Unusual bifid “V” wave in central venous pressure

Sir,

A 42-year-old male patient, with triple vessel disease and diastolic dysfunction, was scheduled for an off pump coronary artery bypass grafting surgery. Intra-operatively, patient had junctional rhythm on electrocardiography (ECG) with regular rate of 80/min with no P waves. Central venous pressure (CVP) waveform showed an unusual bifid “V” wave [Figure 1]. Echocardiography did not reveal tricuspid regurgitation. Systolic arterial pressure was maintained in the range of 120-130 mm Hg without any inotropic or vasopressor support.

Figure 1.

Upper panel showing electrocardiograph – junctional rhythm (no P waves). Lower panel showing central venous pressure in blue and arterial waveform in red. Bifid V wave is marked by arrow. Other waves of CVP – c, x, v, a, and y are also named

In normal CVP waveform, ascent of V wave starts during late systole. The peak of V wave occurs during isovolumic ventricular relaxation, just before the opening of atrio-ventricular valve and the “y” descent. V wave corresponds to venous filling of atria.[1]

In junctional rhythm, normal sequence of atrial contraction prior to ventricular contraction is altered. In such cases, atrial contraction generally occurs during ventricular systole, when the tricuspid valve is closed, giving rise to “cannon ‘a’ wave” in CVP waveform. So there is a loss of normal end diastolic atrial kick which is more evident in CVP than ECG, which has the potential to cause hypotension in presence of hypovolemia.[2]

In the CVP of the present case, 2^nd peak is noted just after V wave peak giving appearance of bifid V wave [Figure 1]. To our best knowledge, it is not discussed in the literature. Bifid V wave may be due to impinging “a” wave on downslope of V wave or early part of “y” descent, i.e., ventricular filling. Retrograde conduction of impulse from atrioventricular (AV) node to atria may be the cause of this late appearing “a” wave. Ideally, intra-cardiac electrocardiogram detects the location of hidden P wave, but this was not available in our case. Retro-gradely conducted P wave may be incorporated into T wave of ECG and so atrial kick was produced in early diastole. Early rapid ventricular filling and atrial contraction phases of diastole occurred simultaneously giving good ventricular filling, thereby arterial pressure was maintained. Junctional rhythm in patients with diastolic dysfunction, especially if atrial contraction occurring during ventricular systole (P wave hidden in QRS complex in ECG), can cause hypotension and pacing may improve hemodynamics in such cases. In our case, CVP helped us in understanding why the arterial pressure was maintained despite junctional rhythm as atrial contraction occurred in early diastole, and pacing was not needed here.