Cannon a-Waves CVP — FRCA Primary MCQ
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Correct answer: D — Complete heart block
Cannon a-waves are classically associated with complete heart block. Complete atrioventricular dissociation allows an atrial contraction occasionally to coincide with ventricular systole, when the tricuspid valve is closed. The resulting abrupt rise in right atrial pressure produces an intermittent, high-amplitude cannon a-wave on the CVP or JVP trace. Normal sinus rhythm produces normally timed a-waves. Atrial fibrillation abolishes organised atrial contraction, so a-waves are absent. Mitral regurgitation primarily alters the left atrial pressure waveform rather than producing cannon waves in the CVP. Cardiac tamponade characteristically preserves a prominent x descent and attenuates the y descent; it does not cause cannon a-waves unless a separate rhythm disturbance is present.
Reference: Morin DP, Bernard ML. Extreme "cannon A waves" and pulsatile skin color in complete heart block. HeartRhythm Case Reports. 2017;3(10):493. https://pubmed.ncbi.nlm.nih.gov/29062706/