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The pediatric ECG is characterized by age-related variations and, because of this, can be very difficult to interpret. The age-related variations reflect the maturation of the pediatric myocardium and vascular system from birth to adulthood. Developmental changes in the pediatric ECG from birth to adolescence include a gradual shift from right to left ventricular dominance, a decrease in the resting heart rate, a lengthening of the PR and QRS intervals, and a change from inverted to upright T waves in the precordial leads.1–3 Use a systematic approach to ECG interpretation, checking rate, rhythm, axis, hypertrophy of the atria and ventricles, and repolarization changes. Reference tables with age-specific values are necessary to deal with the progressive changes in heart rate, axis, interval duration, and morphology. The most important changes are described in the following sections.

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Heart Rate

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The normal heart rate is age dependent (Table 143D-1).4 The neonatal and infant heart has a limited capacity to increase stroke volume, and cardiac output depends largely on rate. Rate is relatively high in the young infant to meet metabolic demands. Significant state-dependent and beat-to-beat variability in resting heart rate is characteristic of the normal neonatal and infant heart. Sinus tachycardia in the neonate can often reach 200 to 220 beats/min, and rates this high are common with fever or pain. In general, bradycardia with normal perfusion and without evidence of heart block (discussed below in Atrioventricular Block) rarely requires treatment or investigation.

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Table Graphic Jump Location
Table 143D-1 Normal Pediatric Heart Rates 
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P and QRS Axes

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The right ventricle predominates in the neonate, because in utero blood is shunted away from the fetal lungs and the right ventricle provides the majority of systemic blood. So the ECG in the first few months of life is characterized by right ventricular dominance and right axis deviation. P waves are upright in leads I and aVF, and the P axis ranges between 0 and +90 degrees. The R-wave amplitude is increased in V1 and V2 and decreased in V5 and V6. As the left ventricle increases in size during infancy and early childhood, the QRS axis shifts leftward, so that R-wave amplitude decreases in V1 and V2 and increases in V5 and V6 (Table 143D-2).1–4

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Table Graphic Jump Location
Table 143D-2 Age-Specific QRS Axis 

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