Download Bundle Branch Blocks and Hemiblocks

Bundle Branch Blocks and
Hemiblocks
Take Home Points
• Bundle branch blocks are best characterized on ECG by:
– prolongation of the QRS > 0.12 sec
– Region of slowed conduction determines the orientation
of the terminal QRS vector and localizes the block
• Hemiblocks do not typically show QRS prolongation,
rather they reveal axis deviation corresponding to the
QRS terminal vector
• Ventricular conduction blocks are common and
can represent a spectrum from normal variant to
serious pathology
Normal Anatomy of the Cardiac
Conduction System
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SA Node
AV Node
Bundle of His
Left and R Bundle
Branches
Septal Fascicle
LAF
LPF
Purkinje fibers
Myocardium
www.nottingham.ac.uk/.../cardiac_conduction.gif
Anatomy of the Ventricular
His-purkinje Conduction System
Left bundle branch
Right bundle branch
Left anterior fascicle
Septal fascicle
Left posterior fascicle
Bundle Branch Blocks
• Intrinsic impairment of conduction in the left or
right bundle branches
• Can be chronic or intermittent
• Can be rate dependant
• Can be present without cardiac disease
• Most often due to CAD or HTN causing
ischemic or degenerative changes
EKG Manifestations of BBBs
• Widened QRS complex > 0.12 sec
– Results from slow myocyte-to-myocyte conduction causing
prolonged ventricular depolarization
• incomplete (0.8-0.11s) or complete (>0.12s)
– Terminal QRS is sluggish and reflects the electric forces in the
affected ventricle.
– LBBB = terminal QRS is superior, posterior, and left
– RBBB = terminal QRS in inferior, anterior, and right
• Repolarization abnormalities
– ST and T-wave oriented opposite of the terminal QRS
Right Bundle Branch Block
Left bundle branch
Right bundle branch
Left anterior fascicle
Septal fascicle
Left posterior fascicle
Phase 1: Initial QRS in RBBB
• The initial QRS deflection
represents the septum
depolarizing from left to
right. This conduction is
mediated by the septal
fascicle arising from the left
bundle branch
• The initial QRS is
unchanged in RBBB because
conduction is independent of
the right bundle branch
Phase Two: RBBB
• Following the initial QRS, the
left ventricle rapidly depolarizes
via conduction from the LAF
and LPF.
• The right ventricle is delayed.
• This produces a QRS vector
oriented to the left and
posterior.
• The left ventricle is normally
dominant during the QRS and
thus the EKG still shows no
abnormally
Phase 3: Terminal QRS in RBBB
• Following left ventricular
depolarization, there continues to
be delayed depolarization of the
right ventricle via slow myocyteto-myocyte spread.
• The right ventricle is now the
dominate electrical force and
therefore the terminal QRS
vector is oriented to the right and
anterior. This shows on an ECG as
an additional tall upright R’ wave
in V1 and a deep S wave in V6.
RBBB
• Initial QRS
remains normal
• Middle portion
of QRS remains
normal
• Terminal QRS
is sluggish and
dominated by
right ventricular
forces
ECG findings in RBBB
QRS duration
> 0.12 sec
RSR’ pattern in
V1, V2
R’ is recorded in the right precordial leads
demonstrating the period of RV electrical dominance
Wide S wave in
leads I, V5, V6
Reflects slow RV conduction oriented towards the
right and anterior. This is the left lateral lead
equivalent finding of the RSR’ in the right lateral
leads
Normal Axis of
initial 0.06-0.08
sec of QRS
qRS, qrS, or RS in I, V6; rsR' or qR in V1 - Reflects
anterior mid-temporal right ventricular enlargement
and left anterior fascicular block
Secondary ST-T
wave changes
ST depression and T inversion in right precordial
leads, upright in left precordial and limb leads - STT vectors are discordant to terminal mean QRS
spatial vector
Right Bundle Branch Block
Notice the wide RSR' complex in lead V1 and the QRS complex in lead V6. Inverted T waves
in the right precordial leads (in this case V1 to V3) are common with right bundle branch
block and are called secondary T wave inversions.
RBBB
RBBB
RBBB
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Incidence increases with age
Can occur as a normal variant
Most common cause is CAD (LAD)
Other causes include both structural and functional
causes
– Structural: anything causing RV dilatation or hypertrophy,
(acute PE, cor pulmonale, DCM, ect), trauma (right heart
cath, steering wheel, CABG, ablation)
– Functional: rate-related bundle branch block
Differential Diagnosis of RBBB
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Myocardial infarction
Pulmonary embolism
Chronic obstructive lung disease/cor pulmonale
Pulmonary hypertension (primary or secondary)
Hypertensive heart disease
Degenerative disease of the conduction system
Brugada syndrome
Arrhythmogenic RV dysplasia
Cardiomyopathy
Chagas disease
Congenital heart disease (eg, Ebstein anomaly)
RBBB: prognosis and treatment
• Prognosis depends on underlying etiology
• Worse prognosis for patients with type II second degree
atrioventricular (AV) block or multifascicular block
• Generally good prognosis for patients without
underlying heart disease
• NO treatment necessary for isolated asymptomatic
RBBB
• Pacing may be necessary for symptomatic patients or
those with other AV or multifascicular block
RBBB and MI
• T-wave inversions may be seen in leads V1-V3, II, III,
and aVF secondary to the additional rSR’-type
complex (changes to QRS axis)
• ST and T wave changes in the same direction as the
terminal QRS complex should be considered primary
abnormalities (ventricular gradient not between 0º and
90º in the frontal plane)
• Since RBBB does not alter initial phase of ventricular
depolarization, RBBB does not mask abnormal Q
waves seen in MI
Left Bundle Branch Block
Left bundle branch
Right bundle branch
Left anterior fascicle
Septal fascicle
Left posterior fascicle
Phase one: Initial QRS in LBBB
• Normally the LBB begins
the initial QRS with left-toright septal depolarization
• In LBBB the first phase is
altered. The initial QRS
vector remains slightly
anterior and oriented rightto-left.
Phase two: LBBB
•The right ventricle is stimulated
first via the intact RBB while the
left ventricle proceeds by slow slow
cell-to-cell depolarization
•The RV is not seen on ECG since
it is overwhelmed by larger forces
from the LV
•This slow depolarization through
the LV creates a widened QRS
complex with upward deflexions in
the lateral leads.
• In LBBB all phases of ventricular
depolarization are effected
LBBB
• Initial QRS
orientation is rightto-left
• Middle and
terminal QRS
forces are
dominated by the
larger left
ventricular forces
• Slow conduction
causes long QRS
deflection
ECG Findings in LBBB
QRS
duration
0.12 sec
Intrinsicoid
deflection
>0.05 sec in lead V6
Common
pattern
Loss of q wave and wide slurred monophasic R in I, aVL, and V6
RS or QS in V1
ST depression and T wave inversion in leftward leads
ST elevation and upright T waves in right precordial leads
These changes reflect relentlessly leftward vectorial forces. V1
morphology depends on initial leftward or rarely rightward forces. ST
and T vectors are usually 180º discordant to the QRS vector.
Variant
pattern
Terminal S wave in V6 but not usually in I.
Mean electrical axis superior and to the left (about -55º).
ST depression and T wave inversion in leftward leads; ST elevation
and upright T waves in right precordial leads
These changes reflect superior and posterior displacement of loop
with a terminal, often rightward, conduction delay. ST and T vectors
are discordant to the QRS vector.
LBBB
LBBB
LBBB
LBBB and MI
• T-waves in leads with tall R waves (left precordial leads) are
inverted secondary to changes in QRS in LBBB
• T-wave inversions in the right precordial leads cannot be
explained by LBBB
• MI can be difficult to diagnose on ECG in LBBB because Q
waves/ ST elevations can be masked
• Exercise stress testing is of limited value in CAD
– The 2002 American College of Cardiology/American Heart Association
(ACC/AHA) guidelines concluded that there is no level of ST segment
depression that confers diagnostic significance during exercise ECG testing
in patients with LBBB
– Can use myocardial perfusion imaging (MPI)
LBBB
• Incidence increases with age
• Almost always associated with underlying heart disease
• Most common causes include CAD, HTN, dilated CM
(hypertrophy/dilatation of LV)
• Other causes include valvular diseases-rheumatic heart
disease, aortic stenosis, ect
• Rarely results from primary degeneration of the
conduction system
• Rate- or acceleration-dependent LBBB
LBBB prognosis and treatment
• Also depends on underlying cardiac conditions
• Worse prognosis for patients with type II second degree
atrioventricular (AV) block or multifascicular block
• Prognosis depends on age- worse with increasing age
• Isolated LBBB is more likely than RBBB to progress to highdegree AV block and has worse mortality
• NO treatment for asymptomatic isolated LBBB is necessary
• Pacing may be necessary for symptomatic patients or those with
other AV or multifascicular block
Hemiblock / Fascicular Block
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The Left Bundle Branch divides into
3 separate fascicles
– Septal fascicle innervates the
ventricular septum
– The anterior fascicle runs
toward the anteriolateral
papillary muscle and projects
anterior, leftward, and superior
– The posterior fascicle runs
toward the posterior papillary
muscle and projects posterior,
rightward, and inferiorly
– Normal electrical activation of
the LV spreads simultaneously
from the base of the two
papillary muscles
LBB
RBB
LAF
SF
LPF
Hemiblock / Fascicular block cont.
• A fascicular block occurs when you have impaired
conduction down one division of the LBB
• The block is manifested on EKG as QRS axis deviation
• No / minimal QRS prolongation (0.09 – 0.11 sec)
• Most commonly due to CAD and MI; also
cardiomyopathies
Left Anterior Fascicular Block
• With LAFB the LPF
carries the initial
depolarization inferior,
posterior and to the
right
• Then the vector shifts
unopposed to the left,
anterior, and
superior
• Common cause of left
axis deviation
LBB
RBB
LAF
LPF
LAFB: ECG findings
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QRS duration < 0.1 sec
Left axis deviation (Usually -45° to -90°)
No other identified cause of left axis deviation
Tall R waves in I and aVL
Big S waves in II, III, and aVF
LAFB
QRS has normal duration
Left axis deviation
LAFB
QRS has normal duration
Left axis deviation
Tall R waves in I and aVL
Deep S waves in II, III, and aVF
http://askdrwiki.com/mediawiki/images/thumb/c/cd/LAFB.jpg/750px-LAFB.jpg
Left Posterior Fascicular Block
• With LPFB the LAF carries the
depolarization left, anterior and
RBB
superior
• THEN the vector shifts
unopposed inferior, posterior,
and to the right
• Rare cause of right axis deviation
• LPFB is less likely to be caused by
ischemia because it receives dual
blood supply from RCA and LAD
LPF
LBB
LAF
LPFB: ECG findings
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Normal duration of QRS < 0.1 sec
Right axis deviation (+90° to +180°)
No other identified cause of right axis deviation
Big S waves in I and aVL
Big R waves in II, III, and aVF
LPFB
Bifascicular blocks: RBBB and LAFB
• QRS > 0.12s
• RSR’ in V1
• Wide and slurred S waves in I,
V5, V6
• First half (0.06s) of QRS
having frontal plane axis of 30° to -90°
• Initial R wave in inferior leads
Bifascicular blocks: RBBB and LPFB
• QRS>0.12s
• RSR’ in V1with R’ broad and
slurred
• Wide and slurred S waves in
I, V5, V6
• First half (0.06s) of QRS
having frontal plane axis of
+90° or further to the right
with rS deflection in lead I
and qR waves in II, III, and
aVF
Unknown?
QRS prolonged > 0.12 sec
Terminal forces are left and posterior
Dx: LBBB
http://sinaiem.org/wp-content/uploads/2007/07/lbbb_ekg1.jpg
Unknown?
QRS Prolongation > 0.12 sec
RSR’ in V1, V2
ST, T-wave abnormalities
www.sbhemresidency.com/assets/images/EKG_2-13
Slurred terminal S wave in I, V3, V4, V5, V6
Dx: RBBB
Unknown?
QRS has normal duration
Right axis deviation
Dx: LAFB
Unknown?
QRS Prolongation > 0.12 sec
RSR’ in V1, V2, V3
ST, T-wave abnormalities
Slurred terminal S wave in I, aVL, V4, V5, V
Dx: RBBB
askdrwiki.com/mediawiki/images/b/bb/RBBB.PNG
Unknown?
QRS prolonged > 0.12 sec
Terminal forces are left and posterior
Dx: LBBB
http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=cardio&part=A39
Unknown?
QRS has normal duration
Left axis deviation
Dx: LAFB
http://askdrwiki.com/mediawiki/images/thumb/c/cd/LAFB.jpg/750px-LAFB.jpg
Take Home Points
• Bundle branch blocks are best characterized on ECG by:
– prolongation of the QRS > 0.12 sec
– Region of slowed conduction determines the orientation
of the terminal QRS vector and localizes the block
• Hemiblocks do not typically show QRS prolongation,
rather they reveal axis deviation corresponding to the
QRS terminal vector
• Ventricular conduction blocks are common and
can represent a spectrum from normal variant to
serious pathology