In an adult with stable or unstable coronary artery disease, how is fractional flow reserve (FFR) used to assess a coronary stenosis and what FFR values dictate revascularization versus medical management?

FFR Assessment of Coronary Stenosis

FFR is measured during maximal hyperemia by dividing the mean distal coronary pressure (Pd) by the mean aortic pressure (Pa), with an FFR ≤0.80 indicating hemodynamically significant stenosis requiring revascularization, while FFR >0.80 supports deferral to medical therapy alone. 1, 2

Measurement Technique

Procedural Steps:

• Position a pressure-sensitive coronary wire distal to the stenosis 1, 3
• Equalize pressures between the guiding catheter and pressure wire before advancing the wire 3
• Administer intracoronary nitrates prior to measurement 3
• Induce maximal hyperemia using adenosine (intravenous or intracoronary) 1
• Calculate FFR = Pd/Pa during steady-state hyperemia 1

Adenosine Administration:

• Intravenous route: Requires at least 1 minute to achieve steady-state hyperemia; use peripheral or central venous access with similar results 1
• Intracoronary route: Simpler and potentially less expensive; requires 60-100 mg for right coronary artery and 160-200 mg for left coronary artery 1
• Both routes show 92.9% classification agreement (Cohen's kappa = 0.887) 1

Critical Threshold Values

Primary Decision Point:

• FFR ≤0.80: Proceed with revascularization (Class I, Level A recommendation) 2, 3
• FFR >0.80: Defer revascularization and manage with optimal medical therapy 2, 3

Historical Context:

• The original ischemic threshold was FFR ≤0.75 based on non-invasive stress testing correlation 1
• The 0.80 threshold was adopted to increase sensitivity for reliably excluding functionally significant stenoses 1

Gray Zone (FFR 0.75-0.80):

• Affects approximately 10% of measurements 2
• Requires integration of additional clinical information including medical history, CAD characteristics, and myocardial territory at risk 1

Clinical Outcomes by FFR Value

Borderline Values (FFR 0.81-0.85):

• Approximately 25% of lesions in this range required subsequent revascularization during follow-up 1, 2
• Higher risk of progression compared to FFR >0.85 1, 2
• Consider intensified preventive pharmacotherapy even when deferring revascularization 2

Prognostic Gradient:

• Clinical events increase progressively as FFR declines, even within the traditionally "normal" range 2
• Lower FFR values (even >0.80) are associated with worse outcomes than near-normal values 2

Special Applications

Left Main Coronary Artery:

• FFR ≤0.80 should prompt revascularization (generally CABG) 2
• FFR >0.80 supports deferral with optimal medical therapy 2
• Class IIa, Level A recommendation for intermediate left main disease 2

Multivessel Disease:

• FFR-guided PCI results in significantly lower composite event rates (13.2%) compared to angiography-guided PCI (18.3%, P=0.02) 4
• Leads to fewer stents placed (1.9±1.3 vs 2.7±1.2, P<0.001) by identifying that 37% of angiographically significant lesions are not functionally significant 4

Technical Considerations and Pitfalls

Right Atrial Pressure:

• Theoretically, FFR calculation should be: FFRmyo = [Pd - Pv]/[Pa - Pv] 1
• In practice, venous pressure is not routinely measured and has minimal influence on FFR values or revascularization decisions 1, 2

Common Pitfalls:

• Catheter damping: Guiding catheter ventricularization can impair coronary flow during hyperemia; disengage catheter from ostium during measurement 3
• Pressure drift: Pull back sensor to equalize pressures if drift occurs 3
• Inadequate hyperemia: Allow sufficient time (≥1 minute) for steady-state conditions with intravenous adenosine 1

Equipment Requirements:

• Use guiding catheters without distal side holes for accurate measurements 3
• The 0.014-inch guide wire cross-sectional area is <10% of minimal lumen area for intermediate lesions, allowing reliable gradient measurement 2

Limitations

Acute Myocardial Infarction:

• FFR data in patients with acute or recent MI are limited 2
• Established criteria should not be extended to this specific patient subgroup 2

Diffuse Coronary Disease:

• Continuous pressure fall along arterial length requires careful interpretation 2
• FFR may underestimate the functional significance of diffuse disease 2