Drug-Induced QT Prolongation and Torsades de Pointes: An All-Exclusive Relationship or Time for an Amicable Separation?

Abstract

QT prolongation was perceived as a major antiarrhythmic mechanism, but soon became a surrogate for torsades de pointes (TdP) instead. Drugs that prolong the QT interval range from having potent torsadogenic activity to no proarrhythmic action and even antiarrhythmic effects. Blockade of hERG channels is theprimary cause of TdP, but blockade/activation of other channels can also be torsadogenic. TdP is primarily caused by disturbances of TRIaD, but disturbance of wavelength can also contribute to TdP (where TRIaD is triangulation, reverse use dependence, instability and dispersion, and wavelength equals conduction velocity times effective refractory period). The above proarrhythmic parameters do not only result in TdP, but can also lead to ventricular tachycardia (VT) and ventricular fibrillation (VF). Note that QT prolongation (not listed as a causal factor) yields many false positives (potentially depriving patients from much needed drugs) and false negatives (potentially exposing patients to lethal arrhythmias). Thus, drug-induced QT prolongation is a bad surrogate for TdP, VT or VF; it is high time to move away from an oversimplified and erroneous surrogate.