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Authors of a recent review shared expert insights and tips for conducting cardiac catheterization procedures to diagnose pulmonary arterial hypertension.

A paper published in International Journal of Cardiology Congenital Heart Disease offered a comprehensive overview of the use of cardiac catheterization for diagnosing pulmonary arterial hypertension (PAH). Konstantinos Dimopoulos, MD, MSc, PhD, and coauthors shared key concepts, practical tips, and potential challenges to help clinicians optimize diagnostic accuracy and treatment outcomes for their patients.

The authors reviewed insertion sites and techniques to ensure catheters reach the appropriate pulmonary structures. Next, they discussed the acquisition of pressures and saturations during the procedure.

Pressure Measurements

Ensuring that transducers are properly zeroed at the mid-chest level is essential to obtaining reliable readings. The authors provided the following key points regarding the pressure measurements in different heart chambers:

Right Atrial (RA) Pressure:

• The RA pressure measurement should capture the mean pressure and waveform components, including a and v waves.
• Low mean RA pressure may indicate dehydration or improper transducer positioning (eg, higher than the chest).
• Increased mean RA pressure in pulmonary hypertension is often associated with right ventricular (RV) dysfunction and elevated RV end-diastolic pressure.
• A prominent a wave is typical, while a pronounced v wave may be present with significant tricuspid regurgitation.
• Additional information can be gained by examining x and y descents, which can suggest RV restriction.

RV Pressure:

• Key RV pressure values include the peak systolic and end-diastolic pressures.
• The peak systolic pressure should be similar to the systolic pulmonary artery (PA) pressure, assuming no pulmonary stenosis is present.
• The end-diastolic RV pressure should approximate the mean RA pressure.
• These measurements are vital, especially in patients with severe heart failure, as they help assess RV preload.

Pulmonary Artery Wedge Pressure (PAWP):

• PAWP is used as a surrogate for left atrial (LA) pressure and involves using a balloon-tipped Swan-Ganz catheter.
• The catheter is advanced until it wedges into a smaller PA branch, creating a “static column of blood” that reflects the pressure in the pulmonary veins, equivalent to LA pressure.
• Correct interpretation of PAWP relies on understanding this principle; obstructions within the “static column,” like in pulmonary veno-occlusive disease, may not be detected.
• Partial occlusion or over-wedging, where the pressure rises during wedging, can lead to overestimating LA pressure. Careful release of the balloon can help obtain accurate waveforms.
• Safety precautions are crucial: never withdraw the catheter with an inflated balloon, as this can cause vessel damage and complications like hemoptysis or tricuspid valve injury.

Respiratory Variations & Measurement Considerations:

• Significant respiratory variations in RA, LA, and PAP are observed in patients with lung disease or obesity.
• Guidelines recommend measuring pressures, especially PAWP, at end expiration over at least four respiratory cycles without breath-holding to account for variability.
• When values appear inconsistent or have excessive variability, measuring left ventricular (LV) end-diastolic pressure can help validate PAWP readings.
• In cases of significant discrepancies, some centers may use electronic mean values, which carries a risk of underestimating PAWP.

“It is recommended that non-invasive aortic pressure and saturation (pulse oximetry) are documented since they cannot be measured invasively unless arterial access (or puncture) is obtained,” Dr. Dimopoulos and colleagues wrote.

Oxygen Saturation

While aortic saturations can be directly measured invasively through arterial blood gas (ABG) analysis, non-invasive methods like plethysmography are often preferred in practice due to ease of use and patient comfort. The authors discussed key considerations for interpreting these measurements, particularly when patients receive supplemental oxygen.

Non-invasive plethysmography is often used to estimate aortic saturations, providing a convenient and less invasive option compared with ABG. ABG analysis offers a precise measurement of aortic saturations but requires arterial access. Invasive measurement may be warranted in complex cases where accuracy is paramount, the authors wrote.

Regarding patients on supplemental oxygen, an inspired oxygen fraction (FiO₂) greater than 0.3 can lead to a significant amount of dissolved oxygen in the blood. The researchers wrote that this phenomenon should be factored into Fick calculations by directly measuring the partial pressure of arterial oxygen (PaO₂), adding that PaO₂ usually does not significantly change the final calculation.

Supplemental oxygen use can artificially increase oxygen saturations across all blood samples, complicating the interpretation of shunt fractions. This is because the elevated saturations may mask the differences between pulmonary and systemic circulations, leading to inaccuracies in determining the extent of any intracardiac shunting.

The authors noted that careful consideration of FiO₂ levels and potential discrepancies in saturation readings is crucial, especially in patients suspected of having shunts or receiving high levels of oxygen. Misinterpretation could lead to incorrect assessment of cardiac function and vascular resistance.

For patients on supplemental oxygen during RHC, the authors advised to account for FiO₂ adjustments in calculations, use PaO₂ measurements when appropriate, and remain cautious about potential overestimation of oxygen saturations. If feasible, temporarily reducing oxygen supplementation may allow for more accurate baseline measurements.

Additional Considerations

The authors discussed provocation tests and formulas for calculating pulmonary vascular resistance and cardiac output, among other measurements. They also offered insight into the usefulness of invasive hemodynamics in predicting mortality in patients with PAH.

Regarding cardiac catheterization procedures, Dr. Dimopoulos and colleagues concluded that “expertise and careful quality control are required to minimize complications and obtain reliable data.”