What is a logical method to interpret Right Heart Catheterization (RHC) findings?

Logical Method for Interpreting Right Heart Catheterization Findings

A systematic approach to interpreting Right Heart Catheterization (RHC) findings should follow a stepwise evaluation of hemodynamic parameters to accurately diagnose and classify pulmonary hypertension and other cardiopulmonary conditions.

Step 1: Verify Technical Adequacy of Measurements

• Ensure proper zeroing of external pressure transducer at mid-thoracic line in supine patient 1
• Confirm accurate PAWP (Pulmonary Artery Wedge Pressure) measurement with:
  • Mean of three measurements taken at end-expiration
  • Blood sampling in wedge position to verify oxygen saturation matches systemic blood 1
• Verify all pressure measurements were taken at end of normal expiration 1

Step 2: Evaluate Key Hemodynamic Parameters

1. Right Atrial Pressure (RAP)

   • Normal: 1-8 mmHg
   • Elevated values (>10 mmHg) suggest right heart failure or volume overload 1

2. Right Ventricular Pressure (RVP)

   • Assess systolic and diastolic values
   • RV systolic pressure normally equals pulmonary artery systolic pressure

3. Pulmonary Artery Pressure (PAP)

   • Normal mean PAP (mPAP): <25 mmHg
   • PH defined as mPAP ≥25 mmHg 1
   • Record systolic, diastolic, and mean values

4. Pulmonary Artery Wedge Pressure (PAWP)

   • Normal: ≤15 mmHg
   • Critical for differentiating pre-capillary from post-capillary PH 1

5. Cardiac Output (CO)

   • Measure in triplicate by thermodilution or Fick method
   • Fick method mandatory with systemic-to-pulmonary shunts 1

6. Pulmonary Vascular Resistance (PVR)

   • Calculate as: PVR = (mPAP - PAWP) / CO × 80 [dynes·sec·cm⁻⁵]
   • Normal: <3 Wood units (or <240 dynes·sec·cm⁻⁵)
   • Essential for distinguishing passive PH from PH due to pulmonary vascular disease 1

Step 3: Classify Hemodynamic Profile

1. Normal Hemodynamics

   • mPAP <25 mmHg
   • PAWP ≤15 mmHg
   • PVR <3 Wood units

2. Pre-capillary Pulmonary Hypertension

   • mPAP ≥25 mmHg
   • PAWP ≤15 mmHg
   • PVR >3 Wood units 1
   • Suggests PAH, PH due to lung disease, CTEPH, etc.

3. Post-capillary Pulmonary Hypertension

   • mPAP ≥25 mmHg
   • PAWP >15 mmHg 1
   • Suggests left heart disease (systolic/diastolic dysfunction, valvular disease)

4. Combined Pre- and Post-capillary PH

   • mPAP ≥25 mmHg
   • PAWP >15 mmHg
   • Elevated PVR >3 Wood units
   • Suggests advanced left heart disease with secondary pulmonary vascular remodeling 1

Step 4: Consider Dynamic Testing When Appropriate

1. Vasoreactivity Testing

   • Indicated in idiopathic, heritable, and drug-induced PAH 1
   • Positive response: decrease in mPAP ≥10 mmHg to reach absolute value ≤40 mmHg with increased/unchanged CO
   • Predicts response to calcium channel blockers

2. Fluid Challenge

   • Consider in patients with suspected occult left heart disease
   • Administer 500 mL saline over 10 minutes
   • Significant rise in PAWP (>15 mmHg) suggests left heart disease 1
   • Particularly useful in scleroderma patients with borderline PAWP

Step 5: Integrate with Clinical Context

• Interpret RHC findings in conjunction with clinical presentation and imaging studies 1
• Complete RHC after other investigations to answer specific diagnostic questions 1
• Consider left heart catheterization when coronary artery disease or left heart dysfunction is suspected 1

Important Caveats and Pitfalls

1. Technical Errors

   • Improper zeroing of transducer
   • Respiratory variation affecting measurements
   • Incomplete wedging of catheter

2. Misclassification Risks

   • Heart failure with preserved ejection fraction may have borderline PAWP at rest 1
   • Occult left heart disease may be unmasked only with fluid challenge 1
   • Pulmonary veno-occlusive disease may have normal PAWP in some segments 1

3. Procedural Considerations

   • RHC has low but real risks (1.1% morbidity, 0.055% mortality) 1
   • Should be performed at experienced centers 1
   • Avoid repeated balloon inflations in end pulmonary arteries due to rupture risk 1

By following this systematic approach, clinicians can accurately interpret RHC findings to guide diagnosis, classification, and management decisions for patients with suspected pulmonary hypertension and other cardiopulmonary conditions.