[Ventricular pro-arrhythmic effects of anti-arrhythmia drugs]

Ventricular pro-arrhythmic effects of antiarrhythmic drugs correspond either to an aggravation of a pre-existing arrhythmia or to the development of a new arrhythmia not yet observed for a patient. More easily inducible ventricular tachycardias (VT) take part in this latter category. The incidence of ventricular pro-arrhythmias is difficult to evaluate but should be close to 3 to 10% during antiarrhythmic treatments. Two main mechanisms can be involved in pro-arrhythmia: 1) reentry can cause sustained VT complicating a pre-existing cardiopathy when a sodium channel blocker is prescribed, 2) early post depolarizations can result in the occurrence of torsades de pointes complicating an antiarrhythmic treatment which prolongs ventricular repolarization and QT interval. The main risk factors of pro-arrhythmia are in the first case the existence of antecedents of VT or V fibrillation with an altered ventricular function and in the second case an important prolongation of QT with bradycardia and hypokalemia. The incidence of pro-arrhythmia should decrease when these risk factors are taken into consideration. However the diagnosis of pro-arrhythmia should be systematically evoked by clinicians since these unwanted side-effects can occur with any class Ia, Ic and III antiarrhythmic drug and any drug which prolongs QT. If this diagnosis is confirmed, the need for an antiarrhythmic treatment should then be systematically evaluated in any patient taking into consideration the benefit/risk ratio of the treatment.