title: Lower loop reentry as a mechanism of clockwise right atrial flutter.
abstract: BACKGROUND
  Right atrial reentrant tachycardia resulting from lower loop reentry (LLR) around the inferior vena cava (IVC) has been described recently. However, all reported cases of LLR in the literature have negative flutter waves on the inferior surface ECG leads similar to that of counterclockwise typical atrial flutter around the tricuspid annulus (TA). Right atrial flutter with positive flutter waves in the inferior ECG leads has been assumed to rotate as a single reentrant activation wave front around the TA, and the role of LLR in those patients is not known.
  
  
  RESULTS
  Twelve consecutive patients with flutter wave morphology on surface ECG consistent with clockwise atrial flutter were studied. The endocardial activation pattern recorded from conventional multipolar electrode catheters was characteristic of clockwise atrial flutter around the TA. Entrainment pacing in all 12 patients and 3D activation sequence mapping in 7 patients, however, revealed clockwise LLR involving the lower right atrium around the IVC in 7 patients, figure-of-8 double-loop reentry around both the IVC and TA in 4, and single reentrant loop around the TA in 1. Linear radiofrequency ablation in the isthmus between the TA and IVC (TI isthmus) terminated the tachycardia in all patients.
  
  
  CONCLUSIONS
  Surface ECG flutter wave morphology and limited recording intracardiac sites proved insufficient to delineate the precise mechanism of the TI isthmus-dependent clockwise right atrial flutters. Most right atrial flutters with positive flutter wave on surface ECG may be supported by a reentrant circuit around the IVC or a figure-of-8 double-loop reentry involving both the IVC and TA.
authors.affiliation: Texas Heart Institute/St. Luke's Episcopal Hospital, Houston, TX 77030, USA. jcheng@heart.thi.tmc.edu
authors.forename: Shulong
authors.initials: S
authors.lastname: Zhang
authors.forename: George
authors.initials: G
authors.lastname: Younis
authors.forename: Ramesh
authors.initials: R
authors.lastname: Hariharan
authors.forename: John
authors.initials: J
authors.lastname: Ho
authors.forename: Yanfei
authors.initials: Y
authors.lastname: Yang
authors.forename: John
authors.initials: J
authors.lastname: Ip
authors.forename: Ranjun K
authors.initials: RK
authors.lastname: Thakur
authors.forename: John
authors.initials: J
authors.lastname: Seger
authors.forename: Melvin M
authors.initials: MM
authors.lastname: Scheinman
authors.forename: Jie
authors.initials: J
authors.lastname: Cheng
mesh_terms: D000368:Aged; D001282:Atrial Flutter / Q000503:physiopathology* / Q000601:surgery; D006328:Cardiac Catheterization; D017115:Catheter Ablation; D004562:Electrocardiography; D005260:Female; D006329:Heart Conduction System / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D014261:Tricuspid Valve; D014682:Vena Cava, Inferior