Supplementary Material for: The Evolution of the Neonatal QRS Axis during the First Four Weeks of Life

<b><i>Background:</i></b> 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. <b><i>Methods:</i></b> 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. <b><i>Results:</i></b> 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 (<i>p</i> &lt; 0.001). We found that girls had a significantly less pronounced right-shifted axis than boys (<i>p</i> &lt; 0.001) and that increasing gestational age (GA) was associated with a more pronounced right-shifted axis (<i>p</i> &lt; 0.05). Infant size did not affect the axis (<i>p</i> &gt; 0.05). Only 0.5% had an axis within the interval 0 to −90° and 1.1% in the interval +240 to +30°. <b><i>Conclusions:</i></b> 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.

<b><i>研究背景：</i></b> QRS电轴（QRS axis）代表心室除极的综合向量与方向。精准解读QRS电轴异常，可助力新生儿心脏疾病的早期诊断。本研究旨在阐明出生后前4周内QRS电轴的动态演变过程，并建立健康新生儿的QRS电轴参考值范围。<b><i>研究方法：</i></b> 哥本哈根婴儿心脏研究（Copenhagen Baby Heart Study）是一项前瞻性普通人群队列研究，为哥本哈根地区所有分娩的新生儿提供出生后1个月内的心脏评估服务。<b><i>研究结果：</i></b> 本研究纳入了12317名经超声心动图检查正常的新生儿心电图数据，其中男性占比52%，平均年龄为12天。出生0~7日龄时，QRS电轴中位数为119°；至22~28日龄时，电轴向左偏移至102°（p < 0.001）。研究发现，女性新生儿的QRS电轴右偏程度显著低于男性（p < 0.001）；胎龄（gestational age, GA）越大，QRS电轴右偏程度越显著（p < 0.05）；而新生儿体格大小对QRS电轴无显著影响（p > 0.05）。仅0.5%的新生儿QRS电轴处于0°至-90°区间，1.1%的新生儿电轴处于+240°至+30°区间。<b><i>研究结论：</i></b> 新生儿出生后前4周内，QRS电轴呈现逐渐左移的动态变化趋势，且受性别与胎龄的影响，但与新生儿体格大小无关。仅有不足1%的新生儿QRS电轴处于0°至-90°区间。本研究提供了更新版的QRS电轴参考值，可为新生儿临床诊疗工作提供参考与支持。