DRUG-INDUCED TORSADE-DE-POINTES - INCIDENCE, MANAGEMENT AND PREVENTION

Torsade de pointes is a particular form of polymorphic ventricular tac hycardia causing few haemodynamic symptoms, but carries a poor prognos is because of recurrence and sudden death in up to 31% of patients. A wide range of agents have been shown to aggravate and even to cause to rsade de pointes by prolonging the QT interval or increasing QT disper sion. For the majority of substances the incidence of torsade de point es remains unclear, but is of the order of 3 to 15% for a wide range o f agents. Elicitation of proarrhythmia by drug-induced QT prolongation is mainly based on increased cellular excitability and/or abnormal di spersion of ventricular repolarisation. Torsade de pointes has been sh own to be related to bradycardia-dependent early after-depolarisations and/or increased dispersion of repolarisation. Clinically, patients w ith predisposing factors prior to medication should be considered at r isk of drug-mediated proarrhythmic therapy. During this phase, QT inte rval measurement and assessment of the QTc time should be performed fr equently. Phases of bradycardia or occurrence of ventricular extra bea ts with a long coupling interval may be of help to identify patients a t high risk of proarrhythmic events. As a first attempt in managing th is arrhythmia, magnesium sulphate has been shown to be effective in ma ny patients. In case of recurrence of torsade de pointes, the use of a temporary pacemaker with pacing at about 100 to 120 beats/min is the therapy of choice until the causative agent has been completely elimin ated.