Large (Cannon) "a" waves:
- Occurs when atria and ventricles contract simultaneously, causing blood to be pushed up against the AV valve and up the venous system
- Cannon "a" waves occur regularly in junctional rhythm
- Cannon "a" waves occur irregularly in AV dissociation accompanying PVCs, VTach, and complete heart block
Other "a" wave morphology:
- "a" wave absent in atrial fibrillation
- flutter "a" waves in atrial flutter
- variable "a" waves in multifocal atrial tachycardia
- very large "a" waves can occur in pulmonary HTN
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