In a stable adult without unstable angina, recent myocardial infarction, left ventricular dysfunction, or extensive multivessel disease who has an intermediate (≈40‑70 % diameter) left main coronary artery stenosis, can fractional flow reserve be used to guide revascularisation, and what FFR cutoff indicates the need for intervention?

FFR-Guided Management of Intermediate Left Main Coronary Artery Stenosis

Yes, FFR can and should be used to guide revascularization decisions in intermediate left main stenosis, with an FFR ≤0.80 indicating the need for intervention (typically CABG), while FFR >0.80 supports deferral of revascularization with medical management. 1, 2

FFR Cutoff Values for Left Main Disease

The established FFR threshold for intervention is ≤0.80, which represents the standard cutoff used in contemporary clinical practice and trials. 2 This cutoff was selected to increase sensitivity for detecting functionally significant stenoses, though the original ischemic threshold was established at 0.75. 2

The Gray Zone (0.75-0.80)

• A "gray zone" exists between FFR values of 0.75-0.80, affecting approximately 10% of measurements. 2
• Patients with borderline FFR values (0.81-0.85) have higher rates of subsequent intervention—approximately one in four stenoses in this range required revascularization during follow-up. 1
• Clinical events increase as FFR decreases, with lower FFR values (even within the "normal" range) associated with worse outcomes compared to near-normal values. 1

Clinical Evidence Supporting FFR in Left Main Disease

Long-term outcomes data specifically for left main stenosis demonstrate the safety and efficacy of FFR-guided management:

• In 213 patients with angiographically equivocal left main stenosis, FFR-guided strategy showed 5-year survival of 89.8% in the nonsurgical group (FFR ≥0.80) versus 85.4% in the surgical group (FFR <0.80), with no significant difference (P=0.48). 3
• Event-free survival at 5 years was 74.2% versus 82.8% in nonsurgical and surgical groups respectively (P=0.50), demonstrating that deferral based on FFR >0.80 is safe. 3

Angiography Alone is Inadequate

Angiographic assessment of left main stenosis severity correlates poorly with functional significance:

• Percent diameter stenosis by quantitative coronary angiography showed only weak correlation with FFR (r=-0.38, P<0.001) with very large scatter. 3
• In 23% of patients with diameter stenosis <50% by angiography, the left main stenosis was hemodynamically significant by FFR. 3
• This discordance means angiography alone does not allow appropriate individual decision-making and often underestimates functional significance. 3

Guideline Recommendations

Current guidelines provide strong support for FFR use in intermediate stenoses:

• FFR has a Class IIa recommendation (Level of Evidence A) for assessing angiographic intermediate coronary lesions (50-70% diameter stenosis) and guiding revascularization decisions in stable ischemic heart disease. 1
• The 2021 ESC guidelines affirm that FFR is the current standard for functional assessment of lesion severity in patients with intermediate-grade stenosis (40-90%) without evidence of ischemia on non-invasive testing. 1
• Revascularization of angiographically intermediate lesions without ischemia or without FFR <0.80 is not recommended (Class III recommendation, Level of Evidence B). 1

Complementary Role of IVUS

IVUS provides additional anatomic information that may be valuable in left main assessment:

• IVUS is reasonable (Class IIa) for assessment of angiographically indeterminate left main CAD. 1
• IVUS minimum lumen area (MLA) <2.8 mm² correlates with FFR <0.75 (sensitivity 79.7%, specificity 80.3%), though vessel size must be considered. 4
• However, case reports suggest IVUS may reveal substantial narrowing even when FFR values fall in the gray zone (0.75-0.80), potentially prompting surgical revascularization. 5

Clinical Algorithm for Left Main Stenosis

When encountering intermediate left main stenosis (40-70% diameter):

1. Measure FFR using a pressure wire during maximal hyperemia (adenosine-induced). 2

2. If FFR ≤0.80: Proceed with revascularization, typically CABG given left main location. 3

3. If FFR >0.80: Defer revascularization and manage medically with optimal medical therapy. 3

4. If FFR 0.75-0.80 (gray zone): Consider IVUS for additional anatomic assessment, particularly if MLA <2.8 mm², which may favor revascularization despite borderline FFR. 4, 5

5. Prescribe more intensive preventative therapy for patients with lower FFR values (even if >0.80), as prognosis worsens progressively with decreasing FFR. 1

Important Caveats

• FFR data in patients with acute or recent myocardial infarction are limited, and established criteria should not be extended to this population. 2
• In diffuse coronary disease with continuous pressure fall, FFR interpretation requires careful consideration. 2
• The cross-sectional area of the 0.014-inch guide wire is <10% of minimal lumen area for intermediate lesions, allowing reliable gradient measurement. 2
• Proper technique requires standardized pressure equalization and achievement of maximum hyperemia for quality assurance. 2