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Flashcards in Bundle Branch Blocks Deck (15)
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1

Describe the regions of the left ventricle supplied by the left anterior and posterior hemifascicles, respectively

  • Anterior: Anterior, superior, and lateral walls
  • Posterior: Posterior, inferior, and medial walls

2

Under normal conditions, septal depolarization is initiated by the _______ bundle branch

Left

3

Compare QRS duration in left fascicular block vs. left or right BBB

In complete BBB the QRS is prolonged. In fascicular block the QRS is of normal duration

4

Left posterior fascicular block is __________ (more/less) common than left anterior fascicular block

less

5

List typical criteria for identifying RBBB

  • QRS duration >= 120ms
  • "M"-shaped QRS in V1 (rsR' pattern)
  • Prominent S in I and aVL
    • Secondary repolarization abnormalities may be seen in V1-2

6

List typical criteria for identifying LBBB

  • QRS duration >= 120ms
  • Broad R-wave in I, aVL, and V6 (often notched)
  • Lack of physiologic q-waves in I and V6
  • Secondary repolarization abnormalities often seen in multiple leads:
    • Downsloping ST-depression with TWI in I, aVL, V6
    • Opposite pattern (deep S-wave with upsloping STE and upright T) in V1-3

7

Describe pathophysiology and ECG characteristics of incomplete BBB

  • Intraventricualr conduction abnormality in which conduction is slowed, but not entirely stopped through one of the bundle branches
  • Generally of similar etiology to complete block. Will often proceed to complete block with time
  • ECG morphology is similar to complete block but with preserved QRS duration

8

List typical criteria for identifying isolated LAFB (left anterior fascicular block / left anterior hemiblock)

note that hemiblock is best assessed in the limb leads

  • preserved QRS duration (100-120ms)
  • left axis deviation (usually beyond -45°)
  • small septal q in lateral limb leads (I, aVL)
  • small R in inferior leads (II, III, aVF)
  • intrinsicoid deflection >45ms in aVL

9

List typical criteria for identifying isolated LPFB (left posterior fascicular block / left posterior hemiblock)

​note that hemiblock is best assessed in the limb leads

  • preserved QRS duration (100-120ms)
  • right axis deviation
  • small q in inferior leads (II, III, aVF)
  • small R in lateral limb leads (I, aVL)
  • intrinsicoid deflection >45ms in aVF
  • No additional evidence of RVH, as all these signs could be produced by RVH

10

QRS duration >120ms without RBBB or LBBB morphology is referred to as:

Non-specific intraventricular conduction delay

11

What is Bifascicular block and what is the most common cause?

RBBB + LAFB/LPFB

Most common cause is CAD

12

Assess the following ECG for signs of intraventricular conduction delay

  • QRS >120ms
  • Broad R-wave in lateral leads (I, aVL, V6)
  • Deep S-waves with STE in V1-V3
  • LAD
  • Secondary repolarization abnormalities in lateral leads

Complete LBBB

13

Assess the following ECG for signs of intraventricular conduction delay

  • Normal QRS duration
  • Normal QRS morphology in V1 and V6
  • RAD
  • Small q-waves in inferior limb leads
  • Small r-waves in lateral limb leads

LPFB

14

Assess the following ECG for signs of intraventricular conduction delay

  • Prolonged QRS (~160ms)
  • Left axis deviation (~-40°)
  • rsR' pattern in V1
  • Wide terminal S in I, aVL, and V6
  • TWI in V1-2

Bifascicular block: RBBB + LAFB

15

Assess the following ECG for signs of intraventricular conduction delay

  • Wide QRS (160-200ms)
  • Borderline LAD (QRS axis ~-30°)
  • Wide terminal R-wave in V1-4
  • Terminal s in V6, I, aVL
  • TWI in V1-4
  • Small r-waves in inferior limb leads

RBBB with atympical morphology (no "slurred s") and potential LAFB