title: Characteristics of virtual unipolar electrograms for detecting isthmus block during radiofrequency ablation of typical atrial flutter.
abstract: OBJECTIVE
  The purpose of this study was to investigate the characteristics of the second component of local virtual unipolar electrograms recorded at the ablation line during coronary sinus (CS) pacing after radiofrequency ablation (RFA) of the cavotricuspid isthmus (CTI) for typical atrial flutter (AFL).
  
  
  BACKGROUND
  Radiofrequency ablation of the CTI can produce local double potentials at the ablation line. The second component of unipolar electrograms represents the approaching wavefront in the right atrium opposite the pacing site. We hypothesized that the morphologic characteristics of the second component of double potentials would be useful in detecting complete CTI block.
  
  
  METHODS
  Radiofrequency ablation of the CTI was performed in 52 patients (males = 37, females = 15, 62 +/- 12 years) with typical AFL. The noncontact mapping system (Ensite 3000, Endocardial Solutions, St. Paul, Minnesota) was used to guide RFA. Virtual unipolar electrograms along the ablation line during CS pacing after RFA were analyzed. Complete or incomplete CTI block was confirmed by the activation sequence on the halo catheter and noncontact mapping.
  
  
  RESULTS
  Three groups were classified after ablation. Group I (n = 37) had complete bidirectional CTI block. During CS pacing, the second component of unipolar electrograms showed an R or Rs pattern. Group II (n = 12) had incomplete CTI block. The second component of unipolar electrograms showed an rS pattern. Group III (n = 3) had complete CTI block with transcristal conduction. The second component of unipolar electrograms showed an rSR pattern.
  
  
  CONCLUSIONS
  A predominant R-wave pattern in the second component of unipolar double potentials at the ablation line indicates complete CTI block, even in the presence of transcristal conduction.
authors.affiliation: Division of Cardiology, Department of Medicine, National Yang-Ming University School of Medicine, Taipei Veterans General Hospital, Taipei, Taiwan.
authors.forename: Yenn-Jiang
authors.initials: YJ
authors.lastname: Lin
authors.forename: Ching-Tai
authors.initials: CT
authors.lastname: Tai
authors.forename: Jin-Long
authors.initials: JL
authors.lastname: Huang
authors.forename: Tu-Ying
authors.initials: TY
authors.lastname: Liu
authors.forename: Pi-Chang
authors.initials: PC
authors.lastname: Lee
authors.forename: Chih-Tai
authors.initials: CT
authors.lastname: Ting
authors.forename: Shih-Ann
authors.initials: SA
authors.lastname: Chen
mesh_terms: D000200:Action Potentials; D000368:Aged; D001282:Atrial Flutter / Q000175:diagnosis* / Q000209:etiology / Q000601:surgery*; D018780:Body Surface Potential Mapping; D017115:Catheter Ablation; D022062:Electrophysiologic Techniques, Cardiac; D005260:Female; D005500:Follow-Up Studies; D006327:Heart Block / Q000175:diagnosis* / Q000209:etiology / Q000601:surgery*; D006329:Heart Conduction System / Q000473:pathology* / Q000601:surgery*; D006801:Humans; D008297:Male; D008875:Middle Aged; D016896:Treatment Outcome; D014584:User-Computer Interface