Atrio-ventricular dissociation occurs when the atrial and ventricular rhythms are independent of each other. It can happen when the atrial rate slows below the intrinsic ventricular rate, or due to inappropriate acceleration of the ventricular rate. Typically in AV dissociation the distal pacemaker, such as the ventricles, beats faster than the proximal pacemaker like the atria. In complete heart block the proximal pacemaker usually beats faster than the distal one. However, there are exceptions to using pacemaker rates to distinguish the two.

1. Atrio-ventricular Dissociation

2. In AV dissociation the atrial and ventricular rhythms are independent of each other.In 3rd degree AV block the atrial and ventricular rhythms are dissociated, however, in clinical practice to avoid confusion we do not add the term “AV dissociation” to “complete heart block”.“AV dissociation” may occura) when the atrial rate becomes slower than the intrinsic rate of a distal pacemaker (AV junction, His-Purkinje system, myocardial cells), that escapesorb) because of inappropriate acceleration of a distal pacemaker (e.g. accelerated junctional rhythm, accelerated idioventricular rhythm, ventricular tachycardia)

3. "Rule of the thumb" to distinguish AV dissociation from complete heart block: In AV Dissociation usually the proximal (sinus or atrial) pacemaker is slower than the distal pacemaker. In this case there is no AV block: the distal pacemaker escapes because it is faster that the proximal one.In Complete Heart Block the distal pacemaker is usually slower that the proximal one.Caution: This is "a rule of the thumb". It is useful, but there can be exceptions to the rule (eg. a patient with Complete Heart Block may have a vasovagal episode and the proximal pacemaker may for a while be slower than the distal.....)