CACNA1C and torsades de pointes: For instance, verapamil inhibits hERG1 channels at clinically relevant concentrations, but it has no known risk for TdP due to its concomitant blockade of the depolarizing inward calcium current (ICa,L, through blockade of the calcium channel subunit Cav1.2), which alleviates the effects of reduced IKr outward current20,61.