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Tipple M*. Interpretation of electrocardiograms in infants and children. Images Paediatr Cardiol 1999;1:3-13 |
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Paediatric Cardiologist, British Columbia Children's Hospital and Clinical Professor, University of British Columbia |
| MeSH | ||
| Electrocardiography | Diagnostic techniques and procedures | Heart defects, congenital |
Article
1. The Normal Electrocardiogram
As the child
develops from the foetus to the neonate, infant, child, adolescent and
adult, growth and development result in major changes of body size and
shape, and with this the size and position of the heart relative to the
body and cardiac physiology.
The most dramatic of these changes occur at birth and within the first year of life. In order to be able to interpret paediatric electrocardiograms (ECGs) it is therefore imperative, to have an understanding of these events.
Prior to birth, the ventricular pressures are equal and the pulmonary resistance is higher than the systemic, resulting in the right ventricular (RV) size and mass being larger than the left ventricular (LV) from 35 weeks gestation.
The placenta which receives 55% of the combined cardiac output provides a low resistance circuit to the systemic circulation. Right to left shunting occurs from the pulmonary artery to aorta via the patent ductus arteriosus (PDA) and from the right atrium to the left atrium via the foramen ovale. The small pulmonary arteries have more muscle than the small systemic arteries and pulmonary vasoconstriction further elevates the pulmonary resistance.
The dramatic changes at birth, with the removal of the low resistance placental circulation, the fall in pulmonary resistance as the lungs open and 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 left ventricle grows rapidly. By 1 month of age the LV/RV ratio has changed to 1.5:1 from the birth ratio 0.8:1, by 6 months 2:1 and then slowly to the adult ratio 2.5:1.
With these rapidly changing haemodynamics, one can expect the interpretation of the neonatal ECG to be the most challenging. There are many normal variables with a wide overlap from normal to abnormal. The less than 35 week gestation premature infant will have a different ECG from the full term infant. 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. Significant differences, however, persist. Unless the interpreter is aware of these, the young patient is in danger of becoming an “electrocardiographic casualty” like several normal children I have seen with the ECG diagnosis of “acute myocardial infarction.”
In order to interpret paediatric electrocardiograms, the age of the patient and a table of normal values are essential. Davignon et al published the most recent values for a normal population. 2141 white children were divided into 12 different age groups, 7 within the first year of life.
Important Normal Variants
T wave inversion:
Infants older than 48 hours of age should have inverted T waves in
the right praecordial 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 praecordial leads from left to right as
the child grows older. Until 8 years of age an upright T wave in V1 is
considered a sign of right ventricular hypertrophy. Many children will
show persistence of an inverted T wave in V1 until their late teens.
RSR’ complex
7% normal children under 5 years of age plus a few older children,
will show an RSR’ complex in the right praecordial 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.
Elevated J point
Early repolarization is commonly seen in adolescence with an elevated
J point, most obvious in the mid praecordial leads. This is a completely
normal finding and must be distinguished from pathological elevation of
the ST segments.
Reading and Interpreting Electrocardiograms
Unless the patient’s age is known, the paediatric ECG cannot be interpreted.
With the age in mind, the tracing may then be read objectively but to be
interpreted fully additional clinical information is required, including:
| Premature infant (<35/40 gestation)
Relative tachycardia <200/min Relative LV dominance, less RV dominance P and QRS axis directed more left and posteriorly Shorter P, QRS, QT intervals Smaller R in V1, taller R in V6 Taller T in V6 More variability than the full term infant |
Full Term Newborn infant
Right axis deviation (up to +180) RV dominance in praecordial leads: - tall R in V1 ( >10mm suggests RVH) - deep S in V6 - R/S ratio >1 in right chest leads, relatively small in left QRS voltages in limb leads relatively small T waves – low voltage T wave in V1 maybe upright for < 48 hours (>48 hours suggests RVH) |
| 1 week - 1 month
Right axis retained R waves remain dominant across to V6, although dominant S maybe normal T wave negative V1 T wave voltage higher in limb leads |
1 – 6 months
QRS axis rotates to leftward (less than +120) R wave remains dominant in V1 R/S ratio in V2 close to I but maybe >1 in V1 RSR’ pattern in V1 not abnormal Large voltages in praecordial leads suggestive of BVH T waves negative across right chest leads |
| 6 months – 3 years
QRS axis usually < +90 R wave dominant in V6 R/S ratio in V1 close to or less than 1 Large voltages in praecordial leads persist |
3 - 8 years
Adult QRS progression in praecordial leads: dominant S in V1, dominant R in V6 Large praecordial voltages persist q waves in left chest leads may be large (< 5mm) T waves remain negative in right praecordial leads |
Example: 1day old infant
Sinus rhythm. Heart rate 125. Axis 130 PR 0.15. QRS 0.06. QT/QTc 0.28/0.40 Upright T waves right chest leads Within normal limits for age |
Example: 2 day old infant
Sinus rhythm. Heart rate 130. Axis +135 PR 0.16. QRS 0.06. QT/QTc 0.28/0.41 Dominant RV voltages. Biphasic T wave V1-4 Within normal limits for age |
| 1 week to 1 month
Right axis retained R waves remain dominant across to V6, although dominant S maybe normal T wave negative V1 T wave voltage higher in limb leads |
Example: 3 week old infant
Sinus rhythm. Heart rate 125. Axis +100 PR 0.12. QRS 0.06. QT/QTc 300/430 Normal ECG for age |
| 1 – 6 months
QRS axis rotates to leftward (less than +120) R wave remains dominant in V1 R/S ratio in V2 close to I but maybe >1 in V1 RSR’ pattern in V1 not abnormal Large voltages in praecordial leads suggestive of BVH T waves negative across right chest leads |
Example: 2 month old infant
Sinus rhythm. Heart rate 150. QRS axis +80 PR 0.08. QRS 0.06. QT / QTc 0.25/0.4 RSR’ pattern V1 Normal tracing for age |
Example: 3 month old infant
Sinus rhythm. Heart rate 130. QRS axis +90 PR 0.10. QRS 0.08. QT/QTc 0.28/0.40 Normal tracing for age |
| 6 months – 3 years
QRS axis usually < +90 R wave dominant in V6 R/S ratio in V1 close to or less than 1 Large voltages in praecordial leads persist |
Example: 8 month old infant
Sinus rhythm. Heart rate 140. QRS axis + 60 PR 0.10. QRS 0.06. QT/QTc 0.28/0.42 Prominent praecordial voltages Normal for age |
Example: 23 month old female
Sinus rhythm. Heart Rate 94. QRS axis +60 PR 0.12. QRS 0.08. QT/QTc 0.32/0.37 Normal electrocardiogram |
Example: 2 year old female
Sinus rhythm. Heart rate 80. QRS axis +80 PR 0.18. QRS 0.08. QT 0.36 RV conduction delay. (R’= 8mm) Within normal limits for age |
| 3 - 8 years
Adult QRS progression in praecordial leads: dominant S in V1, dominant R in V6 Large praecordial voltages persist q waves in left chest leads may be large (< 5mm) T waves remain negative in right praecordial leads |
Example: 6 year old female
Sinus rhythm. Heart rate 75. QRS axis +88. PR 0.18. QRS 0.06. QT/QTc 0.36/0.40 Normal for age |
| 8 – 16 years
QRS axis mean +60, range 0 to +90 Adult QRS progression Large praecordial lead voltages, R in left leads larger than adult High J point T waves variable. Maybe upright in V1 but negative V1-V4 not abnormal |
Example: 15 year old male
Sinus rhythm. Heart Rate 75-80. Axis 0 PR 0.18. QRS 0.08. QT 0.38/0.43 Left axis. Deep posterior praecordial voltages Elevated J point V2-4 = Early repolarization. Within normal limits for age |
| Adult
QRS axis mean +50, range 0 to +100 Dominant LV T waves upright across praecordial leads |
Additional reading
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