FFR Cannot Be Used as a Direct Assessment Tool for Myocardial Viability
FFR is not designed to assess myocardial viability—it measures the physiological significance of coronary stenoses, not the viability of myocardium. However, FFR can serve as an indirect surrogate marker that complements viability testing in specific clinical scenarios, particularly in patients with prior myocardial infarction where revascularization decisions are being considered 1.
Understanding the Distinction
FFR measures the hemodynamic significance of a coronary stenosis by calculating the ratio of maximum achievable blood flow through a stenotic artery compared to a normal artery 2. This is fundamentally different from viability assessment, which determines whether dysfunctional myocardium retains metabolic activity and contractile reserve that could recover after revascularization.
What FFR Actually Tells You
- FFR ≤0.80: Indicates hemodynamically significant stenosis that limits blood flow
- FFR >0.80: Suggests the stenosis is not functionally significant
- In post-MI territories, a high FFR despite severe angiographic stenosis may indicate limited viable myocardium with reduced metabolic demands 3, 4
When FFR Can Provide Indirect Viability Information
Post-Myocardial Infarction Scenarios
In patients with prior MI and severe coronary stenosis, FFR can offer indirect clues about viability:
Lower FFR values (before PCI) correlate with greater myocardial viability 4. In a study of 26 patients with previous MI, those with viable myocardium had significantly lower FFR (0.57 ± 0.14) compared to those without viability (0.76 ± 0.12), despite similar angiographic stenosis severity 4.
The physiological rationale: Viable myocardium maintains metabolic demands and microvascular integrity, creating greater pressure gradients across stenoses during hyperemia. Non-viable scar tissue has minimal metabolic requirements and restricted microvascular beds, resulting in paradoxically higher FFR values despite severe anatomic stenosis 3.
Clinical Application Algorithm
For patients with prior MI and severe coronary stenosis:
If FFR is low (≤0.75-0.80) despite time elapsed since MI: This suggests preserved viable myocardium with ongoing metabolic demands → Consider revascularization 4, 5
If FFR is unexpectedly high (>0.80) with severe angiographic stenosis: This indicates restricted microvascular bed with limited viable myocardium → Defer revascularization and confirm with dedicated viability imaging 3
FFR correlates with functional recovery: Lower pre-PCI FFR values predict improvement in perfusion abnormalities after revascularization 4
The Complementary Strategy: FFR Plus Viability Testing
In surgically ineligible patients with extensive CAD, combining FFR with formal viability assessment provides the most rational approach 1. This strategy:
- Identifies which stenoses are hemodynamically significant (FFR)
- Determines which myocardial territories retain recovery potential (viability imaging)
- Limits unnecessary PCI-related complications (contrast nephropathy, radiation exposure) 1
Guideline Perspective on Viability Assessment
The evidence on routine viability testing remains controversial. The STICH viability substudy argued against using viability as the sole deciding factor for revascularization 1. However, viability assessment combined with anatomic and physiological data helps identify high-risk patients who benefit most from revascularization—specifically those with three-vessel disease, ejection fraction <27%, and end-systolic volume index >79 mL/m² 1.
Critical Limitations and Pitfalls
FFR Is Not a Viability Test
Do not use FFR as a replacement for dedicated viability imaging (PET, SPECT, cardiac MRI with late gadolinium enhancement, or dobutamine stress echocardiography) 6. FFR provides hemodynamic information that may correlate with viability but cannot directly visualize metabolic activity, contractile reserve, or scar burden.
Timing Matters
FFR measurements in acute MI settings have uncertain validity due to dynamic changes in both the culprit lesion and myocardial bed 7. Wait at least 5-7 days post-MI before using FFR to guide decisions about non-culprit lesions 7, 4.
The Paradox of High FFR in Infarcted Territories
A case report demonstrated a patient with severe LAD in-stent restenosis but FFR of 0.88, indicating non-significant physiology 3. Subsequent CMR confirmed extensive non-viable myocardium in the LAD territory. This paradoxically high FFR reflected the restricted microvascular bed and limited metabolic demands of infarcted tissue—not the absence of stenosis 3.
Practical Clinical Approach
When facing intermediate stenoses in patients with prior MI and reduced ejection fraction:
- Measure FFR to assess hemodynamic significance
- If FFR suggests significance (≤0.80) but viability is uncertain, obtain dedicated viability imaging before revascularization
- If FFR is non-significant (>0.80) despite severe angiographic appearance, this may indicate extensive non-viable myocardium—confirm with viability imaging before deferring revascularization
- Use the combination of FFR and viability data to guide revascularization strategy, particularly in patients with multivessel disease where complete revascularization may not be feasible 1
The bottom line: FFR measures stenosis physiology, not myocardial viability. While low FFR in post-MI territories may suggest preserved viability, and high FFR may indicate extensive infarction, these are indirect associations that require confirmation with dedicated viability imaging for definitive clinical decision-making 3, 4.