Pearls of Knowledge: AV Dissociation
Tuesday, November 04, 2025
Rhythm Interpretation: AV Dissociation
Pearls of Knowledge © BrainyNurses.com
In AV dissociation, there is an increase in the automaticity of another pacemaker which causes the ventricles to be refractory to the slower P waves from the SA node. In AV dissociation, the P waves do not cause the QRS complexes except when a capture beat occurs. The rate of the atria and ventricles will be very similar, but they are not “married”. AV dissociation is easy to mistake for third-degree heart block.
Generally, the P waves will appear to “fade” into the QRS complexes and come out the back.
When a capture beat occurs, the SA node “captures” the ventricles, and the configuration will be different than the QRS complexes which are coming from the other pacemaker.
The other pacemaker causing the rhythm and QRS complexes may be the AV junction (QRS complex will be narrow) or the purkinje fibers (QRS complex will be wide).
Types of AV Dissociation
• Complete dissociation is when no capture beats are present. In other words, none of the P waves cause the QRS complexes.
• Incomplete dissociation is when capture beats are present. In other words, some of the P waves cause the QRS complexes.
Complete AV Dissociation
• The P waves fade into the QRS complexes and come out the back.
• All the QRS complexes look the same.
• The P waves are coming from the SA node.
• The QRS complexes are coming from the AV junction (narrow complex).
Incomplete AV Dissociation
• In the middle to the end of the strip, the P waves fade into the QRS complex and come out the back. (they are harder to see in the beginning of the strip)
The P waves are coming from the SA node.
• The QRS complexes are coming from the AV junction (narrow complex).
• The capture beat is the fourth QRS complex. The P wave caused it and the QRS looks “different” because it took the normal path of conduction through the ventricles.
Summary
AV dissociation is not an uncommon rhythm but it is often not recognized. Tracing the P waves through the rhythm is the first step in recognition and the P waves will come out the back of the QRS complexes. Recognizing when capture beats are present is more advanced. In looking at the “different” QRS complex, there was a reason why it occurred. And it was because the P wave was captured.
To enhance care provided for cardiac patients, check out Comprehensive Rhythm Review and Clinical Application. It is on-line, on-demand, with voice-over-power-point. The extensive handout is easy to follow and includes our “In My Pocket” cards as a ready reference tool.
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