Shortening of ventriculoatrial intervals with left bundle branch block during orthodromic reciprocating tachycardia in three patients with a right-sided accessory atrioventricular pathway.

Previous studies of the effects of bundle branch block on ventriculoatrial (VA) intervals during orthodromic reciprocating tachycardia have focused on the timing of the atrial electrograms. However, left bundle branch block importantly affects the timing of initial ventricular activation, and this effect would also be expected to affect VA intervals during orthodromic reciprocating tachycardia. Presented here are three patients with a single right-sided accessory atrioventricular pathway exhibiting left bundle branch block during orthodromic reciprocating tachycardia. Each had shortening of the VA interval by 10 to 30 ms during left bundle branch block beats. This shortening was accompanied by a nearly equal increase in the HV interval, with the His bundle to atrial interval remaining constant. It is concluded that the timing of ventricular as well as atrial electrograms impacts on the VA intervals with left bundle branch block beats during orthodromic reciprocating tachycardia. With left bundle branch block, delay in initial left septal activation results in later onset of the QRS complex and, with right ventricular activation occurring normally, shortening of the VA interval occurs in patients with a right-sided pathway.