The approach to the pediatric electrocardiogram (ECG) is similar to that of the adult ECG with the notable exception of an awareness of age‐related norms regarding rate, interval length, complex width, and so on; in addition, certain findings, both normal and abnormal, are particular to the pediatric ECG. It is important to remember that pediatric ECGs, especially in the neonate and infant, have significant, age‐related differences from their adult counterparts. Nonetheless, a systematic evaluation of rate, rhythm, axis, and evaluation of PR, QRS, and QT intervals will identify the majority of clinically relevant pediatric ECG abnormalities.

For most clinicians, understanding the age‐related findings and trends in the ECG are more important than remembering specific, age‐dependent values. The recognition of normal morphologic findings with respect to age is also important. A brief understanding of fetal circulation, and its transition to adult physiology, is important in the understanding of the pediatric ECG. In fetal circulation, the pulmonary circuit is a high‐pressure system because of the hypoxic vasoconstriction of the pulmonary vessels. Blood is preferentially shunted from the right side to the left side of the heart because of the pressure gradient produced. These factors all contribute to the fetus being right‐heart dominant. In the neonatal period, pulmonary vascular resistance falls, leading to the adult circulatory pattern over the first several years of life. Over time, these changes cause the left ventricle to mature. Thus, early in life, the ECG will demonstrate a right‐sided pattern of morphologic findings; as the heart grows and circulation becomes “more left‐sided,” the adult ECG patterns will predominate and become the age‐related normal. By early to mid‐adolescence, the pediatric and adult heart – and ECGs – become nearly indistinguishable.

Rate and Rhythm

Pediatric heart rates vary as a function of age (Table 14.1). Peaking near the second month of life, the heart rate trends down to adult levels in the adolescent years as the increasingly mature left ventricle is able to contribute to cardiac output by increasing the stroke volume as opposed to increasing its rate. The accepted normal values for pediatric heart rates cover a broader range than those for adults, such that the patient’s clinical status must be taken into account even if the heart rate is within normal ranges for that age.

As with the adult, the normal pediatric rhythm is sinus rhythm with the P wave originating from the sinoatrial (SA) node, a consistent PR interval, and a P wave associated with each QRS complex (Figure 14.1a, b); in the 12‐lead ECG, the T waves are upright in leads I, II, and III (Figure 14.1b). Sinus arrhythmia (Figure 14.1c) is a normal variant rhythm, not indicative of underlying pathology of any sort; it is seen when all aspects of normal sinus rhythm are satisfied with the exception of a regular rhythm – slight irregularity is seen in this rhythm. An analysis of these structures and their relationship to one another will aid in rhythm assessment and will enable the clinician to determine most cardiac rhythms.

QRS Axis

The axis of the pediatric ECG is distinct from that of the adult in that it is predictably dynamic over periods of time. This dynamic nature is primarily the result of changes in right versus left heart forces that occur with the change from fetal to neonatal to adult circulatory patterns. The most pronounced changes occur over the first year of life, when the axis goes from an age‐appropriate right axis to a pattern more consistent with a normal adult axis. Most obvious of these is a prominent R wave in leads V1 and V2, reflecting the dominant right ventricle and diminutive R waves in leads V5 and V6, indicative of the relatively thin‐walled left ventricle (Figures 14.1b and 14.2). As the left ventricle matures under its increased workload, the R wave progression approaches the adult norm, with minimal to no R wave in the right precordial leads (V1–V3) to prominent R wave in the left precordial leads (V4–V6).

T Waves

The T wave on the pediatric ECG is most often upright in the limb leads. In the precordial leads (predominantly lead V1–V4), however, the T wave is frequently inverted and is, in fact, considered normal when inverted, creating an important area of “interpretation disparity” between the adult and pediatric ECG (Figures 14.1b and 14.2). This distribution of T wave inversion is termed the juvenile T wave pattern. This juvenile T wave pattern can persist into adolescence. In fact, in the pediatric population, upright T waves in the right to midprecordial leads can be evidence of cardiac pathology, namely, right ventricular hypertrophy (RVH).

Intervals

As with heart rate, the pediatric PR interval and QRS complex duration vary as a function of age (Table 14.1). Neonates have shorter PR intervals and more narrow QRS complex widths that increase as the cardiac muscle and conduction system mature. In evaluating the ECG, the age‐appropriate intervals must be used to determine the presence of atrioventricular (AV) block and QRS complex widening. For example, a neonate with a PR interval of 0.2 is clearly outside of the normal range, and thus has a first‐degree block, whereas an older child or adult with the same PR interval would be considered normal.

The evaluation of the QT interval is more straightforward in the infant, child, and adolescent. The QT interval is corrected for the heart rate and is expressed as the corrected QT interval, or QTc interval. The calculation of QTc is the same in children as in adults (QTc = QT/√RR). A normal QTc is under 0.450 s.

Common Dysrhythmias

Paroxysmal Supraventricular Tachycardia

Paroxysmal supraventricular tachycardia (PSVT) is the most common pediatric dysrhythmia (Boxes 14.1 and 14.2). It can occur at any age but it most often occurs during infancy. The two common mechanisms by which PSVT occurs are either an accessory pathway (i.e. Wolff–Parkinson–White syndrome) that conducts the electrical impulse (more likely in children) or an AV nodal reentry (more likely in adolescents). Differentiating between these two causes is difficult and largely unnecessary for the emergency clinician.

The clinical presentation of a patient with PSVT often is fussiness, lethargy, or poor feeding in infants, and palpitations, dyspnea, or lightheadedness in older children. The ECG will reveal a regular, narrow QRS complex tachycardia with a heart rate around 220 bpm (range 180–300 bpm) without obvious P waves and little R–R variability (Figure 14.3a [neonate] and Figure 14.3b [adolescent]). With extremely rapid ventricular rates, the QRS complex can widen as a result of the bundle branch system’s inability to repolarize at a sufficiently rapid rate, thus producing bundle fatigue and a widened QRS complex (Figure 14.3c [six month‐old infant]).

P waves can occur in certain individuals, the so‐called retrograde P wave (Figure 14.3d). This type of P wave has nothing to do with rhythm genesis; rather, as the impulse is generated in the supraventricular focus, it moves distally into the ventricle, producing a ventricular depolarization (and QRS complex) and simultaneously, in retrograde manner, back into the atrial tissues, causing depolarization and resultant P wave – the retrograde P wave. These P waves are frequently located immediately adjacent to the QRS complex, before or after, and are usually inverted.