Cardiac CT Thresholds for Hemodynamically Significant Lesions

Established Anatomic Thresholds

• The American College of Cardiology recommends ≥70% diameter stenosis in non-left main coronary vessels as the threshold for revascularization when combined with symptoms or ischemia 1
• ≥50% diameter stenosis in left main coronary arteries warrants consideration for intervention 1
• 75% cross-sectional area reduction corresponds to 50% diameter stenosis and represents the critical point where blood flow begins to dramatically decrease 2

Critical Limitation: Anatomy Does Not Equal Physiology

• For stenoses between 40-70% diameter, only 31-35% are actually hemodynamically significant by FFR measurement 3
• The American College of Cardiology states that intermediate lesions (50-70%) require FFR assessment before intervention 4, 1, 5

Recommended Clinical Approach

• For stenoses 50-69% diameter, proceed to FFR measurement during catheterization (Class IIa recommendation) 4, 5
• FFR ≤0.80 indicates hemodynamically significant stenosis warranting intervention 1, 5

Common Pitfalls to Avoid

• Multiple stenoses have additive hemodynamic effects like resistors in series 6, 7
• Several lesions each measuring <50% individually may collectively cause significant flow limitation 6, 7

Special Considerations for Cardiac CT

• CT-FFR ≤0.75 suggests hemodynamically significant stenosis warranting invasive coronary angiography referral 8
• CT-FFR >0.80 indicates deferral of ICA is appropriate 8
• Presence of low attenuation (<30 HU), positive remodeling, or napkin-ring sign may warrant intervention even with intermediate stenosis 8

Ischemia Prevalence in Anatomical CAD by FFR

Evidence-Based Thresholds and Physiologic Significance

• Stenoses in the 25-50% range fall below the traditional intermediate threshold and are generally not expected to cause flow-limiting ischemia 9

Specific Data on Mild Stenoses

• The FAMOUS-NSTEMI trial enrolled patients with stenoses ≥30% diameter, providing data on the relationship between "mild" lesions and FFR, and acknowledges these lesions as "mild" and generally not flow-limiting 10

Clinical Decision Framework

• FFR measurement is generally not indicated for stenoses 25-50% diameter as these lesions rarely cause ischemia 9
• The European guidelines consider FFR assessment for stenoses ≥50% diameter (or ≥40% for some guidelines) 11
• An FFR ≤0.80 defines hemodynamically significant stenosis, applied to intermediate (50-70%) or higher grade lesions 12, 13

Practical Clinical Implications

• Patients with 25-50% stenosis range should receive aggressive risk factor modification and optimal medical therapy 11
• Revascularization of lesions without ischemia or FFR <0.80 is not recommended (Class III recommendation) 10
• A normal functional test (including FFR >0.80) is associated with <1% annual rate of cardiac death and MI 11