What is Fractional Flow Reserve (FFR) in angioplasty?

Fractional Flow Reserve (FFR) in Angioplasty

Fractional flow reserve (FFR) is a pressure-derived index that measures the maximum achievable blood flow in a coronary artery with stenosis expressed as a ratio of maximum achievable blood flow if that artery were normal, providing essential physiological assessment of coronary artery stenosis significance. 1

Definition and Measurement

• FFR is calculated by dividing the mean coronary pressure distal to a stenosis (Pd) by the mean aortic pressure (Pa) during maximum hyperemia (typically induced by adenosine): FFR = Pd/Pa 1
• FFR measurement requires a pressure-sensitive coronary wire that is positioned distal to the stenosis while simultaneously measuring aortic pressure 1
• For accurate measurements, maximum hyperemia must be achieved to minimize coronary resistance, creating an approximately linear relationship between perfusion pressure and blood flow 1

Clinical Significance and Cutoff Values

• FFR provides well-defined cutoff values that distinguish normal from abnormal coronary flow with high specificity 1
• The established ischemic threshold is 0.75, below which a coronary lesion is considered hemodynamically significant and associated with inducible ischemia 1
• A "gray zone" exists between 0.75-0.80 (affecting approximately 10% of measurements) 1
• For clinical trials and contemporary practice, a single cutoff value of 0.80 is recommended to increase sensitivity in detecting functionally significant stenoses 1

Advantages in Clinical Decision-Making

• FFR provides objective, lesion-specific assessment of stenosis severity that correlates with physiological significance rather than just anatomical appearance 1
• Visual or even quantitative coronary analysis (QCA) of stenosis severity correlates poorly with the physiological significance of lesions 1
• FFR is reproducible with high spatial resolution (a few millimeters) and has high specificity for identifying functionally significant stenoses 1
• FFR-guided management in patients with stable coronary artery disease has received Class I and Class IIa guideline recommendations 1

Applications in Angioplasty

• FFR may be used to guide patient selection for coronary revascularization, particularly for moderate-to-severe coronary lesions (50% diameter stenosis) 1
• FFR can serve as a marker of coronary device performance and provide clinical justification for repeat revascularization in trials 1
• FFR is particularly valuable for assessing isolated coronary stenosis of moderate severity, including left main coronary artery narrowing and jailed side branch lesions 1
• FFR should not be used as a marker of coronary device failure in patients with diffuse coronary atherosclerosis or serial stenoses within one coronary artery 1

Technical Considerations

• For lesions of intermediate angiographic severity, the cross-sectional area of the 0.014-inch guide wire is <10% of the minimal lumen area, allowing FFR to provide a true gradient that reliably reflects epicardial resistance 1
• Temporal drift in pressure measurements should be minimal (<5 mm Hg/h); if drift occurs, the sensor should be pulled back to the guiding catheter tip to equalize pressures and repeat measurements 1
• Quality assurance requires standardized procedures, including proper pressure equalization and achievement of maximum hyperemia 1

Limitations and Caveats

• FFR data in patients with acute or recent myocardial infarction are limited, and established criteria should not be extended to this specific patient subgroup 1
• In diffuse coronary disease with continuous pressure fall along arterial length, interpretation of FFR requires careful consideration 1
• While right atrial pressure (Pv) should theoretically be included in the FFR calculation [FFRmyo = (Pd-Pv)/(Pa-Pv)], it is often omitted in clinical practice as it has minimal influence on FFR values or revascularization decisions 1

FFR has transformed coronary intervention from an "operator-dependent" to a more objective "FFR-dependent" evaluation in intermediate coronary artery stenoses, improving patient outcomes by enabling more precise identification of functionally significant lesions requiring intervention 2.