Child Abnormal ECG: What Does It Mean for My Child?

An abnormal ECG in a child means the heart tracing falls outside what the machine or reader expected, not that a heart condition has been found. Many ECG features change with age, so a child's tracing must be compared with age-specific normal limits. Several patterns that would be unusual in an adult are normal in babies and children.

An ECG (electrocardiogram) records the electrical activity of the heart, including its rate and rhythm. It is quick and painless: sticky patches go on the arms, legs and chest, and nothing is sent into the body. This guide helps parents and carers understand the report and prepare questions. It cannot interpret your child's tracing or decide what happens next.

Do not wait for a routine appointment if your child has any of the signs below. The American Academy of Pediatrics (AAP) advises calling emergency services or going to the nearest emergency department if a child faints while exercising. The NHS also advises calling 999 when someone faints while exercising or lying down, or has chest pain or a pounding, fluttering or irregular heartbeat.

• Fainting during or straight after exercise or sport.
• Fainting while lying down, or not waking up within about a minute.
• Chest pain, a racing or irregular heartbeat, or breathlessness before or with fainting.
• Trouble breathing, talking or moving after a faint, or shaking or jerking.
• Fainting suddenly after a medicine, an insect sting or a possible food allergen.
• Fall injuries with heavy bleeding.

A child's heart and body are still developing, and the ECG reflects this. The Royal Children's Hospital Melbourne (RCH) guideline gives a mean heart rate of about 145 beats per minute for newborns, compared with about 85 for those aged 14 and over. A rate that would be fast for an adult can be normal for a young child.

The electrical axis also differs. In the first weeks of life the heart's right side is relatively dominant, so the axis points further to the right than in adults. The RCH guideline lists different axis ranges for newborns and adults, and stresses that age-specific limits are essential for accurate assessment. Ranges vary with age and between references, so ask the team which limits they used.

Many ECG machines calculate intervals and axes automatically. The RCH guideline says these figures should be seen as a guide and not relied upon, and recommends manual checking. A computer label of 'abnormal' on a child's tracing therefore usually needs a clinician's review before it means anything.

The RCH guideline lists several findings that are often normal in infants, children or teenagers. Whether one applies to your child depends on age, the exact measurements and the rest of the tracing.

• Sinus arrhythmia: the heart rate speeds up and slows with breathing. This is a normal finding.
• T wave changes in the right chest leads: T waves in these leads are usually upright in the first days of life and then turn downward in most babies during the first week. Persistent inversion in lead V1 can be a normal variant.
• Benign early repolarisation: a common finding in adolescents.
• Partial bundle branch block without a widened QRS complex: considered a normal finding.
• Mildly raised voltages in the chest leads: a frequent normal variant.
• Small ST segment shifts: up to 1 mm in limb leads and up to 2 mm in chest leads may be normal in children.

The next step depends on the finding and the story around it. The RCH guideline advises discussing any child with cardiac red flags with a senior clinician, even if the ECG appears normal. Its red flags include chest pain or fainting with exertion, poor exercise tolerance, palpitations and a family history of early cardiac death.

Further tests may include a 24-hour ECG (Holter), an echocardiogram (an ultrasound of the heart's structure and pumping) or an exercise test. The guideline advises discussing with a cardiologist if long QT syndrome is suspected. The AAP notes that a paediatrician may refer a child to a paediatric cardiologist if fainting happens more than once or there are signs of a more serious condition.

An ECG and an echo answer different questions. The ECG shows electrical activity; the echo shows structure. A normal echo does not automatically explain every ECG finding, and a variant ECG does not always need an echo.

Most fainting in young people is not caused by the heart. Common triggers include dehydration, strong emotions and standing for a long time, and most children recover quickly. Fainting during exercise is different. The AAP says it always needs medical follow-up, because heart rhythm problems or structural heart problems can cause it.

Healthdirect Australia's linked resources note that fainting for no clear reason, during or after exercise, should prompt investigation for long QT syndrome. Tell the clinician exactly what your child was doing, whether there were palpitations or chest pain beforehand, and whether any close relative died suddenly at a young age, including unexplained drowning or accidents.

Bring the full ECG report, not just a portal summary. These questions can help you leave the appointment with a clear plan.

• Which finding was labelled abnormal, and was it the machine's label or a clinician's reading?
• Is this finding normal for my child's age, and which age limits were used?
• Does my child's history, including any fainting, palpitations or family history, change how the ECG is read?
• Is a repeat ECG, an echo, a Holter monitor or an exercise test needed, and what would each answer?
• Should my child pause any sport or activity until the review is complete?
• Who will contact us with results, and by when?

On SameCase, patients, families and verified doctors share de-identified cases. Reading how other families' children's ECG findings were described and followed up can help you notice details worth raising, such as the exact report wording or what was asked about family history.

Other children's results cannot tell you what your child's ECG means. We do not offer diagnoses. Use what you read to prepare questions for your child's own care team, and seek urgent care for any warning sign above.

Write down which finding was flagged, the planned next step and the date you expect to hear back. If you have not heard after a few weeks, contact the team that arranged the ECG. A reassuring review does not replace urgent care if new symptoms appear, especially fainting during exercise.