Right Heart Catheterization: Hemodynamic Measurements and Interpretation
Right heart catheterization (RHC) is the gold standard for diagnosing and assessing pulmonary hypertension and heart failure, providing direct measurements of intracardiac pressures, cardiac output, and pulmonary vascular resistance that cannot be reliably obtained through non-invasive methods alone. 1
Core Hemodynamic Measurements Obtained
Direct Pressure Measurements
RHC provides sequential pressure measurements as the catheter advances through the right heart 1:
- Right atrial pressure (RAP): Normal range 2-8 mmHg 2
- Right ventricular pressure (RV): Systolic 15-30 mmHg, diastolic 2-8 mmHg 2
- Pulmonary artery pressure (PAP): Systolic 15-30 mmHg, diastolic 4-12 mmHg, mean 9-18 mmHg 1
- Pulmonary artery wedge pressure (PAWP): Normal ≤15 mmHg, reflects left atrial pressure and left ventricular end-diastolic pressure 1
Cardiac Output Measurement
Cardiac output is measured directly and accurately through thermodilution, where a known volume and temperature of fluid is injected into the right atrium and the temperature change is measured downstream in the pulmonary artery. 1, 2 Modern catheters can measure cardiac output semi-continuously without repeated manual injections 2.
Oxygen Saturation Measurements
Blood samples should be obtained from the superior vena cava, inferior vena cava, and pulmonary artery to assess for intracardiac shunts 1. A wedge position sample with the balloon inflated confirms accurate PAWP measurement, as it should have the same saturation as systemic blood 1.
Calculated Hemodynamic Parameters
Pulmonary Vascular Resistance (PVR)
- Formula: PVR = (mean PAP - PAWP) / cardiac output
- Normal range: <3 Wood units 3
- Interpretation: Elevated PVR distinguishes precapillary from postcapillary pulmonary hypertension 1
Transpulmonary Gradient (TPG)
- Formula: TPG = mean PAP - mean PAWP
- Normal: ≤12 mmHg 1
- Interpretation: TPG >12 mmHg indicates "reactive" or "out of proportion" postcapillary PH 1
Cardiac Index
- Formula: Cardiac output / body surface area
- Normal range: 2.5-4.0 L/min/m² 2
Additional Derived Parameters
Right ventricular stroke work index, pulmonary artery pulsatility index, systemic vascular resistance, and cardiac power output can be calculated 2.
Interpretation in Pulmonary Hypertension
Diagnostic Criteria
Pulmonary hypertension is defined as mean PAP ≥25 mmHg at rest. 1, 3 The normal mean PAP is 14 ± 3 mmHg with an upper limit of 20 mmHg; values between 21-24 mmHg are of unclear significance 1.
Classification by Hemodynamic Profile
Precapillary PH (Groups 1,3,4,5) 1, 3:
- Mean PAP ≥25 mmHg
- PAWP ≤15 mmHg
- PVR >3 Wood units
- Cardiac output normal or reduced
Isolated Postcapillary PH (Group 2) 1, 3:
- Mean PAP ≥25 mmHg
- PAWP >15 mmHg
- TPG ≤12 mmHg (passive)
- Cardiac output normal or reduced
Combined Pre- and Postcapillary PH (Group 2) 1:
- Mean PAP ≥25 mmHg
- PAWP >15 mmHg
- TPG >12 mmHg (reactive)
- Cardiac output normal or reduced
Prognostic Value in PAH
In the NIH Registry era, hemodynamic parameters predicted survival in idiopathic PAH 1. Higher mean PAP, higher mean RAP, and lower cardiac index were associated with worse outcomes, forming the basis of a survival prediction formula 1.
Interpretation in Heart Failure
Left Heart Disease Assessment
Measurement of left ventricular end-diastolic pressure is critical to avoid misclassifying patients with elevated PAWP, particularly when risk factors for heart failure with preserved ejection fraction are absent. 1 The threshold to perform left heart catheterization in addition to RHC should be low in patients with clinical risk factors for coronary artery disease or heart failure with preserved ejection fraction 1.
Distinguishing HFpEF from PAH
- PAWP >15 mmHg: Indicates left heart disease as the cause of PH 1
- Normal left atrial size and absence of echocardiographic markers of elevated LV filling pressures: Should prompt direct measurement of LV end-diastolic pressure if PAWP is unexpectedly elevated 1
Assessing Right Heart Dysfunction
RAP and cardiac output measurements assess the degree of right heart dysfunction in heart failure 1, 2. Elevated RAP with reduced cardiac output indicates decompensated right ventricular failure 1.
Interpretation in Congenital Heart Disease
Shunt Detection and Quantification
Oxygen saturation measurements from multiple sites (superior vena cava, inferior vena cava, right atrium, right ventricle, pulmonary artery) identify and quantify intracardiac shunts. 1, 4 A step-up in oxygen saturation >7% between chambers indicates a significant left-to-right shunt 4.
Calculating Shunt Ratios
- Qp/Qs ratio: Pulmonary blood flow / systemic blood flow
- Qp/Qs >1.5: Indicates hemodynamically significant left-to-right shunt requiring intervention 4
Assessing Operability
In congenital heart disease with PAH, PVR and vasoreactivity testing determine operability 1. PVR >8 Wood units or PVR/systemic vascular resistance ratio >0.3 generally contraindicates shunt closure 4.
Interpretation in Valvular Disease
Mitral Stenosis
Catheterization is indicated when there is discrepancy between Doppler-derived mean gradient and valve area, or when symptoms appear out of proportion to noninvasive assessment. 1 Absolute left- and right-side pressure measurements should be obtained when pulmonary artery pressure is elevated out of proportion to mean gradient and valve area 1.
Assessing Pulmonary Hypertension Severity
In severe mitral regurgitation or tricuspid regurgitation with severe pulmonary arterial hypertension, PA catheter placement may be reasonable to guide therapy when persistently severe symptoms exist or hemodynamics cannot be adequately assessed non-invasively 2.
Exercise Hemodynamics
If symptoms appear out of proportion to resting hemodynamics, right- and left-heart catheterization with exercise may be useful 1. This unmasks exercise-induced elevation in PAWP or pulmonary artery pressure 1.
Critical Technical Considerations
Proper Zero Referencing
The external pressure transducer must be zeroed at the mid-thoracic line in a supine patient, halfway between the anterior sternum and the bed surface, representing the level of the left atrium. 1 Incorrect zeroing leads to systematic errors in all pressure measurements 1.
Timing of Measurements
All pressure measurements should be determined at end-expiration without breath holding 1. Alternatively, averaging pulmonary vascular pressures over several respiratory cycles is acceptable except in dynamic hyperinflation states 1.
PAWP Accuracy Verification
- Record PAWP as the mean of three measurements 1
- Obtain blood sample with balloon inflated in wedge position to confirm saturation matches systemic blood 1
- Avoid repeated balloon inflations/deflations in distal pulmonary arteries due to rupture risk 1
High-Fidelity Tracings
Use high-fidelity tracings that can be printed on paper rather than small moving traces on a cardiac monitor 1. This allows accurate identification of pressure waveforms and detection of artifacts 1.
Common Pitfalls and How to Avoid Them
Measurement Variability
Prolonged measurement in PAH patients demonstrates wide intraindividual spontaneous variability in pulmonary arterial pressure, by up to 20 mmHg in some patients, with a mean coefficient of variability of 8%. 1 This emphasizes the importance of obtaining multiple measurements and interpreting them in clinical context 1.
Inaccurate PAWP
PAWP may be inaccurate in the presence of changes in left atrial or left ventricular compliance, especially after mitral balloon valvotomy or with concomitant aortic regurgitation 1. Transseptal catheterization for direct left atrial pressure measurement may rarely be required if doubt exists about PAWP accuracy 1.
Thermodilution Errors
When concomitant mitral regurgitation is present, measures of forward flow by thermodilution or Fick method will underestimate mitral valve area 1. In this setting, rely more heavily on pressure gradients and valve morphology 1.
Overreliance on Single Parameters
Estimates of pulmonary hypertension severity should be based on all data, including transmitral gradient, valve area, PAWP, and pulmonary artery pressure, not a single valve area measurement. 1 There may be inaccuracies with both Doppler and catheter-derived measurements 1.
Safety Profile
When performed at expert centers, RHC has a morbidity rate of 1.1% and mortality rate of 0.055%. 1 The procedure should be limited to expert centers with meticulous attention to technical detail to obtain high-quality results and minimize risk 1.
Integration with Non-Invasive Testing
Cardiac catheterization should be performed after completion of other investigations so it can answer specific questions that arise from these investigations and avoid unnecessary procedures where alternative diagnoses are revealed. 1 The interpretation of invasive hemodynamics must be made in the context of the clinical picture and imaging, particularly echocardiography 1.