CRAT Bundle Branch Blocks and Fascicular Blocks

Question 1

What minimum QRS duration is required to diagnose a complete bundle branch block?

Accepted Answer

≥0.12 seconds

Answer

A complete bundle branch block requires a QRS duration of ≥0.12 seconds (3 small squares at standard paper speed) on the ECG.

Question 2

In right bundle branch block (RBBB), which leads classically display the rSR' ('rabbit ears') pattern?

Accepted Answer

Leads V1 and V2

Answer

RBBB produces a classic rSR' (or RSR') pattern in the right precordial leads V1 and V2, reflecting delayed right ventricular depolarization traveling toward those leads.

Question 3

In right bundle branch block, a wide, slurred S wave is characteristically seen in which leads?

Accepted Answer

I, aVL, V5, and V6

Answer

The terminal slurred S wave in leads I, aVL, V5, and V6 represents the delayed right ventricular depolarization force traveling away from these left-sided lateral leads in RBBB.

Question 4

Which of the following correctly describes an INCOMPLETE right bundle branch block?

Accepted Answer

QRS 0.10–0.11 sec with rSR' in V1

Answer

Incomplete RBBB shows the characteristic rSR' morphology in V1 but with a QRS duration between 0.10 and 0.11 seconds, indicating partial rather than complete conduction delay.

Question 5

The secondary R wave (R') seen in lead V1 during RBBB represents delayed depolarization of which cardiac structure?

Accepted Answer

Right ventricle

Answer

The R' in V1 during RBBB represents delayed activation of the right ventricle, which depolarizes late after normal left ventricular activation has already occurred.

CRAT - Certified Rhythm Analysis Technician Practice Test

CRAT - Certified Rhythm Analysis Technician Practice Test

CRAT Bundle Branch Blocks and Fascicular Blocks