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Figure 7 Incidence of spontaneous and programmed electrical stimulation (PES)-induced Torsade de Pointes (TdP) in the LQT1 (A), LQT2 (B) and LQT3 (C) models. Under control conditions (C), neither spontaneous nor PES-induced TdP were observed in any of the three models. In LQT1, TdP could be induced only after addition of isoproterenol (Iso) (at both 2 and 10 min). 0.5 or 1 µmol/L propranolol (Prop) completely suppressed the influence of isoproterenol to provoke both spontaneous and PES-induced TdP in this model. In the LQT2 and LQT3 models, TdP occurred in the presence of d-Sotalol (d-Sot) and ATX-II alone. In the LQT2 model, isoproterenol transiently increased the incidence of both spontaneous and PES-induced TdP (2 min) and then decreased it (10 min). Propranolol completely prevented these effects of isoproterenol. In contrast, isoproterenol always suppressed both spontaneous and PES-induced TdP (at both 2 and 10 min) in the LQT3 model. Propranolol reversed the protective effect of isoproterenol in LQT3, causing an increase in the incidence of TdP. LQT1, 2, 3 = long QT syndrome 1, 2, 3.
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