title: Reentry within the cavotricuspid isthmus: an isthmus dependent circuit.
abstract: BACKGROUND
  We describe a new cavotricuspid isthmus (CTI) circuit.
  
  
  METHODS
  This study includes 8 patients referred for atrial flutter (AFL) ablation whose tachycardia circuit was confined to the septal CTI and the os of the coronary sinus (CS(OS)) region. Entrainment mapping was performed within the CTI, CS(OS), and other right atrial annular sites (tricuspid annulus (TA)). Electroanatomic mapping was available in 2 patients.
  
  
  RESULTS
  Sustained AFL occurred in all patients with mean tachycardia cycle length (TCL) of 318 +/- 54 (276 - 420) ms. During tachycardia, fractionated or double potentials were recorded at either the septal CTI and/or the region of CS(OS) in all, and concealed entrainment with post-pacing interval (PPI)--TCL < or = 25 ms occurred in this area; but manifest entrainment with PPI > TCL was demonstrated from the anteroinferior CTI and other annular sites in 7/8 patients. In one, tachycardia continued with conduction block at the anteroinferior CTI during ablation. Up to three different right atrial activation patterns (identical TCL) were observed. The tachycardia showed a counterclockwise (CCW) pattern in 6, a clockwise pattern in 2, and simultaneous activation of both low lateral right atrium and septum in 5. Electroanatomic mapping was available in 2, showing an early area arising from the septal CTI in 1, and a CCW activation sequence along the TA in another. Radiofrequency application to the septal CTI terminated tachycardia in 4, and tachycardia no longer inducible in all.
  
  
  CONCLUSIONS
  We describe a tachycardia circuit confined to the septal CTI/CS(OS) region, and hypothesize that this circuit involves slow conduction within the CTI and around the CS(OS), which acts as a central obstacle.
authors.affiliation: Department of Medicine/Cardiac Electrophysiology Section, University of California, San Francisco, CA 94143, USA.
authors.forename: Yanfei
authors.initials: Y
authors.lastname: Yang
authors.forename: Niraj
authors.initials: N
authors.lastname: Varma
authors.forename: Edmund C
authors.initials: EC
authors.lastname: Keung
authors.forename: Melvin M
authors.initials: MM
authors.lastname: Scheinman
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001282:Atrial Flutter / Q000503:physiopathology* / Q000601:surgery; D018780:Body Surface Potential Mapping; D017115:Catheter Ablation; D022062:Electrophysiologic Techniques, Cardiac; D005260:Female; D006329:Heart Conduction System / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D013611:Tachycardia, Atrioventricular Nodal Reentry / Q000503:physiopathology* / Q000601:surgery; D014261:Tricuspid Valve / Q000503:physiopathology*