Excessive delay and configurational change of ventricular responses to atrial premature beats in the dog heart were shown to be due to functional block of the right bundle branch.
This preclinical study demonstrates that aberrant A-V impulse propagation and functional bundle branch block are primarily due to the refractory period of the right bundle branch exceeding that of the A-V node at slow heart rates.
Excessive delay and configurational change of ventricular responses to atrial premature beats, previously attributed to dissociation within the A-V node, were shown to be due to functional block of the right bundle branch. It was found that the refractory period (RP) of the right bundle branch often exceeded the functional refractory period (FRP) of the A-V node at slow heart rates, permitting an early premature atrial response to reach the ventricles before recovery of the right bundle. Vagal stimulation and rapid driving frequencies, by delaying the intranodal transit of the premature response, prevented the exposure of bundle branch block. Epinephrine in low doses sometimes facilitated its occurrence. Premature responses initiated in the His bundle in open heart preparations were commonly blocked in the right bundle under conditions in which atrial premature responses were normally propagated to the ventricles. Evidence was obtained in such preparations that the portion of the right bundle system beyond the site of the block was activated retrogradely from the left side. Under certain conditions the retrograde activation process returned to the His bundle and the atrium as an echo.
Moe et al. (Mon,) conducted a other in Functional bundle branch block. Vagal stimulation, rapid driving frequencies, and epinephrine was evaluated on Aberrant A-V impulse propagation and functional block of the right bundle branch. Excessive delay and configurational change of ventricular responses to atrial premature beats in the dog heart were shown to be due to functional block of the right bundle branch.