The central venous pressure (CVP) waveform is measured using a central venous catheter positioned just above the right atrium (RA), within the superior vena cava. Starting from mid-diastole, key features of the normal CVP waveform are (Figure 38.1).
The central venous pressure (CVP) waveform is measured using a central venous catheter positioned just above the right atrium (RA), within the superior vena cava. Starting from mid-diastole, key features of the normal CVP waveform are (Figure 38.1):
The a-wave corresponds to the increase in pressure when the RA contracts, occurring just after the P‑wave on the electrocardiogram.
The c‑wave occurs in time with the carotid pulsation. In early systole, right ventricular contraction causes the tricuspid valve to bulge into the RA, leading to a small increase in CVP.
The x‑descent corresponds to atrial relaxation and the downward movement of the RA during right ventricular contraction. The resultant low CVP leads to rapid right atrial filling.
The v‑wave corresponds to the continued venous return to the RA during ventricular systole; that is, right atrial filling with a closed tricuspid valve.
The y‑descent corresponds to the decrease in CVP after the tricuspid valve opens, when blood flows from the RA into the right ventricle (RV).
Figure 38.1 The CVP waveform.
A number of cardiac conditions impact on the CVP waveform:
Atrial fibrillation. The loss of coordinated atrial contraction leads to the absence of a‑waves.
Third-degree heart block. Electrical impulses cannot pass through the atrioventricular node. As a result, atrial and ventricular contraction occur independently. There will be times when the atria contract at the same time as the ventricles (i.e. when the tricuspid valve is closed), resulting in the occasional larger a‑wave on the CVP waveform; this is called a ‘cannon a‑wave’.
Tricuspid regurgitation. During ventricular systole, blood is ejected from the RV into the RA, increasing the CVP. The CVP waveform has a ‘giant v‑wave’, a large positive deflection that replaces the c‑wave, the x‑descent and the v‑wave.