Intraventricular reentry with narrow QRS complex.

Reentry within the His-Purkinje System (V3 phenomenon) where the reentry pathway incorporates both bundle branches and the bundle of His is a frequent phenomenon during ventricular refractory period studies. In this form of reentry, both divisions of the left bundle branch function as a single limb and the reentrant beats (V3) have either left bundle branch block or right bundle branch block pattern. In this report, we describe in three patients the occurrence of a new type of reentrant beat (V3) whose characteristics suggested reentry within a circuit in which the retrograde limb of the reentrant circuit was constituted by one of the two divisions of the left bundle branch and the antegrade limb(s) by right bundle branch and the remaining division of the left bundle branch; i.e., the two divisions of the left bundle branch functioned as two separate limbs. We reached this conclusion because 1) reentry occurred within a narrow range of V1V2 intervals and was dependent upon critical retrograde His-Purkinje conduction (V2H2) delays; 2) reentry did not occur when the V2 impulse blocked retrogradely within the His-Purkinje system below the site of His bundle recording; 3) the QRS duration of V3 was less than 90 msec; and 4) in two-thirds of the patients, the HV interval of V3 was the same as that of sinus beats.