Left bundle branch block classification

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Cafer Zorkun, M.D., Ph.D. [2]; Raviteja Guddeti, M.B.B.S. [3]; Aarti Narayan, M.B.B.S [4]

Classification

Classification Based on Duration

New Left Bundle Branch Block

New LBBB is defined as the presence of a new left bundle branch block and:

1. A prior ECG with normal QRS duration (<110 ms) within 24 hours before the LBBB tracing without T-wave abnormalities.
2. Acute-onset illness with LBBB on the admission tracing resolving within 24 hours without T-wave abnormalities on the subsequent narrow QRS tracings (to exclude LBBB lasting more than 24 hours) in patients with no history of LBBB.

Old Left Bundle Branch Block

An old LBBB is defined as an LBBB that has existed for more than 24 hours (by prior tracings or reports in the electronic medical record).

Left Bundle Branch Block of Unknown Duration

The LBBB duration is unknown on tracings obtained within the first 24 hours of admission in which there is not any prior EKG information.

Classification Based on Extent of Block

Another classification system commonly used for LBBB is as follows:

Complete LBBB

The criteria to diagnose a complete left bundle branch block on an electrocardiogram includes the following:

1. The heart rhythm must be supraventricular in origin. A wide QRS complex that is not preceded by P waves would not qualify.
2. The QRS duration must be greater than or equal to 120 milliseconds.
3. There should be a QS or rS complex in lead V1.
4. There should be a monophasic R wave in lead I and lead V6.

Incomplete LBBB

The criteria for diagnosing an incomplete LBBB include:

1. QRS duration between 110 and 119 ms in adults, between 90 and 100 ms in children 8 to 16 years of age, and between 80 and 90 ms in children less than 8 years of age.
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.
5. ST and T wave displacement opposite to the major deflection of the QRS complex.