Supraventricular tachycardia that mimics ventricular tachycardia.

A short PR interval, a delta wave, and attacks of paroxysmal tachycardia are the principal features of the WPW syndrome. A grossly irregular rhythm with bizzare QRS complexes at rates exceeding 180 per minute is one of the paroxysmal tachycardias characteristic of the WPW syndrome. This arrhythmia deserves special attention, because it is often misinterpretated as ventricular tachycardia. The interpretation is atrial fibrillation with varying degrees of ventricular fusion and phasic ventricular aberration. Prompt electrical cardioversion is indicated because, at times, ventricular fibrillation may result. Quinidine sulfate used prophylactically because of its negative dromotropic effect on the accessory pathway promotes A-V transmission via the A-V node.