The surface electrocardiogram in complete intra-his heart block

In some cases, the surface ECG may be useful in predicting that the level of heart block is intra-His rather than supra-His. In five patients with third degree heart block the level of block was documented to be within the His bundle. In all five, the surface ECG showed an escape rhythm with QRS complexes of less than 0.10s. duration. The initial QRS forces were abnormal in that "septal" q waves were not present in leads 1 and V6. Two of the five patients had occasional conducted beats with normal "septal" q waves. Thus, heart block associated with an escape rhythm of narrow QRS morphology but abnormal septal depolarization may indicate that the level of the block is intra-His rather than supra-His.