Torsades de pointes: unanswered questions

Torsade de pointes (Tdp) is a polymorphic ventricular tachycardia (VT) in which the axis of the QRS complex changes direction after a certain number of complexes as if the complex rotated around the baseline. Tdp is usually associated with QT prolongation, and dispersion of ventricular repolarlization (DR). Experimental models of tdp are usually associated with induction of early after depolarizations (EADs). Several aspects of the pathogenesis of tdp are incompletely understood. The purpose of this article is to propose the directions in research that may increase our current understanding of the factors responsible for tdp. The most plausible hypotheses requiring further supporting evidence are: 1. The occurrence of tdp requires the presence of DR i.e. tdp does not occur in the absence of DR. 2. EADs appear to play an important role as a trigger to tdp in the animal models, but more evidence are needed at the clinical level. 3. EADs may be responsible for arrhythmias other than tdp. 4. The greater incidence of tdp in the females than in tha males may be attributed to differences in the duration of the QT interval and different morphology of the ST-segment and the T-wave. The above gender differences may be caused by the effects of gonadal hormones which modulate some of the membrane currents flowing during early ventricular repolarization.