P2A099: Significance of Northwest Axis on Neonatal Electrocardiograms

Background: In infants with findings that may suggest congenital heart disease (CHD), such as a murmur or cyanosis, an electrocardiogram (ECG) is often obtained as a screening tool to determine the need for further cardiac evaluation. The QRS axis on ECG represents the mean vector of forces generated by ventricular depolarization. A normal QRS axis for a newborn is approximately +90o to +180o. Northwest axis (NWA) on ECG is conventionally thought to be associated with CHD, though there is a paucity of data regarding the types and incidence of CHD that may be associated with this finding. The purpose of our study is to evaluate the incidence of CHD among patients with NWA on ECG who also received an echocardiogram.

Methods: This is a retrospective, single-center study of infants ≤ 60 days of age who had NWA (QRS axis +180o to +270o) on a first-time ECG and an echocardiogram performed between January 1, 2015 and December 31, 2021 at The Children’s Hospital at Montefiore. Data regarding age, sex, degree of axis deviation, reason for ordering the ECG, oxygen saturation, the presence of a heart murmur, and echocardiogram findings were collected from patients’ charts. Data were described using standard summary statistics.

Results: There were 2,276 infants ≤ 60 days of age who received an ECG during our study period. Of those patients, a total of 268 infants (median age 4 days, IQR 2-24) were found to have NWA on ECG and also had an echocardiogram, and were therefore included for analysis. One hundred sixty-eight (63%) of the infants were male. The most common reason for an ECG to be obtained was the presence of a heart murmur (n=102, 38%). 131 infants (49%) were found to have congenital heart disease. Among those found to have CHD on echocardiogram (n=131), CHD types included ventricular septal defect (n=36, 28%), severe pulmonary valve stenosis (n=17, 13%), atrioventricular canal defect (n=16, 12%), and single ventricle disease (n=16, 12%).

Conclusion: Nearly half (49%) of infants ≤ 60 days of age who had NWA on ECG and had an echocardiogram performed were found to have congenital heart disease. The ECG remains an important screening tool for infants with a murmur, cyanosis, or other possible cardiac findings. The data suggests that an echocardiogram is warranted for infants found to have NWA on ECG. Further studies involving prospective analysis of this patient population are needed.