In the JVP, 'a' waves are absent in -: (A) Atrial fibrillation, (B) Mitral stenosis, (C) Tricuspid atresia, (D) myocardial infarction
Answer is A. The a wave reflects right atrial presystolic contraction and occurs just after the electrocardiographic P wave, preceding the first hea sound (S1).A prominent a wave is seen in patients with reduced right ventricular compliance; a cannon a wave occurs with atrioventricular (AV) dissociation and right atrial contraction against a closed tricuspid valve. In a patient with a wide complex tachycardia, the appreciation of cannon a waves in the jugular venous waveform identifies the rhythm as ventricular in origin. The a wave is not present with atrial fibrillation. Ref Harrisons internal medicine 20e p1668