title: [Transmural optical mapping of pause dependent torsade de pointes in canine long QT models].
abstract: OBJECTIVE
  To investigate the mechanism of pause dependent torsade de pointes (TdP) in long QT (LQT) conditions.
  
  
  METHODS
  Optical mapping was used to measure transmural action potentials from the arterially perfused left ventricular canine wedge preparation. D-sotalol and ATX-II were administered to mimic LQT 2 and LQT 3, respectively.
  
  
  RESULTS
  In LQT models, the pause significantly enhanced M cell action potential (control group Steady state stimulation S1S1: (291 +/- 27) ms, after pause: (307 +/- 28) ms, P > 0.05; LQT 2 S1S1: (356 +/- 20) ms, after pause: (381 +/- 25) ms, P < 0.05; LQT 3 S1S1: (609 +/- 92) ms, after pause: (675 +/- 98) ms P < 0.05), dispersion of transmural repolarization (control group S1S1: (24 +/- 6) ms, after pause: (27 +/- 6) ms, P > 0.05; LQT 2 S1S1: (35 +/- 9) ms, after pause: (46 +/- 11) ms, P < 0.05; LQT 3 S1S1: (121 +/- 85) ms, after pause: (171 +/- 98) ms, P < 0.05) and the M cell island-like distribution more clearly compared to baseline pacing. Pause dependent early afterdepolarizations (EADs), EAD-induced triggered activity and TdP more likely occurred under LQT 3 condition (82%, P < 0.05). The triggered beat after pause often broke through at the margin of M cells island where the repolarization gradients was maximal. The unidirectional conduction block and slow conduction were observed vividly at this region.
  
  
  CONCLUSIONS
  These data suggest that M cells island plays an important role in origination and maintenance of pause dependent TdP.
authors.affiliation: Heart Center, The First Affiliated Hospital of Dalian Medical University, Dalian 116011, China.
authors.forename: Jin-qiu
authors.initials: JQ
authors.lastname: Liu
authors.forename: Yan-zong
authors.initials: YZ
authors.lastname: Yang
authors.forename: David S
authors.initials: DS
authors.lastname: Rosenbaum
authors.forename: Kenneth R
authors.initials: KR
authors.lastname: Laurita
mesh_terms: D000200:Action Potentials; D000818:Animals; D004195:Disease Models, Animal; D004285:Dogs; D008133:Long QT Syndrome / Q000503:physiopathology*; D017180:Tachycardia, Ventricular / Q000503:physiopathology; D016171:Torsades de Pointes / Q000503:physiopathology*; D056969:Voltage-Sensitive Dye Imaging / Q000379:methods*