Week 3- 12 Lead ECG- BBB

Question 1

How many bundle branches do we have?

Answer 1

• Two bundle branches
• Right and left bundle branch
• Left bundle branch: it anterior fascicle & it posterior fascicle

Question 2

What is the normal pathway of an impulse?

Answer 2

Impulses generated by pacemakers in atria or AV node are normally conducted down bundle branches
- innervate myocardium in organized fashion

Question 3

Bundle Branch Blocks

Answer 3

• If the pt. has has an MI or something that blocks the normal conduction
• If the impulse hits an obstacle it would not be able to proceed this way
• It would have to travel cell-to-cell transmission rather than down the bundle branches
• This is a slow chaotic way to innervate the myocardium
• This method of the depolarizing the ventricles will give rise to abnormal looking complexes on the ECG
  
  • Increased QRS width (>0.12s)
  • Different appearing morphologies of the QRS complex
    
    • 2 different morphologies= RBBB & LBBB

Question 4

Right Bundle Branch Block

Answer 4

• Pattern caused by a block of the right bundle branch somewhere near its inception
• Left side of the heart depolarizes normally- this creates a normally looking QRS initially (first 0.04-0.08s)
• End of the complex will then appear wide and bizarre because of the slowed conduction
• Often shows a RSR or “rabbit ears” (caused by the interruption and differences in left sided and right sided ventricular depolarization)

Question 5

How to diagnose RBBB?

Answer 5

1. wide QRS complex
2. Slurred S wave in leads I and V6
3. Now look at V1- if the complexes are positive here then you can confirm a RBBB

Question 6

What are causes of RBBB?

Answer 6

• Right ventricular hypertrophy/ cor pulmonale
• Pulmonary embolism
• Ischemic heart disease
• Rheumatic heart disease
• Myocarditis or cardiomyopathy
• Degenerative disease of the conduction system
• Congenital heart disease (eg. atrial septal defect)

Question 7

Left Bundle Branch Block

Answer 7

• LBBB is always 0.12s wide or more
• Have ST depression or elevation

Caused by:
- Block or left bundle or
- Block of both fascicles of left bundle

• Block causes electrical potential to travel down right bundle first
• Depolarization occurs right to left by direct cell to cell transmission
• Left ventricle is so big, transmission is delayed

Question 8

What are causes of LBBB?

Answer 8

1. Hypertension
2. Coronary artery disease
3. Dilated cardiomyopathy
4. Rheumatic heart disease

Vast majority due to hypertension, CAD, or both

Question 9

How do you diagnose LBBB?

Answer 9

• Wide QRS duration
• The QRS complex typically has a less sharp appearance than in a RBBB due to the larger size of the LV. This leads to broad, monomorphic complexes
• Discordant T waves- if the QRS complex is positive, the T waves should be negative and vice versa
• Look in V1 and V6 again- if the complexes match this description (broad and monomorphic), you have a LBBB

Question 10

Ventricular Paced Rhythms

Answer 10

• In many ways, a ventricular paced beat is a manmade LBBB
• When LBBB occurs, the electrical impulse travels down the right bundle branch, depolarizes the right ventricle
• Then the impulse spreads through the myocardium to depolarize the left ventricle
• Pacemakers are often introduced into the right ventricle