Natural history of the electrical axis during the first four weeks of life

Abstract Background The QRS axis represents the sum of the amplitudes and orientation of the ventricular depolarization. In newborns, the QRS axis is generally directed downward and to the right and left axis deviation (LAD) may be associated with heart disease. Accurate interpretation of abnormalities in the QRS axis may facilitate early diagnosis of heart diseases in newborns. Purpose To describe the evolution of the QRS axis during the first four weeks of life and provide updated, digitalized, normal values from healthy newborns. Methods Electrocardiograms from 12,317 newborns (age 0–28 days) included in a regional, prospective, general population study from 2016–2018 were analyzed. Electrocardiograms were obtained and analyzed with a computerized algorithm with manual validation. The algorithm calculated the QRS mean axis using the net amplitudes of three leads I, II, and III. The four main QRS axis classifications were: “adult normal” axis (+1° to +90°), left axis deviation (LAD, 0° to −90°), right axis deviation (RAD, +91° to +180°), and extreme axis deviation (EAD, +181° to +270°). Echocardiograms were performed according to standard guidelines. Only newborns with an echocardiography excluding structural heart disease were included. Results Electrocardiograms from 12,317 newborns with a median age at examination of 12 days (52% boys) were included. The median QRS axis was 119° at the ages 0–7 days and shifted leftwards to 102° at the ages 22–28 days (p