Bundle Branch Blocks

J. Huffman, PGY-4July 2, 2009

Outline

• LBBB• RBBB• Hemiblock• PRACTICE!

Unblocked ventricle

Blocked ventricle

RR’

On ECG

Two QRS’s out of ‘sync’ Single, wide QRS

Physiologically

LBBB

RBBB

RBBB

RBBB

LBBB

LBBB

“WiLLiaM MoRRoW”

V1 V6W LBBB M WiLLiaMM RBBB W MoRRoW

LBBB

LBBB

ECG Changes:• Hemiblock (unlike a full LBBB or RBBB)

does not widen the QRS complex.

• Main effect is a change in the QRS axis:

Left anterior fascicular block results in marked left axis deviation (-30° or more) QISIII pattern

Left posterior fascicular block produces marked right axis deviation (+120° or more) SIQIII pattern

aVL

aVF

I

IIIII

Anterior Hemiblock

Posterior Hemiblock

Axis?

Between -30 and -90 deg LAD

Anterior Fascicular Block

Posterior Fascicular Block

LAFB

Bifascicular Block(RBBB & LAFB)

RBBB + LAFB

Trifascicular Block(RBBB + LAFB + 1° AV block)

1. V1 & V2 have the best “view” of the RV

2. V5 & V6 look at the LV

3. Look for the RR’ pattern in those pairs of leads

4. Incomplete = <120ms but meets morphology criteria

5. Hemiblocks: look at the axis!