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Module 02

CVP waveform lab

The mean pressure is one number; the waveform is a story told five times a second. Change the physiology and watch the a, c and v waves and the x and y descents respond. The tracings are generated from a parametric model, so every feature you see is one the text describes.Damrongwatanasuk 2026

Condition

Pick a physiology

Physiology dials

Shifts the whole tracing; the shape is what diagnoses.

Breathing

Spontaneous inspiration lowers the trace; positive pressure raises it; Kussmaul is a rise during spontaneous inspiration.

Display

Normal sinus rhythm

Three positive waves (a, c, v) and two descents (x, y); a ≥ v in the right atrium.

Mean (trace)

3.0mmHg

End-expiratory

4.3mmHg

-5051015mmHg1 s / divisionECGend-expiratory meanacxvyacxvyacxvyacxvyacxvyacxvyacxvyacxvyacxvyacxRA pressureSynthetic example, not patient data

What to look for

  • a wave after the P wave
  • c wave at the end of the QRS
  • x descent during systole
  • v wave after the T wave
  • y descent after the v wave

Original illustration

Damrongwatanasuk, Shan & Hu

Illustration of the CVP waveform in Normal sinus rhythm
A practical sequence for reading any CVP tracing
  1. Confirm the catheter records an atrial signal, not a ventricular one (diastole is the clue).
  2. Display the ECG and the pressure on the same time scale.
  3. Find the v wave first, just after the T wave; then the a wave after the P; then the c at the end of the QRS.
  4. Identify the x and y descents and decide which is dominant.
  5. Ask whether the waves recur regularly with similar amplitude.
  6. Watch several respiratory cycles and read the pressure at end-expiration.
  7. Integrate with rhythm, exam, echo, and the ventricular tracings.

After Damrongwatanasuk, Shan & Hu Damrongwatanasuk 2026 and Naderi's “find v first” rule Naderi 2024.

Why the shape matters more than the number

Mean vs morphology

A patient in complete heart block can have a normal mean RAP and still show cannon a waves; early tamponade can have a normal mean before the y descent disappears.

Mean CVP and fluids

Mean CVP correlates poorly with blood volume and with the response to a fluid bolus; consensus guidance advises against using it alone as a fluid target. Marik 2013

Where to read it

Two separate decisions, not one fixed point on the tracing

1. Cardiac-cycle timing: mean or end-diastolic?

  • Mean: the average over the whole cardiac cycle. It includes the v wave, so it is not read at any single point. Baratto 2023
  • End-diastolic: mid-a wave in sinus rhythm; in AF, mid-c or just before the v wave. It is a good surrogate for LVEDP, though imprecise (limits about ±11 mmHg during exercise). Baratto 2023
  • Tall v waves lift the mean above the end-diastolic value and above LVEDP.
  • App convention: PVR is defined from mean pressures, so Swanology uses the mean PAWP for PVR and PH classification and the end-diastolic wedge as the LVEDP surrogate.

2. Respiratory timing: end-expiration or a breath average?

  • End-expiration is the usual choice in US centres; ERS recommends averaging over the respiratory cycle when swings are large. The two can differ substantially (during exercise the median peak mean PAWP was 33 versus 26 mmHg). Baratto 2023
  • Spontaneous breathing: end-expiration is the top of the swing; on a ventilator it is the low point. In forced expiration (for example COPD) read early in expiration. Bootsma 2022Kern 2022
  • In AF, average several beats whichever respiratory convention you use.
  • Respiratory timing never replaces the cardiac-cycle choice, and the reverse. Pick each deliberately and say which you used.

Try it: the or the Pitfalls station on the same idea.

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