8
6
tricular depolarization and the beginning of repolariza-
tion.
Rate: This is age dependent faster at 1/12 than at birth,
gradually slowing with increasing age thereafter.
In calculating the rate, either:
T wave is a rounded upright (positive) wave following
QRS, and represents ventricular repolarization.
QT interval is measured from the beginning of QRS to
the end of the T wave. It represents total ventricular ac-
tivity.
•
•
•
•
Divide 300 by the number of large squares in be-
tween R waves of successive beats OR
Divide 1500 by the number of small squares in be-
tween R waves of successive beats OR
Multiply the number of R-R cycles in 6 large
squares (1.2 sec.) by 50. OR
Multiply the number of R-R cycles between 2 mark-
ers on a rhythm strip (3 sec.) by 20.
U wave is a small rounded, upright wave following T
wave. It is most easily seen with a slow heart rate and
represents repolarization of purkinje fibres.
Rhythm: (the pace maker)
Paediatric ECG
•
Sinus: normal, tachycardia, bradycardia, arrhyth-
mia.
Proper interpretation of ECG relies on comparisons with
standards derived from normal population. While ECG
standards for normal adults have been firmly estab-
lished, few studies are available for children. Many au-
thors have demonstrated that these ECG standards could
be influenced by age, sex, nutrition and race. Paediatric
ECG is unique and also difficult to interpret in the neo-
natal period because of the rapid perinatal hemodynamic
changes and the wide overlap of normal and abnormal
values. Adequate analysis of the tracing requires a well-
standardized recording technique (size and position of
electrode and calibration). Information is particularly
scarce for some of the leads frequently used in the new
born infants and young children (V4R, V3R and V7). In
addition, data are often grouped together over relatively
wide period of time. Most of the age related changes in
paediatric ECG are related to the changes in the ratio of
left ventricular (LV) to right ventricular (RV) weight. At
birth, the right ventricle is thicker than the left ventricle,
thus making a right axis deviation (LAD) a normal find-
ing in the ECG of a term new born. As the child grows,
the normal RV dominance of the new born period is
gradually replaced by the LV dominance of the latter
childhood and adult. There is a tremendous variation of
the normal ECG at each age group. The ECG can diag-
nose many conditions and these can be inferred from
measurement of various intervals or specific patterns.
However, ECG could be normal in a child with a cardiac
disease and abnormal in a perfectly normal heart. There-
fore, electrocardiogram should be correlated with his-
tory, physical examination, radiographs and echocardio-
graph of the heart and should only be rarely used to di-
agnose cardiac disease outside this context.
•
•
Junctional: accelerated, tachycardia, PJC.
Atrial: flutter, fibrillation, paroxysmal supraven-
tricular tachycardia (PSVT), Parox-A-T, Wolff-
Parkinson-White syndrome
Ventricular: tachycardia, fibrillation, torsade de
pointes, premature ventricular contraction (PVC).
Pace maker rhythm: Atrial or ventricular.
•
•
P waves
•
•
•
Normal P wave: < 2.5mm in height (at normal
standardisation) ie 0.25mv. < 0.10 sec in duration.
Right atrial hypertrophy: P waves tall and peaked
(
>2.5mm high)
Left atrial hypertrophy: P waves broad (>0.10
sec in duration), broad and flat topped, broad and
notched (M-shaped) = P mitrale, broad and bi-
phasic.
COMBINE hypertrophy: there is tall and wide p
wave.
•
PR interval
•
The normal interval is age and heart rate dependent.
Usually
0.07 - 0.12 sec in children under 1 year of age
•
•
•
•
0.08 - 0.16 sec in children over 1 year of
0.10 - 0.18 sec in adolescents
age
0.10 - 0.20 sec in adults Shortened in pre
excitation syndromes, for example WPW
syndrome (short PR interval, widened QRS
interval, delta wave preceding the QRS com-
plex)
•
•
Prolonged in heart block
In the standard ECG recording:
•
•
•
•
•
1st degree heart block prolonged PR interval
2nd degree heart block
-Mobitz type I (Wenckebach).
-Mobitz type II
Paper speed
= 25mm/sec
small square (horizontal) = 0.04 sec
large square (horizontal) = 0.2 sec
0mm (vertical) = 1 mV
1
1
1
3rd degree (complete) heart block
(
Avdissociation
Variable in - wandering atrial pacemaker
-multi-focal atrial tachycardia
After the recording has been made, each strip of the
electrocardiograph should be analyzed for each of the
following: Rate, rhythm, P waves, PR Interval, QRS
Axis, QRS morphology, QT interval, T wave, U wave,
ST Segment, and RS progression
•
Electrical axis of the heart
The electrical axis is the sum total of all electrical cur-
rents generated by the ventricular myocardium during