bundle branch blocks
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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!
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