[Supraventricular tachycardia with wide QRS complexes during Vaughan-Williams class I anti-arrhythmic treatment. Diagnostic and therapeutic implications].

The authors report 8 cases of regular tachycardia with wide QRS complexes during treatment with Vaughan-Williams class 1 antiarrhythmic drugs. These antiarrhythmics, prescribed to prevent atrial fibrillation (3 patients) and atrial flutter (5 patients), were flecainide in 4 cases, propafenone in 2 cases and cibenzoline and hydroquinidine respectively associated with digitoxine and propranolol. These wide complex tachycardias were regular atrial tachycardias with 1/1 conduction to the ventricle. The action of the drug, more pronounced on intra-atrial conduction velocities than on atrioventricular node refractoriness resulted in transformation of flutter at 300 cycles/min with 2/1 conduction and a ventricular rate of 150 cycles/min to atrial flutter at 210 cycles/min with 1/1 ventricular conduction. This acceleration of the ventricular rate was accompanied by widening of the QRS complex. Using the new ventricular tachycardia criteria recently published by Brugada resulted in a diagnostic error in 7 out of the 8 cases. The recording of a wide QRS complex tachycardia in a patient on class 1 antiarrhythmic therapy for an atrial arrhythmia should alert the physician to 1/1 atrial tachycardia despite morphological electrocardiographic criteria of ventricular tachycardia. The 1/1 atrial tachycardia may be poorly tolerated and require emergency treatment. The preventive association of a drug which slows conduction through the atrioventricular node is not always effective.