Beat-by-beat QT interval variability, but not QT prolongation per se, predicts drug-induced torsades de pointes in the anaesthetised methoxamine-sensitized rabbit

Abstract Introduction Accumulating evidence suggest that drug-induced QT prolongation per se poorly predicts repolarisation-related proarrhythmia liability. We examined whether beat-by-beat variability of the QT interval may be a complementary proarrhythmia marker to QT prolongation. Methods Anaesthetised rabbits sensitized towards developing torsades de pointes (TdP) were infused for 30 min maximum with explorative antiarrhythmic compounds characterised as mixed ion channel blockers. Based on the outcome in this model the compounds were classified as having a low (TdPlow; n  = 5), intermediate (TdPintermediate; n  = 7) or high (TdPhigh; n  = 10) proarrhythmic potential. Dofetilide ( n  = 4) was included as a representative of a selective IKr-blocking antiarrhythmic with known high proarrhythmic potential. QT interval prolongation and beat-by-beat QT variability (quantified as the short-term variability, STV) were continuously assessed during the infusion or up to the point where ventricular proarrhythmias were induced. Results All compounds significantly prolonged the QT interval. For TdPlow and TdPhigh compounds the QT interval maximally increased from 169 ± 14 to 225 ± 28 ms ( p p p p Discussion It is concluded from the present series of experiments in a sensitive rabbit model of TdP that increased beat-by-beat QT interval variability precedes drug-induced TdP. In addition, assessment of this potential proarrhythmia marker may be useful in discriminating highly proarrhythmic compounds from compounds with a low proarrhythmic potential.