Figure 2.
(a and b) Representative Poincaré plots illustrate the increase in short-term variability of the QT interval (STV(QT)) following combined IKr and IKs inhibition in conscious dogs. Right and upward shift on this figure represents QT interval prolongation while the scatter of data points represents QT interval variability. (c and d) Grouped data show that STV(QT) was not increased by HMR 1556 (1 mg kg−1 intravenously) or dofetilide (25 μg kg−1 intravenously) alone, only by their combination given in either order. (e and f) STV(R) increased only when pharmacological inhibition of IKr preceded IKs block. #P<0.05 vs control in the same group of conscious dogs, n=6–8 animals in each group. IKs, the slow component of the delayed rectifier potassium current; IKr, the rapid component of the delayed rectifier potassium current; STV(QT), short-term variability of the QT interval; STV(R), short-term variability of the RR interval.