[Anterograde decremental conduction by left free wall accessory pathway in the permanent form of junctional reciprocating tachycardia].

We present the case of a 2-month-old infant, diagnosed prenatally with tachycardia. The characteristics of the surface electrocardiogram were consistent with the diagnosis of the permanent form of junctional reciprocating tachycardia: narrow-complex tachycardia at 200 beats/min, negative P' wave in inferior leads (II, III, aVF), I, aVL and from V4 to V6. The tachycardia was incessant despite medical treatment with digoxin, quinidine, amiodarone and flecainide. The electrophysiological study confirmed that the mechanism of the tachycardia was a left posterolateral pathway with long conduction time and decremental properties. The ablation procedure was tried by transseptal approach. During transseptal puncture complete atrioventricular block and interruption of the tachycardia were produced. Decremental ventricular preexcitation was evident during isoproterenol infusion. After recovery of the atrioventricular conduction and incessant tachycardia, radiofrequency ablation of the pathway was performed twelve months later by retrograde approach.