Type I, Type II, and Type III Gaps in Bundle-Branch Conduction

Abstract

Gaps" in bundle-branch conduction were observed in three patients using the combined technic of premature atrial stimulation and His bundle recordings.In type I gap a complete LBBB pattern disappeared at shorter coupling intervals because the premature atrial impulses encountered enough delay at the A-V node to reach the left bundle branch after the end of its effective refractory period. When this occurred, the H,-H2 intervals were longer and the H2-V2 intervals shorter than that at which complete LBBB had been present.In type II gap a complete RBBB pattern disappeared at shorter coupling intervals because the premature atrial impulses were so delayed within the proximal His-Purkinje system that they reached the right bundle branch after the end of its effective refractory period. When this occurred the

Nature of the Gap Phenomenon in Man

“…In type 2 gap, both the distal and the proximal site of conduction delay are distal to the His bundle recording site (5). A third kind of gap has recently been described by Agha and co-workers (6) in a patient with AV block; however, this kind of gap appears to reflect supernormal conduction, and proximal and distal sites of delay have not been defined (6).…”

“…• One type of supernormal conduction, i.e., the paradoxical propagation of closely coupled stimuli when stimuli at longer coupling intervals are blocked, reflects a gap phenomenon (1)(2)(3)(4)(5)(6). This phenomenon occurs when the refractory period of a distal conduction site limits conduction.…”

Supernormal conduction in the right bundle branch: Lack of influence of autonomic blockade

“…The HV intervals during this phase of improved conduction were unchanged compared with the HV interval of the other conducted beats. An improved conduction at shorter coupling intervals may sometimes be explained by the so-called gap phenomenon [2,3,5,11]. This phenomenon may occur when a very early electrical impulse is proximally delayed to the original site of block for so long that it regains its excitability and restores the conduction to the ventricles [5].…”

Untitled

“…"Gaps" in the propagation of a response may occur at ~ny level in the A-V conduction system (Agha et al, 1973;Camm et al, 1978;Gallagher et al, 1973;Moe et al, 1965;Waleffe et al, 1977;Wu et al, 1974). Unrecognised gaps in propagation due to proximal block may lead to an overestimation of refractoriness.…”