Double atrial response to a single ventricular extrastimulus in a patient with Wolff-Parkinson-White syndrome.

Electrophysiological examination in a 39-year-old male disclosed an accessory pathway between the right atrium and the right ventricle and AV nodal dual pathways. Atrial and ventricular extrastimuli induced paroxysmal supraventricular tachycardia (PSVT), which was shown to be AV reciprocating tachycardia. Double atrial response was noted during ventricular extrastimuli at V1V2 of 280 msec and V1V2 of 250 msec. The first atrial response is considered to have been transmitted in a retrograde fashion in the accessory pathway, and the second atrial response similarly in the slow pathway of the AV node.