In an adult patient with significant cardiovascular disease, if the diastolic pressure falls to zero on a Pulmonary Artery Catheter (PAC), does it indicate a right ventricular (RV) waveform or a pulmonary artery (PA) waveform?

Diastolic Pressure Falling to Zero on PAC Indicates RV Waveform

When diastolic pressure falls to zero on a pulmonary artery catheter, this indicates a right ventricular (RV) waveform, not a pulmonary artery (PA) waveform. This occurs because the catheter has been pulled back into the RV or was never properly advanced into the PA 1.

Key Distinguishing Features

Normal PA Waveform Characteristics

• PA diastolic pressure is always positive and elevated above zero 2
• The PA maintains positive diastolic pressure due to the competent pulmonic valve preventing backflow into the RV during diastole 1
• Normal PA diastolic pressure ranges from approximately 8-15 mmHg in healthy individuals 2
• Even in severe pulmonary hypertension or acute RV failure, PA diastolic pressure remains substantially above zero 2

RV Waveform Characteristics

• RV pressure falls to near-zero or zero during diastole as the ventricle relaxes and fills 1
• The RV waveform shows a characteristic sharp upstroke during systole followed by a rapid decline to baseline (near-zero) during diastole 1
• Normal RV end-diastolic pressure is typically 0-8 mmHg 2

Clinical Implications and Troubleshooting

Immediate Action Required

• The catheter must be advanced further into the PA to obtain accurate hemodynamic measurements 1
• Confirm proper catheter position by observing the transition from RV to PA waveform, which shows:
  • Loss of the near-zero diastolic pressure
  • Appearance of a dicrotic notch (representing pulmonic valve closure)
  • Elevated and sustained diastolic pressure 1

Common Pitfall to Avoid

• Do not use RV systolic pressure as a substitute for PA systolic pressure for clinical decision-making, even though they are often similar in the absence of RV outflow obstruction 3
• The critical difference is the diastolic component—PA diastolic pressure provides essential information about left heart filling pressures, while RV diastolic pressure does not 4, 5

Relationship Between PA Diastolic and Wedge Pressure

• Once properly positioned in the PA, the PA diastolic pressure typically approximates the pulmonary capillary wedge pressure (PCWP) in most patients 4, 5
• However, this relationship breaks down in right ventricular failure and pulmonary hypertension, where PA diastolic pressure may exceed PCWP by ≥6 mmHg, indicating elevated pulmonary vascular resistance and worse prognosis 5, 6
• In right ventricular-predominant cardiogenic shock specifically, the correlation between PA diastolic pressure and PCWP is weak (r = 0.43), making direct wedge pressure measurement essential 6

Technical Verification

Confirming PA Position

• Observe for the dicrotic notch on the pressure waveform, which represents pulmonic valve closure and confirms PA location 1
• PA systolic pressure should match or slightly exceed RV systolic pressure (typically within 0-5 mmHg) 1
• PA diastolic pressure should be 5-15 mmHg higher than RV diastolic pressure in normal conditions 5

When PA Diastolic Exceeds Wedge Pressure

• If PA diastolic pressure is ≥6 mmHg higher than wedge pressure, this indicates pulmonary hypertension with elevated pulmonary vascular resistance (>257 dyne/s/cm⁻⁵) and is associated with significantly increased mortality (59% vs 34%) 5
• This finding is particularly important in patients with cardiovascular disease, as it suggests intrinsic pulmonary vascular pathology rather than passive congestion alone 5