Shortening of the electromechanical window in the ketamine/xylazine-anesthetized guinea pig model to assess pro-arrhythmic risk in early drug development

Background: A negative electromechanical window (EMw) was recently proposed as a better preclinical tool than QTc interval to predict clinical pro-arrhythmic potential. As such, we utilized the ketamine/xylazine anesthetized guinea pig to characterize the EMw and QTc interval for a diverse set of reference agents with known clinical pro-arrhythmic potential. Then we determined the clinical proarrhythmia predictive capacity of EMw shortening compared to hERG inhibition or QTc interval prolongation alone.

Methods: Changes in EMw and QTc interval by 26 reference agents were evaluated in the ketamine/xylazine-anesthetized guinea pig. Confusion matrix analysis using the hERG, QTc and EMw indexes (hERG IC50, QTc EC5 or the EMw EC-10 divided by their respective free therapeutic maximal plasma concentration) at various folds the therapeutic concentrations was conducted to assess the concordance of each index to predict clinical pro-arrhythmic risk.

Results: Shortening of the EMw concomitant to an increase in QTc interval was observed in the GP with known pro-arrhythmic drugs. Non-torsadogenic compounds did not cause EMw shortening, although some prolonged the QTc interval. The preclinical:clinical concordance of the EMw index (88%) was similar (p>0.05) to using QTc interval prolongation alone (85%) but significantly greater (p<0.05) than using hERG inhibition alone (69%). In addition, the specificity when using the EMw (87%) was largely greater (p<0.05) than using QTc interval (73%) or hERG inhibition (60%) alone. When the components of the response (duration of left ventricular pressure (LVP) cycle (QLVPend) or QT interval) that caused EMw shortening were considered, the concordance is further improved (>95%).

Conclusion: EMw shortening improves QTc interval prolongation recording in early drug development and increases the translatability over existing preclinical tools in predicting clinical arrhythmias.