What’s up with this pacing Swan?

Labs and Lytes 007

Author: Andrew Woolley
Reviewer: Chris Nickson

A 70 year old woman has been in ICU for a week after a car collided with her scooter, resulting in isolated chest injuries.  She appeared ready for the ward but has since markedly deteriorated due to urosepsis.

During the night shift the following happened:

  • An asystolic arrest leading to prolonged CPR and transcutaneous pacing
  • A pacing Swan-Ganz catheter was inserted for transvenous pacing
  • The Swan had been pacing well overnight with an underlying bradycardia

Now the patient has a spontaneous rhythm of 100/min and the ICU nurse reports that the pacing wire is not sensing.

This is what her monitor shows on the morning ward round:

Wooley image 1

Q1. What are the key abnormalities shown on the monitor?

The key abnormalities are:

The right ventricular pressure (RVP) and pulmonary artery pressure (PAP) waveforms are remarkably similar, as are the systolic, diastolic and mean pressures of each.

The mean and diastolic RVPs are higher than the central venous pressure (CVP).

These findings are also present:

  •  pulse oximeter isn’t reading
  • fever
  •  irregular tachycardia

Q2. Which of the waveforms mentioned in Q1 is truly abnormal and why?

The RVP trace is abnormal because:

  • RVP should have a lower diastolic number than PAP (normal diastolic RVP is 2-8 mmHg, normal diastolic PAP is 8-15 mmHg)
  • The CVP on the monitor is lower than the diastolic RVP – i.e. blood according to this monitor should flowing from LOW to HIGH pressure
  • If you look closely you can see dichrotic notches in the RVP trace – this is seen on arterial pressure waveforms due to valve closures and is usually absent from the RVP trace

Except for showing values consistent with mild-moderate pulmonary hypertension, the PAP waveform is normal and so is the CVP trace.

Q3. What investigation will help confirm the cause of the problem?

A CXR is an easy way to confirm the position of lines.

It showed that the pulmonary artery cather was looped in the right heart and was inserted too far into the pulmonary artery. This meant that the RV pressure transducer was also in the pulmonary artery – hence its pressures and waveforms are abnormal and it was no longer pacing/sensing.

All case-based scenarios on INTENSIVE are fictional. They may include realistic non-identifiable clinical data and are derived from learning points taken from clinical practice. Clinical details are not those of any particular person; they are created to add educational value to the scenarios.

One comment on “What’s up with this pacing Swan?
  1. Another way to differentiate RV from PA pressure trace is the slope of the pressure curve during diastole. It slopes up during diastole in the RV and slopes down in the PA.

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