What is CT FFR (FFR-CT)?
CT-derived Fractional Flow Reserve (FFR-CT or FFRCT) is a non-invasive computational technique that calculates the hemodynamic significance of coronary stenoses using standard coronary CT angiography images acquired at rest, without requiring additional imaging, medications, or stress testing. 1
How FFR-CT Works
FFR-CT uses computational fluid dynamics to simulate coronary blood flow and pressure gradients from the 3D anatomic data already obtained during a routine coronary CTA scan 1, 2. The technology models coronary flow dynamics based on the anatomical dataset acquired at rest, with FFR results simulated off-line after the CT scan is complete 1. This means no additional radiation exposure, contrast administration, or patient preparation beyond the standard coronary CTA is required 2, 3.
Clinical Purpose and Interpretation
FFR-CT addresses a critical limitation of coronary CTA: while CTA excels at visualizing coronary anatomy, it cannot determine whether a stenosis is causing ischemia 1, 4. FFR-CT bridges this gap by providing functional information alongside anatomic data 1.
Interpretation Thresholds:
- FFR-CT > 0.80: Normal, no hemodynamically significant ischemia 2
- FFR-CT 0.76-0.80: Borderline, clinical context determines management 2
- FFR-CT ≤ 0.75: Abnormal, indicates hemodynamically significant stenosis 2
FFR-CT values are measured 2 cm distal to a stenotic lesion to evaluate lesion-specific ischemia 2.
Diagnostic Performance
FFR-CT significantly improves diagnostic accuracy over coronary CTA alone (84% vs 59%), particularly by improving specificity 1. The American College of Radiology guidelines report:
- Sensitivity: 85-93% at per-patient level, 85-89% at per-vessel level 1
- Specificity: 65-82% (substantially higher than CTA alone at 32-46%) 1
- Positive Predictive Value: 74% 1
- Negative Predictive Value: High, supporting safe deferral of invasive angiography 1
FFR-CT correctly reclassified 68% of false-positive CTA results as true negatives, establishing its role as a gatekeeper to cardiac catheterization 1.
Clinical Applications and Benefits
Primary Use Case:
FFR-CT is most valuable for patients with intermediate-range coronary stenosis (typically 50-70%) on CTA where the functional significance is uncertain 1, 4. It helps differentiate patients who can be safely managed medically from those requiring invasive coronary angiography and potential revascularization 1.
Prognostic Value:
The ADVANCE trial with 5,083 patients demonstrated that negative FFR-CT values are associated with favorable prognosis, with trends toward lower major adverse cardiac events and reduced cardiovascular death or myocardial infarction 1.
Impact on Clinical Decision-Making:
- Reduces unnecessary invasive angiography by identifying non-ischemic stenoses 1
- Guides revascularization decisions by coupling anatomic and functional data 1
- Suitable for diagnosing and guiding revascularization even in advanced multivessel disease 1
Important Limitations and Contraindications
Technical Limitations:
FFR-CT analysis cannot be performed in approximately 17% of cases due to inadequate image quality 5. The European Society of Cardiology notes that misalignment artifacts significantly impair FFR-CT sensitivity (43% vs 86% without artifacts) and overall accuracy (56% vs 71%) 6.
Patient Preparation Matters:
- Beta-blocker administration before CTA improves FFR-CT specificity (51% vs 66%, p=0.03) with lower bias 6
- Nitroglycerin pretreatment within 30 minutes of CT improves specificity (54% vs 75%, p=0.013) 6
Validated Only for Native Coronary Arteries:
FFR-CT is NOT validated and should NOT be used in patients with: 1, 7, 2
- Coronary artery bypass grafts
- Coronary stents (in-stent assessment)
- Coronary anomalies
- Coronary dissection
- Transcatheter aortic valve replacement
- Unstable angina or acute/recent myocardial infarction
Other Technical Considerations:
- Coronary artery calcium does not significantly impair FFR-CT diagnostic performance 6
- Coronary motion artifacts do not significantly affect FFR-CT accuracy 6
- Gradually decreasing FFR-CT values without focal stenosis may indicate diffuse atherosclerosis rather than focal ischemia 2
Common Pitfalls to Avoid
Discordant anatomy-physiology findings: Abnormal FFR-CT can occur with mild stenosis, and normal FFR-CT can occur with severe stenosis 2. Always interpret FFR-CT in correlation with clinical presentation and anatomic CTA findings 2.
Borderline values (0.76-0.80): These require clinical judgment—many cases can be safely managed with medical therapy rather than automatic referral for invasive procedures 2.
Limited evidence in acute settings: Most FFR-CT evidence comes from stable coronary artery disease patients, with limited data for acute chest pain in emergency departments 7.
Lack of standardization: Multiple computational approaches exist without standardization across platforms, though this is primarily a research concern 7.