An Unusual Case of Second-Degree A-V Block—A Study Using His Bundle Electrograms

¹ Department of Cardiology, Cedars-Sinai Medical Center and the Department of Medicine, University of California at Los Angeles

His bundle electrograms were recorded in a patient with second degree A-V block, 2:1 conduction and a normal QRS duration. With this technique, the site of A-V block was localized to the area of the A-V node (intranodal block, usually Mobitz type I). Long-term monitoring did not demonstrate Wenckebach periods. Increasing the atrial rate by pacing was associated with increasing degrees of AV block (ie 2:1 to 4:1 AV conduction). This phenomenon has primarily been described with subnodal block. The findings in this case suggest that the decision for transvenous pacemaker insertion should, therefore, not be made solely on the determination of the site of A-V block.