Differentiating multichannel block on the guinea pig ECG: Use of Tpeak-Tend and J-Tpeak.

INTRODUCTION

The anaesthetised guinea pig is a well characterised assay for early assessment of drug effects on ventricular repolarisation and risk of Torsade de Pointes (TdP). We assessed whether a selective hERG blocker with known TdP risk could be differentiated from lower risk, balanced ion channel blockers in the guinea pig, using corrected QT (QTc) interval alongside novel electrocardiogram (ECG) biomarkers J-Tpeakc and Tpeak-Tend. Effects were compared with previous clinical investigations at similar plasma concentrations and with another index of TdP risk, the electromechanical window (EMW).

METHODS

Twenty-two Dunkin Hartley guinea pigs anaesthetised with sodium pentobarbitone were instrumented for haemodynamic measurement and ECG recording. Three ascending doses of vehicle (n = 6), dofetilide (2, 6 or 20 μg/kg; n = 7), ranolazine (2, 6 or 20 mg/kg; n = 5) or verapamil (0.1, 0.3 or 1.0 mg/kg; n = 4) were administered intravenously.

RESULTS

As reported in previous clinical studies, dofetilide induced dose-dependent increases in QTc interval, with increases in both J-TpeakC or Tpeak-Tend, while verapamil caused no significant increase in QTc interval, J-TpeakC or Tpeak-Tend. Ranolazine caused dose-dependent increases in QTc interval and corrected J-Tpeakc, but had no effect on Tpeak-Tend, which is in contrast to the effects reported in humans at similar concentrations. Only dofetilide caused a clear, dose-related decrease in the EMW.

DISCUSSION: These findings suggest that measurements of J-Tpeakc and Tpeak-Tend in addition to QT interval, may help differentiate pure hERG channel blockers with high risk of TdP from lower risk, multichannel blockers.