Cannon "a" waves observed in a patient are best explained by which condition?

• A. Atrioventricular dissociation
• B. Aortic stenosis
• C. Systolic hypertension
• D. Left ventricular hypertrophy

Answer: (A)

Cannon A waves arise when the atria contract against a closed tricuspid valve due to atrioventricular dissociation, where atrial and ventricular rhythms are not synchronized. In this situation, the atrial kick can occur during ventricular systole, when the tricuspid valve is closed, causing a strong backward pressure into the right atrium and a prominent, “cannon” jugular venous pulse. This is most classically seen with complete heart block or other states that disrupt AV synchrony. The other conditions listed do not disrupt the timing between atrial contraction and valve closure, so they don’t produce cannon A waves.