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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_2818_Библиотеки_им_академика_М_И_Перельмана
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Apex
Left bundle branch block
branch bloc
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Right bundle branch
Right bundle
k
Purkinje fibres
X
X
X
X
14 Bundle Branch Block
Left anterior
fascicle block
Left posterior
fascicle block
Purkinje
fibres
Left ventricle
Fig. 14.1 Diagram of bundle branch blocks
14.1 Right Bundle Branch Block
In right bundle branch block (RBBB), there is delay or interruption in conduction of
impulse through the right bundle branch (Fig.14.2). Due to block in conduction,
there is delay in activation of the right ventricle, and it is represented in ECG by a
wide QRS complex. The other important feature of RBBB is the presence of a second positive wave in lead V1, which is known as R’ wave.
RBBB is a common ECG nding and alone it is not suggestive of any disease,
because it is frequently present in normal persons also. It may be transient or permanent in the same or serial tracings of ECG depending upon the cause. Acute
exacerbation of COPD or acute pulmonary embolism can lead to a transient
RBBB.It may be a rate related phenomenon also. The various causes of RBBB are
enumerated in Box 14.1.
The ECG manifestations of complete RBBB are the following:
• In lead V1 or V2, there is wide, slurred QRS complex with rsR’ or rSR’ pattern
(Figs.14.3 and 14.4). This is also called ‘M’ pattern (rabbit ear).
Right atrium
Right bundle
branch block
Right ventricl
Apex
25 mm/s. 10 mm = 1 mV
14.1 Right Bundle Branch Block
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e
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Left atrium
Left ventricle
Left bundle
branch
Fig. 14.2 Right bundle branch block
III III aVR aVL aVF
V1 V2 V3 V4 V5 V6
Fig. 14.3 Right bundle branch block. Note the rsR’ complex in lead V1
• QRS duration is more than 0.12s.
• In lead V1 or V2, S-T segment depression and T wave inversion may be seen.
• VAT is more than 0.06s in lead V1 or V2.
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IIIIII aVR aVL aVF
V1 V2 V3 V4 V5 V6
Fig. 14.4 Right bundle branch block. Note the RSR’ complex in lead V1 (M pattern)
14 Bundle Branch Block
• In leads I, aVL, V5 and V6, a wide slurred S wave may be present.
• There is a small r wave in lead V1 and a small q wave in lead V6.
Box 14.1 Causes of RBBB
Present in normal persons without heart disease
Coronary artery disease
Congenital
Cardiomyopathies
Acute massive pulmonary embolism
ASD (ostium primum type)
Ebstein’s anomaly
Associated with right ventricular hypertrophy
Cardiac contusion
Idiopathic
Tips and Tricks
• Look for wide QRS complex with rSR’ pattern in lead V1 to make a diagnosis
of RBBB.
• There will be ‘M’ pattern in lead V1 and ‘W’ pattern in lead V6.
• The QRS becomes wide due to the extra time it takes for complete ventricular
depolarization due to conduction block in right bundle branch.
• Do not jump into making a diagnosis of heart disease on diagnosing RBBB.It is
commonly seen in normal healthy persons.
• No specic treatment is required.
14.1.1 Genesis ofrsR’ Complex inLead V1
The electrical impulse comes via bundle of His and at the beginning there is activation of the ventricular septum via the left to right septal vector. The vector is directed
towards lead V1, resulting in a small r wave in lead V1 (Fig.14.5).
14.1 Right Bundle Branch Block
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Fig. 14.5 Genesis of r
wave (arrow) of rsR’
complex in lead V1
Fig. 14.6 Genesis of s
wave (arrow) of rsR’
complex in lead V1
185
V1
V1
Fig. 14.7 Genesis of R’
wave (arrow) of rsR’
complex in lead V1
V1
Since the impulse cannot pass through the right bundle, it passes via the left
bundle and depolarizes the left ventricle. The vector is directed away from lead V1
resulting in s wave (Fig.14.6).
The impulse then passes round the blocked right bundle into the right ventricle.
The impulse instead of passing through the Purkinje bres passes through the ventricular myocardium. As a result, there is delay in right ventricular activation. This
vector is directed towards lead V1 resulting in the R’ wave (Fig.14.7). Because of
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delay in ventricular depolarization (especially right ventricular delay), there is wide
QRS complex.
14 Bundle Branch Block
14.1.2 Incomplete RBBB
In incomplete RBBB, the QRS duration is between 0.11 s and 0.12 s and the VAT in
lead V1 is less than 0.06s. There is diminution of S wave in lead V2 with slurring
in the upstroke of S wave and it is the earliest feature of incomplete RBBB.Diminution
of S wave may be the only feature of incomplete RBBB sometimes.
With further delay in conduction, there is development of a small r wave in lead
V2 which results in a rsr’ complex. With further increase in block, there may be
development of rsR’ complex in lead V2. Incomplete RBBB may be due to right
ventricular hypertrophy or strain. Besides the delay in conduction, incomplete
RBBB may be also due to increase in length of the right bundle in right ventricle
dilatation due to volume overload, in conditions like cor pulmonale, atrial septal
defect, etc.
Thus, it can be said that the development of incomplete RBBB can be studied by
observing the following two changes in lead V2:
1. Progressive loss in amplitude of S wave.
2. Development and gradual increase in amplitude of r’ or R’ wave with nal wid-
ening of this deection.
14.1.3 Distinguishing Features ofRBBB andRVH
Often it becomes difcult to differentiate between RBBB and RVH.Complete or
incomplete RBBB may be a feature of RVH and it may be impossible to diagnose
RVH in presence of RBBB.The following features help to distinguish between the
two conditions:
• In RVH, the QRS duration is less than 0.12s and in RBBB it is more than 0.12s.
• In RVH, there is tall R wave in lead V1, whereas in RBBB there is rSR’ complex
in lead V1.
• In RVH, the VAT in lead V1 is usually between 0.03 and 0.05s, while in RBBB,
VAT is more than 0.06s in lead V1.
14.1.4 RBBB inPresence ofLVH
The ECG changes of LVH are present in leads V4–V6 and leads I and aVL.The
features of RBBB are also present (rsR’ complex in lead V1).
Right atrium
Right bundle
branc
Right ventricl
x
14.2 Left Bundle Branch Block
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14.2 Left Bundle Branch Block
In left bundle branch block (LBBB), there is delay or complete block of transmission of impulse through the left bundle branch (Fig.14.8). The conduction delay
leads to incomplete LBBB and complete block produces complete LBBB.LBBB
may be found in almost all types of cardiac disease and always it indicates some
organic heart disease unlike RBBB.It may be transient or permanent. It may commonly be observed in conditions that cause LVH like hypertension or aortic stenosis. It is uncommon in congenital heart disease. LBBB may be transient or permanent
in the same tracing or in serial tracings. Transient LBBB occurs after myocardial
infarction or after consumption of drugs like digitalis, acute myocarditis, heart failure, etc. Permanent LBBB indicates organic heart disease. LBBB may be related to
heart rate. The various causes of LBBB are enumerated in Box 14.2.
The ECG manifestations of complete LBBB are the following:
• In lead V5 or V6, there is wide, slurred, bizarre QRS complex. QRS duration is
more than 0.12s. There may be rsR’ pattern (M pattern) in leads V5 or V6 (Figs.
14.9 and 14.10). In incomplete LBBB, the QRS duration is between 0.10 and 0.12s.
• In leads V5 or V6, VAT is prolonged to more than 0.09s.
h
e
Fig. 14.8 Left bundle branch block
Left atrium
Left ventricle
Left bundle
branch block
Ape
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25 mm/s. 10 mm = 1 mV
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14 Bundle Branch Block
Box 14.2 Causes of LBBB
Coronary artery disease
Myocarditis
Hypertensive heart disease
Acute myocarditis
Aortic valve disease
Cardiomyopathies
Degenerative disease of the conducting system
III III aVR aVL aVF
V1 V2 V3 V4 V5 V6
Fig. 14.9 Left bundle branch block
III III aVRaVL aVF
V1 V2 V3 V4 V5 V6
Fig. 14.10 Left bundle branch block. This ECG is taken from a 62-year-old gentleman suffering
from a long-standing hypertension with coronary artery disease. Note the widening of QRS complex and the notching of the R wave in leads aVL and lead V6
• Q or q wave is absent in leads V5 or V6. Presence of q wave signies myocardial
infarction.
• QS wave in lead V1 may show a small notch, giving the wave a characteristic
‘W’ pattern.
• The S-T segment and T wave are directed opposite to the QRS deection. Hence, in lead
V5 or lead V6, S-T segment is depressed and the T wave is inverted. Complete LBBB
often mimics anterior wall myocardial infarction (pseudo- anterior wall infarction).
14.2 Left Bundle Branch Block
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Tips and Tricks
• Look for wide QRS complex with rSR’ pattern in lead V5 (M pattern) and ‘W’
pattern in lead V1 to make a diagnosis of LBBB.
• LBBB, unlike RBBB is always an indicator of heart disease, usually of the left
ventricle.
• LBBB in presence of severe chest pain may be due to acute myocardial infarction.
• LBBB in asymptomatic patient does not require any treatment.
14.2.1 Genesis ofrsR’ Complex inLead V6
The electrical impulse reaches up to the bundle of His by the normal pathway of
conduction. After this the impulse is not able to enter into the left bundle hence it
enters into the right bundle rst and activates the septum. This vector is oriented
from right to left and hence produces a small r wave in lead V6. This is exactly the
opposite of what happens in RBBB (Fig.14.11).
The impulse then enters into the right ventricle and activates it. The net vector is
moving away from the lead V6 resulting in s wave. Because of thin right ventricular
wall, this s wave may not go below the base line and merely may produce a notch in
the R wave (Fig.14.12).
The impulse then bypasses the blocked left bundle and enters into the left ventricle and activates it. The net vector is directed towards the lead V6 resulting in R’
wave (Figs.14.13 and 14.14).
Fig. 14.11 Genesis of r
wave (arrow) of rsR’
complex in lead V6
V6
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Fig. 14.12 Genesis of s
wave (arrow) of rsR’
complex in lead V6
Fig. 14.13 Genesis of R’
wave (arrow) of rsR’
complex in lead V6
14 Bundle Branch Block
V6
V6
a
Fig. 14.14 Types of rsr’ complexes in lead V6. The rsR’ complex in lead V6 may show only widening of QRS complex with T wave inversion (a) or it may show a notch in R wave with T wave
inversion (b) and (c) or it may show a typical M pattern (d)
b
cd
14.2 Left Bundle Branch Block
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14.2.2 Distinguishing Features ofLBBB andLVH
LBBB is often present in association with LVH.It is very important to distinguish
between these two conditions. The main thing that one should look for is the initial
q wave in leads V5, V6 and aVL.The presence of q wave rules out LBBB or indicates associated myocardial infarction. The other feature that one should look for is
the feature of left atrial enlargement. If it is present, it indicates the presence of
LVH. The voltage criteria for the diagnosis of LVH are not valid in presence
of LBBB.
14.2.3 Incomplete Left Bundle Branch Block
In incomplete LBBB, there is delayed conduction through the left bundle. The features of incomplete LBBB are the following:
• Small q wave in lead V5 or V6 disappears and there is a tall R wave.
• Small r wave in lead V1 disappears and there is a big QS complex.
• Gradually, the other features of complete LBBB appear, but the width of QRS
complex is less than 0.12s and VAT is less than 0.09s.
Self-Assessment Questions
1. RBBB may be rate dependent. True or false?
2. LBBB may occur transiently. True or false?
3. In RBBB, there is widening of QRS complex. True or false?
4. LBBB is characterized by a wide R wave in lead V6. True or false?
5. RVH and RBBB cannot be distinguished on the basis of QRS duration. True
or false?
6. In absence of structural heart diseases, which of the following is
more common?
a. RBBB b. LBBB c. LAHB d. LPHB
7. rSR’ pattern is seen in lead V1 with S-T depression and T wave inversion.
It suggests:
a. LBBB b. RBBB c. LAHB d. First degree AV block
8. ECG shows rsR’ pattern in lead V6 and there is T wave inversion. Which
of the following type of block is suggested?
a. AV block b. SA block c. Bifascicular block d. LBBB
9. The duration of QRS complex in complete LBBB is more than:
a. 0.08s b. 0.10s c. 0.11s d. 0.12s
10. LBBB is seen in which of the following condition:
a. Ebstein’s anomaly b. Ostium primum ASD c. Acute massive pulmonary
embolism d. Hypertensive heart disease
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