DOUBLE RESPONSES

Double response is a rare electrocardiographic phenomenon requiring tw o atrioventricular conduction pathways with very different electrophys iological properties. Double ventricular responses are the usual manif estation: an atrial depolarisation (spontaneous or provoked, anticipat ed or not) is followed by a first ventricular response dependant on an accessory pathway or a rapid nodal pathway and then a second response resulting from sufficiently delayed transmission through a nodal path way for the ventricles to have recovered their excitability when the s econd wave of activation reaches them. A simple curiosity when isolate d and occurring under unusual conditions, particularly during electrop hysiological investigation of the Wolff-Parkinson-White syndrome, the double response may initiate symptomatic non-reentrant junctional tach ycardia when associated with nodal duality and repeating from atria in sinus rhythm. The functional incapacity and resistance to antiarrhyth mic therapy may require referral for ablation of the slow pathway.