RBBB

Question 1

In the RBBB ECG, normal depolarization occurs in the (Left bundle of His/Right bundle of His)

Answer 1

Left bundle of His

Question 2

Describe the vectors that produce ECG changes in the right bundle branch ECG.

Answer 2

• Blockage of normal depolarization of the right Bundle of His produces ECG changes.
  - LBB depolarizes normally - meaning the early part of the QRS is unchanged
  - Delayed RBB activation changes the vector of depolarization (right ventricle is depolarized by the action potential spreading from the left bundle branch)
  - This delayed RBB depolarization adds a prime wave in the right precordial leads (V1-V3) and a slurred S save in the lateral leads (V4-V6)
  - There may also be STD/TWI in the right precordial leads

Question 3

What is the Dx criteria for RBBB?

Answer 3

• QRS > 120 ms (.12 s)
• RSR’ pattern in V1-V3
• Wide, slurred S-waves in I, aVL, V5-V6

Question 4

Occasionally, a _____ may be found in V1 of the RBBB.

A. QRS < 120 ms
B. Monophasic R/qR complex
C. STE

Answer 4

B. Monophasic R/qR complex

Question 5

What are the causes of RBBB?

Answer 5

• RVH/cor pulmonale
• PE
• Ischemia
• Rheumatic heart disease
• Myocarditis/cardiomyopathy
• Degenerative diseases of conduction
• Atrial septal defect

Question 6

Mnemonic for differentiating RBBB vs. LBBB

Answer 6

“WiLLiaM MaRRoW”

WiLLiaM:

- Block: Left Bundle
- Lead I findings: W-shaped QRS (Slurred S)
- Lead V6 findings: M-shaped QRS (RSR’)

MaRRoW:

- Block: Right Bundle
- Lead I findings: M-shaped QRS (RSR’)
- Lead V6 findings: W-shaped QRS (Slurred S)

Question 7

Occasionally, the right precordial leads in RBBB exhibit what feature?

Answer 7

T-wave inversion/STD

Question 8

Sometimes rather than an RSR’ pattern in V1, there may be _____ in RBBB.

Answer 8

a broad monophasic R wave or a qR complex