Mechanism of QRS electrical alternans.

In patients with latent dual atrioventricular nodal pathways a 2:1 ventriculoatrial block often occurs during ventricular pacing and is generally associated with the concomitant appearance of QRS alternans. This type of QRS alternans is related to retrograde conduction, and a concealed retrograde conduction in the His Purkinje system could explain the QRS alternans. A case that confirms the hypothesis that electrical alternans is secondary to a 2:1 block in the activation of some part of the ventricles is reported.