CRAT Bundle Branch Blocks and Fascicular Blocks 3

Question 1

The left bundle branch divides into how many main fascicles?

Accepted Answer

Two

Answer

The left bundle branch divides into two main fascicles: the left anterior fascicle and the left posterior fascicle, each of which can be independently blocked.

Question 2

Left anterior fascicular block (LAFB) is characterized by which QRS axis on a 12-lead ECG?

Accepted Answer

Left axis deviation (−45° to −90°)

Answer

LAFB produces marked left axis deviation (typically −45° to −90°) because the depolarization wave must travel inferiorly via the posterior fascicle before activating the anterior wall superiorly.

Question 3

Which set of criteria correctly describes left anterior fascicular block (LAFB)?

Accepted Answer

Left axis deviation, small Q in I and aVL, small R in II/III/aVF, QRS <0.12 sec

Answer

LAFB criteria include left axis deviation (−45° to −90°), small Q waves in I and aVL, small R waves in II, III, and aVF, and a QRS duration less than 0.12 seconds.

Question 4

The combination of right bundle branch block (RBBB) and left anterior fascicular block (LAFB) is called:

Accepted Answer

Bifascicular block

Answer

Bifascicular block refers to simultaneous blockage of two of the three fascicles; RBBB + LAFB is the most common combination, involving two-thirds of the trifascicular conduction system.

Question 5

A patient with bifascicular block (RBBB + LAFB) also has a prolonged PR interval. This pattern is clinically significant because it suggests:

Accepted Answer

Disease in all three fascicles with risk of progressing to complete AV block

Answer

Bifascicular block with a prolonged PR interval (trifascicular block pattern) indicates disease affecting all three conduction fascicles and carries significant risk of progression to complete third-degree AV block.

CRAT - Certified Rhythm Analysis Technician Practice Test

CRAT - Certified Rhythm Analysis Technician Practice Test

CRAT Bundle Branch Blocks and Fascicular Blocks 3