Aberrant Ventricular Conduction of Escaped Beats

Escape beats recorded in clinical electrocardiograms sometimes differ in contour and QRS duration from conducted beats, and this in spite of their having a relatively short cycle length. This suggests a location of the subsidiary pacemaker above the bifurcation of the common A-V bundle. While this, unlike other types of aberrant ventricular conduction, cannot be explained on a functional basis, recent investigations on the structure of the normal A-V junction suggest that "paraspecific" A-V connections may act as preferential pathways to the ventricles in some A-V nodal escape beats. Difficulties and guides in differentiating A-V nodal from ventricular escapes under such circumstances are pointed out. On the basis of clinical, electrocardiographic and anatomic facts such a normal preferential A-V conduction must be distinguished from an abnormal accessory A-V conduction causing the pre-excitation (Wolff-Parkinson-White) syndrome. However, the two may occur in association.