Can fractional flow reserve (FFR) be determined during cardiac catheterization?

Fractional Flow Reserve Determination During Cardiac Catheterization

Yes, fractional flow reserve (FFR) can be determined during cardiac catheterization using a pressure wire to measure the ratio of distal coronary pressure to aortic pressure during maximal hyperemia. 1

What is FFR?

• FFR is a well-validated, accurate, and objective index for assessing lesion-specific physiological stenosis severity and predicting long-term outcomes 1
• FFR measures the maximum achievable myocardial blood flow in the presence of a coronary artery stenosis as a percentage of the maximum blood flow in a hypothetically normal artery 1
• The normal value of FFR is 1.0 for every patient and every coronary artery 1

How FFR is Measured During Cardiac Catheterization

The standardized procedure for FFR measurement includes:

1. Catheter Selection: Guiding catheters without distal side holes are required for research measurements, though diagnostic catheters are technically feasible 1

2. Pressure Wire Insertion:

   • Insert the pressure sensor guide wire into the guide catheter 1
   • Equalize the pressures registered by the guiding catheter and pressure wire 1

3. Wire Advancement:

   • Advance the pressure wire sensor to the distal two-thirds of the coronary artery, at least 2-3 cm distal to the index lesion 1
   • Document the final position angiographically 1

4. Inducing Maximal Hyperemia:

   • Administer intracoronary nitrates (2 mg isosorbide dinitrate or 200 μg nitroglycerin) to abolish epicardial vasoconstrictor tone 1
   • Induce maximal hyperemia with intravenous adenosine at 140 μg/kg/min for at least 2 minutes 1

5. FFR Calculation:

   • FFR is calculated as the ratio of distal coronary pressure (Pd) to aortic pressure (Pa) at maximal hyperemia 1
   • The nadir of Pd/Pa ratio during hyperemia represents the FFR value 1

6. Pullback Assessment:

   • If needed, perform a pullback curve to determine the exact location of the lesion responsible for ischemia 1
   • This can differentiate focal from diffuse disease 1

7. Signal Drift Check:

   • Pull back the wire to verify equal pressure signals at the end of the procedure 1
   • If difference is ≤5 mmHg, account for it in the final FFR calculation 1
   • If difference is >5 mmHg, repeat the measurement 1

Clinical Significance and Thresholds

• An FFR ≤0.75 is associated with inducible ischemia (specificity 100%) 1
• An FFR ≥0.80 indicates absence of inducible ischemia in most patients (sensitivity 90%) 1
• For research purposes, a single cutoff value of 0.80 is proposed 1
• The "gray zone" between 0.75 and 0.80 (approximately 10% of measurements) requires clinical judgment 1

Potential Pitfalls and Artifacts

Several technical issues can affect FFR measurement accuracy:

1. Catheter Ventricularization/Damping:

   • The guiding catheter can impair coronary flow during hyperemia 1
   • Solution: Disengage the guiding catheter from the ostium during measurement while continuing adenosine infusion 1

2. Pressure Signal Drift:

   • Can be detected by parallel pressure signals with similar morphology throughout diastole and systole 1
   • Solution: Pull back the sensor to equalize pressures and repeat measurements 1

3. Diffuse Disease vs. Focal Lesions:

   • Pullback tracing helps differentiate between diffuse disease (gradual pressure increase) and focal lesions (abrupt changes) 1

4. Pseudostenosis:

   • Can occur in tortuous vessels where the wire itself creates artifacts 1
   • May render FFR measurements uninterpretable 1

5. Wire Position:

   • Diagnostic performance is highest when measured 1-2 cm distal to the stenosis rather than at far distal segments 2

Advantages of FFR

• High reproducibility and low intra-individual variability 1
• Independent of gender, CAD risk factors, heart rate, blood pressure, and contractility 1
• Provides a well-defined cutoff value with a narrow "gray zone" 1
• Allows for physiological assessment of intermediate coronary stenoses that may appear ambiguous on angiography alone 3