title: Endocardial mapping of ventricular tachycardia in the intact human heart. II. Evidence for multiuse reentry in a functional sheet of surviving myocardium.
abstract: OBJECTIVE
  The purpose of this study was to obtain improved detection and characterization of reentrant circuits in the infarcted human ventricle.
  
  
  BACKGROUND
  The return path of reentrant ventricular arrhythmias usually is not manifested in clinical mapping studies but is thought to be formed by isolated bundles of surviving myocytes whose presence is difficult to detect by standard recording techniques.
  
  
  METHODS
  We obtained simultaneous unipolar and high gain bipolar recordings using a left ventricular endocardial balloon array in 10 patients with chronic ischemic heart disease undergoing intraoperative mapping of ventricular tachycardia.
  
  
  RESULTS
  Three patients demonstrated seven separate ventricular tachycardias that utilized a return tract that was manifested on up to 20% of all left ventricular electrode sites. The recordings suggested an extensive sheet of surviving myocardial fibers with multiple entry and exit points allowing for different reentrant paths at different times all in the same heart. In one patient, five different ventricular tachycardias could be induced, four of which utilized such a sheet. Two of these tachycardias had the same exit point (site of origin) but two different entry points with a long and short return path resulting in long and short tachycardia cycle lengths. The same sheet sustained another tachycardia with one entry and two exit points resulting in two separate "sites of origin" on the endocardium. Such sheets also were seen to insert into the left bundle system. In one patient portions of the sheet could be detected epicardially.
  
  
  CONCLUSIONS
  The existence of such a structure of surviving myocardium with functional pleomorphism may account for unexplained changes in tachycardia cycle length, epicardial entrainment and spontaneous morphologic changes during ventricular tachycardia.
authors.affiliation: Division of Cardiology, Toronto General Hospital, Ontario, Canada.
authors.forename: E
authors.initials: E
authors.lastname: Downar
authors.forename: S
authors.initials: S
authors.lastname: Kimber
authors.forename: L
authors.initials: L
authors.lastname: Harris
authors.forename: L
authors.initials: L
authors.lastname: Mickleborough
authors.forename: E
authors.initials: E
authors.lastname: Sevaptsidis
authors.forename: S
authors.initials: S
authors.lastname: Masse
authors.forename: T C
authors.initials: TC
authors.lastname: Chen
authors.forename: A
authors.initials: A
authors.lastname: Genga
mesh_terms: D002304:Cardiac Pacing, Artificial / Q000379:methods*; D004562:Electrocardiography / Q000379:methods*; D004594:Electrophysiology; D004699:Endocardium / Q000502:physiology; D005260:Female; D006329:Heart Conduction System / Q000503:physiopathology*; D006801:Humans; D007430:Intraoperative Care / Q000379:methods; D008297:Male; D008875:Middle Aged; D013610:Tachycardia / Q000209:etiology / Q000503:physiopathology*