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Bundle Branch and
Fascicular Block
Chapter 13
Robert J. Huszar, MD
Instructor
Patricia L. Thomas, MBA, RCIS
Outline
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Student Demonstration of Axis
Electrical Conduction system and Blood supply
Physiology of the Electrical Conduction System
Pathophysiology of the Bundle Branch and
Fascicular Blocks
• Right Bundle Branch Block
• QRS Complexes
• Left Bundle Branch Block
A&P of the Electrical Conduction System
• RBB runs down the right side of the IS to conduct
the electrical impulses to the RV.
• LBB short, thick, flat (main stem) conducts the
electrical impulses to IS & LV. It is divided into
two parts:
– LAF conducts electrical impulses from the main stem
to the anterior and lateral walls of LV.
– LPF conducts electrical impulses to the posterior wall
of the LV.
Blood Supply to the Electrical
Conduction System
• Anterior two thirds of the interventricular septum is
supplied by the left anterior descending CA.
• Posterior third of the septum is supplied by the posterior
descending CA.
• AV Node and Proximal Bundle of His is the AV node
artery.
• Distal Bundle of His, RBB, Main stem of LBB and Lt
Anterior Fascicle are supplied by the LAD septals.
• Left Posterior Fascicle is supplied by the LAD and PDA.
Intact viable vs. Not Intact or viable
• IVIS-is capable of conducting an electrical
impulse and depolarizing from left to right
producing and initial small q or r wave in the QRS
complex in V1,V2 & V6. Resulting synchronous
depolarization with the smaller RV buried in that
generated by the LV.
• NVIS- results because of some form of Heart
Disease, (MI) is unable to conduct an electrical
impulse and depolarize normally ( absence of a q
or r wave)
Steps for Normal Depolarization
The electrical impulse progress through the RBB
and LBB and Fascicles simultaneously.
• Depolarization of IVS
• Synchronous Depolarization of RV & LV
• Note: The electrical activity generated by the
depolarization of the smaller RV is buried in that
generated by the LV.
Depolarization of Septum
• Depolarization of the Interventricular
Septum of the endocardial to epicardial of
the ventricular wall is call the Ventricular
Activation time (VAT) or the Preintrinsicoid
Deflection (IDT), the duration of the
Intrinsicoid Deflection or the R peak time.
VAT Measurement
• Onset of the QRS complex to the peak of
the last R wave in the QRS complex.
• Normally less than .04 second in V1 or V2
or less than .06 second in V5 and V6.
• RBBB & RVH -the VAT is prolonged in
leads V1 & V2
• LBBB & LVH-the VAT is prolonged in
Leads V5 & V6
Pathophysiology of the BB and
Fascicular Blocks
• Ischemia heart disease
• Acute Mi
• Idiopathic degenerative disease of Conduction
system
• Cardiomyopathy
• LVH
• Aberrant ventricular conduction
• Miscellaneous causes such as
– Acute or chronic HF, PE, AoValve Disease, Tumors,
Trauma, Potassium overdose
Right Bundle Branch Block
• The electrical impulses are prevented from
entering the RV directly because of disruption of
conduction system.
• RBBB present with intact viable IVS
• RBBB present without intact viable IVS
• ECG characteristics of the two RBBB’s differ
significantly
• Compare Leads 1 & V1, V6
RBBB
• Impulses travel down the LBB in to the IS &
LV-(Normal)
• IS to right to enter the RV after a short delay
• LV depolarize in normal way: first the septum
from left to right
• Then the LV from right to left
• LV depolarization
• RV depolarizes in a normal direction
• Delay results in a wide bizarre shape/appearance
• .12 seconds or greater (complete)
• .10 and .11 seconds (incomplete)
Pathophysiology of the Left
Bundle Branch Block
• The electrical impulses are prevented from entering the
LV directly because of the disruption of conduction of the
electrical impulses through the LBB.
• LBBB present with intact viable IVS
• LBBB present without intact viable IVS
• ECG characteristics of the two LBBB”s differ
significantly
• Compare Leads 1, aVL,V1, V3, V5,V6
• Complete LBBB - QRS >.12
• Incomplete LBBB - QRS .10-.11 sec.
LBBB
• Impulses travel down the RBB into the RV
(normal)
• Impulse travels slowly across IS from Right to
Left (abnormal)
• Depolarization of the RV (normal)
• Depolarization of the LV (normal direction)
• Depolarization of the LV results from the impulse
from the right instead of the LBB
• The LV depolarizes behind schedule
• QRS > .10 seconds
• .12 or greater complete
THE END
OF
CHAPTER 13
Hauszar Robert, Basic Dysrhythmias, Interpretation & Management, Third Edition, Mosby,
Inc. 2002, pp. 271-288.