The high frequency relationship: implications for torsadogenic hERG blockers

Background and PurposeVentricular arrhythmias induced by human ether-a-go-go related gene (hERG; K(v)11.1 channel) blockers are a consequence of alterations in ventricular repolarisation in association with high-frequency (HF) oscillations, which act as a primary trigger; the autonomic nervous system plays a modulatory role. In the present study, we investigated the role of (1)-adrenoceptors in the HF relationship between magnitude of heart rate and QT interval changes within discrete 10s intervals (sorted into 5bpm heart rate increments) and its implications for torsadogenic hERG blockers. Experimental ApproachThe HF relationship was studied under conditions of autonomic blockade with atenolol ((1)-adrenoceptor blocker) in the absence or presence of five hERG blockers in beagle dogs. In total, the effects of 14 hERG blockers on the HF relationship were investigated. Key ResultsAll the torsadogenic hERG blockers tested caused a vertical shift in the HF relationship, while hERG blockers associated with a low risk of Torsades de Pointes did not cause any vertical shift. Atenolol completely prevented the effects four torsadogenic agents (quinidine, thioridazine, risperidone and terfenadine) on the HF relationship, but only partially reduced those of dofetilide, leading to the characterization of two types of torsadogenic agent. Conclusions and ImplicationsAnalysis of the vertical shift in the HF relationship demonstrated that signs of transient sympathetic activation during HF oscillations in the presence of torsadogenic hERG blockers are mediated by (1)-adrenoceptors. We suggest the HF relationship as a new biomarker for assessing Torsades de pointes liability, with potential implications in both preclinical studies and the clinic.