title: Exact location of the branching bundle in the living heart.
abstract: OBJECTIVE
  The His bundle electrogram is believed to reflect the exact location of the His bundle. However, the distinction between distal His bundle potential and proximal right bundle branch potential is challenging. The aim of this study was to pinpoint the location of the branching point of the His bundle, and to compare that site with the site of recording of the largest His bundle electrogram (LH) during sinus rhythm.
  
  
  METHODS
  We hypothesized that the site of earliest His activation (EH) during retrograde conduction via the left bundle branch is the branching point. We studied 15 nonconsecutive patients (mean age = 40 +/- 22 years; eight men). We performed a programmed stimulation from right ventricular apex until retrograde right bundle branch block appeared. At that point we measured (1) the distance between antegrade LH site and retrograde EH site and (2) the atrial-to-ventricular amplitude ratio (A/V ratio) at both sites.
  
  
  RESULTS
  EH was recorded at the proximal electrode of the His bundle catheter in all patients. Mean distance between EH and LH was 9.8 +/- 2.5 mm. The mean A/V ratios at the EH site and the LH site were 1.01 +/- 0.42 and 0.08 +/- 0.06, respectively.
  
  
  CONCLUSIONS
  This study showed that the EH site is located approximately 10-mm proximal to the LH site. The mean A/V ratio at the EH site during sinus rhythm is approximately 1.0. These observations suggest that the majority of His potentials reflect proximal right bundle activation. Before delivering radiofrequency energy in the para-Hisian area, attention should be paid to the presence of a His potential and to the A/V ratio, rather to the amplitude of the His electrogram.
authors.affiliation: Department of Cardiovascular Medicine, Tottori University Hospital, Yonago, Japan.
authors.forename: Masamitsu
authors.initials: M
authors.lastname: Adachi
authors.forename: Osamu
authors.initials: O
authors.lastname: Igawa
authors.forename: Akio
authors.initials: A
authors.lastname: Yano
authors.forename: Junichiro
authors.initials: J
authors.lastname: Miake
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Inoue
authors.forename: Kazuyoshi
authors.initials: K
authors.lastname: Ogura
authors.forename: Masaru
authors.initials: M
authors.lastname: Kato
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Iitsuka
authors.forename: Ichiro
authors.initials: I
authors.lastname: Hisatome
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D018780:Body Surface Potential Mapping / Q000379:methods*; D002036:Bundle of His / Q000503:physiopathology*; D002037:Bundle-Branch Block / Q000175:diagnosis* / Q000503:physiopathology*; D022062:Electrophysiologic Techniques, Cardiac / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D055815:Young Adult