[Transmural optical mapping of pause dependent torsade de pointes in canine long QT models].
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.
Liu
Jin-qiu
JQ
Heart Center, The First Affiliated Hospital of Dalian Medical University, Dalian 116011, China.
Yang
Yan-zong
YZ
Rosenbaum
David S
DS
Laurita
Kenneth R
KR
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*