Bundle Branch Blocks

Updated March 22, 2020

RBBB + LBBB | LAFB + LPFB | Incomplete LBBB + Nonspecific IVCD | Related Topics | Further Reading

Right Bundle Branch Block

Criteria

1. QRS > 120 ms in adults (>100 ms in children 4-16yo, and > 90 ms <4yo
2. Leads V1 or V2:
   1. rsr’ , rsR’ , or rSR’ pattern
   2. The R or r deflection is usually wider than the initial R wave.
   3. A wide and notched R wave pattern may be seen in lead V1 and/or V2.
3. Leads 1 and V6: S > R in duration OR >40 ms in leads I and V6 in adults.
4. R-wave Peak Time (When a pure dominant R wave with or without a notch is present in V1)
   1. Normal in V5/6, but >50 ms in V1

Examples

Left Bundle Branch Block

Criteria

1. QRS ≥ 120ms in adults (>100ms children 4-16, >90ms children <4yo)
2. Lateral Leads (I, aVL, V5, V6)
   1. Broad notched/slurred R-wave in LATERAL leads (I, aVL, V5, V6) (Sometimes V5-6 can have RS pattern, due to displaced transition of QRS)
   2. Absent q-waves in LATERAL LEADS (I, V5, V6) (aVL may have q)
   3. R-wave peak-time WIDE in LATERAL > 60ms in V5-6 (Normal in V1-3)
3. ST and T-waves usually opposite direction of QRS
   1. Positive concordance can be normal (Positive T-wave in leads with upright QRS)
   2. NOTE: Negative concordance is abnormal. (Depressed ST or T-waves in leads with negative QRS)
4. Axis Deviation can be RIGHT, LEFT, or SUPERIOR

Examples

Left Anterior Fascicular Block

Criteria

1. Left Axis Deviation (-45° and -90°)
2. qR pattern in lead aVL.
3. R-peak time in lead aVL ≥45 ms.
4. QRS < 120 ms.

Examples

Left Posterior Fascicular Block

Criteria

1. Axis 90° to 180°
2. rS pattern in leads I and aVL.
3. qR pattern in leads III and aVF.
4. QRS duration < 120 ms

Examples

Incomplete Left Bundle Branch Block

Criteria

1. Same criteria as RBBB except: QRS 110-120ms (adultsL

Nonspecific Intraventricular Conduction Delay

Criteria

• QRS > 110ms
• Does not meet criteria for LBBB or RBBB OR Limb leads have LBBB pattern and precordial limbs have RBBB pattern (or vice versa

Related Topics

• ECG Fundamentals (coming soon)
• LVH
• RVH

Further Reading

• Surawicz B, Childers R, Deal BJ, et al. AHA/ACCF/HRS recommendations for the standardization and interpretation of the electrocardiogram: part III: intraventricular conduction disturbances. Journal of the American College of Cardiology. 2009; 53(11):976-81.