title: Where to draw the mitral isthmus line in catheter ablation of atrial fibrillation: histological analysis.
abstract: OBJECTIVE
  A linear lesion between the left inferior pulmonary vein orifice and mitral annulus, the so-called mitral isthmus, may improve the success of catheter ablation for atrial fibrillation. Gaps in the lesion line, however, may facilitate left atrial flutter. The aim of the study was to determine the optimal location of the lesion line by serial sectioning of the isthmus area.
  
  
  RESULTS
  In a post-mortem study of 16 patients with normal left atria, serial sections of the isthmus area from 10 mm superior to and 30 mm inferior to the isthmus were studied by light microscopy. The length of the isthmus was 35+/-7 mm. On average, the muscle sleeve around the coronary sinus ended 10 mm inferior to the isthmus. The prevalence of a ramus circumflexus <5 mm from the endocardial surface, decreased from 60% in the most superior section to 0% in the most inferior section. Atrial arteries were frequently present in all sections.
  
  
  CONCLUSIONS
  The thickness of atrial myocardium, the ramus circumflexus sometimes very close to the endocardium, a myocardial sleeve around the coronary sinus, and local cooling by atrial arteries and veins may complicate the creation of conduction block in the mitral isthmus.
authors.affiliation: Heart Lung Center Utrecht, University Medical Center E03-406, PO Box 85500, 3508 GA Utrecht, The Netherlands. fredwittkampf@mac.com
authors.forename: Fred H M
authors.initials: FH
authors.lastname: Wittkampf
authors.forename: Matthijs F
authors.initials: MF
authors.lastname: van Oosterhout
authors.forename: Peter
authors.initials: P
authors.lastname: Loh
authors.forename: Richard
authors.initials: R
authors.lastname: Derksen
authors.forename: Evert-jan
authors.initials: EJ
authors.lastname: Vonken
authors.forename: Piet J
authors.initials: PJ
authors.lastname: Slootweg
authors.forename: Siew Yen
authors.initials: SY
authors.lastname: Ho
mesh_terms: D001281:Atrial Fibrillation / Q000473:pathology / Q000601:surgery*; D001344:Autopsy; D009202:Cardiomyopathies / Q000473:pathology*; D017115:Catheter Ablation / Q000379:methods*; D006801:Humans; D008875:Middle Aged; D008943:Mitral Valve / Q000473:pathology*