Here is the ECG of a 3-year-old boy. Is there cause for concern? The ECG shows a sinus rhythm with significant sinus arrhythmia. The heart rate increases with inspiration and decreases with expiration, which is called respiratory sinus arrhythmia. The QRS-axis is between 60 and 90 degrees, which is physiological at this age. The negative T-waves in V1-V3 (V4) are also age-appropriately normal. Therefore, there is no reason for concern; the ECG is considered normal for the child's age.
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