12 Leads Part 3.1 BBB

Question 1

What is the definition of Bundle branch block?

Answer 1

A disruption in the conduction of the electrical signal through the left or right bundle branches leading to a delay in ventricular depolarization

Question 2

What is the mechanism of bundle branch block?

Answer 2

• the impulse first travels down the unblocked bundle branch which stimulates the respective ventricle
• the blocked ventricle depolarizes later due to cell to cell electrical conduction
• results in a widened QRS complex

Question 3

What are the causes of bandle branch blocks? (Only a CHAD gets a bundle branch block)

Answer 3

• congenital defects
• hypertension
• acute ischemia
• degenerative heart disease

Question 4

Why is BBB considered a master mimic?

Answer 4

Because it can mask ECG changes associated with acute coronary syndrome and things like ST elevation/depression may be hidden with the presence of BBB

Question 5

60-70% of BBBs can be caused by an MI,, especially if the infarct involves which part of the heart?

Answer 5

The septum (this is where the branch bundles are located)

Question 6

BBB can hide but also can produce…

Answer 6

• ST elevation
• ST depression
• Tall T waves
• T wave inversion
• Wide Q waves

Question 7

Why is the right bundle branch more susceptible to complete blockages?

Answer 7

This is because its smaller and less robust compared to the left bundle branch

Question 8

ECG characteristics of RBBB?

Answer 8

• in V1 you can see a RSR pattern that resembles bunny ears
• in lateral leads like V6 and lead 1 you see a wide slurred S wave
• in precordial leads T wave inversion can be seen
• wide QRS complex

Question 9

The left bundle branch is more robust and begins as a single pathway but splits into two branches. What are they and what do they do?

Answer 9

1. Anterior fascicle : conducts impulses to the anterior portion of the left ventricle
2. Posterior fascicle : conducts impulses to the posterior portion of the left ventricle

Question 10

ECG characteristics of LBBB

Answer 10

• significantly widened QRS complex >120 milli seconds
• absence of a normal q wave in lateral leads (1, aVL, 5,6)
• ST and T wave are in the opposite direction of the QRS complex
• V6 R wave might have a notch at the top
• slurred S wave in Lead 1 and V6

Question 11

How can i assess for bundle branch block?

Answer 11

• check if it’s supraventricular (p waves are present)
• is there a wide QRS
• is it MARROW of VILLIAM patterned

*if no P waves are present its probably coming from the ventricles (PVC)

Question 12

What is scarbosas criteria?

Question 13

With thinking about scarbosas criteria and the general characteristics of LBBB. What would be shown on the ECG for you to start suspecting a STEMI?

Answer 13

Extreme discordance or concordance is present