title: Protected circumferential conduction in the posterior atrioventricular vestibule of the left atrium: electrophysiologic and anatomic correlates.
abstract: BACKGROUND
  The anatomic substrate for protected isthmus conduction in the right atrium has been well defined. Little is known of similar substrates in the left atrium (LA).
  
  
  METHODS
  Patients (pts) with reentrant tachycardia (AVRT) supported by a single left-sided accessory pathway were studied retrospectively (n = 64) and prospectively (n = 31). Intracardiac electrograms were recorded from the His bundle position and coronary sinus (CS). The LA was mapped with a steerable catheter using the transseptal approach. LA anatomy was examined grossly and histologically in six cadaver hearts after removal of endocardium.
  
  
  RESULTS
  A distal-to-proximal CS activation sequence during AVRT was seen in all patients with a left lateral accessory pathway before ablation. After one to three radiofrequency (RF) energy deliveries that did not interrupt accessory pathway conduction, the CS activation sequence was reversed in three patients in the retrospective group and bidirectional conduction block in the posterior atrioventricular vestibule of the LA (PAVV) was demonstrated in nine patients in the prospective group. Four of the six cadaver hearts showed a distinct circumferential inferoposterior myocardial bundle that coursed parallel to the CS in the PAVV.
  
  
  CONCLUSIONS
  We described evidence of bidirectional intraatrial block in the PAVV after application of RF energy during accessory pathway ablation. Such conduction block may mimic the presence of a second accessory pathway. Our data suggest that circumferential conduction in the PAVV may be poorly coupled to the rest of the LA and may be involved in the macro-reentrant circuit around the mitral annulus. The circumferential inferoposterior myocardial bundle may serve as the underlying anatomic substrate.
authors: Cardiac Electrophysiology, University of California, San Francisco, CA 94143-1354, USA.
authors: Jie
authors: J
authors: Cheng
authors: Yanfei
authors: Y
authors: Yang
authors: Philip C
authors: PC
authors: Ursell
authors: Randall J
authors: RJ
authors: Lee
authors: Parvin C
authors: PC
authors: Dorostkar
authors: Kwabena A
authors: KA
authors: Boahene
authors: Melvin M
authors: MM
authors: Scheinman
mesh_terms: D000328:Adult; D016275:Atrial Function; D018780:Body Surface Potential Mapping; D017115:Catheter Ablation; D004594:Electrophysiology; D005260:Female; D006325:Heart Atria / Q000033:anatomy & histology*; D006329:Heart Conduction System / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D012032:Refractory Period, Electrophysiological / Q000502:physiology; D012189:Retrospective Studies; D013611:Tachycardia, Atrioventricular Nodal Reentry / Q000503:physiopathology