Atrioventricular or heart block describes an alteration in the normal pattern of transmission of action potentials between the atria and the ventricles. The normal function of the AV node is to delay the transmission of action potentials and hence protect the ventricles from transmission of atrial rates fast enough to impair cardiac filling. Block at the AV node may result in (see Fig. 2.10)
¬∑ a prolongation of the time required for transmission (first degree block).
¬∑ intermittent failure of transmission (second degree block).
¬∑ complete failure of transmission (third-degree heart block).