title: Myocardial bundles with slow conduction properties are present on the left interventricular septal surface of normal human hearts.
abstract: BACKGROUND
  The aim of this study was to examine the electrophysiologic characteristics of the normal left interventricular septum (LIVS).
  
  
  RESULTS
  We explored the LIVS in search of endocardial potentials following ventricular electrograms during sinus rhythm in 28 patients without structural heart disease. In all patients, low-frequency (mean amplitude: 0.81 +/- 0.33 mV) systolic potentials (LA1) were detected in a basal-to-apical activation sequence (earliest to latest QRS-LA1 interval: 93.3 +/- 10.8 ms to 127.1 +/- 16.6 ms). Programmed stimulation demonstrated decremental conduction properties, and the effective refractory period of the tissue between the ventricular electrogram and LA1 at baseline (376.7 +/- 48.8 ms) was significantly prolonged by disopyramide (421.3 +/- 54.1 ms, P < 0.05 vs baseline). In 21 patients (75%), diastolic potentials (LA2) morphologically similar to LA1 (mean amplitude: 0.52 +/- 0.17 mV) were detected in an apical-to-basal activation sequence (earliest to latest QRS-LA2 interval: 368.9 +/- 32.4 ms to 440.7 +/- 45.8 ms). Para-Hisian pacing with capture of the His bundle showed shorter S-LA1 and S-LA2 intervals compared to the beats without His-bundle capture but with ventricular capture (156.3 +/- 11.2 ms vs 183.2 +/- 12.3 ms, and 385.7 +/- 21.6 ms vs 397.4 +/- 23.4 ms, respectively, P < 0.0001). At the same rate, the LA1-LA2 interval was significantly shorter during right ventricular apical than atrial overdrive pacing (220.4 +/- 23.1 ms vs 261.4 +/- 30.7 ms, P < 0.0001).
  
  
  CONCLUSIONS
  Unique myocardial bundles with slow conduction properties and various electrical connections with the specialized conduction system may exist in the LIVS of normal human hearts.
authors.affiliation: Department of Medicine and Biological Science, Gunma University Graduate School of Medicine, Maebashi, Japan. kanekoy@showa.gunma-u.ac.jp
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Kaneko
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Taniguchi
authors.forename: Tadashi
authors.initials: T
authors.lastname: Nakajima
authors.forename: Mamoru
authors.initials: M
authors.lastname: Manita
authors.forename: Toshio
authors.initials: T
authors.lastname: Ito
authors.forename: Masahiro
authors.initials: M
authors.lastname: Akiyama
authors.forename: Masahiko
authors.initials: M
authors.lastname: Kurabayashi
mesh_terms: D000328:Adult; D000368:Aged; D022062:Electrophysiologic Techniques, Cardiac; D005260:Female; D006329:Heart Conduction System / Q000502:physiology*; D006346:Heart Septum / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009206:Myocardium; D016276:Ventricular Function