Supraventricular tachycardia that mimics ventricular tachycardia. Part II.

Concealed WPW is a newly described clinical entity. The existence of this syndrome can be ascertained only through specific electrophysiologic intracardiac studies. From the clinical standpoint, the existence of an accessory unidirectional A-V pathway anatomically located in the general area of the Kent bundle should be suspected in those patients with chronic BBB who have recurrent paroxysmal atrial tachycardias initiated by sinus arrhythmias or premature atrial beats. It should be noted that functional BBB can occur following a premature atrial beat. This will also set the stage for the initiation of a reciprocating tachycardia in concealed WPW. Pharmacological therapy aimed at preventing the recurrent tachycardias is disappointing. Pacemaker implantation appears to be successful by rendering one of the bundle branches refractory through concealed conduction. With chronic block of the remaining bundle branch, the natural pathway of A-V conduction is totally blocked at a critical time during the tachycardias, thus eliminating the reciprocating tachycardia.