What pair of waveform features best distinguishes a true wedge tracing from a pulmonary artery (PA) tracing?

Distinguishing True Wedge from Pulmonary Artery Tracing

The correct answer is (c): damped contour with identifiable a and v waves and loss of dicrotic notch. This combination of features definitively distinguishes a true pulmonary capillary wedge pressure (PCWP) tracing from a pulmonary artery (PA) tracing.

Key Distinguishing Features

Loss of Dicrotic Notch

• The dicrotic notch disappears when the catheter is properly wedged because you are no longer recording pulsatile arterial flow but rather the dampened left atrial pressure transmitted retrograde through the pulmonary capillaries 1.
• The PA tracing characteristically shows a dicrotic notch on the downslope of the systolic waveform, representing pulmonic valve closure 1.

Identifiable A and V Waves

• True wedge tracings display left atrial waveform morphology with distinct a and v waves, reflecting atrial contraction and ventricular systole respectively 2, 3.
• The a wave represents atrial systole and the v wave represents passive atrial filling during ventricular systole 4.

Damped Contour

• The overall waveform becomes damped when wedged because the pressure is transmitted through the static column of blood in the pulmonary capillaries rather than directly measured in the pulsatile PA 1.

Timing Relationships for Verification

A critical method to confirm true wedge position involves comparing timing with the arterial waveform:

• When properly wedged, there is an immediate rightward shift in both the upstroke and peak of the pressure trace compared to the radial arterial trace 2.
• The v wave upstroke occurs significantly later in the cardiac cycle (280 ± 20 ms after the Q wave) compared to the PA upstroke (170 ± 20 ms) 2.
• The v wave peak occurs significantly later (570 ± 20 ms) compared to both PA peak (350 ± 20 ms) and radial arterial peak (360 ± 10 ms) 2.

Why Other Options Are Incorrect

Option (a): Presence of dicrotic notch and steep systolic upstroke

• These features characterize a PA tracing, not a wedge tracing 1.
• The dicrotic notch is lost upon wedging 2.

Option (b): Higher systolic peak and lower diastolic trough

• This describes pressure amplitude differences but does not reliably distinguish wedge from PA position 1.
• Both tracings can have variable pressure amplitudes depending on hemodynamic conditions.

Option (d): Diastolic pressure step up and prominent y descent

• While the y descent may be visible in wedge tracings, a diastolic pressure "step up" is not a defining feature of wedge position 3, 5.
• The mean wedge pressure is typically lower than mean PA pressure, not higher 3.

Clinical Pitfalls to Avoid

• Giant v waves in severe mitral regurgitation can make wedge tracings appear similar to PA tracings with high systolic peaks 2, 3.
• In patients with large v waves, use the timing relationship with the arterial trace to confirm position: the v wave peak will occur significantly later than the arterial peak when truly wedged 2.
• Overwedging can create artifactually elevated pressures that don't reflect true left atrial pressure 1.
• Always verify wedge position by checking for blood oxygen saturation >95% from the distal port and confirming the pressure is lower than PA diastolic pressure 1.