["Torsades de pointe" and reentry induced by anti-arrhythmia agents]

Some anti-arrhythmic agents which have a stabilising effect on the membrane, particularly those belonging to Group I of Vaughan William's classification, are likely to cause rythmic disturbances by a re-entry phenomenon (atrial flutter 1/1, premature ventricular contractions, ventricular tachycardia, "torsades de pointe", even fatal ventricular fibrillation). The quinidines have been the most often condemned due to their effect on the action potential and on the speed of conduction. The fact that these re-entry phenomena are more frequent at therapeutic doses than at high or toxic doses suggests an individual susceptibility and the interaction of various predisposing factors: renal insufficiency, potassium depletion, pre-existing conduction disturbances, potentialsing drugs. In order to prevent these incidents it is advisable not to prescribe such anti-arrhythmic agents for susceptible patients, to control individual tolerance and to watch for the first ECG signs of conduction disturbances or of re-entry, such as premature contraction with fixed coupling. Treatment consists in an electrosystolic stimulus and the possible administration of potassium and bretylium.