From Ask Dr Wiki
Causes of Intermittent LBBB
- Acceleration-dependent block form in which conduction delay occurs when the heart rate exceeds a critical value and is usually present in patients with diseased HPS disease
- Phase 3 block in which the first QRS complex with LBBB pattern occurs when the left bundle branch effective refractory period exceeds sinus cycle length. This occurs due to encroachment of the impulse on the relative refractory period, usually in phase 3 of the action potential, of the preceding impulse. It is a physiologic phenomenon and can be seen in normal subjects.
- Deceleration dependent block in which conduction delay occurs when the heart rate falls below a critical level, possibly due to abnormal phase 4 depolarization of cells.
