Calculation of Pulmonary Artery Pulsatility Index (PAPi)
The pulmonary artery pulsatility index (PAPi) is calculated as the pulmonary artery pulse pressure (systolic pressure minus diastolic pressure) divided by the right atrial pressure: PAPi = (PASP - PADP) / RAP.
Formula Components
- PASP: Pulmonary Artery Systolic Pressure
- PADP: Pulmonary Artery Diastolic Pressure
- RAP: Right Atrial Pressure
Measurement Methods
Invasive Measurement (Gold Standard)
- Obtained via right heart catheterization
- Direct measurement of all pressure values
Non-invasive Estimation (Echocardiography)
- PASP: Estimated using tricuspid regurgitation velocity (TRV)
- PASP = 4 × (TRV)² + RAP 1
- PADP: Can be estimated from pulmonary valve regurgitation velocity 1
- RAP: Estimated based on inferior vena cava diameter and collapsibility with respiration 1
Clinical Significance of PAPi
PAPi has emerged as an important hemodynamic parameter with significant prognostic value:
- Low PAPi (<3): Associated with 1.96-fold increased risk of death in pulmonary hypertension patients 2
- PAPi <2.46: Independent predictor of worse outcomes in heart failure patients with mitral regurgitation 3
- PAPi ≤2.2: Associated with higher rates of early rehospitalization for heart failure 3
Advantages of PAPi Over Other Parameters
- Incorporates both pulmonary artery pressure dynamics and right atrial pressure
- Independently associated with survival in pulmonary arterial hypertension 4
- Provides incremental prognostic information beyond traditional hemodynamic parameters 5
- Can be calculated using non-invasive echocardiographic measurements 2
Common Pitfalls in PAPi Calculation
- Inaccurate RAP estimation: RAP estimation by echocardiography may be less reliable than direct measurement
- Suboptimal TR jet visualization: TRV may be underestimated if alignment is not optimal
- Severe TR: May lead to inaccurate pressure estimations
- Pulmonic stenosis: Will invalidate the PASP estimation using TR velocity
PAPi represents an important hemodynamic parameter that should be incorporated into the assessment of patients with suspected pulmonary hypertension or right ventricular dysfunction, as it provides valuable prognostic information beyond conventional measurements.