Bundle branch blocks

Question 1

What is appearance of RBBB and LBBB in V1?
What limitations of diagnosing underlying disease when RBBB/LBBB present?

Answer 1

• RBBB severely limits the ability to diagnose RVH
• LBBB severely limits the ability to diagnose LVH, and an ST elevation MI

Question 2

What is appearance of RBBB/LBBB in V6?

Answer 2

Question 3

What is criteria for RBBB?

Answer 3

• QRS duration >120ms
• An M shaped QRS complex in V1
• Prominent S wave in lead I and lead aVL
• Secondary repolarization abnormalities are usually seen in V1-V2

Question 4

Answer 4

In lead V1: R’ is more prominent than R
In lead I and lead aVL: prominent S wave

Question 5

What is the criteria for LBBB?

Answer 5

• QRS duration >120ms
• Broad R wave in lead I, aVL, and V6
• Lack of septal q waves in lead I, and V6

Widespread secondary repolarization abnormalities should also be present
* Leads I, aVL, V6 usually display a downsloping zst depression leading to an inverted T wave
* Leads V1-V3 usually display a deep S wave, with upsloping ST elevation leading into a upright and prominent T wave

Question 6

Answer 6

LBBB
* Broad R wave and deeply inverted T waves in lead I, aVL and V6
* Deep S wave and ST elevation and prominent T wave in V1-V3

Question 7

Causes of RBBB

Answer 7

• Coronary artery disease
• Pulmonary hypertension
• Acute pulmonary embolism
• Idiopathic
• Iatrogenic during right sided cardiac catheterization
• Congenital heart disease

Question 8

Causes of LBBB

Answer 8

• Acute anterior MI
• Coronary artery disease
• LVH (any cause)
• Heart failure (any cause)
• idiopathic
• HyperK
• Digoxin toxicity

Question 9

What is criteria of left anterior fascicular block (LAFB)?

Answer 9

• LAD (usually beyond -45): as only depolarization is from inferior septal/medial rotation upwards
• Small q in leads I and aVL
• Small r in leads II, III and aVF
• Intrinsicoid deflection in aVL >45ms

Precordial leads are not typically affected

Question 10

What is criteria of left posterior fascicular block (LPFB)?

Answer 10

Not as common as left anterior fascicular block
* RAD: depolarization only from anterolateral rotation (goes down and back)
* Small r in leads I and aVL
* Small q in leads II, III and aVF
* Intrinsicoid deflection in aVF >45ms
* No additional evidence of RVH (tall R wave in V1 or RAE)

Question 11

Define bifascicular block?
What is the causes?

Answer 11

RBBB + either LAFB/LPFB

Causes
* CAD (most common)
* Degenerative disease of conduction system
* Hypertension
* Aortic stenosis
* Congenital heart disease

Question 12

Answer 12

Bifascicular block: RBBB combined with LAFB

Axis: Lead I +ve, lead aVF negative, lead II -ve = left axis deviation

RBBB results:
Prominent S wave in lead V1 and lead aVL
M shaped QRS complex in lead V1
Secondary repolarization abnormalities in lead V1-2: T wave inversion in lead V1

LAFB results:
Small q waves in lead I and aVL
Small r waves in leads II, III and aVF

Question 13

Answer 13

RBBB:

LPFB results:
Axis: lead I is -ve, lead aVF is +ve = right axis deviation
rS (small r) pattern in leads I and aVL
qR (small q) pattern in leads II, III and aVF

Question 14

What are the progressive cardiac conduction diseases causing bundle branch block?

Answer 14

Levs disease: sclerosis and calcification of the cardiac skeleton
Lenegres disease: primary degenerative disease of the conduction system

Question 15

Answer 15

Mobitz type 2 second degree heart block: same PR interval than drops
Mobitz type 2 (below AVN): widened QRS complex

Goes from 3:1 type 2 mobitz second degree heart block to mobitz type 2 2nd degree heart block with a 2:1 AV block