CVP Waveform Analysis — FFICM MCQ

Correct answer: C — Complete heart block with intermittent AV dissociation

CVP waveform analysis: the 'a' wave represents atrial contraction. In complete (third-degree) heart block, the atria and ventricles contract independently (AV dissociation). When the atrium contracts against a closed tricuspid valve (i.e. during ventricular systole), a large 'cannon' wave is produced. Because the timing of atrial and ventricular contractions is random in complete heart block, cannon waves occur irregularly. Regular 'a' waves are absent because the relationship between atrial contraction and the cardiac cycle is disrupted. In atrial fibrillation (Option B), 'a' waves are absent entirely (no organised atrial contraction), but there are no cannon waves. In sinus rhythm (Option A), normal 'a' waves are present. In first-degree block (Option D), the 'a' wave is present but may be displaced. In atrial flutter (Option E), flutter waves may replace normal 'a' waves.

Reference: McGee (2018): Physical Diagnosis - CVP Waveform Analysis; Mark (1998): Atlas of Cardiovascular Monitoring