Specificities of Pediatric Electrocardiography

Abstract

Electrocardiography is a simple method for assessing the electrical activity of the heart and indirectly its motor function. The basic principles of ECG interpretation in children are identical to those in adults. However, as a child develops from a fetus, newborn, infant, preschooler, school-aged child, to adolescent, the physiology of the heart and its position relative to the anterior chest wall change, resulting in age-specific characteristics. The most rapid changes in certain variables occur during infancy.

The characteristics of pediatric ECGs are primarily determined by hemodynamic conditions. At birth, the muscle mass ratio of the left and right ventricles is 1:1.3 in favor of the right ventricle. With the reduction of pulmonary vascular resistance, the definitive balance of resistance and pressure in the pulmonary and systemic circulations is established within 2–6 weeks of postnatal life. By the end of the neonatal period, the left ventricle assumes electrical dominance. By six months of age, the ventricular muscle mass ratio becomes 2:1 in favor of the left ventricle, and by preadolescence, the final ratio of 2.5:1 is reached. In healthy infants and children, the main ECG changes are characterized by age-dependent transitions in QRS complex morphology, QRS duration, and ST-segment and T-wave patterns. With development, heart rate gradually decreases, while the duration of the P-wave, PR interval, and QRS complex increases. In the first months of life, QRS voltages are lower compared to later ages. The mean QRS electrical axis in the frontal plane shifts from right to left. The normal right ventricular dominance observed in the neonatal period is gradually replaced by left ventricular dominance in later childhood and adulthood. This is reflected in the ECG as progressive R-wave increase in the precordial leads.

At birth and during the first few weeks of life, high R-waves and small S-waves are seen in leads V3R, V4R, and V1, while deep S-waves and small R-waves appear in left precordial leads V6 and V7. As left ventricular dominance develops, by two months of age, the precordial leads take on a more adult-like pattern, with deeper S-waves in the right precordial leads and higher R-waves in the left precordial leads. At this stage, a prominent R-wave is still seen in V1. By one year of age, precordial R-wave progression resembles that of adults, with small R-waves and deep S-waves in the right precordial leads. T-waves also change characteristically. In the first few minutes after birth, the T-wave is positive in V1 and V6. Within a few hours, it may flatten or invert in the left precordial leads. Over the next few days, T-wave inversion occurs in V1, while it remains positive in V6. Finally, T-waves become positive again in V1 after 7–8 years of age, although they may remain inverted during adolescence (the so-called juvenile pattern).

There is considerable variation within the normal range for each age group, but in general, the younger the age group, the broader the normal ranges. A systematic approach to ECG analysis is important to minimize the risk of oversight. Interval measurements are performed in lead II. When interpreting heart rate, the child’s age and physiological state must be considered.

Incomplete (partial) right bundle branch block is found in 7–10% of children, raising questions about its clinical significance. From an electrophysiological standpoint, it is not considered a true block but rather a consequence of different right ventricular activation. It may be a normal variant in healthy children, but it is most commonly associated with volume overload of the right ventricle due to an atrial septal defect. Provided that electrodes are placed correctly during ECG recording, findings should be interpreted within the clinical context. If the voltages of the r and r' waves are within normal limits and the QRS complex has normal duration, the finding can be considered normal. If R' exceeds 10 mm, additional evaluation with echocardiography is indicated.

In conclusion, ECG findings should always be interpreted within the clinical context. The distinction between a normal and pathological ECG is not always clear. Careful ECG analysis is invaluable, as it has long been said that "more people suffer from their ECG than from heart disease"; Special attention should be given to the specific characteristics of pediatric ECGs, as the well-known principle still holds: a child is not just a small adult.