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Bundle Branch Block
Fast & Easy ECGs, 2nd E – A SelfPaced Learning Program
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Bundle Branches
• Bundle of His divides
into right and left
bundle branches
• Left bundle branch
further divides into
septal, anterior and
posterior fascicles
I
Fast & Easy ECGs, 2E
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Normal QRS Complex
• Narrow – 0.06 to
0.10 seconds in
duration
• Electrical axis is
between 0° and +90°
Fast & Easy ECGs, 2E
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Bundle Branch Block
• Leads to one or both
bundle branches
failing to conduct
impulses
• Produces delay in
depolarization of the
ventricle it supplies
I
Fast & Easy ECGs, 2E
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Bundle Branch Block
• Key characteristic are widened
QRS complexes
– 0.12 seconds or greater in
duration
• As such, the first step to
identifying bundle branch
block is to analyze the QRS
complex width
• Next, look at the appearance
of the QRS complexes
– They may be notched,
slurred or M shaped in the
chest leads
I
Fast & Easy ECGs, 2E
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Bundle Branch Block
• Only occurs in supraventricular rhythms
because the impulse originates above the
ventricles and travels down through the
bundle branches in these rhythms
Fast & Easy ECGs, 2E
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Bundle Branch Block
• Possible sites of block within the ventricular
conduction system include:
– Right bundle branch (right bundle branch block)
– Left bundle branch (left bundle branch block)
– Left anterior fascicle (left anterior fascicular block),
also called left anterior hemiblock
– Left posterior fascicle (left posterior fascicular block),
also called left posterior hemiblock
– Any combination of these or along with prolongation
of the PR interval (first degree AV block)
Fast & Easy ECGs, 2E
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Right Bundle Branch Block (RBBB)
• Conduction
through the right
bundle branch is
blocked causing
delayed right
ventricular
depolarization
• Look for wide, tall,
and notched QRS
complexes in
leads V1, V2 and
slurred S waves in
leads I, V5 and V6
I
Fast & Easy ECGs, 2E
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Right Bundle Branch Block
Fast & Easy ECGs, 2E
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Causes of Right Bundle Branch Block
• Occurs with anterior wall MI, coronary artery
disease, hypertension, scar tissue that
develops after heart surgery, viral or bacterial
myocarditis and pulmonary embolism
• May also be caused by drug toxicity or be due
to a congenital heart abnormality such as
atrial septal defect
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Left Bundle Branch Block
•
•
Conduction through the
left bundle branch is
blocked, causing
depolarization of the left
ventricle to be delayed
Look for wide, tall,
notched or slurred QRS
complexes in leads V5, V6
and wide, largely
negative rS complexes or
entirely negative QS
complexes in V1 and V2
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Left Bundle Branch Block
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Causes of Left Bundle Branch Block
• Anterior wall MI, hypertensive heart disease,
aortic stenosis, degenerative changes of the
conduction system or cardiomyopathy
Fast & Easy ECGs, 2E
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Repolarization Changes
• Look for wide, tall, notched or slurred QRS
complexes in leads V5, V6
– In RBBB, ST segment depression and T-wave
inversion is seen in leads V1 and V2
– In LBBB, ST segment depression and T-wave
inversion may be seen in most leads, particularly
leads V5 and V6
Fast & Easy ECGs, 2E
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Incomplete Bundle Branch Block
• Sometimes either the right or
left bundle branch conducts the
electrical impulse more slowly
but it is not completely blocked
• Results in QRS complexes with a
similar appearance to bundle
branch block and slightly wider
than normal but not as wide as
with complete bundle branch
block
– duration is no greater 0.11 seconds
Fast & Easy ECGs, 2E
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Hemiblocks
• Occur when one or more of the LBB fascicles is
blocked
• While the ECG appearance of anterior and
posterior hemiblocks differs from that of bundle
branch blocks, the mechanism is essentially the
same
• Minimal prolongation with hemiblock, it is not
enough to widen the QRS complex to any real
degree but the morphology of the QRS complex
does change
Fast & Easy ECGs, 2E
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Hemiblocks
• Axis deviation is the key ECG characteristic of
hemiblocks
– It occurs because when one fascicle is blocked, the
electrical current travels down the other to
stimulate the heart. This causes the axis to shift
accordingly
• When diagnosing hemiblock, be sure to rule
out other causes of axis deviation, such as
ventricular hypertrophy
Fast & Easy ECGs, 2E
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Hemiblocks
• The anterior fascicle is longer and thinner and
has a more fragile blood supply than the
posterior fascicle, so LAHB is far more
common than LPHB
• While LAHB can be seen in both normal and
diseased hearts, LPHB is almost always
associated with heart disease
Fast & Easy ECGs, 2E
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Left Anterior Hemiblock
• Conduction down the left
anterior fascicle is blocked
• Depolarization of the left
ventricle occurs,
progressing in an inferiorto-superior and right-toleft direction
• The axis of ventricular
depolarization is
redirected upward and
slightly to the left,
producing tall positive R
waves in the left lateral
leads and deep S waves
inferiorly resulting in left
axis deviation
Fast & Easy ECGs, 2E
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Left Posterior Hemiblock
• Conduction down left
posterior fascicle is blocked
• Electrical impulse rushes
down left anterior fascicle,
resulting in ventricular
myocardial depolarization
occurring in a superior-toinferior and left-to-right
direction
• Main electrical axis is
directed downward and to
the right, producing tall R
waves inferiorly and deep S
waves in left lateral leads
resulting in right axis
deviation
Fast & Easy ECGs, 2E
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Combination of Blocks
• Patients with any type of ventricular
conduction block and especially those with a
combination of blocks are at high risk of
developing complete heart block
Fast & Easy ECGs, 2E
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Bifascicular Block
• Is a conduction disturbance in which two of
the three main fascicles of the His/Purkinje
system are blocked
– Most often, it refers to a combination of RBBB and
either LAHB (more commonly) or LPHB
– Some include LBBB in the definition of bifascicular
block because the block occurs above the
bifurcation of the left anterior and left posterior
fascicles of the left bundle branch
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Trifascicular Block
• Is a conduction
disturbance in which
there are three features
seen on the ECG such
as:
– Prolongation of the PR
interval (first degree AV
block)
– RBBB
– Either LAFB or LPFB
• Is uncommon
Fast & Easy ECGs, 2E
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Practice Makes Perfect
• Determine the condition
I
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Practice Makes Perfect
• Determine the condition
I
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Practice Makes Perfect
• Determine the condition
I
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Practice Makes Perfect
• Determine the condition
I
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Practice Makes Perfect
• Determine the condition
I
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Practice Makes Perfect
• Determine the condition
I
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Practice Makes Perfect
• Identify this condition
I
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Summary
• Bundle branch block is a disorder that leads to
one or both of the bundle branches failing to
conduct impulses. This produces a delay in the
depolarization of the ventricle it supplies
• In bundle branch block a widened QRS complex is
seen in the chest leads. It may be tall and
notched or slurred and/or have an “M” shaped
appearance
• To diagnose right bundle branch block look for
wide, tall, and notched QRS complexes in leads
V1, V2 and slurred S waves in leads I, V5 and V6
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Summary
• To diagnose left bundle branch block Look for wide, tall,
notched or slurred QRS complexes in leads V5, V6
• Sometimes an R, R’ wave is seen in a QRS complex of
normal duration. This is called incomplete bundle branch
block
• Similar to the repolarization abnormalities seen in
hypertrophy, so too can these changes be seen in both
RBBB and LBBB
• If only a portion of the left bundle branch is blocked, it is
called a fascicular block
• Hemiblocks cause axis deviation. LAHB results in left axis
deviation. LPHB results in right axis deviation
• Bundle branch block often does not require treatment
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Summary
• Bifascicular block is a conduction disturbance in which
two of the three main fascicles of the His/Purkinje system
are blocked
– Most often, it refers to a combination of RBBB and
either LAHB (more commonly) or LPHB
• Trifascicular block is a conduction disturbance in which
there are three features seen on the ECG:
– Prolongation of the PR interval (first degree AV block)
– RBBB
– Either LAFB or LPFB
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.