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.

Three cases of acute inferior wall myocardial infarction associated with complete atrioventricular block and junctional escape rhythm showing left posterior hemiblock are presented. The triad appears to consitiute a distinct syndrome. It is postuated that the subsidiary pacemaker is situated either in the bundle of His or the proximal part of the anterior division of the left bundle-branch.

Background The accessory electrical pathway in Wolff-Parkinson-White (WPW) syndrome predisposes to tachycardia and may increase risk of sudden cardiac death. Studies investigating the prevalence of this condition in newborns are few. Purpose To describe the prevalence of WPW syndrome and assess the localization of the accessory pathway and associated structural heart disease in newborns from a large general population study. Methods Electrocardiograms (ECG's) and echocardiograms of 17.489 newborns (aged 0–30 days) from a large, prospective general population study were included. WPW cases were identified through manual evaluation of outliers in measurements of PR-interval, QRS-duration, QTcB interval and QRS axis. Newborns suspected for WPW syndrome were offered a secondary echocardiogram and ECG recording. Localization of the accessory pathway was assessed based on a QRS polarity algorithm. The control group consisted of 5,000 randomly selected newborns with a normal echocardiogram. Results Among the 17,489 ECG's we manually analyzed 5,166 and found 15 newborns (80% boys) with WPW syndrome (secondary confirmatory ECG's will be available at ESC 2020) consistent with prevalence of WPW syndrome of 0.1%. The median values of the PR-interval, QRS-duration and QTcB in cases and controls were 80 vs 98 ms, 74 vs 56 ms, and 449 vs 420 ms, respectively (all p&lt;0.0001). The accessory electrical pathway was left-sided in 13 (87%) of the newborns. One newborn had moderate mitral regurgitation while all other newborns had structurally normal hearts and no cases of Ebstein's anomaly. Conclusion The prevalence of WPW syndrome in our cohort was 0.1%. The syndrome was more frequent in boys, and the accessory pathways were mainly left-sided. All but one of the affected newborns had structurally normal hearts. 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.

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&lt;0.001). We found that girls had significant less pronounced right axis deviation than boys (111° vs 117°, p&lt;0.001) and that increasing gestational age was associated with more pronounced right axis deviation (104° vs 116°, p&lt;0.05). Infant size did not affect the axis (p&gt;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.

No abstract