The mechanism of A-V conduction delay in A-V nodal gap.

Initial block in the His-Purkinje system was demonstrated in 17 of 71 patients during atrial extrastimulus testing. Of the 17 patients who demonstrated initial block in the His-Purkinje system, ten patients had A-V nodal gap (a type 1 gap). Of these ten patients, progressive increase in A-V nodal conduction was responsible for a resumption of A-V conduction in six patients, dual pathways within the A-V node was responsible in three patients, and the presence of an extra nodal pathway of the A-V node was responsible in one patient.