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EeroJokinen

Interpretation of ECG in Children

Essentials

  • ECG must always be interpreted in respect to the age of the child.
  • Modern recorders of twelve lead ECG often give a summary of the findings. The reliability of the interpretation varies markedly depending on the reference values used. The interpretation may be misleading, especially when the rhythm is evaluated. The summary often includes a comment like "possible hypertrophy". This may be due to high voltage measured in the recording of a single lead. Thus, the physician must always evaluate the ECG as an entity.
  • Because of large individual variation and changes occurring with age the reference intervals are rather wide. ECG in children is not a very sensitive and accurate method for evaluating, for example, ventricular hypertrophy.

Heart rate

Heart rate reference limits in different age groups

AgeReference limits, beats per min
1-6 d75-185
1-4 wk105-200
1-5 mo90-195
6-11 mo80-175
1-3 yrs60-170
4-7 yrs45-140
8-11 yrs40-125
12-17 yrs35-115

Conduction intervals and QRS axis

  • The ECG of a newborn and of an infant usually shows right ventricular dominance and the electrical axis of the heart is predominantly to the right up to +180°. The electrical axis will shift to the left as the child grows. In 8- to 12-year-olds, right ventricular dominance up to +120° may still prevail and the QRS axis is more to the right than in adults. Not until teenage will the ECG resemble that of an adult, and the electrical axis is no more than +90°.
  • See table T2.

Conduction intervals (upper limits of reference values) and QRS axis in different age groups

1-6 d1-4 wk1-5 mo6-11 mo1-3 yrs4-7 yrs8-11 yrs12-15 yrs16-17 yrs
P wave (ms)75859010095115120120120
PR interval (ms) 150140145150155160170175185
QRS duration75859010095115115120120
QRS axis (degrees) 60-18045-15030-1350-1350-1100-110−15-110−15-110−15-110

QT interval

  • Corresponds to the systole of the heart. The duration of this interval depends on heart rate.
  • Table T3

The longest normal QT interval at various heart rates (sec.)

Heart rate (/min.)Longest normal QT interval (sec.)
500.49
600.44
700.42
800.39
1000.35
1200.32
1500.28
1700.27

ST segment and T wave

  • ST segment may normally be elevated or depressed by one mm from the baseline in limb leads and slightly more in precordial leads.
  • T wave is normally always positive in leads I and II. It may be positive or negative in lead III, and it is normally negative in lead aVR.
  • T wave is negative in right-sided precordial leads throughout childhood until ca. 16 years of age (table T4). In infants and in children of preschool age, a positive T wave in lead V1 suggests right ventricular hypertrophy.

Physiological T inversions in precordial leads in children

LeadAge
V1ad 16 yrs
V2ad 12 yrs
V3ad 10 yrs
V4ad 5 yrs
V5ad 15 h
V6ad 8 h

Estimation of ventricular hypertrophy

  • It is easiest to evaluate the degree of ventricular hypertrophy in precordial leads. However, deviation of the electrical axis to the right is suggestive of right ventricular hypertrophy and deviation to the left is suggestive of left ventricular hypertrophy.
  • However, when assessing ventricular hypertrophy, it must be kept in mind that in 8- to 12-year-olds both the R and S waves are 0.5 to 1 mV (5 to 10 mm when the amplification is 10 mm/mV) higher than in adults. Thus, in children of this age, the ventricular hypertrophy cannot be reliably measured from the sum of Q, R and S waves alone.
  • When assessing ventricular hypertrophy, check the amplification used in the ECG recording: 5 mm/mV or 10 mm/mV?

Electrical axis

  • Count the sum of R and S peaks in two limb leads (for example, lead I = horizontal axis and aVF = vertical axis; R = positive value, S = negative value). Draw a vector (the length of which is equivalent to the RS sum measured) on each of the two respective axis. Draw lines that are in 90° angles in respect to the tips of these vectors. Then draw a line that connects the starting point of the vectors and the crossing point of these lines. The sum vector drawn in this manner shows the electrical axis.
  • The analyzers in modern ECG devices automatically calculate the electrical axis of the R wave.

Right ventricular hypertrophy

  • RV1 is higher than normally by age
  • SV6 is deeper than normally by age
  • Positive T wave in lead V1 during childhood after the first week of life
  • QR complex in V1
  • QRS complex with RSR' morphology in V1; an R' greater than 1 mV (10 mm) is suggestive of either right ventricular hypertrophy or right bundle branch block or both.
  • Reference values for different age groups: see table T5.

Upper limits of R and S waves in children

AgeV1V1V6V6
-R wave (mm)S wave (mm)R wave (mm)S wave (mm)
1-6 d23141613
-4 wk21142014
1-5 mo26163019
6-11 mo21163014
1-3 yrs18172810
4-7 yrs1319309
8-11 yrs1219308
12-15 yrs (girls/boys)9/1119/2025/325/9
16-17 yrs (girls/boys)7/1016/2021/304/7

Left ventricular hypertrophy

  • RV6 is higher than normally by age.
  • SV1 is deeper than normally by age.
  • Negative T wave in leads V5-V6 after the first day of life
  • Deep Q in left sided precordial leads (in infants younger than 1 year, a Q wave deeper than 3 mm, in 1- to 5-year-olds, a Q wave deeper than 3.5 mm).
  • Reference values for different age groups: see table T5.

Biventricular hypertrophy

  • The criteria for both right and left ventricular hypertrophy are fulfilled separately.
  • Tall QRS complexes (R + S > 50 mm) in leads V3-V4

Left atrial hypertrophy

  • Broad-P waves in leads I and II (P mitral) and broad biphasic P wave that has a negative terminal portion in V1

Right atrial hypertrophy

  • High (> 2.5 mm) and sharp P waves in leads II, III, aVF and V1

Heart defects where right ventricular hypertrophy is common

  • Pulmonary stenosis
  • Various defects with left to right shunts and with increased pulmonary vascular pressure
  • Coarctation in a neonate (usually)
  • Partial right bundle branch block, almost invariable in connection with atrial septal defect
  • Pulmonary hypertension

Heart defects where left ventricular hypertrophy is common

  • Aortic stenosis
  • Aortic coarctation in an older child (usually the ECG finding is minor)
  • Patent ductus arteriosus (usually the ECG finding is minor)
  • Hypertrophic cardiomyopathy

Biventricular hypertrophy

  • Ventricular septal defects (either of the ventricles may dominate depending on pressure and flow circumstances)

Arrhythmias

Breathing variation

  • In many children, phases of inspiration and expiration cause marked variance in beat intervals. If the P wave precedes the QRS complex with a normal conduction interval, this irregularity in pulse rate is totally normal phenomenon.

Tachycardias

  • Approximately one child in five hundred is congenitally predisposed to supraventricular tachyarrhythmias. The pulse rate is usually "uncountable" during the attack, with ECG showing mostly a pulse rate exceeding 200/min.
  • If the tachycardia first appears already during infancy, the child almost certainly has a re-entry tachycardia even if no delta-waves are found in ECG.
  • In Wolff-Parkinson-White syndrome, the anomalous pathway is able to conduct the impulse from the atria to the ventricles, and a delta wave is often visible during sinus rhythm.
  • In such cases, an atrial arrhythmia may cause a dangerously rapid ventricular response, and a paediatric cardiologist should assess the patient for treatment. In tachycardias caused by either an extra pathway or by a so-called duplicated AV node, eventual catheter ablation is preferably postponed until school age, if possible.

Long QT syndrome

  • ECG must be registered in every child presenting with an attack of unconsciousness or an epileptiform attack to exclude prolonged QT interval. It is also worthwhile to measure the QT interval if deaths from drowning have occurred in close relatives.
  • Long QT-syndrome is a hereditary repolarisation disorder that predisposes to ventricular tachycardia. The disorder usually becomes symptomatic at school age or during young adulthood, presenting as a sensation of tachycardia or as a sudden syncope associated with physical exercise, excitement or startle. If a child with sudden unconsciousness or suspected epileptic seizure has a QT interval longer than appropriate for pulse rate (tableT3; best assessed in leads V4-5 and II), further examinations are absolutely necessary.

    References

    • Bratincsák A, Kimata C, Limm-Chan BN, et al. Electrocardiogram Standards for Children and Young Adults Using Z-Scores. Circ Arrhythm Electrophysiol 2020;13(8):e008253. [PubMed]
    • Rijnbeek PR, Witsenburg M, Schrama E, et al. New normal limits for the paediatric electrocardiogram. Eur Heart J 2001;22(8):702-11. [PubMed]

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