This chapter is relevant to Section G7(iii) of the 2017 CICM Primary Syllabus, which asks the exam candidate to "describe the invasive and non-invasive measurement of blood pressure, including limitations and potential sources of error". The college examiners have never expected their candidates to analyse any CVP waveforms and so the time-poor exam candidate can safely ignore this page and probably all the other pages in this CVP section.
Anatomy of the CVP waveform
The peaks and troughs of the CVP waveform represent pressure changes in the right atrium.
- a is for atrium… this is the right atrial contraction.
- It correlates with the P wave on the ECG.
- It disappears with atrial fibrillation
- c is for cusp… this is the cusp of the tricuspid valve, protruding backwards through the atrium, as the right ventricle begins to contract.
- It correlates with the end of the QRS complex on the ECG
- This is the movement of the right ventricle, which descends as it contracts
- The downward movement decreases the pressure in the right atrium. At this stage, there is also atrial diastolic relaxation, which further decreases the right atrial pressure.
- It happens before the T wave on the ECG
- As blood fills the right atrium, it hits the tricuspid valve and this is the back-pressure wave
- It happens after the T wave on the ECG
- It also gives an impression of tricuspid competence.
- A huge V wave is suggestive of tricuspid regurgitation, as it represents blood flowing back out of the contracting right ventricle; in this situation the V wave would be the most prominent wave, and would reach right ventricular systolic pressure ( ~ 30mmHg)
- This is a pressure decrease caused by the tricuspid valve opening in early ventricular diastole.
- This happens before the P wave of the ECG
- A loss of y-descent suggests tamponade; it means there is restriction to right ventricular filling.