Accelerated A-V conduction associated with complete A-V block

HBE's were recorded in a 70-year-old female patient with complete heart block, narrow QRS, and past episodes of supraventricular tachycardia. The HBE revealed split His potentials with intra-His block. Atrial pacing at increased rates failed to increase the AH1 interval, suggesting an accelerated pathway between the atria and the proximal His bundle bypassing the A-V node. Below the site of block, the ventricles were paced by a distal His bundle (H2) with a resultant normal QRS interval.