Ten ‘not to be missed’ paediatric ECGs

Cite this article as:
Jordan Evans, Megan Thomas, Amos Wong and Jeff Morgan. Ten ‘not to be missed’ paediatric ECGs, Don't Forget the Bubbles, 2020. Available at:

To refresh your memory on how to read paediatric ECGs take a look at Anna McCorquodale’s fantastic article: Approaching the paediatric ECG.

Here we review ten ‘not to be missed’ abnormal ECGs that may be encountered in acute paediatrics. 

#1 Supraventricular Tachycardia (SVT)

What is it?

SVT is a narrow complex tachycardia, the electrical activity originates above the ventricles (‘supraventricular’). SVT is classified based on whether it originates from the atrium or from the AV node. Finding where the position of the P wave is (with respect to the QRS complex) during tachycardia (‘P wave hunting’) is essential for the diagnosis of SVT.

Why does it happen?

It usually occurs due to one of the following mechanisms:

  • An accessory pathway linking the ventricle to the atrium, which impulses can travel along returning into the atria (AVRT, Atrioventricular Re-entrant Tachycardia)
  • A micro re-entrant circuit in the AV node itself (AVNRT, AV node re-entrant tachycardia)
  • An enhanced automatic focus in the atrium which fires impulses out 

These all lead to excessive impulses being conducted to the ventricles.

So what do we see on ECG?

  • A fast narrow complex tachycardia (approx. 150-220 bpm)
  • SVT – The hunt for the missing P wave:  It is a common misconception  in SVT that there are no P waves. Whilst this may appear to be the case, this is because the P wave is in fact hidden elsewhere.  The location of the missing P wave will depend on the type of SVT.
  • Lack of beat to beat variability i.e. you will see on the monitor that the rate stays pretty much constant

Atrioventricular Re-entrant Tachycardia (AVRT)

This is when there is an accessory electrical pathway connecting the ventricles and the atria. This creates a re-entrant circuit, with impulses either being conducted down the AV node and then back up the accessory pathway (orthodromic) or vice versa (antidromic).  You may see a retrograde P wave at the end of the QRS complex. (See #2 for further info on Wolff-Parkinson-White Syndrome, a classic type of AVRT).

Atrioventricular Nodal Re-entrant Tachycardia (AVNRT)

A micro re-entrant circuit forms in, or adjacent to, the AV node itself.  Here, P waves are very hard to find as they are usually buried in the QRS complex. The circuit often stimulates both the atria and ventricles and therefore the P-wave is hidden, buried within the QRS complex. 

AVNRT: N for No P waves!

Permanent junctional reciprocating tachycardia (PJRT)

This is a type of orthodromic AVRT where the concealed accessory pathway is near the coronary sinus. This means it can conduct at a relatively slow rate for a tachycardia. The characteristic of PJRT is Long RP tachycardia where the P wave is inverted in the inferior leads (hence NOT in sinus rhythm!) and the RP interval is longer than PR interval.

PJRT is commonly misdiagnosed as sinus tachycardia.  If PJRT is suspected seek cardiology input as adenosine is often ineffective and therefore needing multiple anti-arrhythmic therapy.

#2 Wolff-Parkinson-White Syndrome (WPW)

What is it?

Wolff-Parkinson-White is a conduction abnormality, where there is an accessory pathway connecting the atria and the ventricles. If this accessory pathway conducts from the atria to the ventricles (anterogradely) then it can be seen on the ECG as ‘pre-excitation’, as the impulse will travel faster down the accessory pathway than the rate-limited AV node.  WPW can lead to SVT (AVRT type).

What do we see on ECG?

A short PR interval (<120ms) is seen.

The most distinguishing feature is a delta wave which appears as a slow upslope between the Q wave and the R wave – with the Q wave being much earlier than usual. This means that the QRS is wide (>100ms).  The delta wave reflects fusion between the accessory pathway and the normal QRS as conducted via the AV node.

#3 Complete Heart Block

What is it?

Complete heart block (also known as ‘Third Degree’ heart block) occurs when an impulse isn’t conducted from the atria to the ventricles, usually due to AV node pathology. This means that whilst the atrial rate is determined by the SA node, the ventricular rate is a ventricular escape rhythm –which is much slower than the rate of the SA node. This means that the ventricles and atria, therefore, contract completely independent of one another. In AVN block a narrow QRS is seen, whereas, in an infranodal block, a wide QRS is seen. The former is more stable as the pacemaker site is more proximal (Bundle of His) so asystole is less likely.

Why does it happen?

Heart block can occur for a variety of reasons in children, but often it is congenital- secondary to either structural disease (i.e congenitally corrected transposition of the great arteries) or maternal antibodies, as seen in neonatal lupus. Congenital heart block associated with underlying structural heart disease has a poorer prognosis.

So what do we see on ECG?

There are regular P waves and regular QRS complexes, but these are completely unrelated to one another.

But what about the other blocks?

#4 Myocarditis

What is it?

As suggested in the name, myocarditis is inflammation of the myocardium. This can occur due to infection (viruses, bacteria, spirochetes, fungi, and other organisms) having a direct toxic effect on the myocardium.  It is important to consider the diagnosis in children who have recently suffered a systemic illness (esp. Coxsackie). Certain drugs may also be responsible (anthracycline chemotherapy and alcohol).  Myocarditis may occur alongside pericarditis. The inflamed myocardium is unable to contract and conduct as well as usual resulting in poor function of the heart.

So what do we see on ECG?

Usually, myocarditis presents with sinus tachycardia and non-specific T-wave and ST-segment changes (e.g. T wave inversion). We may also see:

  • QRS/QT prolongation
  • Low voltage QRS (<5mm in precordial leads)
  • Pathological Q waves
  • Ventricular arrhythmias (can be ectopics or VT)
  • AV block 

#5 Dilated Cardiomyopathy (DCM)

What is it?

Dilated Cardiomyopathy (DCM) is characterized by weak and floppy myocardium.  It may be inherited or develop as a result of myocarditis secondary to infection or drugs.

So what do we see on ECG?

Cardiomyopathies show similar features to myocarditis.  Pathologically it’s a spectrum, the inflammation in myocarditis is the ‘active phase’ leading to muscle damage present in cardiomyopathy. Changes may include:

  • QRS/QT prolongation
  • Low voltage QRS (<5mm in precordial leads)
  • T wave / ST segment changes
  • Pathological Q waves
  • Ventricular arrhythmias (can be ectopics or VT)
  • AV block 

#6 Hypertrophic Cardiomyopathy (HOCM)

What is it?

HOCM is a genetic condition that affects the sarcomeres in the heart causing left ventricular hypertrophy (LVH), which cannot be explained by other causes. It is very important as it’s the most common cause of sudden cardiac death in those <35, and those who have HOCM may require an internal cardiac defibrillator.

So how do we figure out if there is HOCM?

There are many criteria that can be used to describe HOCM, however no one criteria has been determined to be the most reliable (especially in children).

So what do we see on ECG?

Whereas in DCM there are small QRS complexes, in HOCM they are large due to the hypertrophied muscle.  As above with myocarditis and dilated cardiomyopathy: T wave inversion and ST changes indicate unhealthy myocardium. Pathological Q waves may also be seen.

#7 Long QT

What is it?

As the name suggests, this is when the QT interval is prolonged. In order to determine if the QT is prolonged then we need to determine the QTc using Bazetts formula.

Source: litfl.com/bazett-formula/
  • In boys, a prolonged QTc is >450ms
  • In girls a prolonged QTc is >460ms.

The most important tool in trying to determine the cause of a prolonged QT interval is history! Certain features make a congenital cause of a prolonged QT interval much more likely:

  • Syncope (+/- stress)
  • Congenital deafness (suggests LQT5)
  • FHx of sudden cardiac death <30 yr in immediate family
  • FHx of Long QT syndrome
  • Certain medications

What causes it?

There are many causes of a prolonged QT interval, including:

Acquired prolonged QT: This is when a child has a prolonged QT interval secondary to an underlying cause such as:

  • Drugs: antibiotics, antidepressants, antipsychotics, antihistamines, antiarrythmics, antifungals
  • Electrolyte disturbances
  • Hypothermia

Congenital long QT syndrome: This is an inherited channelopathy, where the child has a prolonged QT interval present either at baseline or unmasked by a stimulus.

There are 17 different forms of long QT syndrome (and counting!), which each have a different genetic mutation.

Three main types of Long QT syndrome (LQTS):

NameGeneTriggersFrequencyT waves
LQT1KCNQ1Peak exercise40%Early onset broad based.
LQT2KCNH2Sudden loud noises, swimming, emotion, stress30%Low voltage double bumped ‘bifid’ T wave with notching
LQT3SCN5ARest, sleep10%Late onset T wave  

ECG changes may be seen at rest or the child may need to go through exercise tolerance testing or an adrenaline challenge in order to unmask the prolonged QT interval.

So what do we see on ECG?

Nice one, Sherlock, you guessed it!  The main feature is a prolonged QTc interval.      

Why do we care so much about a prolonged QT interval?

Those who have a prolonged QT interval are at a higher risk of developing VT or Torsades de Pointes and therefore sudden cardiac death. This means it is important to identify these children so that they can receive medical therapy or an ICD if deemed necessary.

In paediatric cardiology, Schwartz criteria is used to determine the likelihood of Long QT syndrome. Whilst we do not reach an ultimate diagnosis in the ED, it is useful to note the risky features.

#8 Catecholaminergic Polymorphic Ventricular Tachycardia (CPVT)

What is it?

As the name suggests, it is a polymorphic (i.e. of multiple morphologies) ventricular tachycardia that is stimulated by catecholamines such as adrenaline. It is an inherited condition, which affects ion channels causing altered calcium flux leading to delayed after-depolarisations causing VT. Whilst baseline ECG may be normal, states in which there is a high adrenaline surge can unmask the CPVT (i.e. heavy exercise). If detected, these children need to be sent for further investigation for medical management or potentially an ICD.

So what do we see on ECG?

A polymorphic ventricular tachycardia. There are two types:

  • Normal baseline ECG!
  • Typical polymorphic / bidirectional VT – where both QRS complexes and T wave change in axis.

Differential for bidirectional VT = CPVT, LQTS Type 7 and Digoxin toxicity.

Do not shock CPVT! This may induce ‘electrical storm’ perpetuate the catecholamine release.  Seek advice from your local Paediatric Cardiologist.

#9 Brugada Syndrome

What is it?

This is an inherited channelopathy which affects impulse conduction, causing ventricular tachyarrhythmias and potentially sudden cardiac death. It is more common in males and commonly seen in carbohydrates consuming nations e.g. rice in South East Asia and pasta in the Western population. Interestingly, the same gene that causes LQT3 (see above) causes Brugada (SCN5A), however in the former there is a gain in function, whereas in Brugada there is a loss of function.

#10 Anomalous Left Coronary Artery arising from the Pulmonary Artery (ALCAPA)

What is it?

This is when the left coronary artery is connected to the pulmonary artery instead of the aorta. This means that instead of receiving oxygenated blood, the left side of the myocardium will receive deoxygenated blood. This can lead to myocardial ischaemia, which is initially transient occurring only in periods of increased myocardial demand (feeding, crying). However, as oxygen demand increases, infarction of the anterolateral left ventricular wall can occur.

So what ECG changes do we see?

  • Pathological Q waves (esp. in leads I, aVL and V6) – 50% of kids with Q waves in aVL have ALCAPA!
  • Ischaemic / T wave changes in inferolateral leads (II, III, aVF, V5-6).  Note on ECG below T waves in V5 and V6 are flattened