240 to +30°. Conclusions: The QRS axis showed a gradual leftward-shift during the first 4 weeks of life and was affected by sex and GA but unaffected by infant size. Less than 1% of the newborns had a QRS axis between 0 and −90°. This study represents updated reference values, which may facilitate the clinical handling of newborns.

The Impact of Maternal and Perinatal Factors on the Neonatal Electrocardiogram

“…Rapid changes occur in the cardiac conduction system within the neonatal phase [16,17]. In accordance with previously described association between the QRS axis and postnatal age [16], neonates exposed to multiple maternal/perinatal factors showed a higher postnatal age and a more left-shifted QRS axis.…”

“…Rapid changes occur in the cardiac conduction system within the neonatal phase [16,17]. In accordance with previously described association between the QRS axis and postnatal age [16], neonates exposed to multiple maternal/perinatal factors showed a higher postnatal age and a more left-shifted QRS axis. Furthermore, when interpreting QT interval prolongation in neonates examined within first week of life it is important to take into account the high variability of the QT interval within this time period [17].…”

“…Our results suggest a relatively lower right ventricular dominance and QT interval prolongation, with the greatest cumulative effect within the first week of life, in neonates exposed to multiple maternal/perinatal factors. However, these differences are as expected – in the context of a predominantly healthy study cohort – within normal reference ranges [13‒17].…”

“…Our results suggest a relatively lower right ventricular dominance and QT interval prolongation, with the greatest cumulative effect within the first week of life, in neonates exposed to multiple maternal/perinatal factors. However, these differences are as expectedin the context of a predominantly healthy study cohortwithin normal reference ranges [13][14][15][16][17]. Perinatal asphyxia represents a spectrum of clinical presentations and cardiac involvement has been reported in approximately 30% of severe cases [9,18]; clinical findings may include cyanosis, respiratory distress, decreased cardiac output, arrhythmias, hypotension, and ECG abnormalities [9,18].…”

The Impact of Maternal Age on the Neonatal Electrocardiogram

“…Precordial amplitudes and the QRS axis evolve during the first month of life [13, 14], but our findings persisted when subdividing the newborns after age at inclusion. Furthermore, differences between the maternal age groups in newborn, pregnancy, and other maternal characteristics could also confound the results [2, 3, 5, 7, 15‒18], as, e.g., GA has an established association with the QRS axis [14]. Our multivariate regression analysis with adjustment for multiple factors showed that the effect of maternal age on the QRS axis and R-V1 remained significant suggesting a direct effect of maternal age on these two parameters.…”