Paediatric ECG Basics

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Appcardio ECG Academy

Paediatric ECG Basics

A practical, age-aware approach to acquiring and interpreting the paediatric electrocardiogram—from normal developmental patterns to common rhythm and repolarisation abnormalities.

Foundational · IntermediateApprox. 12–15 minClinical ECG interpretation

Learning objectives

01 · RecogniseExplain why normal paediatric ECG appearances change with age.

02 · AcquireCheck standardisation and apply correct paediatric lead placement.

03 · InterpretUse a consistent sequence to assess rate, rhythm, axis, intervals and morphology.

1. Why the paediatric ECG is different

A child's ECG is not simply a smaller adult ECG. During the transition from fetal to postnatal circulation, pulmonary vascular resistance falls and the relative dominance of the right ventricle gradually gives way to a more balanced—and eventually left-ventricular-dominant—pattern. Heart rate, electrical axis, QRS voltages, repolarisation and conduction intervals therefore vary with age.

Core principle: interpret every paediatric ECG against age-appropriate reference limits and the child's clinical presentation. An adult reference range can incorrectly label normal developmental findings as disease—or miss genuine abnormalities.

Expected developmental patterns

Heart rate is generally faster in infants and young children than in adults.
Right ventricular forces are prominent in the newborn; the QRS axis is often rightward and the right precordial R wave may be relatively tall.
PR and QRS durations are generally shorter in younger children.
Right precordial T-wave inversion is a common developmental pattern after the first few days of life and may persist into adolescence.
Voltage criteria for chamber enlargement must be judged against age-specific standards; isolated high voltage is not sufficient to diagnose hypertrophy.

2. ECG acquisition and lead placement

Before interpreting morphology, confirm that the tracing is technically reliable. A misplaced electrode can produce apparent axis, bundle-branch or repolarisation abnormalities.

Technical checklist

Confirm the child's identity, age and date/time of recording.
Check calibration and paper speed. Standard settings are usually 25 mm/s and 10 mm/mV.
Ensure the child is warm, as still and comfortable as possible; reduce movement and muscle artefact.
Use appropriately sized electrodes and ensure good skin contact.
Confirm limb and precordial electrode positions before accepting an unexpected pattern.

Standard precordial landmarks

V1: fourth intercostal space, right sternal border.
V2: fourth intercostal space, left sternal border.
V3: midway between V2 and V4.
V4: fifth intercostal space, midclavicular line.
V5: level with V4, anterior axillary line.
V6: level with V4, midaxillary line.

Lead group	Placement	Practical note
Limb electrodes	Right arm, left arm, right leg and left leg	Use the standard limb positions; keep limb labels consistent and avoid swapping right and left.
V1–V2	Fourth intercostal spaces at the sternal borders	High placement can alter P-wave and QRS morphology, particularly in V1–V2.
V3–V6	Follow the anatomical landmarks listed above	V4 should be positioned before V3; V5 and V6 remain horizontally level with V4.
Additional right-sided leads	V4R is the mirror position of V4 on the right chest	May be useful when right ventricular pathology is suspected; document additional leads clearly.

Common pitfall: do not place V1 and V2 too high. If the tracing is unexpected or inconsistent with the clinical picture, re-check electrode positions and consider repeating the ECG.

Illustration: original Appcardio schematic for orientation; it is not a substitute for palpating anatomical landmarks.

3. A stepwise approach to interpretation

Use the same disciplined sequence for every tracing. Automated measurements can support interpretation but should not replace visual review and manual verification.

Patient and technical details. Verify identity, age, clinical indication, paper speed, calibration, artefact and lead placement.
Rate. Calculate atrial and ventricular rates when they differ. Decide whether the rate is appropriate for age and clinical state.
Rhythm. Assess regularity, P-wave presence and morphology, the relationship between P waves and QRS complexes, and PR consistency.
Axis. Determine the QRS axis and compare it with the expected range for age.
Intervals. Measure PR, QRS and QT; calculate QTc using an appropriate correction method and interpret in context.
Waveform morphology. Review P-wave morphology, Q waves, R/S progression, voltages and evidence of chamber enlargement or conduction abnormality.
ST segments and T waves. Look for repolarisation changes, remembering normal age-related T-wave patterns.
Overall synthesis. State whether the ECG is normal or abnormal for age, identify key abnormalities and relate them to the clinical question.

Paper speed and calibration

Measurement	At 25 mm/s	At 10 mm/mV
One small horizontal square (1 mm)	0.04 seconds (40 ms)	—
One large horizontal square (5 mm)	0.20 seconds (200 ms)	—
Vertical deflection of 1 mm	—	0.1 mV
Vertical deflection of 10 mm	—	1 mV

Rate estimate: for a regular rhythm at 25 mm/s, heart rate ≈ 300 divided by the number of large squares between consecutive R waves, or 1,500 divided by the number of small squares. For an irregular rhythm, count QRS complexes over a known interval (for example, 10 seconds × 6).

4. Normal values change with age

The values below are selected reference data from the Royal Children's Hospital Melbourne paediatric ECG guideline. They are guides rather than universal cut-offs: reference ranges vary by population, age grouping, heart rate and measurement method.

Heart rate and QRS axis

Age	Mean heart rate (bpm)	Heart-rate range (bpm)	Mean QRS axis	QRS-axis range
Newborn	145	120–170	—	—
6 months	145	110–170	—	—
1 year	132	105–150	—	—
2 years	120	95–150	+60°	+10° to +110°
4 years	108	80–150	+60°	+10° to +110°
6 years	100	75–140	+60°	+20° to +120°
10 years	90	60–130	+60°	+20° to +120°
14 years and older	85	60–115	+60°	+20° to +120°

The RCH guideline separately reports QRS axis of +110° (range +30° to +180°) from 1 week to 1 month, and +70° (range +10° to +125°) from 1 to 3 months. Its reference for children older than 3 years is +60° (range +20° to +120°); adult limits are listed separately. Dashes above mean the selected age-specific table did not provide a corresponding value at that row.

Conduction intervals: upper limits of normal

Age band	PR upper limit (ms)*	QRS upper limit (ms)
0–1 month	Up to 120–140, depending on rate	70
1–6 months	Up to 130–140, depending on rate	75
6–12 months	Up to 130–140, depending on rate	75
1–3 years	Up to 140, depending on rate	75
3–8 years	Up to 150–170, depending on rate	75
8–12 years	Up to 150–180, depending on rate	85
12–16 years	Up to 160–190, depending on rate	85

*PR upper limits are heart-rate dependent in the RCH reference table; the ranges shown are a concise summary of the tabulated upper limits, not a single threshold for all rates. Consult the full age- and rate-stratified table when borderline measurements matter. RCH QRS upper limits are based on the 98th percentile.

Interpretation tip: always record the child's age and heart rate beside borderline interval measurements. A PR interval that is acceptable in an adolescent may be prolonged in an infant; a QRS duration should also be judged against age.

5. Recognising normal paediatric patterns

Sinus rhythm and sinus arrhythmia

Sinus rhythm is supported by a consistent P wave before each QRS, a stable PR relationship, and a P-wave axis compatible with sinus origin (upright in leads I and aVF in the RCH guideline). Respiratory sinus arrhythmia—gradual variation in R–R intervals with breathing—is common in children and is usually physiological.

Right ventricular dominance in early life

Right-sided forces are expected to be more prominent in neonates and young infants. With growth, the QRS axis and precordial R/S balance evolve. Do not apply adult voltage or axis expectations to a newborn.

Juvenile T-wave pattern

T waves are often inverted in V1–V3 during childhood. They generally become upright progressively during adolescence, but persistent inversion in V1 can remain a normal variant. T waves in V5 and V6 should ordinarily be upright.

ST segments

Small ST shifts can occur in children: the RCH guideline notes that up to 1 mm in limb leads and up to 2 mm in precordial leads may be normal. Persistent horizontal ST depression, marked elevation or changes that fit the clinical picture require assessment rather than dismissal as a variant.

Do not overcall: isolated high precordial voltage, rightward axis in a young infant, or T-wave inversion in the right precordial leads may be age-appropriate. Diagnose ventricular hypertrophy or pathology only after considering the full pattern, age and clinical context.

6. Common paediatric arrhythmias

The supplied LITFL lesson identifies common paediatric arrhythmias as a core topic but does not provide diagnostic criteria in the supplied PDF extract. The following is a concise supplementary teaching overview; rhythm diagnosis should be made from the complete tracing and clinical state.

Rhythm	ECG pattern to assess	Clinical interpretation
Sinus tachycardia	Sinus P waves before each QRS; rate varies with physiological demand and may show gradual onset/offset.	Look for causes such as fever, pain, dehydration, hypovolaemia, sepsis, hypoxia or medication.
Supraventricular tachycardia (SVT)	Often a very regular narrow-complex tachycardia; P waves may be absent, hidden or retrograde. Rate alone is not diagnostic.	Assess perfusion and haemodynamic stability immediately; obtain expert paediatric support.
Ventricular tachycardia	Usually a broad-complex tachycardia; AV dissociation, capture or fusion beats may support the diagnosis when present.	Potentially life-threatening. Treat an undifferentiated broad-complex tachycardia as VT until expert assessment indicates otherwise.
Atrial flutter / atrial fibrillation	Look for organised flutter activity or an irregularly irregular ventricular response without consistent P waves.	Uncommon in otherwise healthy children; consider underlying cardiac disease, surgery or systemic illness.
Bradycardia / AV block	Assess P-wave rate, QRS rate, PR behaviour and whether atrial impulses conduct to the ventricles.	Correlate with age, sleep, medication, hypoxia and signs of raised intracranial pressure or conduction disease.

Safety first: a child with poor perfusion, altered consciousness, hypotension, respiratory compromise or other signs of instability needs urgent clinical management. Do not delay treatment to complete an educational ECG checklist.

7. Other ECG abnormalities in children

The supplied LITFL source specifically lists the following additional abnormalities as relevant paediatric ECG topics:

Inflammatory and myocardial conditions

Pericarditis: often viral in children; consider diffuse ST–T changes in the appropriate clinical setting.
Myocarditis: may produce non-specific ST–T changes, low voltage, conduction disturbance or arrhythmia; ECG can also be non-diagnostic.

Electrolyte-related changes

Hypokalaemia: may cause T-wave flattening, ST depression and prominent U waves.
Hyperkalaemia: may cause peaked T waves, PR prolongation, QRS widening and, in severe cases, loss of visible P waves.
Hypocalcaemia: typically prolongs the QT interval through ST-segment prolongation.
Hypercalcaemia: typically shortens the QT interval.

These are pattern-recognition prompts, not stand-alone diagnostic criteria. Confirm suspected electrolyte abnormalities with laboratory testing and interpret ECG changes in clinical context.

8. Red flags and interpretation pitfalls

Clinical red flags

Exertional syncope or exertional chest pain.
Palpitations associated with syncope, near-syncope or haemodynamic compromise.
Reduced exercise tolerance or unexplained breathlessness.
Family history of premature sudden cardiac death, inherited arrhythmia or cardiomyopathy.
Abnormal cardiac examination or known congenital/acquired heart disease.

Common interpretation errors

Using adult reference values in infants and children.
Accepting automated axis, QT or interval measurements without checking the tracing.
Misplacing V1–V2 or swapping limb leads.
Calling right ventricular hypertrophy from voltage alone.
Labelling a juvenile T-wave pattern as ischaemia without considering age and distribution.
Reassuring solely on the basis of a normal ECG when the history contains cardiac red flags.

Escalation: the RCH guideline recommends senior review of abnormal paediatric ECG findings and discussion with a senior clinician when cardiac red flags are present—even if the ECG appears normal. Suspected long QT syndrome warrants cardiology discussion.

9. Knowledge check

Test the key principles from this lesson. Select an answer and check the explanation.

Question 1. What is the most important principle when interpreting a child's ECG? Apply adult normal values, then adjust only for heart rate. Use age-appropriate reference values and clinical context. Diagnose hypertrophy whenever precordial voltage is high.

Question 2. Which finding can be a normal developmental variant? Persistent horizontal ST depression. New broad-complex tachycardia. T-wave inversion in V1–V3 in an age-appropriate child.

Question 3. An unexpected axis or repolarisation pattern is inconsistent with the clinical picture. What should you do first? Re-check lead placement and technical quality; repeat the ECG if appropriate. Assume the automated interpretation is correct. Ignore the finding if the child looks well.

10. Key takeaways

Paediatric ECGs change substantially with age; they must not be interpreted using adult norms alone.
Check identity, calibration, paper speed and electrode placement before interpreting the tracing.
Follow a reproducible sequence: rate, rhythm, axis, intervals, morphology, ST segments and T waves.
Right ventricular dominance in early life and juvenile T-wave inversion can be normal developmental findings.
Interpret the ECG alongside the history and examination. A normal tracing does not exclude important cardiac disease in a child with red flags.

References

Burns E, Buttner R. Paediatric ECG Basics.Life in the Fast Lane (LITFL), ECG Library. Published June 1, 2021. Supplied lesson source. The supplied PDF (pp. 1 and 4) provides the topic outline and identifies the original LITFL resource as licensed under Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International (CC BY-NC-SA 4.0). This page is an independently written educational adaptation with supplementary clinical references; the original source is attributed here. Source article · License.

Royal Children's Hospital Melbourne. Basic paediatric ECG interpretation.Clinical Practice Guideline. Last updated September 2023. Used as a supplementary source for age-related rate, axis, interval and voltage interpretation, technical review and red flags. Guideline.

How to interpret an electrocardiogram in children.Open-access review, PMC7808076. Supplementary reference for systematic paediatric ECG interpretation and technical aspects. Full text.

Society for Academic Emergency Medicine (SAEM). Rhythm Interpretation.Paediatric emergency medicine educational resource. Supplementary overview of age-related differences and systematic rhythm interpretation. Resource.

Medical education disclaimer: This page is intended for educational purposes and does not replace clinical assessment, specialist consultation, current resuscitation guidance or local institutional protocols. Normal ranges vary between reference populations and measurement methods. Decisions for an individual child must be made by appropriately trained clinicians using the full clinical context.