1. Prepared
By
Dr.Aso Faeq SALIH

2.  In the clinical diagnosis of congenital or acquired heart disease, the
presence of electrocardiographic (ECG) abnormalities is often helpful
 What is the vectorial approach?
The vectorial approach views the standard scalar ECG as three-dimensional
vector forces that vary with time.
A vector is a quantity that possesses magnitude and direction; a scalar is a
quantity that has magnitude only.
A scalar ECG, which is routinely obtained in clinical practice, shows only the
magnitude of the forces against time. However, by combining scalar leads
that represent the frontal projection and the horizontal projections of the
vector cardiogram, one can derive the direction of the force from scalar
ECGs. The limb leads (leads I, II, III, aVR, aVL, and aVF) provide information
about the frontal projection (reflecting superior-inferior and right-to-left
forces), and the precordial leads (leads V1 through V6, V3R, and V4R)
provide information about the horizontal plane that reflects forces that are right
to left and anterior-posterior It is important for the readers to become
familiar with the orientation of each scalar ECG lead. Once learned, the
vectorial approach helps the readers to retain the knowledge gained and
even helps them recall what has been forgotten.

3.  Figure 3-1 Hexaxial reference system (A) shows the frontal
projection of a vector loop, and horizontal reference system (B)

4. It is necessary to memorize the orientation of the hexaxial reference system The
hexaxial reference system is made up by the six limb leads (leads I, II, III, aVR, aVL,
and aVF) and provides information about the superoinferior and right-left
relationships of the electromotive forces. In this system, leads I and aVF cross at a
right angle at the electrical center The bipolar limb leads (I, II, and III) are clockwise
with an angle between them of 60 degrees. Note that the positive poles of aVR, aVL,
and aVF are directed toward the right and left shoulders and the foot, respectively.
The positive pole of lead I is labeled as 0 degree and the negative pole of the same
lead as ±180 degrees. The positive pole of aVF is designated as +90 degrees and
the negative pole of the same lead as -90 degrees. The positive poles of leads II
and III are +60 and +120 degrees, respectively, and so on.
The lead I axis represents the left-right relationship with the positive pole on the left and
the negative pole on the right. The aVF lead represents the superior-inferior
relationship with the positive pole directed inferiorly and the negative pole directed
superiorly. The R wave in each lead represents the depolarization force directed
toward the positive pole; the Q and S waves are the depolarization force directed
toward the negative pole. Therefore, the R wave of lead I represents the leftward
force and the S wave of the same lead represents the rightward force .The R wave in
aVF represents the inferiorly directed force and the S wave the superiorly directed
force. By the same token, the R wave in lead II represents the leftward and inferior
force and the R wave in lead III represents the rightward and inferior force. The R
wave in aVR represents the rightward and superior force and the R wave in aVL
represents the leftward and superior force.

6. The horizontal reference system consists of precordial leads (leads V1
through V6, V3R, and V4R) and provides information about the
anterior-posterior and the left-right relationship. Leads V2 and V6
cross approximately at a right angle at the electrical center of the
heart. The V6 axis represents the left-right relationship and the V2
axis represents the anterior-posterior relationship.
The precordial leads V3R and V4R are at the mirror image points of V3
and V4, respectively, in the right chest, and these leads are quite
popular in pediatric cardiology because right ventricular (RV) forces
are more prominent in infants and children.
Therefore, the R wave of V6 represents the leftward force and the R
wave of V2 the anterior force. Conversely, the S wave of V6
represents the rightward force and the S wave of V2 the posterior
force.
The R wave in V1, V3R, and V4R represents the rightward and anterior
force and the S wave of these leads represents the leftward and
posterior force The R wave of lead V5 in general represents the
leftward force, and the R waves of leads V3 and V4 represent a
transition between the right and left precordial leads.

7.  Three major types of information are available in the commonly available form of a 12-lead ECG
tracing
1. The lower part of the tracing is a rhythm strip (of lead II).
2. The upper left side of the recording gives frontal plane information and the upper right
side of the
recording presents horizontal plane information. The frontal plane information is provided by the six limb
leads (leads I, II, III, aVR, aVL, and aVF) and the horizontal plane information by the precordial leads.
In Figure 3-3 , the QRS vector is predominantly directed inferiorly (judged by predominant R waves in
leads II, III, and aVF, so-called inferior leads) and is equally anterior and posterior, judged by the
equiphasic QRS complex in V2.
3. There is also a calibration marker at the right (or left) margin, which is used to
determine the
magnitude of the forces. The calibration marker consists of two vertical deflections of 2.5 mm width. The
initial deflection shows the calibration factor for the six limb leads, and the latter part of the deflection
shows the calibration factor for the six precordial leads. With the full standardization, a 1- millivolt
signal introduced into the circuit causes a deflection of 10 mm on the record. With the half
standardization, the same signal produces a 5-mm deflection. The amplitude of ECG deflections is
read in millimeters rather than in millivolts. When the deflections are too big to be recorded, the
sensitivity may be reduced to one fourth. With half standardization, the measured height in
millimeters should be multiplied by 2 to obtain the correct amplitude of the deflection.
Thus, from the scalar ECG tracing, one can gain information about the frontal and horizontal orientations
of the QRS (or ventricular) complexes and other electrical activities of the heart as well as the
magnitude of such forces.

8. A common form of a routine 12-lead scalar electrocardiogram. There are three types of
information available on the recording. Frontal and horizontal plane information is
given on the upper part of the tracing. Calibration factors are shown on the right edge
of the recording. Rhythm strip (lead II) is shown at the bottom.

9. ECGs of normal infants and children are quite different from those of normal adults. The
most remarkable difference is RV dominance in infants. RV dominance is most
noticeable in newborns, and it gradually changes to left ventricular (LV) dominance
of adults. By 3 years of age, the child's ECG resembles that of young adults. The age-
related difference in the ECG reflects age-related anatomic differences; the right
ventricle (RV) is thicker than the left ventricle (LV) in newborns and infants, and the
LV is much thicker than the RV in adults.
RV dominance of infants is expressed in the ECG by right axis deviation (RAD) and large
rightward and/or anterior QRS forces (i.e., tall R waves in lead aVR and the right
precordial leads [V4R, V1, and V2] and deep S waves in lead I and the left precordial
leads [V5 and V6]), compared with the adult ECG.
An ECG from a 1-week old neonate is compared with that of a young adult .
The infant's ECG demonstrates RAD (+140 degrees) and dominant R waves in the right
precordial leads. The T wave in V1 is usually negative. Upright T waves in V1 in this
age group suggest right ventricular hypertrophy (RVH). Adult-type R/S progression in
the precordial leads (deep S waves in V1 and V2 and tall R waves in V5 and V6; is
rarely seen in the first month of life; instead, there may be complete reversal of the
adult-type R/S progression, with tall R waves in V1 and V2 and deep S waves in V5
and V6. Partial reversal is usually present, with dominant R waves in V1 and V2 as
well as in V5 and V6, in children between the ages of 1 month and 3 years.

10. The normal adult ECG demonstrates the QRS axis
near +60 degrees and the QRS forces directed to
the left, inferiorly and posteriorly, which is
manifested by dominant R waves in the left
precordial leads and dominant S waves in the right
precordial leads, the so-called adult R/S
progression.
The T waves are usually anteriorly oriented, resulting
in upright T waves in V2 through V6 and
sometimes in V1.

11. 1 month
Adult

12. They are briefly discussed in the order listed. This sequence is one of
many approaches that can be used in routine interpretation of an
ECG. The methods of their measurements are followed by their
normal and abnormal values and the significance of abnormal
values.
1. Rhythm (sinus or nonsinus) by considering the P axis
2. Heart rate (atrial and ventricular rates, if different)
3. The QRS axis, the T axis, and the QRS-T angle
4. Intervals: PR, QRS, and QT
5. The P-wave amplitude and duration
6. The QRS amplitude and R/S ratio; also abnormal Q waves
7. ST-segment and T-wave abnormalities

13. Sinus rhythm is the normal rhythm at any age and is characterized by P
waves preceding each QRS complex and a normal P axis (0 to +90
degrees); the latter is an often neglected criterion. The requirement
of a normal P axis is important in discriminating sinus from non sinus
rhythm. In sinus rhythm, the PR interval is regular but is not
necessarily normal. (The PR interval may be prolonged as seen in
sinus rhythm with first degree AV block.)
Because the sinoatrial node is located in the right upper part of the
atrial mass, the direction of atrial depolarization is from the right
upper part toward the left lower part, with the resulting P axis in the
lower left quadrant (0 to +90 degrees) .
Some atrial (nonsinus) rhythms may have P waves preceding each QRS
complex, but they have an abnormal P axis. For the P axis to be
between 0 and +90 degrees, P waves must be upright in leads I and
aVF or at least not inverted in these leads; simple inspection of these
two leads suffices. A normal P axis also results in upright P waves in
lead II and inverted P waves in aVR.

15. There are many different ways to calculate the heart rate, but they are all based on the
known time scale of ECG papers. At the usual paper speed of 25 mm/second, 1 mm
= 0.04 second and 5 mm = 0.20 second . The following methods are often used to
calculate the heart rate.
1. Count the R-R cycle in six large divisions (1/50 minute) and multiply it
by 50
2. When the heart rate is slow, count the number of large divisions
between two R waves and divide
that into 300 (because 1 minute = 300 large divisions)
3. Measure the R-R interval (in seconds) and divide 60 by the R-R
interval. The R-R interval is 0.36: 60 ÷ 0.36 = 166.
4. Use a convenient ECG ruler.
5. An approximate heart rate can be determined by memorizing heart
rates for selected R-R intervals
When R-R intervals are 5, 10, 15, 20, and 25 mm, the respective heart rates are 300,
150, 100, 75, and 60 beats/minute.
When the ventricular and atrial rates are different, as in complete heart block or atrial
flutter, the atrial rate can be calculated using the same methods as described for the
ventricular rate; for the atrial rate, the P-P interval rather than the R-R interval is
used.

16. ELECTROCARDIOGRAM PAPER. TIME IS MEASURED
ON THE HORIZONTAL AXIS. EACH 1 MM EQUALS 0.04
SECOND, AND EACH 5 MM
(A LARGE DIVISION) EQUALS 0.20 SECOND. THIRTY
MILLIMETERS (OR SIX LARGE DIVISIONS) EQUAL 1.2
SECOND OR 1/50 MINUTE.
HEART RATE OF 165 BEATS/MINUTE. THERE
ARE ABOUT 3.3 CARDIAC CYCLES (R-R
INTERVALS) IN SIX LARGE DIVISIONS.
THEREFORE
THE HEART RATE IS 3.3 × 50 = 165 (BY
METHOD 1).
BY METHOD 3, THE R-R INTERVAL IS 0.36
SECOND; 60 ÷ 0.36 = 166.
THE RATES DERIVED
BY THE TWO METHODS ARE VERY CLOSE.

17. HEART RATE OF 52 BEATS/MINUTE. THERE
ARE 5.8 LARGE DIVISIONS BETWEEN THE
TWO ARROWS. THEREFORE, THE HEART
RATE IS
300 ÷ 5.8 = 52.
QUICK ESTIMATION OF HEART RATE. WHEN
THE R-R INTERVAL IS 5 MM, THE HEART
RATE IS 300 BEATS/MINUTE. WHEN THE R-R
INTERVAL IS 10 MM, THE RATE IS 150
BEATS/MINUTE, AND SO ON
Heart rate according to age groups
Newborn 145 (90–180)
6 months 145 (105–185)
1 year 132 (105–170)
4 years 108 (72–135)
14 years 85 (60–120)

18. QRS AXIS, T AXIS, AND QRS-T
ANGLE
QRS Axis.
The most convenient way to determine
the QRS axis is the successive
approximation method using the
hexaxial reference system.
The same approach is also used for
the determination of the T axis .
For the determination of the QRS axis
(as well as the T axis), one uses only
the hexaxial reference system (or the
six limb leads), not the horizontal
reference system.
Successive Approximation
Method.
Step 1.
Locate a quadrant, using leads I and
aVF

19. In the top panel, the net QRS deflection of lead I is positive. This means
that the QRS axis is in the left hemicircle (i.e., from –90 degrees
through 0 to +90 degrees) from the lead I point of view. The net
positive QRS deflection in aVF means that the QRS axis is in the lower
hemicircle (i.e., from 0 through +90 degrees to +180 degrees) from
the aVF point of view. To satisfy the polarity of both leads I and aVF,
the QRS axis must be in the lower left quadrant (i.e., 0 to +90
degrees).
Four quadrants can be easily identified based on the QRS complexes in
leads I and aVF .
Step 2.
Among the remaining four limb leads, find a lead with an equiphasic
QRS complex (in which the height of the R wave and the depth of the
S wave are equal).
The QRS axis is perpendicular to the lead with an equiphasic QRS
complex in the predetermined quadrant.

20. Determine the QRS axis in Figure 3-12 .
Step 1.
The axis is in the lower left quadrant (0 to +90 degrees) because the R waves are
upright in leads I and aVF.
Step 2.
The QRS complex is equiphasic in aVL. Therefore, the QRS axis is +60 degrees,
which is perpendicular to
aVL.
Figure 3-12
A, Set of six limb leads.
B, Plotted QRS axis is shown.

21. Normal QRS Axis.
Normal ranges of QRS axis vary with age. Newborns normally
have RAD compared with the adult standard.
By 3 years of age, the QRS axis approaches the adult mean
value of +50 degrees.
Table 3-1 -- Mean and Ranges of Normal QRS Axes by
Age
Age Mean (Range)
1 wk–1 mo + 110° (+30 to +180)
1–3 mo + 70° (+10 to +125)
3 mo–3 yr + 60° (+10 to +110)
Older than 3 yr + 60° (+20 to +120)
Adult + 50° (- 30 to +105)

22. The QRS axis outside normal ranges signifies abnormalities in the ventricular depolarization process.
1. Left axis deviation (LAD) is present when the QRS axis is less than the lower limit of
normal for the
patient's age. LAD occurs with left ventricular hypertrophy (LVH), left bundle branch block (LBBB), and left
anterior hemiblock.
2. RAD is present when the QRS axis is greater than the upper limit of normal for the
patient's age.
RAD occurs with RVH and right bundle branch block (RBBB).
3. “Superior” QRS axis is present when the S wave is greater than the R wave in aVF. The
overlap with
LAD should be noted. It may occur with left anterior hemiblock (in the range of –30 to –90 degrees, seen in
endocardial cushion defect (ECD) or tricuspid atresia) or with RBBB. It is rarely seen in otherwise normal
children.
T Axis.
The T axis is determined by the same methods used to determine the QRS axis. In normal children, including
newborns, the mean T axis is +45 degrees, with a range of 0 to +90 degrees, the same as in normal
adults. This means that the T waves must be upright in leads I and aVF. The T waves can be flat, but must
not be inverted, in these leads. The T axis outside the normal quadrant suggests conditions with
myocardial dysfunction similar to those listed for abnormal QRS-T angle.
QRS-T Angle.
The QRS-T angle is formed by the QRS axis and the T axis. A QRS-T angle greater than 60 degrees is unusual,
and one greater than 90 degrees is certainly abnormal. An abnormally wide QRS-T angle with the T axis
outside the normal quadrant (0 to +90 degrees) is seen in severe ventricular hypertrophy with “strain,”
ventricular conduction disturbances, and myocardial dysfunction of a metabolic or ischemic nature.

23. Three important intervals are routinely measured in the interpretation of
an ECG: PR interval, QRS duration, and QT interval. The duration of
the P wave is also inspected .
PR Interval.
The normal PR interval varies with age and heart rate . The older the
person and the slower the heart rate, the longer is the PR interval.
A short PR interval is present in Wolff-Parkinson-White (WPW)
preexcitation, Lown-Ganong-Levine syndrome, myocardiopathies of
glycogenosis, Duchenne's muscular dystrophy (or relatives of these
patients), Friedreich's ataxia, pheochromocytoma, and otherwise
normal children. The lower limits of normal PR interval are shown
under WPW preexcitation
Variable PR intervals are seen in wandering atrial pacemaker and
Wenckebach's phenomenon (Mobitz type I second-degree AV block).

26. The QRS duration varies with age It is short in infants and
increases with age.
The QRS duration is prolonged in conditions grouped as
ventricular conduction disturbances, which include RBBB,
LBBB, preexcitation (e.g., WPW preexcitation), and
intraventricular block (as seen in hyperkalemia, toxicity from
quinidine or procainamide, myocardial fibrosis, myocardial
dysfunction of a metabolic or ischemic nature).
Ventricular arrhythmias (e.g., premature ventricular
contractions, ventricular tachycardia, implanted ventricular
pacemaker) also produce a wide QRS duration. Because the
QRS duration varies with age, the definition of bundle branch
block or other ventricular conduction disturbances should
vary with age.

28. The QT interval varies primarily with heart rate. The heart rate-corrected QT (QTc) interval is calculated by
the use of Bazett's formula:
According to Bazett's formula, the normal QTc interval (mean ± SD) is 0.40 (± 0.014) second with the
upper limit of normal 0.44 second in children 6 months and older. The QTc interval is slightly longer
in the newborn and small infants with the upper limit of normal QTc 0.47 second in the first week of life and
0.45 second in the first 6 months of life.
Long QT intervals may be seen in long QT syndrome (e.g., Jervell and Lange-Nielsen syndrome, Romano- Ward
syndrome), hypocalcemia, myocarditis, diffuse myocardial diseases (including hypertrophic and dilated
cardiomyopathies), head injury, severe malnutrition, and so on. A number of drugs are also known to prolong
the QT interval. Among these are antiarrhythmic agents (especially class IA, IC, and III), antipsychotic
phenothiazines (e.g., thioridazine, chlorpromazine), tricyclic antidepressants (e.g., imipramine, amitriptyline),
arsenics, organophosphates, antibiotics (e.g., ampicillin, erythromycin, trimethoprim-sulfa, amantadine), and
antihistamines (e.g., terfenadine).
A short QT interval is a sign of a digitalis effect or of hypercalcemia. It is also seen with hyperthermia and in
short QT syndrome (a familial cause of sudden death with QTc 300 milliseconds).
The JT interval is measured from the J point (the junction between the S wave and the ST segment) to the end of
the T wave. A prolonged JT interval has the same significance as a prolonged QT interval. The JT interval is
measured only when the QT interval is prolonged or when the QRS duration is prolonged as seen with
ventricular conduction disturbances. The JT interval is also expressed as a rate corrected interval (called JTc)
using Bazett's formula. Normal JTc (mean ± SD) is 0.32 ± 0.02 second with the upper limit of normal 0.34
second in normal children and adolescents.

29. P-WAVE DURATION AND AMPLITUDE
The P-wave duration and amplitude are important in the diagnosis of
atrial hypertrophy. Normally, the P amplitude is less than 3 mm. The
duration of P waves is shorter than 0.09 second in children and
shorter than 0.07 second in infants
QRS AMPLITUDE, R/S RATIO, AND ABNORMAL Q WAVES
The QRS amplitude and R/S ratio are important in the diagnosis of
ventricular hypertrophy. These values also vary with age , Because of
the normal dominance of RV forces in infants and small children, R
waves are taller than S waves in the right precordial leads (i.e., V4R,
V1, V2) and S waves are deeper than R waves in the left precordial
leads (i.e., V5, V6) in this age group.
Accordingly, the R/S ratio (the ratio of the R-wave and S-wave voltages)
is large in the right precordial leads and small in the left precordial
leads in infants and small children.

30. The normal ST segment is isoelectric. However, in the limb
leads, elevation or depression of the ST segment up to 1
mm is not necessarily abnormal in infants and children.
An elevation or a depression of the ST segment is
judged in relation to the PR segment as the baseline.
Some ST-segment changes are normal (nonpathologic)
and others are abnormal (pathologic). (See a later
section on nonpathologic and pathologic ST-T changes
in this chapter.)
Tall peaked T waves may be seen in hyperkalemia and LVH
(of the volume overload type). Flat or low T waves may
occur in normal newborns or with hypothyroidism,
hypokalemia, pericarditis, myocarditis, and myocardial
ischemia.

32. GENERAL CHANGES
Ventricular hypertrophy produces abnormalities in one or more of the following: the QRS axis, the QRS
voltages, the R/S ratio, the T axis, and miscellaneous areas.
1. Changes in the QRS axis. The QRS axis is usually directed toward the ventricle that
is hypertrophied. Although RAD is present with RVH, LAD is seen with the volume overload type,
but not with the pressure overload type, of LVH. Marked LAD usually indicates ventricular
conduction disturbances (e.g., left anterior hemiblock or “superior” QRS axis).
2. Changes in QRS voltages. Anatomically, the RV occupies the right and anterior
aspect, and the LV occupies the left, inferior, and posterior aspect of the
ventricular mass. With ventricular hypertrophy, the voltage of the QRS complex increases in the
direction of the respective ventricle.
In the frontal plane ,LVH shows increased R voltages in leads I, II, aVL, aVF, and sometimes III,
especially in small infants. RVH shows increased R voltages in aVR and III and increased S voltages
in lead I.
In the horizontal plane,with RVH , tall R waves in V4R, V1, and V2 or deep S waves in V5 and V6 , With
LVH, tall R waves in V5 and V6 and/or deep S waves in V4R, V1, and V2 are present
3. Changes in R/S ratio. The R/S ratio represents the relative electromotive force of opposing
ventricles in a given lead.
In ventricular hypertrophy, a change may be seen only in the R/S ratio, without an increase in the
absolute voltage. An increase in the R/S ratio in the right precordial leads suggests RVH; a
decrease in the R/S ratio in these leads suggests LVH.
Likewise, an increase in the R/S ratio in the left precordial leads suggests LVH, and a decrease in the
ratio suggests RVH.

33. 4. Changes in the T axis. Changes in the T axis are seen in severe
ventricular hypertrophy with relative ischemia of the hypertrophied
myocardium. In the presence of other criteria of ventricular hypertrophy, a
wide QRS-T angle (i.e., >90 degrees) with the T axis outside the normal
range indicates a strain pattern. When the T axis remains in the normal
quadrant (0 to +90 degrees), a wide QRS-T angle alone indicates a possible
strain pattern.
5. Miscellaneous nonspecific changes
a. RVH
1). A q wave in V1 (qR or qRs pattern) suggests RVH, although it
may be present in ventricular inversion.
2). An upright T wave in V1 after 3 days of age is a sign of
probable RVH.
b. LVH
Deep Q waves (>5 mm) and/or tall T waves in V5 and V6 are signs of LVH of
volume overload type. These may be seen with a large-shunt ventricular
septal defect (VSD)

34. In RVH, some or all of the following criteria are present.
1. RAD for the patient's age
2. Increased rightward and anterior QRS voltages (in the absence of prolonged QRS
duration)
a wide QRS complex with increased QRS voltages suggests ventricular conduction disturbances
(e.g., RBBB) rather than ventricular hypertrophy.
a. R waves in V1, V2, or aVR greater than the upper limits of normal for the
patient's age
b. S waves in I and V6 greater than the upper limits of normal for the patient's age
3. Abnormal R/S ratio in favor of the RV (in the absence of bundle branch block)
a. R/S ratio in V1 and V2 greater than the upper limits of normal for age
b. R/S ratio in V6 less than 1 after 1 month of age.
4. Upright T waves in V1 in patients more than 3 days of age, provided that the T is
upright in the left precordial leads (V5, V6); upright T waves in V1 are not
abnormal in patients older than 6 years.
5. A q wave in V1 (qR or qRs patterns) suggests RVH (the physician should ascertain that
there is not asmall r in an rsR configuration).
6. In the presence of RVH, a wide QRS-T angle with T axis outside the normal range
(in the 0 to –90
degree quadrant) indicates a strain pattern. A wide QRS-T angle with the T axis within the normal
range suggests a possible strain pattern.

36. The diagnosis of RVH in newborns is particularly difficult because of the
normal dominance of the RV during this period of life. Helpful signs in
the diagnosis of RVH in newborns are as follows.
1. S waves in lead I that are 12 mm or greater
2. Pure R waves (with no S waves) in V1 that are greater
than 10 mm
3. R waves in V1 that are greater than 25 mm or R waves in
aVR that are greater than 8 mm
4. A qR pattern seen in V1 (this is also seen in 10% of
normal newborns)
5. Upright T waves seen in V1 after 3 days of age
6. RAD with the QRS axis greater than +180 degrees

37. In LVH, some or all of the following abnormalities are present.
1. LAD for the patient's age
2. QRS voltages in favor of the LV (in the absence of a prolonged QRS duration for
age)
a. R waves in leads I, II, III, aVL, aVF, V5, or V6 greater than the upper limits of
normal for
age
b. S waves in V1 or V2 greater than the upper limits of normal for age
In general, the presence of abnormal forces to more than one direction (e.g., to the left, inferiorly,
and posteriorly) is a stronger criterion than the abnormality in only one direction.
3. Abnormal R/S ratio in favor of the LV: R/S ratio in V1 and V2 less than the lower
limits of normal
for the patient's age
4. Q waves in V5 and V6, greater than 5 mm, as well as tall symmetrical T waves in
the same leads
(“LV diastolic overload”)
5. In the presence of LVH, a wide QRS-T angle with the T axis outside the normal range
indicates a strain pattern; this is manifested by inverted T waves in lead I or aVF. A wide
QRS-T angle with the T axis within the normal range suggests a possible strain
pattern.
The R waves in leads I, aVL, V5, and V6 are beyond the upper limits of normal, indicating abnormal
leftward force. The QRS duration is normal. The T axis (+55 degrees) remains in the normal
quadrant. This tracing

39. BVH may be manifested in one of the following ways.
1. Positive voltage criteria for RVH and LVH in the absence of bundle
branch block or preexcitation (i.e., with normal QRS duration)
2. Positive voltage criteria for RVH or LVH and relatively large voltages for
the other ventricle
3. Large equiphasic QRS complexes in two or more of the limb leads and
in the mid-precordial leads (i.e., V2 through V5), called the Katz-Wachtel
phenomenon (with normal QRS duration)
It is difficult to plot the QRS axis because of large diphasic QRS complexes in limb leads.
The R and S voltages are large in some limb leads and in the mid precordial leads
(Katz-Wachtel phenomenon). The S waves in leads I and V6 are abnormally deep
(i.e., abnormal rightward force), and the R wave in V1 (i.e., rightward and anterior
force) is also abnormally large, suggesting RVH. The R waves in leads I and aVL (i.e.,
leftward force) are also abnormally large. Therefore, this tracing shows BVH.

40. Conditions that are grouped together as ventricular conduction disturbances have
abnormal prolongation of the QRS duration in common. Ventricular conduction
disturbances include the following:
1. Bundle branch block, right and left
2. Preexcitation (e.g., WPW-type preexcitation)
3. Intraventricular block
In bundle branch blocks (and ventricular rhythms), the prolongation is in the terminal
portion of the QRS complex (i.e., “terminal slurring”). In preexcitation, the
prolongation is in the initial portion of the QRS complex (i.e., “initial slurring”),
producing “delta” waves. In intraventricular block, the prolongation is throughout the
duration of the QRS complex ( Fig. 3-19 ). Normal QRS duration varies with age; it is
shorter in infants than in older children or adults . In adults, a QRS duration greater
than 0.10 second is required for diagnosis of bundle branch block or ventricular
conduction disturbance. In infants, a QRS duration of 0.08 second meets the
requirement for bundle branch block.
By far the most commonly encountered form of ventricular conduction disturbance is
RBBB. Although uncommon, WPW preexcitation is a well-defined entity that deserves
a brief description. LBBB is extremely rare in children, although it is common in
adults with ischemic and hypertensive heart disease.
Intraventricular block is associated with metabolic disorders and diffuse myocardial
diseases.

42. In RBBB, delayed conduction through the right bundle branch prolongs the time required
for a depolarization of the RV. When the LV is completely depolarized, RV
depolarization is still in progress.
This produces prolongation of the QRS duration, involving the terminal portion of the QRS
complex, called terminal slurring and the slurring is directed to the right and
anteriorly because the RV is located rightward and anteriorly in relation to the LV.
In RBBB (and other ventricular conduction disturbances), asynchronous depolarization of
the opposing electromotive forces may produce a lesser degree of cancellation of the
opposing forces and thus result in greater manifest potentials for both ventricles.
Consequently, abnormally large voltages for both RV and LV may result even in the
absence of ventricular hypertrophy. Therefore, the diagnosis of ventricular
hypertrophy in the presence of bundle branch block (or WPW preexcitation or
intraventricular block) is insecure.
Criteria for Right Bundle Branch Block
1. RAD, at least for the terminal portion of the QRS complex (the initial
QRS force is normal)
2. QRS duration longer than the upper limit of normal for the patient's
age .
3. Terminal slurring of the QRS complex that is directed to the right and
usually, but not always, anteriorly:
a. Wide and slurred S waves in leads I, V5, and V6
b. Terminal, slurred R in aVR and the right precordial leads (V4R, V1, and
V2)
4. ST-segment shift and T-wave inversion are common in adults but not in
children

43. Figure 3-20 is an example of RBBB. The QRS duration is increased (0.11 second), indicating a
ventricular conduction disturbance. There is slurring of the terminal portion of the QRS
complex, indicating a bundle branch block, and the slurring is directed to the right (slurred S
waves in leads I and V6 and slurred R waves in aVR) and anteriorly (slurred R waves in V4R and
V1), satisfying the criteria for RBBB. Although the S waves in leads I, V5, and V6 are abnormally
deep and the R/S ratio in V1 is abnormally large, it cannot be interpreted as RVH in the
presence of RBBB.

44. Two pediatric conditions commonly associated with RBBB are ASD and
conduction disturbances after open heart surgery involving right
ventriculotomy. Other congenital heart defects often associated with RBBB
include Ebstein's anomaly, COA in infants younger than 6 months, ECD, and
PAPVR; it is also occasionally seen in normal children. Rarely, RBBB is seen
in myocardial diseases (cardiomyopathy, myocarditis), muscle diseases
(Duchenne's muscular dystrophy, myotonic dystrophy), and Brugada
syndrome.
In ASD, the prolonged QRS duration is the result of a longer pathway through a
dilated RV rather than an actual block in the right bundle. Right
ventriculotomy for repair of VSD or tetralogy of Fallot disrupts the RV
subendocardial Purkinje network and causes prolongation of the QRS
duration without necessarily injuring the main right bundle, although the
latter may occasionally be disrupted.
Some pediatricians are concerned with the rsR pattern in V1. Although it is
unusual to see this in adults, the rsR pattern in V1 not only is normal but is
expected to be present in infants and small children, provided that the QRS
duration is not prolonged and the voltage of the primary or secondary R
waves is not abnormally large. This is because the terminal QRS vector is
normally more rightward and anterior in infants and children than adults.

45. LEFT BUNDLE BRANCH BLOCK
LBBB is extremely rare in children. In LBBB, the duration of the QRS complex is
prolonged for age and the slurred portion of the QRS complex is directed
leftward and posteriorly. A Q wave is absent in V6. A prominent QS pattern is
seen in V1 and a tall R wave is seen in V6. LBBB in children is associated
with cardiac disease or surgery in the LV outflow tract, septal
myomectomy, and replacement of the aortic valve. Other
conditions rarely associated with LBBB include LVH, progressive
conduction system disease, myocarditis, cardiomyopathy,
myocardial infarction, and aortic valve endocarditis.
LBBB alone may rarely progress to complete heart block and sudden death, but
the prognosis is more dependent on associated disease than on the LBBB
itself.
INTRAVENTRICULAR BLOCK
In intraventricular block, the prolongation is throughout the duration of the QRS
complex (see Fig. 3-19D ). This usually suggests serious conditions such as
metabolic disorders (e.g., hyperkalemia), diffuse myocardial
diseases (e.g., myocardial fibrosis, systemic diseases with
myocardial involvement), severe hypoxia, myocardial ischemia,
or drug toxicity (quinidine or procainamide).

46. WPW preexcitation results from an anomalous conduction pathway (i.e., bundle of Kent)
between the atrium and the ventricle, bypassing the normal delay of conduction in
the AV node. The premature depolarization of a ventricle produces a delta wave and
results in prolongation of the QRS duration .
Criteria for Wolff-Parkinson-White Syndrome
1. Short PR interval, less than the lower limit of normal for the patient's
age.
2. Delta wave (initial slurring of the QRS complex)
3. Wide QRS duration beyond the upper limit of normal
Patients with WPW preexcitation are susceptible to attacks of paroxysmal
supraventricular tachycardia (SVT) When there is a history of SVT, the diagnosis of
WPW syndrome is justified.
WPW preexcitation may mimic other ECG abnormalities such as ventricular hypertrophy,
RBBB, or myocardial disorders. In the presence of preexcitation, the diagnosis of
ventricular hypertrophy cannot be safely made.
The most striking abnormalities are a short PR interval (0.08 second) and a wide QRS
duration (0.11 second). There are delta waves in most of the leads. Some delta
waves are negative, as seen in leads III, aVR, V4R, and V1. The ST segments and T
waves are shifted in the opposite direction of the QRS vector, resulting in a wide
QRS-T angle. The leftward voltages are abnormally large, but the diagnosis of LVH
cannot safely be made in the presence of WPW preexcitation.

47. Two other forms of preexcitation can also result in extreme tachycardia.
1. Lown-Ganong-Levine syndrome is characterized by a short PR interval and normal QRS
duration. in
this condition, James fibers (which connect the atrium and the bundle of His) bypass the upper AV
node and produce a short PR interval, but the ventricles are depolarized normally through the His-
Purkinje system. When there is no history of SVT, the ECG tracing should simply be read as
showing a short PR interval rather than Lown-Ganong-Levine syndrome.
2. Mahaim-type preexcitation syndrome is characterized by a normal PR interval and
long QRS
duration with a delta wave. There is an abnormal Mahaim fiber that connects the AV node and one
of the ventricles, bypassing the bundle of His, and “short-circuits” into the ventricle.

48. Two common ECG abnormalities in children, ventricular hypertrophy and
ventricular conduction disturbances, are not always easy to
distinguish; both arise with increased QRS amplitudes. The following
approach may aid in the correct diagnosis of these conditions ( Fig. 3-
22 ). An accurate measurement of the QRS duration is essential.
1. When the QRS duration is normal, normal QRS voltages
indicate a normal ECG. Increased QRS voltages indicate
ventricular hypertrophy.
2. When the QRS duration is clearly prolonged, a ventricular
conduction disturbance is present whether the QRS voltages
are normal or increased. Additional diagnosis of ventricular
hypertrophy should not be made.
3. When the QRS duration is borderline prolonged,
distinguishing these two conditions is difficult.
Normal QRS voltages favor a normal ECG or a mild (right or left
ventricular) conduction disturbance. An increased QRS voltage favors
ventricular hypertrophy.

49. ECG changes involving the ST segment and the T wave are common in adults but
relatively rare in children. This is because of a high incidence of ischemic heart
disease, bundle branch block, myocardial infarction, and other myocardial disorders
in adults. Some ST-segment changes are normal (nonpathologic) and others are
abnormal (pathologic).
NONPATHOLOGIC ST-SEGMENT SHIFT
Not all ST-segment shifts are abnormal. Slight shift of the ST segment is common in
normal children. Elevation or depression of up to 1 mm in the limb leads and up to 2
mm in the precordial leads is within normal limits. Two common types of
nonpathologic ST-segment shifts are J-depression and early repolarization. The T
vector remains normal in these conditions. J-Depression. J-depression is a shift of
the junction between the QRS complex and the ST segment (J-point) without
sustained ST segment depression ( Fig. 3-23 A ). The J-depression is seen more
often in the precordial leads than in the limb leads .

50. Early Repolarization.
In early repolarization, all leads with upright T waves have elevated ST segments, and leads with
inverted T waves have depressed ST segments (see Fig. 3-24 ). The T vector remains normal. This
condition, seen in healthy adolescents and young adults, resembles the ST-segment shift seen in acute
pericarditis; in the former, the ST segment is stable, and in the latter, the ST segment returns to the
isoelectric line.

51. PATHOLOGIC ST-SEGMENT SHIFT
Abnormal shifts of the ST segment are often accompanied by T-wave inversion. A pathologic ST-segment
shift assumes one of the following forms:
1. Downward slant followed by a diphasic or inverted T wave (see Fig. 3-23B )
2. Horizontal elevation or depression sustained for more than 0.08 second (see Fig. 3-
23C )
Pathologic ST-segment shifts are seen in left or right ventricular hypertrophy with strain (discussed under
ventricular hypertrophy); digitalis effect; pericarditis, including postoperative state; myocarditis ;
myocardial infarction; and some electrolyte disturbances (hypokalemia and hyperkalemia).
T-WAVE CHANGES
T-wave changes are usually associated with the conditions manifesting with pathologic ST-segment shift.
Twave changes with or without ST-segment shift are also seen with bundle branch block and
ventricular arrhythmias. Pericarditis.
The ECG changes seen in pericarditis are the result of subepicardial myocardial damage or pericardial
effusion and consist of the following:
1. Pericardial effusion may produce low QRS voltages (QRS voltages <5 mm in every one
of the limb
leads).
2. Subepicardial myocardial damage produces the following time-dependent changes in
the ST segment
and T wave ( Fig. 3-25 ):
a. ST-segment elevation occurs in the leads representing the left ventricle.
b. The ST-segment shift returns to normal within 2 to 3 days.
c. T-wave inversion (with isoelectric ST segment) occurs 2 to 4 weeks after the onset of
pericarditis.