<prompt> Cannon a wave in venous waveform is suggestive ofAV dissociationAtrial fibrillationTricuspid incompetencyAll of the above  <response>: The venous waveform is divided into several distinct peaks. The a wave reflects right atrial presystolic contraction and occurs just after the electrocardiographic P wave, preceding the first heart sound S. A prominent a wave is seen in patients with reduced right ventricular compliance; cannon a wave occurs with atrioventricular AV dissociation 