The significance of second degree atrioventricular block and bundle branch block. Observations regarding site and type of block

His bundle (H) electrograms were recorded in 15 patients with second degree atrioventricular (A-V) block and bundle branch block and these patients were prospectively followed. Site of block was proximal to H in 4 (BPH), distal to H in 4 (BDH), and undetermined in 2 (studied during 1:1 conduction). Surface electrocardiographic features were retrospectively examined to determine the value of these recordings in predicting the site of block. Patients with type I block, with or without type II or 2:1 block, had BPH. Patients with type II block, 2:1 block, or type II combined with 2:1 block had BDH. Heart failure was more common in those with BPH (3 of 4 patients as compared to 3 of 9 patients with BDH). Syncope developed more commonly in patients with BDH (6 of 9 patients) as compared to those with BPH (one of 4 patients). Permanent pacing was indicated in 3 of 4 patients with BPH, 9 of 9 patients with BDH, and one of 2 patients with block at undetermined site because of syncope or heart failure. Five of 9 patients with BDH required pacemakers within 10 days of initial admission. Most patients with second degree A-V block and bundle branch block will need permanent pacing. In patients with 2° BDH, pacemakers are indicated whether or not symptoms are present because of high risk of syncope and potential risk of sudden death. In asymptomatic patients with 2° BPH, careful observation is indicated.