Paediatric ECG interpretation becomes significantly easier once the clinician understands one key physiological principle:
The neonatal heart is right ventricular dominant. The mature heart is left ventricular dominant.
Most normal paediatric ECG findings are explained by this transition.
During fetal life:
- pulmonary vascular resistance is high
- the right ventricle performs most of the cardiac work
- right ventricular muscle mass exceeds left ventricular mass
After birth:
- pulmonary vascular resistance falls
- pulmonary blood flow increases
- left ventricular workload progressively increases
- the ECG gradually shifts toward the adult pattern
This physiological transition explains why:
- right axis deviation is normal in neonates
- dominant R waves in V1 are normal in infancy
- juvenile T-wave inversion occurs in children
Understanding the physiology prevents overcalling normal findings as pathology.
When Should a Paediatric ECG Be Performed?
A Safe Systematic Approach
Interpret every paediatric ECG in the same sequence:
- Calibration and technical quality
- Heart rate
- Rhythm
- Axis
- P waves
- PR interval
- QRS complex
- QTc
- ST segments and T waves
A fixed sequence reduces missed pathology.
Step 1 — Calibration and Technical Quality
Always confirm:
- correct patient
- exact age
- paper speed
- amplitude calibration
Standard calibration:
- 25 mm/sec
- 10 mm/mV
Movement artefact is extremely common in children and may imitate arrhythmia.
Incorrect lead placement is another common cause of misinterpretation.
Before diagnosing pathology:
Confirm the ECG is technically adequate.
Step 2 — Heart Rate
Important Clinical Distinction
Sinus tachycardia:
- gradual onset
- variable rate
- identifiable P waves
- associated with fever, dehydration, pain
Supraventricular tachycardia:
- abrupt onset
- fixed rapid rate
- often absent P waves
- usually >220 bpm in infants
Any infant with a heart rate above 220 bpm should be assumed to have SVT until proven otherwise.
Step 3 — Rhythm
First determine whether sinus rhythm is present.
Features of sinus rhythm:
- P wave before every QRS
- consistent PR interval
- upright P waves in leads I and aVF
Sinus Arrhythmia
Sinus arrhythmia is normal in children.
Heart rate:
- increases during inspiration
- decreases during expiration
This reflects normal vagal tone and should not be mistaken for pathological irregular rhythm.
Step 4 — Axis
Normal Neonatal Axis
When Axis Becomes Abnormal
Persistent right axis deviation beyond infancy may suggest:
- pulmonary hypertension
- atrial septal defect
- right ventricular hypertrophy
Left axis deviation in a neonate should raise concern for:
- atrioventricular septal defect
- congenital heart disease
Extreme axis deviation at any age requires further investigation.
Step 5 — P Waves
Normal P-wave duration:
- less than 0.09 seconds in children
Tall peaked P waves
Suggest:
- right atrial enlargement
Broad bifid P waves
Suggest:
- left atrial enlargement
Absent P waves
Consider:
- junctional rhythm
- atrial fibrillation
- SVT
Atrial fibrillation is uncommon in children and usually implies underlying pathology.
Step 6 — PR Interval
Prolonged PR Interval
Consider:
- first-degree heart block
- myocarditis
- beta-blockers
- digoxin toxicity
Short PR Interval with Delta Wave
Classic for Wolff-Parkinson-White syndrome.
Features:
- short PR interval
- slurred QRS upstroke
- widened QRS complex
WPW predisposes to re-entry tachyarrhythmias and sudden cardiac death.
All confirmed WPW should be referred to paediatric cardiology.
Step 7 — QRS Complex
Normal QRS duration in young children:
- less than 0.08 seconds
Narrow QRS
Usually supraventricular origin.
Wide QRS
Consider:
- bundle branch block
- ventricular rhythm
- hyperkalaemia
- pre-excitation syndromes
Important Neonatal QRS Findings
The following are normal in neonates:
- dominant R wave in V1
- right ventricular voltages
- rightward axis
These findings are physiological before approximately 6 months of age.
Right Ventricular Hypertrophy
Consider RVH if:
- dominant R wave in V1 persists beyond infancy
- upright T wave persists in V1 after infancy
- qR pattern appears in V1
Common causes:
- pulmonary hypertension
- congenital heart disease
Left Ventricular Hypertrophy
Consider LVH if:
- tall R waves in V5–V6
- deep S waves in V1–V2
- associated ST-T abnormalities
In older children:
Always consider hypertrophic cardiomyopathy.
Step 8 — QTc
QTc assessment is one of the most important components of paediatric ECG interpretation.
Prolonged QTc may lead to:
- Torsades de Pointes
- ventricular fibrillation
- sudden cardiac death
QTc Interpretation
Causes of QT Prolongation
Important causes include:
- congenital long QT syndrome
- hypocalcaemia
- hypomagnesaemia
- myocarditis
- head injury
Common QT-Prolonging Medications
Step 9 — ST Segments and T Waves
Juvenile T-Wave Pattern
T-wave inversion in V1–V3 is frequently normal in children and may persist into adolescence.
This normal juvenile pattern is commonly overcalled as pathology.
Significant ST-T Abnormalities
Diffuse ST elevation:
- myocarditis
- pericarditis
Tall peaked T waves:
- hyperkalaemia
Dynamic ECG changes:
- always clinically significant
Hyperkalaemia ECG Progression
Memorise the sequence:
- Tall peaked T waves
- PR prolongation
- QRS widening
- Sine-wave appearance
- Cardiac arrest
Hyperkalaemia is immediately life-threatening.
Important Emergency ECG Patterns
Supraventricular Tachycardia
Typical findings:
- narrow complex tachycardia
- 220–300 bpm in infants
- absent or retrograde P waves
- abrupt onset and termination
Wolff-Parkinson-White Syndrome
Typical findings:
- short PR interval
- delta wave
- widened QRS
WPW can precipitate sudden cardiac death if atrial fibrillation occurs.
Complete Heart Block
Findings:
- P waves independent of QRS complexes
- atria and ventricles beat separately
- slow ventricular escape rhythm
Important causes:
- neonatal lupus
- congenital heart disease
- myocarditis
- postoperative complications
Long QT Syndrome
Suspect in:
- exercise-induced syncope
- emotional-trigger syncope
- family history of sudden death
- recurrent unexplained seizures
- prolonged QTc on repeated ECGs
Management includes:
- avoiding QT-prolonging medications
- beta-blockers
- cardiology referral
- family screening
Common Diagnostic Pitfalls
Red Flags Requiring Urgent Cardiology Review
- QTc >0.50 sec
- Delta wave with syncope
- Complete heart block
- Exertional syncope
- LVH in a young athlete
- Family history of sudden death
- Sustained tachyarrhythmia
- Dynamic ST changes
Final Clinical Advice
Do not memorise paediatric ECG patterns blindly.
Interpret the ECG through physiology.
Most normal paediatric ECG findings reflect:
- postnatal circulatory adaptation
- developmental physiology
- changing ventricular dominance with age
The ECG should never be interpreted in isolation.
Always correlate with:
- symptoms
- examination findings
- family history
- haemodynamic status
- previous ECGs
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