Paediatric ECG: Stepwise approach

Stepwise assessment of the paediatric ECG

2.1 Rhythm

Sinus: Atrial depolarisation starts from the sinoatrial node. This requires:

  • P wave preceding each QRS complex, with a constant PR interval
  • Normal P wave axis (zero to +90 degrees), i.e. P wave is upright in leads I and aVF

Non-sinus: Some atrial rhythms may have P waves in front of every QRS but with an abnormal P axis (inverted in lead II).

Note prominent sinus arrhythmia is commonly seen in children.

2.2. Rate

As per rate interpretation for adults.

Heart rates are highest in neonates and infants and decrease with age. The younger the child, the higher the metabolic rate and lower vagal tone:

  • Newborn: 110 – 150 bpm
  • 2 years: 85 – 125 bpm
  • 4 years: 75 – 115 bpm
  • > 6 years: 60 – 100 bpm

2.3 QRS axis

As per adult interpretation, calculated using the hexaxial reference system that shows the frontal view of the electrical activity of the heart via the six limb leads.

A suggested method of axis calculation
ECG AXIS Lead 1 and aVF Axis measurement QUADRANT 2021
Normal QRS axis varies with age:
  • 1 week – 1 month: + 110° (range +30° to +180°)
  • 1 month – 3 months: + 70° (range +10° to +125°)
  • 3 months – 3 years: + 60° (range +10° to +110°)
  • Over 3 years: + 60° (range +20° to +120°)
  • Adult: + 50° (range -30° to 105°)

Initial right ventricular (RV) dominance

In utero, blood is shunted away from the pulmonary vasculature leading to higher pulmonary pressures and a relatively larger and thicker right ventricle. Right axis deviation is thus a normal finding at birth, and usually resolves by 6 months of age.

A north-west axis (-90 to -180 degrees) is seen at birth with AV canal or ostium primum atrial septal defects

2.4 ECG intervals

  • PR interval and QRS duration are shorter at birth due to smaller cardiac size
  • Normal QT interval is slightly prolonged at birth

PR Interval

The normal PR interval varies with age and heart rate:

Prolonged PR interval (first degree heart block) may be normal or be seen in:

Short PR interval occurs in:

Variable PR interval occurs in:

  • Wandering atrial pacemaker
  • Wenckebach (Mobitz type 1) second degree heart block

QRS Duration

QRS duration varies with age:

Prolonged QRS is characteristic of ventricular conduction disturbances:

QT Interval

QT interval varies with heart rate:

Bazett formula is used to correct the QT for HR:

  • QTc = QT measured / (√R–R interval)

Normal QTc

  • Infants less than 6 months = < 490 ms
  • Older than 6 months = < 440 ms

QTc is prolonged in:

QTc is short in:

2.5 P wave amplitude and duration

2.6 QRS amplitude (voltages)

High QRS amplitudes are found in:

  • Ventricular hypertrophy
  • Ventricular conduction disturbances eg BBB’s, WPW

Low QRS amplitudes are seen in:

Ventricular hypertrophy

Ventricular hypertrophy produces changes in one or more of the following areas: the QRS axis, the QRS voltages, the R/S ratio and/or the T axis.

The presence of ECG features of left ventricular hypertrophy in a paediatric patient should prompt the clinician to look for other ECG and clinical features of hypertrophic cardiomyopathy and investigate as appropriate.

R and S wave voltages children
Right ventricular hypertrophy

Axis: RAD for the patients age


  • Tall R waves (greater than limits for patient’s age) in right-sided leads V4R and V1
  • Deep S waves (greater than limits for patient’s age) in left-sided leads V5 and V6

R/S ratio: Abnormal R/S ratio in favour of RVH.

  • Increased R/S ratio (greater than upper limits for child’s age) in V1-2
  • R/S ratio < 1 in V6 (after one month of age)

Abnormal T waves: Upright T waves in V1 and V4R in children 3 days to 6 years (provided that T waves are normal elsewhere, i.e. upright in V6). This is evidence alone of significant RVH.

Abnormal Q waves: qR pattern in V1 (small Q wave, tall R wave) = highly specific for RVH.

Left ventricular hypertrophy

Axis: LAD for the patients age (marked LAD is rare with LVH).


  • Tall R waves in the left-sided leads V5 and V6 (greater than limits for patient’s age)
  • Deep S waves in the right-sided leads V4R and V1 (greater than limits for patient’s age)

R/S ratio:

  • Abnormal R/S ratio in favour of LV
  • Decreased R/S ratio in V1-2 (less than upper limits for child’s age)

Abnormal Q waves in V5 and V6

Inverted T waves in I and aVL (LV strain pattern)

Biventricular hypertrophy
  • Positive voltage criteria for RVH and LVH (with normal QRS duration)
  • Positive voltage criteria for RVH or LVH and relatively large voltages for other ventricle
  • Large equiphasic QRS complexes in two or more limb leads and in mid-precordial leads (V2-5)

Evans Rules

Small chest walls exaggerate precordial voltages. Evans et al proposed a practical approach to evaluation:

Abnormal Left Ventricular Large Voltage (“LVH”)

Use only V6 (the left most precordial lead)

  • If R wave of V6 intersects with baseline of V5, this is ABNORMAL

Abnormal Right Ventricular Large Voltage (“RVH”)

Use only V1 (the right most precordial lead)

  • Upright T wave in V1: In first week of life is NORMAL. Between week 1 and adolescence this is  ABNORMAL
  • RSR’ in V1: If R’ is taller than R – this is ABNORMAL
  • Pure R wave in V1: If child > 6 months old – this is ABNORMAL

2.7 Q waves

Normal Q waves:

  • Narrow (average 0.02 seconds and less than 0.03 seconds)
  • Usually less than 5mm deep in left precordial leads and aVF
  • May be as deep as 8mm in lead III in children younger than 3 years

Q waves are abnormal if they are:

  • Present in the right precordial leads ie V1 (eg severe RVH)
  • Absent in the left precordial leads (e.g. LBBB)
  • Abnormally deep (ventricular hypertrophy) – look for “dagger” Q waves in leads I, aVL and V5-6, often seen in hypertrophic cardiomyopathy
  • Abnormally deep and wide (myocardial infarction or fibrosis)

2.8 ST segment

Interpretation is as per adults – the normal ST segment is isoelectric. Elevation or depression is judged in relation to the TP segment.

Some ST changes may be normal:

  • J-point depression: the J point (junction between the QRS and ST segment) is depressed without sustained ST depression, i.e. upsloping ST depression.
  • Benign early repolarisation is a common finding in adolescents: the ST segment is elevated and concave in leads with an upright T wave
ST segment depression upsloping downsloping horizontal

Others are pathological:

  • Coved or saddle-back ST elevation in V1-3 should raise concern for Brugada syndrome
  • A sustained horizontal ST segment depression 0.08 sec or longer is abnormal

Pathological ST segment changes are commonly associated with T wave changes and occur in:

2.9 T Waves

The precordial T-wave configuration changes over time:

  • For the first week of life, T waves are upright throughout the precordial leads
  • After the first week, the T waves become inverted in V1-3 (= the “juvenile T-wave pattern”)
  • This T-wave inversion usually remains until ~ age 8; thereafter the T waves become upright
  • However, the juvenile T-wave pattern can persist into adolescence and early adulthood (= “persistent juvenile T waves”)

Tall, peaked T waves are seen in:

Flat T waves are seen in:

Large, deeply inverted T waves are seen with:

2.10 U waves

U Waves are the extra positive deflection at the end of a T wave. Most common causes:


Advanced Reading



LITFL Further Reading


MBBS (UWA) CCPU (RCE, Biliary, DVT, E-FAST, AAA) Adult/Paediatric Emergency Medicine Advanced Trainee in Melbourne, Australia. Special interests in diagnostic and procedural ultrasound, medical education, and ECG interpretation. Editor-in-chief of the LITFL ECG Library. Twitter: @rob_buttner

Emergency Physician in Prehospital and Retrieval Medicine in Sydney, Australia. He has a passion for ECG interpretation and medical education | ECG Library |

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