Conversion of paroxysmal supraventricular tachycardia due to a concealed extranodal pathway with intravenous bolus of lidocaine

In a recent report, Josephson and coworkers demonstrated marked slowing of ventricular response with administration of lidocaine in a patient with paroxysmal atrial fibrillation and preexcitation. This slowing reflected an increase in the refractoriness of an anomalous pathway (total failure of anomalous pathway), so that antegrade conduction during atrial fibrillation occurred only via the atrioventricular node. In the present study, conversion of paroxysmal supraventricular tachycardia in a patient with a known concealed Kent's bundle (unidirectionally conducting extranodal anomalous pathway) is reported. The significance of this conversion is discussed.