title: Properties and substrate of slow pathway exposed with a compact node targeted fast pathway ablation in rabbit atrioventricular node.
abstract: BACKGROUND
  The properties and substrates of slow and fast AV nodal pathway remain unclear. This applies particularly to the slow pathway (SP), which is largely concealed by fast pathway (FP) conduction. We designed a new FP ablation approach that exposes the SP over the entire cycle length range and allows for its independent characterization and ablation.
  
  
  RESULTS
  Premature stimulation was performed before and after FP ablation with 5.4 +/- 1.9 lesions (300-microm diameter each; overall lesion size 1.4 +/- 0.5 mm) targeting the junction between perinodal and compact node tissues in seven rabbit heart preparations. The resulting SP recovery curve and control curve had the same maximum nodal conduction time (165 +/- 22 msec vs 164 +/- 24 msec; P = NS) and effective refractory period (101 +/- 10 msec vs 100 +/- 9 msec; P = NS). The two curves covered the same cycle length range. However, the SP curve was shifted up with respect to control one at intermediate and long cycle lengths and thus showed a longer minimum nodal conduction time (81 +/- 15 msec vs 66 +/- 10 msec; P < 0.01) and functional refractory period (180 +/- 11 msec vs 170 +/- 12 msec; P < 0.05). The SP curve was continuous and closely fitted by a single exponential function. Small local lesions (2 +/- 1) applied to the posterior nodal extension resulted in third-degree nodal block in all preparations.
  
  
  CONCLUSIONS
  The posterior nodal extension can sustain effective atrial-His conduction at all cycle lengths and account for both the manifest and concealed portion of SP. Slow and FP conduction primarily arise from the posterior extension and compact node, respectively.
authors.affiliation: Département de Physiologie, Faculté de Médecine, Université de Montréal, Québec, Canada.
authors.forename: L J
authors.initials: LJ
authors.lastname: Lin
authors.forename: J
authors.initials: J
authors.lastname: Billette
authors.forename: D
authors.initials: D
authors.lastname: Medkour
authors.forename: M C
authors.initials: MC
authors.lastname: Reid
authors.forename: M
authors.initials: M
authors.lastname: Tremblay
authors.forename: K
authors.initials: K
authors.lastname: Khalife
mesh_terms: D000818:Animals; D016275:Atrial Function; D001283:Atrioventricular Node / Q000502:physiology*; D002036:Bundle of His / Q000502:physiology; D006324:Heart Arrest, Induced; D066298:In Vitro Techniques; D009431:Neural Conduction / Q000502:physiology; D009434:Neural Pathways / Q000502:physiology; D011817:Rabbits; D012032:Refractory Period, Electrophysiological; D013997:Time Factors