title: The variable contribution of functional and anatomic barriers in human ventricular tachycardia: an analysis with resetting from two sites.
abstract: OBJECTIVE
  This study sought to investigate the influence of stimulation site on the properties of the circuit in ventricular tachycardia.
  
  
  BACKGROUND
  A fully excitable gap can be demonstrated in most human ventricular tachycardias. This requires the presence of an arc of block so that the entire circuit can recover from refractoriness within the period of the cycle length. Resetting characterizes the conduction properties of the tissue within the ventricular tachycardia circuit. Previous studies have not investigated the possibility of site-dependent differences in the resetting response.
  
  
  METHODS
  Resetting was performed from the right ventricular apex and outflow tract in 23 patients. Two characteristics of the resetting response were analyzed: 1) the total duration of the flat portion, and 2) the slope of the increasing portion.
  
  
  RESULTS
  A flat portion of the resetting response was observed in 18 tachycardias; in 8 of the 18, there was a significant site-dependent difference (> or = 40 ms) in the duration of the flat portion. A significant site-dependent difference in the slope of the increasing portion of the resetting curve was seen in 6 of 22 tachycardias. In all, a stimulation site-dependent change in at least one characteristic of the resetting response was seen in 12 (52%) of the 23 tachycardias.
  
  
  CONCLUSIONS
  A stimulation site-dependent change in the flat portion of the resetting response is compatible with an arc of block that is at least partially functional in nature. A change in the slope of the increasing portion is compatible with either partially functional circuit barriers or variation in properties of conduction and refractoriness at different locations within the circuit, or both. These observations suggest that a spectrum of circuit properties may exist in humans, with a variable contribution of anatomic and functional characteristics.
authors.affiliation: Clinical Electrophysiology Laboratories, Philadelphia Heart Institute, Presbyterian Medical Center, Philadelphia, PA, USA.
authors.forename: D J
authors.initials: DJ
authors.lastname: Callans
authors.forename: M
authors.initials: M
authors.lastname: Zardini
authors.forename: C D
authors.initials: CD
authors.lastname: Gottlieb
authors.forename: M E
authors.initials: ME
authors.lastname: Josephson
mesh_terms: D000328:Adult; D000368:Aged; D004599:Electric Stimulation Therapy; D004562:Electrocardiography; D005260:Female; D006329:Heart Conduction System / Q000503:physiopathology; D006801:Humans; D008297:Male; D008875:Middle Aged; D017180:Tachycardia, Ventricular / Q000503:physiopathology* / Q000628:therapy