Bundle Branch and Fascicular Block Chapter 13

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Bundle Branch and Fascicular Block Chapter 13

• Robert J. Huszar, MD
• Instructor
• Patricia L. Thomas, MBA, RCIS

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Outline

• 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

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AP 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.

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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.

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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)

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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.

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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.

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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

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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

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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 RBBBs differ
  significantly
• Compare Leads 1 V1, V6

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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)

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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 LBBBs differ
  significantly
• Compare Leads 1, aVL,V1, V3, V5,V6
• Complete LBBB - QRS gt.12
• Incomplete LBBB - QRS .10-.11 sec.

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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 gt .10 seconds
• .12 or greater complete

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THE ENDOFCHAPTER 13

• Hauszar Robert, Basic Dysrhythmias,
  Interpretation Management, Third Edition,
  Mosby, Inc. 2002, pp. 271-288.