Bundle Branch Block, Left

CARDIOLOGY, ECG

Left Bundle Branch Block (LBBB)

Criteria for complete LBBB in adults from the AHA/ACC.

  1. QRS ≥ 120 msec (or 110-119 for incomplete BBB)
  2. I, aVL, V5-V6: Presence of broad, slurred, monophasic R wave. ± RS in leads V5-V6 in patients with cardiomegaly.
  3. I, V5-V6: Absence of  Q wave. aVL may have a small q wave.
  4. R wave peak time greater than 60 ms in leads V5 and V6.
  5. Appropriate discordance: ST segment and T waves usually opposite in direction to the major QRS vector.
  6. Positive T wave in leads with upright QRS may be normal (positive concordance).
  7. Depressed ST segment and/or negative T wave in leads with negative QRS (negative concordance) are abnormal.
  8. Axis deviation: The presence of LBBB may change the mean QRS axis in the frontal plane to the right, to the left, or to a superior, in some cases in a rate-dependent manner
  9. Poor R wave progression (PRWP) in the chest leads

Incomplete LBBB

  1. QRS duration between 110 and 119 ms in adults
  2. Presence of left ventricular hypertrophy pattern.
  3. R peak time greater than 60 ms in leads V4, V5, and V6.
  4. Absence of q wave in leads I, V5, and V6.

***R-wave peak time is defined as the interval from the onset of the QRS complex to the peak of the R wave in leads that do not have a small initial R wave. R-wave peak time is used in preference to the term intrinsicoid deflection.

 

References

J Am Coll Cardiol. 2009 Mar 17;53(11):976-81. https://www.ncbi.nlm.nih.gov/pubmed/19281930

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