How do you measure aortic pressure and distal coronary pressure during Percutaneous Coronary Intervention (PCI) to calculate Fractional Flow Reserve (FFR)?

Measuring Aortic and Distal Coronary Pressure During PCI for FFR Calculation

Aortic pressure is measured via a fluid-filled guiding catheter connected to a standard pressure transducer, while distal coronary pressure is measured using a specialized 0.014-inch pressure wire with a sensor located 3 cm from the tip, and FFR is calculated as the ratio of mean distal coronary pressure (Pd) to mean aortic pressure (Pa) during maximal hyperemia induced by intravenous adenosine. 1

Equipment Setup and Preparation

Aortic Pressure Measurement System

• Use a standard fluid-filled pressure transducer connected to the guiding catheter for aortic pressure recordings 1
• Purge all air from the system meticulously and zero the catheter tubing system to atmosphere before starting 1
• Flush the guiding catheter with normal saline at least every 10 minutes to maintain optimal pressure waveform 1
• Remove all contrast medium from the catheter during zeroing steps, as contrast can subtly dampen the pressure waveform 1

Distal Coronary Pressure Measurement System

• Use a 0.014-inch pressure wire with a solid-state electronic sensor mounted 3 cm from the radiopaque tip 1
• Zero the pressure wire sensor ex vivo following manufacturer instructions before insertion 1
• The cross-sectional area of the sensor wire is negligible and does not significantly obstruct flow except in the most critical stenoses 1

Standardized 5-Step FFR Measurement Protocol

Step 1: Zero Both Pressure Systems

• Zero the guiding catheter pressure transducer to atmospheric pressure 1
• Zero the pressure wire sensor ex vivo per manufacturer protocol 1
• Ensure optimal aortic pressure waveform without damping or ventricularization 1

Step 2: Equalize Pressures In Vivo

• Advance the pressure wire sensor a few millimeters beyond the guiding catheter tip 1
• For aorto-ostial lesions, perform equalization with the catheter disengaged in the ascending aorta 1
• Equalize the pressures registered by both the guiding catheter and pressure wire at this position 1
• Document that both pressure signals are identical before proceeding 1

Step 3: Position the Pressure Wire Distally

• Advance the sensor to the distal two-thirds of the coronary artery, at least 2-3 cm distal to the index lesion 1, 2
• Document the final wire position angiographically 1
• Verify the wire tip rotates freely and no resistance is felt when torque is applied 1
• Note: Wire sensor location significantly impacts measurements—more distal positioning yields lower pressure readings 3

Step 4: Induce Maximal Hyperemia and Calculate FFR

• Administer intracoronary nitrates (isosorbide dinitrate 2 mg or nitroglycerin 200 μg) at least 2 minutes before FFR measurement to abolish epicardial vasoconstrictor tone 1
• Infuse intravenous adenosine at 140 μg/kg/min through a large-bore cannula for at least 2 minutes to achieve steady-state maximal hyperemia 1, 2
• Continuous IV adenosine infusion is preferred over intracoronary boluses, which can cause artifacts and provide only transient hyperemia 1
• Calculate FFR as the ratio of mean distal coronary pressure (Pd) to mean aortic pressure (Pa) at the nadir of hyperemia 1, 2
• FFR = Pd/Pa during maximal hyperemia 1, 2

Step 5: Verify for Signal Drift

• Pull the pressure wire back to the guiding catheter tip and verify equal pressures at the end of the procedure 1
• If drift is ≤5 mm Hg, account for this difference in the final FFR calculation 1
• If drift is >5 mm Hg, repeat the entire measurement 1
• Store all measurements on external media for quality review 1

Critical Technical Considerations

Avoiding Catheter-Induced Flow Impairment

• Watch for pressure damping or ventricularization of the aortic pressure waveform, which indicates the guiding catheter is obstructing coronary flow 1
• If damping occurs, gently disengage the guiding catheter from the ostium during measurement while continuing adenosine infusion 1
• This is the most common technical pitfall during FFR measurement 1, 2

Pressure Pullback Technique for Serial Lesions

• For diffuse disease or serial stenoses, perform a slow pullback during sustained hyperemia to identify the location of hemodynamically significant lesions 1
• Focal stenoses show abrupt pressure increases, while diffuse disease shows gradual pressure changes 1
• Obtain an angiogram before pullback and keep the image intensifier position fixed 1

Clinical Interpretation

FFR Thresholds

• FFR ≤0.75 indicates hemodynamically significant stenosis causing ischemia (specificity 100%) 1, 2
• FFR ≥0.80 indicates absence of inducible ischemia (sensitivity 90%) 1, 2
• The "gray zone" between 0.75-0.80 requires clinical judgment 2

Advantages of FFR Over Other Indices

• FFR has high reproducibility and is independent of heart rate, blood pressure, contractility, gender, and CAD risk factors 1, 2
• Unlike resting indices (instantaneous wave-free ratio), FFR requires hyperemia but provides superior diagnostic accuracy 4, 5
• FFR-guided PCI reduces adverse events compared to angiography-guided PCI 2

Common Pitfalls to Avoid

• Never use intracoronary adenosine boluses for FFR measurement—they create artifacts and transient hyperemia 1
• Avoid papaverine or sodium nitroprusside—they provide only transient steady state 1
• In tortuous vessels, the wire itself may create pseudostenoses rendering FFR uninterpretable 1, 2
• Remember that sensor location matters—measurements vary significantly with distance from the lesion, especially near cutoff values 3
• Ensure adequate hyperemia duration (minimum 2 minutes IV adenosine) before recording FFR 1