Catheter-induced intra-Hisian and intrafascicular block during recording of His bundle electrograms.

or even complete A-V block. Two cases are reported in which catheter-induced transient high grade Mobitz II A-V block, acute reversible prolongation of infranodal conduction time with probable intra-Hisian conduction delay, and persistent (6 hours duration) complete A-V block occurred in patients with left bundle branch block. The observations made indicate that A-V conduction times and the appearance of "split His" potentials may be influenced by the recording catheter itself, and suggest that the operators be prepared to institute immediate right ventricular pacing when His bundle recordings are obtained in patients with left bundle branch block.