The third cause of atrioventricular (AV) dissociation is sinoatrial or AV block, which decreases the effective or conducted atrial rate and allows the escape of a subsidiary focus. As a general rule, when AV block occasions AV dissociation, the actual atrial rate exceeds the discharge rate of the escape pacemaker.
Before we proceed further, it is important to emphasize that complete AV dissociation is not synonymous with complete AV block. Complete AV dissociation indicates that atria and ventricles are completely dissociated, ie, separate pacemakers control the atria and ventricles without anterograde or retrograde captures. Complete AV block is but one cause of complete AV dissociation. The diagnosis of complete AV block should be restricted to instances in which the escape ventricular rate is less than 40 beats per minute.
In Figure 1, the ventricles discharged regularly (30 beats per minute), uninfluenced by atrial activity (85 beats per minute). Complete AV