Intra-His bundle block following ligation of anterior septal artery in dog.

Intra-His bundle block was produced by ligation of the anterior septal artery in dogs. The duration of the His bundle potential was gradually increased following the ligation, and an obvious splitting of the His bundle deflection was observed thereafter. Finally, spontaneous second and/or third degree intra-His bundle block appeared. Before the development of spontaneous block, a pacing induced intra-His bundle block was observed when the duration of the His bundle deflection was prolonged approximately to twice the control value. Careful measurements of the intervals between two split His bundle deflections (H1-H2) in spontaneous as well as in pacing induced block revealed atypical Wenckebach periodicity in all analyzed periods except in one. Repeating and/or transient decreases of H1-H2 intervals were frequently observed as atypical findings.