2 Electrocardiography
2.1 Basics
The “ECG” is one of the basic diagnostic tests in pediatric cardiology. The standard electrocardiogram (ECG) in childhood includes 12 leads:
Bipolar limb leads (Einthoven triangle) (I, II, III)
Unipolar limb leads (Goldberger augmented leads) (aVR, aVL, aVF)
Precordial leads (Wilson) (V1 to V6; Fig. 2.1). In pediatric cardiology, the Wilson leads V1 to V6 are often complemented by the right precordial leads V3R and V4R that can contribute additional information for diagnosing hypertrophy:
V1: right sternal border in the 4th intercostal space (ICS)
V2: left sternal border in the 4th ICS
V3: midway between V2 and V4
V4: left mid-clavicular line (MCL) in the 5th ICS
V5: left anterior axillary line in the 5th ICS
V6: left mid-axillary line in the 5th ICS
Fig. 2.1 Locations of the Wilson leads on the thorax wall.
The additional right precordial leads are designated with an “R.” They correspond with the location of the left precordial leads on the right side of the thorax (i.e., V4R: right MCL in the 5th ICS).
Leads I, aVL, and V4 to V6 (left precordial leads) normally represent the left ventricle; while leads V1 to V3 and the right ventricular Wilson leads V3R and V4R (right precordial leads) represent the right ventricle.
The standard paper feed speed when recording is 50 mm/s. For recording over a long period, the feed speed can be reduced to 25 mm/s (“rhythm strips”). In the English-speaking world, a paper feed speed of 25 mm/s is routinely used.
Generally, the amplitude on the paper is set so that 1 cm of paper is equivalent to 1 mV. For very high amplitudes (e.g., with ventricular hypertrophy) amplification can be modified so that an amplitude of 0.5 cm is equivalent to 1 mV.
2.2 Special Features of the Pediatric ECG
Compared with an adult ECG, an ECG in childhood has the following special features (Fig. 2.2):
Higher heart rate
Shorter conduction intervals (PQ interval, QRS duration, QT interval)
Right ventricular dominance:
Axis deviation of the QRS complex to the right
High R wave in the right precordial leads (V4R, V3R, V1, V2, aVR)
Deep S wave in the left precordial leads (V5, V6, I)
Negative T wave in V1. Immediately after birth, the T waves are positive in all precordial leads in the first 4 to 8 days of life. After this, negative T waves are found in children in the right precordial leads (V4R to V1) and positive T waves in the left precordial leads. This pattern persists into adolescence before only positive T waves can be found in the precordial leads in adults.
Since the right ventricular muscle mass increases primarily in the last weeks of gestation, right ventricular dominance is less pronounced in premature infants. In addition, the amplitudes of the QRS complex and T wave are lower.
A bundle branch block features an M-shaped QRS complex. The second notch of the R wave is then designated R′ or r′, a second S notch is S′ or s′ by analogy. A capital or lower-case letter is used depending on the amplitude of the respective notch. A large notch is given a capital letter and a small notch, a lower-case letter.
An entirely negative QRS complex is described as QS. Examples are shown in Fig. 2.3.
ECG findings associated with some congenital heart defects are listed in Table 2.1.
Heart defect | Indicative findings |
Atrioventricular septal defect (“AV canal”) | Left axis deviation, possibly AV block I° |
Atrial septal defect, ostium secundum (ASD II) | Incomplete right bundle branch block of the volume overload type (rsR′) |
Atrial septal defect, ostium primum (ASD I) | Left axis deviation (minimal variant of an AV canal) |
Bland–White–Garland syndrome (abnormal origin of the left coronary artery from the pulmonary) | Anterolateral myocardial infarction (I, aVL, V5, V6) |
Tricuspid atresia | Left axis deviation |
Congenitally corrected transposition of the great arteries | Q waves in V1, no Q waves in the left precordial leads V5 and V6, frequently AV block I–III, sometimes accessory pathways with pre-excitation and supraventricular tachycardia |
Single ventricle | Monomorphic QRS complexes in all precordial leads, unusual Q waves |
Mitral valve prolapse | Usually unremarkable ECG, sometimes abnormal repolarization in II, III, aVF: non-specific ST segment changes, conspicuous T waves, T wave inversion, etc. |
2.3 Evaluation
The routine evaluation of an ECG should include the following points:
Heart rhythm (e.g., sinus rhythm, ectopic atrial rhythm, escape rhythm)
Heart rate
Cardiac axis or QRS axis, T axis
Conduction intervals: PQ, QRS, QT, and QTc
Evaluation of the P wave: amplitude, duration, shape
Evaluation of the QRS complex: amplitude, duration, shape, evaluation of the R/S ratio in the precordial leads
Evaluation of the ST segment: take-off and course in relation to the PQ segment
Evaluation of the T wave: amplitude, duration, direction of deflection in comparison with the QRS complex (concordant, discordant)
Possibly evidence and evaluation of a U wave
Evidence or exclusion of extrasystoles
Overall assessment: Is the ECG consistent with a heart defect? Are there changes from the previous ECG?
2.3.1 Cardiac Rhythm
In an anatomically normal heart, the electrical impulse spreads from the sinus node in the upper right atrium to the lower left towards the AV node. This results in a P wave vector between 0° and 90°. Correspondingly, the P wave is positive in leads I and aVF. If the P wave has a different axis, there is usually an ectopic pacemaker in the atrial region.
Normally, every P wave is followed by a QRS complex. Otherwise there is an AV block or an escape rhythm or re-entrant tachycardia. If the P waves are missing and the QRS complexes are narrow, there is usually a junctional escape rhythm located around the AV node. Less frequently there may be a ventricular escape rhythm with wide ventricular complexes.
2.3.2 Heart Rate
The heart rate at rest is age dependent. The younger the child is, the higher the normal heart rate is:
Neonates: 90 to 160/min
1 to 5 years: 70 to 150/min
6 to 10 years: 60 to 140/min
10 to 15 years: 60 to 130/min
Over 15 years: 60 to 100/min
The heart rate is generally determined using an ECG ruler. Alternatively, it can be calculated using the R-R interval:
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