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His-bundle (H) electrograms were recorded in 49 adults with chronic heart block. Heart failure was noted in five (29%) patients having block proximal to H, in seven (87%) with "split" H potentials, and in ten (42%) with block distal to H. Syncope occurred in five patients (29%) with block proximal to H, in two patients (25%) with "split" H potentials, and in 15 patients (63%) with block distal to H, in whom syncope was significantly more frequent (P<.05). Of the total group, QRS complexes were narrow in 16 and wide in 33. Although symptoms related to bradycardia occurred in all groups, syncope was significantly more common with block distal to H. Neither ventricular rate or QRS duration could be used as an absolute guide to the site of block.
Kenneth M. Rosen (Tue,) studied this question.