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?
Clinical Scenario Important Diagnoses Syncope Long QT syndrome, WPW, heart block Exertional collapse Hypertrophic cardiomyopathy, catecholaminergic VT Chest pain Myocarditis, pericarditis Palpitations Supraventricular tachycardia Cyanosis Congenital heart disease Seizure-like episodes Arrhythmia masquerading as seizure Electrolyte disturbance Hyperkalaemia, hypocalcaemia Drug overdose QT prolongation Family history of sudden death Inherited channelopathy
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
Children normally have faster heart rates than adults. Age Normal Heart Rate Neonate 100–180 bpm Infant 100–160 bpm Toddler 90–150 bpm School-age child 70–120 bpm Adolescent 60–100 bpm
Heart rate can be estimated rapidly by:
300 divided by the number of large squares between R waves.
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
Right axis deviation is physiological in neonates because of right ventricular dominance. Age Group Expected Axis Neonate Right axis deviation Infant Gradual normalization Child Normal axis Adolescent Adult pattern
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
The PR interval reflects conduction from atria to ventricles. Age Normal PR Interval Infant 0.08–0.15 sec Child 0.10–0.17 sec Adolescent 0.12–0.20 sec
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
QTc Interpretation <0.44 sec Normal 0.44–0.46 sec Borderline 0.46–0.50 sec Prolonged >0.50 sec High risk
QTc should ideally be measured in:
- lead II
- alternatively V5 if unclear
Avoid V2 and V3 because U waves may falsely prolong the QT interval.
Causes of QT Prolongation
Important causes include:
- congenital long QT syndrome
- hypocalcaemia
- hypomagnesaemia
- myocarditis
- head injury
Common QT-Prolonging Medications
Drug Group Examples Antiemetics Ondansetron, metoclopramide Macrolides Erythromycin, azithromycin Antifungals Fluconazole Antipsychotics Haloperidol Antidepressants SSRIs, tricyclics Antiarrhythmics Amiodarone, sotalol
Always review QTc before prescribing 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
Pitfall Reality Right axis deviation in neonate called abnormal Usually physiological Dominant R in V1 labelled RVH in neonate Often normal Juvenile T-wave inversion called ischaemia Commonly physiological Sinus arrhythmia diagnosed as pathology Normal vagal tone Subtle delta wave missed Always assess PR interval carefully SVT mistaken for sinus tachycardia SVT has abrupt onset and fixed rate
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
© stethal.wordpress.com | For educational purposes. Always refer to local guidelines and senior clinicians for clinical decision-making.
