Mechanism of Torsade de Pointes Arrhythmias

Torsade de pointes (TdP) arrhythmias are defined as polymorphic tachycardias which can terminale by themselves or degenerate to ventricular fibrillation. The prolongation of the repolarization time is a very important factor to initate arrhythmias. Phasic variations in electrical polarity and amplitude of the QRS complexes are observed. TdP may occur as a congenital disorder. Recently there has been a marked progress in the understanding of their genetic basis. On the other hand, drug-induced Tdp occurs due to proarrhythmic effects of some antiarrhythmic drugs. Bradycardia, frequency changes, prolongation of the QT time, dispersion of repolarization, early afterdepolarizations and delayed afterdepolarizations are precipitating factors of TdP. In addition, electrolyte abnormalities, changes in T and U waves and presence of ventricular hypertrophy may contribute to the initiation of TdP.