Cannon a Wave
The a wave of the jugular venous waveform occurs as a result of right atrial contraction. When there is resistance to right ventricular filling, right atrial contraction generates increased pressure, resulting in large a waves. Cannon a waves usually occur intermittently, unlike giant a waves, which occur with every beat. The cannon a wave occurs as a result of atrial contraction against a closed tricuspid valve, which occurs sporadically as a result of atrioventricular dissociation. When cannon a waves occur with every beat, it indicates atrioventricular dissociation with retrograde atrial activation from supraventricular tachycardia (e.g., junctional rhythm).
Patient 1:
This patient was admitted to the hospital with complete heart block. These videos demonstrate a jugular venous waveform with cannon a waves. Note that the large outward wave occurs intermittently, distinguishing it from giant a waves, which occur with every beat. Notice that there is a normal jugular venous waveform between the cannon a waves.
Cannon a Wave
Annotated
Patient 2:
This is an older woman with complete heart block