Fractional Flow Reserve (FFR) in Angioplasty

Definition and Measurement

• The European Society of Cardiology recommends FFR as a pressure-derived index that measures the maximum achievable blood flow in a coronary artery with stenosis, providing essential physiological assessment of coronary artery stenosis significance 1, 2
• FFR is calculated by dividing the mean coronary pressure distal to a stenosis (Pd) by the mean aortic pressure (Pa) during maximum hyperemia: FFR = Pd/Pa, requiring a pressure-sensitive coronary wire positioned distal to the stenosis 3
• For accurate measurements, maximum hyperemia must be achieved to minimize coronary resistance, creating an approximately linear relationship between perfusion pressure and blood flow, as recommended by the European Heart Journal 3

Clinical Significance and Cutoff Values

• The American Heart Association suggests that FFR provides well-defined cutoff values that distinguish normal from abnormal coronary flow with high specificity, with an established ischemic threshold of 0.75 4
• A "gray zone" exists between 0.75-0.80, affecting approximately 10% of measurements, and for clinical trials and contemporary practice, a single cutoff value of 0.80 is recommended to increase sensitivity in detecting functionally significant stenoses, as stated by the European Heart Journal and Circulation 3, 4

Advantages in Clinical Decision-Making

• The European Society of Cardiology states that FFR provides objective, lesion-specific assessment of stenosis severity that correlates with physiological significance rather than just anatomical appearance, and is reproducible with high spatial resolution and high specificity for identifying functionally significant stenoses 3, 4
• FFR-guided management in patients with stable coronary artery disease has received Class I and Class IIa guideline recommendations from the European Heart Journal, providing a valuable tool for clinical decision-making 1, 2

Applications in Angioplasty

• FFR may be used to guide patient selection for coronary revascularization, particularly for moderate-to-severe coronary lesions, as recommended by Circulation, and can serve as a marker of coronary device performance and provide clinical justification for repeat revascularization in trials 4
• FFR is particularly valuable for assessing isolated coronary stenosis of moderate severity, including left main coronary artery narrowing and jailed side branch lesions, as stated by Circulation 4

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, as recommended by Circulation 4
• Quality assurance requires standardized procedures, including proper pressure equalization and achievement of maximum hyperemia, as stated by Circulation 5

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, as noted by Circulation 4
• In diffuse coronary disease with continuous pressure fall along arterial length, interpretation of FFR requires careful consideration, as stated by Circulation, and while right atrial pressure should theoretically be included in the FFR calculation, it is often omitted in clinical practice as it has minimal influence on FFR values or revascularization decisions, as recommended by the European Heart Journal 3, 4

FFR‑Guided Decision‑Making in Intermediate Left‑Main Coronary Stenosis

Clinical Indications and Thresholds

• In patients with angiographically intermediate left‑main disease, an FFR ≤ 0.80 should prompt revascularization (generally coronary‑artery bypass grafting), whereas an FFR > 0.80 supports deferral of invasive treatment and management with optimal medical therapy. Class IIa, Level A evidence. 6

Prognostic Implications of Borderline FFR Values

• Among lesions with borderline FFR values (0.81–0.85), approximately 25 % required subsequent revascularization during follow‑up, indicating a higher risk of progression compared with higher FFR values. Observational cohort. [7][8]
• Clinical events rise as FFR declines; even within the traditionally “normal” range, lower FFR measurements are linked to worse outcomes than near‑normal values. Observational cohort. [7][8]
• Intensified preventive pharmacotherapy is recommended for patients whose FFR values are lower (even when >0.80) because prognosis deteriorates progressively with decreasing FFR. Observational cohort. [7][8]

Guideline Recommendations

• The American College of Cardiology/American Heart Association (ACC/AHA) gives FFR a Class IIa recommendation (Level A) for evaluating angiographic intermediate coronary lesions (50–70 % diameter stenosis) and guiding revascularization decisions in stable ischemic heart disease. 6
• The 2021 European Society of Cardiology (ESC) guidelines state that FFR is the current standard for functional assessment of lesion severity in patients with intermediate‑grade stenosis (40–90 %) when non‑invasive testing does not demonstrate ischemia. Class I, Level A. 9
• Revascularization of angiographically intermediate lesions without documented ischemia or without an FFR < 0.80 is not recommended (Class III, Level B). 10

Complementary Role of Intravascular Ultrasound (IVUS)

• IVUS is considered reasonable (Class IIa) for evaluating angiographically indeterminate left‑main coronary artery disease when functional data are ambiguous. Level A evidence. 6

Fractional Flow Reserve (FFR) Assessment of Coronary Stenosis

Definition and Decision Thresholds

• FFR is obtained during maximal hyperemia by dividing mean distal coronary pressure (Pd) by mean aortic pressure (Pa); an FFR ≤ 0.80 identifies a hemodynamically significant stenosis that warrants revascularization, whereas an FFR > 0.80 supports deferral to optimal medical therapy. 11

Measurement Technique

• The pressure‑sensitive coronary wire must be positioned distal to the target lesion before pressure recordings are taken. 12
• FFR is calculated as Pd/Pa during a steady‑state hyperemic period after adenosine administration. [12][13]

Adenosine‑Induced Hyperemia

• Intravenous adenosine achieves steady‑state hyperemia after at least 1 minute; peripheral or central venous access yields comparable results. [11][13]
• Intracoronary adenosine is simpler and less costly; typical doses are 60–100 mg for the right coronary artery and 160–200 mg for the left coronary artery. [11][13]
• Both intravenous and intracoronary routes produce a 92.9 % classification agreement (Cohen’s κ = 0.887) for FFR categorisation. [11][13]

Historical Evolution of the Ischemic Threshold

• The original ischemic cut‑off was FFR ≤ 0.75, derived from correlation with non‑invasive stress testing. [11][13]
• The threshold was raised to 0.80 to improve sensitivity for reliably excluding functionally significant stenoses. [11][13]

Gray‑Zone (FFR 0.75–0.80) Management

• When FFR falls within the 0.75–0.80 “gray zone” (≈10 % of measurements), clinicians should incorporate additional information such as patient history, coronary disease characteristics, and the myocardial territory at risk before deciding on revascularization. [11][13]

Clinical Outcomes for Borderline FFR Values (0.81–0.85)

• Approximately 25 % of lesions with FFR between 0.81 and 0.85 required subsequent revascularization during follow‑up. 14
• Lesions in this range exhibit a higher risk of disease progression compared with lesions having FFR > 0.85. 14

Technical Considerations – Venous Pressure Influence

• Theoretically, FFR should be corrected for right atrial pressure (Pv) using the formula FFR_myocardial = (Pd − Pv)/(Pa − Pv). [11][13]
• In routine practice, Pv is not measured because its omission has minimal impact on calculated FFR values and on revascularization decisions. [11][13]

Ensuring Adequate Hyperemia

• When using intravenous adenosine, a minimum infusion time of 1 minute is required to guarantee steady‑state hyperemia before recording Pd and Pa. [11][13]