In the emergency department, EKGs are utilized more frequently during the routine workup for adult patients.
However, in pediatric population, EKGs are particularly helpful tool when working up common chief complaints including syncope and chest pain. They also aid in the investigation of potential dysrhythmias, ingestions, or structural/congenital anomalies.
Studies investigating the accuracy of pediatric ECG interpretation in the ED have found discrepancy rates in the interpretation between ED providers and pediatric cardiologists of 13%-32%.
In this presentation we will review:
Basic neonatal physiology and how this impacts normal pediatric EKG findings
Normal age-related changes in the pediatric ECG
Interpretation of EKGs in the pediatric population is highly dependent on age, and changes dramatically throughout childhood.
Many of these changes are reflective of the anatomical dominance of the right ventricle during development.
During gestation, the fetus diverts a large proportion of the circulation away from the developing lungs towards the placenta, which serves as the primary organ of gas exchange, by maintaining an elevated pulmonary vascular resistance (PVR) and a low placental vascular resistance.
The high PVR during the fetal period is created by a combination of mechanical factors (compression of the small arteries by the fluid filled alveoli), interactions between / ratios of vasoconstrictor mediators (endothelin-1 and thromboxane vs prostacyclin and endothelium derived nitric oxide), and relative hypoxemia working in concert.
Additionally, early in gestation, the cross-sectional area of pulmonary vasculature is low, maintaining a high PVR, and the lungs receive only approximately 13% of the cardiac output at 20 weeks, which increases to 25–30% at 30 weeks owing to the rapid proliferation of pulmonary vessels with a resultant fall in PVR.
In adults, the left ventricle is considerably larger than the right ventricle due to ventricular adaptation to the resistance that must be overcome by the ventricles.
The left ventricle must overcome the pressure in the aorta and systemic circulation (normally 120 mmHg in adults). The right ventricle must overcome the pressure in the pulmonary circulation (normally 15 mmHg in adults).
Hence, the pressure in the systemic circulation is many times greater than the pressure in the pulmonary circulation, the left ventricle is much larger (ventricular volume and muscle mass) than the right ventricle.
At birth, the right ventricle is larger than the left because of the need to overcome high pulmonary artery pressures maintained in utero.
In one study, normal newborns pulmonary artery pressure showed a gradually decline after birth, the upper 95% limit reference range for PA pressure measured in normal newborns <72 h of age was 39.97 mm Hg.
Therefore, the diagnostic criteria of newborns pulmonary hypertension may be >40.00 mm Hg according to this limited study.
Therefore in the fetus, as well as in the newborn, the QRS complex is dominated by electrical currents generated by the right ventricle.
Large R-waves in leads V1–V3 are therefore normal. Right ventricular dominance also explains why the electrical axis of the heart is more rightwards in newborns.
With the expected fall in pulmonary artery pressure during infancy, right ventricular wall stress and thickness decrease, until right ventricular pressure approximates that of the adult, typically by 6 months of age.
EXPECTED NEONATAL ECG FINDINGS
This physiology produces an ECG picture reflective of right ventricular strain in adults.
T-wave inversions in V1-3
Right axis deviation
Dominant R wave in V1
Conduction intervals (PR interval, QRS duration) are shorter than adults due to the smaller cardiac size.
High PVR -> R ventricular hypertrophy -> = R axis deviation, R wave predominance, and t wave inversions in V1-V3
Important normal variants
The dramatic changes that occur at birth, with the removal of the low resistance placental circulation, and the fall in pulmonary resistance as the lungs open as well as the functional (later permanent) closure of the PDA and foramen ovale, require significant physiological adaptation.
Most of these changes occur rapidly over the first few hours and days of life but continue throughout the early childhood period and more gradually into adulthood.
The normal infant ECG changes rapidly over the first few weeks of life and it is not until 3 years of age that it begins to resemble that of an adult (regarding R wave progression). Significant differences, however, persist.
Age related changes
Heart rates are the most obvious manifestation of age-related variability within the pediatric ECG.
The normal mean heart rate for newborn infants 1 to 6 months of age ranges from 125 to 145 beats/min (bpm) with the normal resting heart rate of 80 bpm in adults typically not achieved until mid-adolescence.
These changes can be accounted for by the gradual increase in vagal tone that accompanies aging. Young children may also be anxious during ECG acquisition, causing an artifactual increase in the heart rate.
NORMAL VARIANTS: T WAVE INVERSION
Infants older than 48 hours of age should have inverted T waves in the right precordial leads. These findings persist throughout childhood with inversion to V4 being accepted as normal.
There is a progressive change to an upright T wave across the precordial leads from left to right as the child grows older. The T wave in lead V1 inverts by 7 days and typically remains inverted until at least age 7 years.
Many children will show persistence of an inverted T wave in V1 until their late teens.
7% normal children under 5 years of age plus a few older children, will show an RSR’ complex in the right precordial leads.
To be considered normal the width of the QRS should be no more than 10msec longer than normal, and the R’ voltage in V1 should be less than 15mm in infants under 1 year and less than 10mm over 1 year.
Incomplete RBBB in a normal ECG of a 2 year old
Elevated J point
Early repolarization is a common finding in young, healthy individuals. It appears as mild ST segment elevation that can be diffuse; however, it is more prominent in the precordial leads. The ST elevation in this setting appears like an elevated “J point.”
This is a completely normal finding and must be distinguished from pathological elevation of the ST segments.
PR interval is shorter.
Smaller muscle mass.
Young kids should have PR < 160 msec (<4 small boxes)
A PR > 200 msec (> 1 large box) is abnormal for any age
QT interval varies with heart rate:
Bazett formula is used to correct the QT for HR:
QTc = QT measured / (√R–R interval)
Normal QTc Infants less than 6 months = < 490 ms
Older than 6 months = < 440 ms
R axis deviation expected up to 6 months of age at which point it should begin to be left axis
QT normalizes after 6 months
R wave progression begins around age 2-3.
Incomplete RSR’ / RBBB morphology in precordial leads acceptable up to age 5
T wave inversions expected in the precordial leads up to age 7/8.
HR parameters begin to normalize in early adolescence >age 10
J point is often elevated in the precordial leads of young healthy individuals
Can use MD Calc to correct QTC intervals based on HR using Bazett formula
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Gina Polizzo, MD