Elimination of the delta wave in the Wolff-Parkinson-White syndrome. A misleading indicator of therapeutic effectiveness.

A 66-year-old white woman with a greater than 20-year history of electrocardiographic evidence of the Wolff-Parkinson-White syndrome, including documented recurrent supraventricular tachycardias, was studied. Despite the disappearance of the delta wave after initiation of therapy with digoxin and quinidine sulfate, the patient continued to have frequent episodes of supraventricular tachycardia. At a time when the serum levels of digoxin and quinidine were in the therapeutic range, extensive electrophysiologic studies were performed. Supraventricular tachycardia at a rate of 160 beats per minute was initiated by induced atrial premature depolarizations. The circuit of tachycardia involved anterograde conduction through the pathway of the atrioventricular node and His bundle and retrograde conduction through the bypass tract. We concluded that elimination of the delta wave and other electrocardiographic characteristics of the Wolff-Parkinson-White syndrome cannot be relied upon to indicate successful pharmacologic prophylaxis for induction of tachyarrhythmia associated with this syndrome.