Diagnosis of abnormality on a paediatric electrocardiogram will require knowledge of normal age related values, particularly for criteria relating to right or left ventricular hypertrophy.
P wave amplitude varies little with age and is best evaluated from lead II, V1, or V4R. Wide P waves indicate left atrial hypertrophy, and P waves taller than 2.5 mm in lead II indicate right atrial hypertrophy. P waves showing an abnormal pattern, such as inversion in leads II or aVF, indicate atrial activation from a site other than the sinoatrial node.
Electrocardiogram from 3 year old with restrictive cardiomyopathy and severe right and left atrial enlargement. Tall (>2.5 mm), wide P waves are clearly seen in lead II, and P wave in V1 is markedly biphasic
Prolongation of the QRS complex may be due to bundle branch block, ventricular hypertrophy, metabolic disturbances, or drugs.
Diagnosis of ventricular hypertrophy by "voltage criteria" will depend on age adjusted values for R wave and S wave amplitudes. However, several electrocardiographic features may be useful in making a diagnosis. A qR complex or an rSR' pattern in lead V1, upright T waves in the right precordial leads between ages 7 days and 7 years, marked right axis deviation (particularly associated with right atrial enlargement), and complete reversal of the adult precordial pattern of R and S waves will all suggest right ventricular hypertrophy. Left ventricular hypertrophy may be indicated by deep Q waves in the left precordial leads or the typical adult changes of lateral ST depression and T wave inversion.
Electrocardiogram from 13 year old boy with transposition of great arteries and previous Mustard's procedure. The right ventricle is the systemic ventricle and the trace shows right ventricular hypertrophy with marked right axis deviation and a dominant R wave in the right precordial leads
Electrocardiogram from 11 year old girl with left ventricular hypertrophy secondary to systemic hypertension. There are tall voltages in the left precordial and limb leads with secondary ST depression and T wave inversion
The QT interval must be corrected for heart rate by dividing its value by the square root of the R-R interval. A corrected QT interval exceeding 0.45 s should be considered prolonged, but it should be noted that the QT interval is highly variable in the first three days of life. QT prolongation may be seen in association with hypokalaemia, hypocalcaemia, hypothermia, drug treatment, cerebral injury, and the congenital long QT syndrome. Other features of the long QT syndrome include notching of the T waves, abnormal U waves, relative bradycardia for age, and T wave alternans. These children may be at risk of ventricular arrhythmia and sudden cardiac death.
Electrocardiogram from 3 year old girl with long QT syndrome
Prolongation of QT interval in association with T wave alternans (note alternating upright and inverted T waves )
Q waves are normally present in leads II, III, aVF, V5, and V6. Q waves in other leads are rare and associated with disease (for example, an anomalous left coronary artery, or myocardial infarction secondary to Kawasaki syndrome). ST segment elevation may be a normal finding in teenagers as a result of early repolarisation. It may also be seen in myocardial infarction, myocarditis, or pericarditis.
In addition to the changes seen in ventricular hypertrophy, T waves may be inverted as a result of myocardial disease (inflammation, infarction, or contusion). Flat T waves are seen in association with hypothyroidism. Abnormally tall T waves occur with hyperkalaemia.