1. Ventricular Conduction Disturbances
Chapter 7

2. Bundle Branches
Normal conduction speed through the bundles is about 0.1 seconds

3. Bundle Branch Block Right Left
Consider a blocked or slowed branch or bundle
Right
Left

5. Right Bundle Branch Block
First Phase will be normal
Second Phase -
Normal
Third Phase - ?
After the left ventricle has completely depolarized, the right ventricle continues to depolarize

6. Right Bundle Branch Block1. 2. 3.
1. r wave in V1
q wave in V6
2. S wave in V1
R wave in V6
3. R’ wave in V1
S wave in V6

7. Right Bundle Branch Block Criteria
V1 or V2 = rSR’ - “M” or rabbit ear shape
V5 or V6 = qRS
Large R waves
Right chest leads: T wave inversion (“secondary changes” since they reflect a delay in depolarization not an actual change in depolarization).
Complete RBBB: QRS > 0.12 sec.
Incomplete RBBB: QRS = 0.10 to 0.12 sec.

8. Right Bundle Branch Block
V1 = rSR’
V6 = qRS

9. Right Bundle Branch Block
V2 = rSR’
V6 = qRS

10. Right Bundle Branch Block
Clinical Significance
Healthy heart
Organic heart disease
atrial septal defect
pulmonary disease
valvular lesions
degenerative changes in conduction system
chronic coronary artery disease
pulmonary embolism
after bypass graft surgery
Permanent or transient
RBBB by itself requires no treatment

11. Left Bundle Branch Block
RBBB affects mainly the terminal phase of depolarization
LBBB affects the early and terminal phases of depolarization
Septum is depolarized from right to left (rather than left to right)
Depolarization of the left ventricle takes longer

12. Left Bundle Branch Block
1. r wave in V1
R wave in V6
2. S wave in V1
R wave in V6

13. Left Bundle Branch Block
Loss of septal R in V1 and septal Q in V6.
Wide QRS
Negative in V1
Positive in V6

14. Left Bundle Branch Block Criteria
Wide QRS complex
V1 = QS (or rS) and may have a “W” shape to it.
V6 = R or notched R showing a “M” shape or rabbit ears
Secondary T wave inversion
Secondary if in lead with tall R waves
Primary if in right precordial leads

15. Left Bundle Branch Block

16. RBBB versus LBBB ? ?

17. Left Bundle Branch Block
Causes
long standing hypertension
valvular lesion
cardiomyopathy
coronary artery disease
Precursor
Advanced CAD
Valvular heart disease
Hypertensive heart disease
Cardiomyopathy

18. Rate-Related (Exercise-Induced) Bundle Branch Blocks
Ischemia or other factors during exercise may produce BBB not seen at rest
Rate-limited bundle branch block
Exercise induced bundle branch block

19. Incomplete Bundle Branch Blocks
RBBB or LBBB where QRS is between .10 and .12 with same QRS features
Incomplete RBBB normal variant
Incomplete LBBB a progression of LVH

20. Intraventricular Delay or Intraventricular Conduction Defect
General term for wide QRS complexes that are not typical of RBBB or LBBB

21. Pacemaker Pattern

22. Pacemaker Patterns

23. Trifascicular Conduction System

24. Tri-fascicular Conduction System
Right bundle
Left anterior (superior) fascicle
Left posterior (inferior) fascicle
Fascicular block (or hemiblock) = a block in either the LAF or LPF.

25. Fascicular Blocks Fascicular blocks only slightly prolongs the QRS.
Fascicular blocks cause axis deviation as do infarcts and hypertrophy.
Left or right axis deviation without signs of infarct or hypertrophy are fascicular blocks.

26. Left Anterior Fascicular Block
Limb leads
QRS less width less than 0.12 sec.
QRS axis = Left axis deviation (-45° or more)
if S wave in aVF is greater than R wave in lead I
small Q wave in lead I, aVL, or V6

27. Left Posterior Fascicular Block
Right axis deviation (QRS axis +120° or more)
S wave in lead I and a Q wave in lead III (S1Q3)
Rare

28. Bifascicular Block Two of the three fascicles are blocked.
Most common is RBBB with left anterior fascicular block.

29. Summary
The last component of the QRS vector will be shifted in the direction of the last part of the ventricles to be depolarized.
In other words, the major QRS vector shifts toward the regions of the heart that are most delayed in being stimulated.
RBBB: late QRS forces point toward the right ventricle (Rabbit ears, M shape in V1)
LBBB: late QRS forces point toward the left ventricle (negative in V1 and R or notched R in V6)
LAFB: late QRS forces point in a leftward and superior direction (LAD with deep S wave in aVF ).

30. Hypertrophy In The Presence of Bundle Branch Block
RVH and RBBB
RAD is typically seen; also look for RAE and its peaked P waves.
RBBB with RAD indicates RVH is likely present, too.
LVH and RBB
usual criteria can be used but also look for LAE