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

Abstract

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<0.001). We found that girls had significant less pronounced right axis deviation than boys (111° vs 117°, p<0.001) and that increasing gestational age was associated with more pronounced right axis deviation (104° vs 116°, p<0.05). Infant size did not affect the axis (p>0.05). Only 0.5% had LAD (0° to −90°) and 1.1% had an axis within the interval +240° to +30° indicating that a QRS axis in this expanded interval is unusual in healthy newborns. Conclusion The QRS axis showed a gradual leftward-shift during the first four weeks of life and was affected by sex and gestation age but unaffected by infant size. LAD occurred in only 0.5% of the newborns. Our data serve as updated reference values, which may facilitate clinical handling of newborns. Funding Acknowledgement Type of funding source: Foundation. Main funding source(s): This work was supported by the Danish Children Heart Foundation, Snedkermester Sophus Jacobsen and wife Astrid Jacobsen's foundation (Grant 19-R112-A5248-26048), the Research Council at Herlev-Gentofte Hospital and Toyota-Fonden, Denmark.