Interpretation of Electrocardiogram in Children

Electrocardiogram Interpretation in Children

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    Electrocardiography is critical in the diagnosis of electrical disorders of the heart. It may serve as a useful screening tool in the evaluation of patients of suspected structural defects or abnormalities of the myocardium.
    Newborns have a large variability in electrocardiogram (ECG) voltages and intervals due in large part to hemodynamic and myocardial adaptations that are needed once the placenta is no longer part of the circulatory system.
    Changes continue, albeit at a slower pace, from infancy through adolescence.
    Algorithms used to interpret ECGs in adults cannot be used in children. This section is a basic, although incomplete, guide to the pediatric ECG.
Rate
    The usual recording speed is 25 mm/sec; each little box (1 mm) is 0.04 seconds and each big box (5 mm) is 0.2 seconds.
    With a fast heart rate, count the R-R cycles in 6 large boxes (1.2 seconds) and multiply by 50.
    With a slow heart rate, count the number of large boxes between R waves and divide into 300 (1 box = 300, 2 boxes = 150, 3 boxes = 100, 4 boxes = 75).
    Table below lists normal heart rates.
Rhythm

    Are the QRS deflections regular? Variation in the rate up and down in concert with respirations is normal (sinus arrhythmia) and can be pronounced in young healthy hearts.
    Irregular QRS pattern suggests the possibility of an atrial arrhythmia. With pauses and narrow QRS, look for evidence of atrial premature contractions with P waves of different of appearance and/or axis as compared with sinus beats. The early P wave may not conduct, leading to longer pauses (blocked atrial premature contractions).
    The QRS may be prolonged if conduction down the atrioventricular (AV) node is delayed (aberrant conduction). Wide QRS complexes with pauses may represent premature contractions from a ventricular focus, especially if the T-wave morphology is also altered with the opposite axis.
    Look for a P wave before each QRS at an expected interval, usually between 100 and 150 milliseconds. The P wave should be upright in I and aVF for the typical location of sinus node. The sinus P wave is up in leads I, II, aVF, pure negative in aVR, and usually biphasic in lead V1—first positive, then negative.
        Inverted P waves associated with slower heart rates, along with a low atrial rhythm, are a normal finding.
        Inverted P waves associated with tachycardias are abnormal and may be ectopic atrial tachycardia or other forms of supraventricular tachycardia (SVT).
PR Interval

    The PR interval represents atrial depolarization.
QRS Axis and Duration

    The QRS axis shows the direction of ventricular depolarization.
        Left axis deviation can suggest left ventricular hypertrophy or left bundle branch block (LBBB).
        Right axis deviation can suggest right ventricular hypertrophy or right bundle branch block (RBBB)
    The QRS duration represents ventricular depolarization. Normal times for depolarization depend on age. A prolonged QRS may indicate bundle branch block, hypertrophy, or arrhythmia.
    Normal Heart Rates in Children*
    Age     Heart rate (beats/ min)
    0–1 mo     145 (90–180)
    6 mo     145 (105–185)
    1 yr     132 (105–170)
    2 yr     120 (90–150)
    4 yr     108 (72–135)
    6 yr     100 (65–135)
    10 yr     90 (65–130)
    14 yr     85 (60–120)

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