title: Characterization of left atrial activation in the intact human heart.
abstract: BACKGROUND
  The patterns of activation of the human left atrium (LA), how they relate to atrial myocardial architecture, and their role in arrhythmogenesis remain largely unknown.
  
  
  RESULTS
  Left atrial endocardial activation was mapped in 19 patients with a percutaneous noncontact mapping system. Earliest endocardial breakthrough during sinus rhythm (SR) occurred more frequently in the septal (63%, principally posteroseptal) than anterosuperior (37%) LA and varied little with isoproterenol or high right atrial pacing rate. Regardless of site of breakthrough, LA activation was characterized in all patients by propagation around a variably complete line of functional conduction block, descending on the posterior wall from the roof, passing between the ostia of the superior and then inferior pulmonary veins (PVs) before turning septally, passing below the oval fossa, and merging further anteriorly with the septal mitral annulus. Examination of the myocardial architecture in 10 normal adult postmortem hearts revealed an abrupt change in subendocardial fiber orientation along a line following the same course. During episodes of focal initiation of atrial fibrillation (AF), interaction was observed between wavefronts entering the LA from PVs and this functional line of conduction block that resulted in LA macroreentry or formation of daughter wavefronts.
  
  
  CONCLUSIONS
  The LA endocardium has complex but characteristic patterns of activation during sinus rhythm, pacing, and AF initiation by PV ectopy that are determined largely by the functional properties of atrial musculature. These findings have important implications for both pacing and ablative strategies for the prevention of initiation of AF.
authors.affiliation: St Mary's Hospital, Imperial College, London, UK.
authors.forename: Vias
authors.initials: V
authors.lastname: Markides
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Schilling
authors.forename: Siew Yen
authors.initials: SY
authors.lastname: Ho
authors.forename: Anthony W C
authors.initials: AW
authors.lastname: Chow
authors.forename: D Wyn
authors.initials: DW
authors.lastname: Davies
authors.forename: Nicholas S
authors.initials: NS
authors.lastname: Peters
mesh_terms: D000328:Adult; D000368:Aged; D001281:Atrial Fibrillation / Q000175:diagnosis* / Q000503:physiopathology / Q000628:therapy; D016275:Atrial Function / Q000502:physiology*; D018880:Atrial Premature Complexes / Q000175:diagnosis / Q000503:physiopathology; D018780:Body Surface Potential Mapping; D002304:Cardiac Pacing, Artificial; D003331:Coronary Vessels / Q000502:physiology; D022062:Electrophysiologic Techniques, Cardiac; D005260:Female; D006321:Heart / Q000033:anatomy & histology / Q000502:physiology*; D006329:Heart Conduction System / Q000502:physiology*; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D018485:Muscle Fibers, Skeletal / Q000166:cytology; D011667:Pulmonary Veins / Q000502:physiology; D012849:Sinoatrial Node / Q000502:physiology