Northwest axis on an electrocardiogram is conventionally thought to be associated with CHD, but there is a paucity of data regarding the types and incidence of CHD associated with this finding. The purpose of this study was to report the types and incidence of CHD found at our institution to determine the efficacy of electrocardiograms as a screening test in infants.

Retrospective, single-centre study of all infants ≤ 60 days of age who underwent a first-time electrocardiogram from 2015 to 2021. Our inclusion criteria included those found to have a northwest axis on electrocardiogram and who also had an echocardiogram performed. Data were described using standard summary statistics.

Two hundred sixty-eight infants met inclusion criteria (median age 4 days, interquartile range 2–24). The most common reason for an electrocardiogram to be obtained was the presence of a heart murmur (n = 102, 38%). One hundred thirty-one infants (49%) were found to have significant CHD. Cardiac defects 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%).

In this study, nearly half (49%) of these infants with northwest axis on electrocardiogram were found to have significant CHD. Electrocardiograms remain an important screening tool for infants with findings associated with potential cardiac disease and echocardiogram is warranted for infants found to have northwest axis on a first-time electrocardiogram.