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Published on 07.08.2018
This review aims at addressing the physiological concepts and patient outcome evidence supporting the use of iFR and discuss the recent development of novel iFR-based applications allowing full integration of invasive coronary physiology in percutaneous coronary intervention planning strategy.
Table 1: Invasive physiological indices to assess the functional significance of coronary artery stenosis. | ||||
Index | Conditions of measurement | Interrogation level | Advantages | Disadvantages |
FFR | Hyperaemia | Epicardial level | • Established cut-off | • Need for hyperaemic agents • High inter-patient variability in microvascular resistance during vasodilatation induced by adenosine • Affected by haemodynamic variables |
iFR | Baseline | Epicardial level | • No need for hyperaemic agents • Established cut-off • Assessment of tandem and/or diffuse coronary lesions | • Requires proprietary software • Longer-term outcome results warranted • Outcome data in higher-risk patient subgroups needed |
Resting Pd/Pa | Baseline | Epicardial level | • No need for hyperaemic agents | • Not validated in randomised controlled trials |
Contrast FFR | Hyperaemia | Epicardial level | • Resting index correlating best with FFR | • No contrast dose established in randomised controlled trials • Contrast induces short-lived hyperaemia |
CFR | Hyperaemia | Epicardial level and microcirculation | • Prognostic marker | • Inability to differentiate the effects of microvascular dysfunction from effects of the epicardial lesion • Need for hyperaemic agents • Affected by haemodynamic variables |
HSR | Hyperaemia | Epicardial level | • Combination of flow and pressure measurement • Established cut-off | • Need for hyperaemic agents • Largely confined to research setting owing to difficulty of measurement technique |
BSR | Baseline | Epicardial level | • Combination of flow and pressure measurement • No need for hyperaemic agents | • No established cut-off • Less accurate than HSR • Largely confined to research setting owing to difficulty of measurement technique |
BSR: basal stenosis resistance; CFR: coronary flow reserve; FFR: fractional flow reserve; HSR: hyperaemic stenosis resistance; iFR: instantaneous wave-free ratio; Pd/Pa: ratio of the mean distal coronary pressure to the mean proximal coronary pressure. |
Table 2: Summary of FFR pivotal patient outcome trials. | ||||||||
Trial | Study question | Study population | Patients (n) | Patients in the coronary physiology-guided group (n) | Study primary endpoint | FFR cut-off for treatment | Mean FFR values | Conclusion |
DEFER [6] | Safety of deferral of PCI in patients with FFR >0.75 | Stable CAD | 325 | 325 | MACE1 at 4 months | ≤0.75 | • Defer group: 0.87 ± 0.07 (n = 91) • Performance group: 0.87 ± 0.06 (n = 90) • Reference group: 0.56 ± 0.16 (n = 144) | Deferral of PCI in lesions with FFR >0.75 is safe |
FAME [8] | Efficacy of FFR-guided PCI vs angiography alone-guided PCI | Multivessel stable CAD / ACS with non-culprit stenosis | 1005 | 509 | MACE2 at 12 months | ≤0.80 | • Overall cohort: 0.71 ± 0.18 • Ischaemic lesions: 0.60 ± 0.14 • Non-ischaemic lesions: 0.88 ± 0.05 | FFR-guided PCI is superior to angiography alone-guided PCI |
FAME 2 [9] | FFR-guided PCI + OMT vs OMT alone in patients with FFR ≤0.80 | Multivessel stable CAD | 1220 | 1220 | MACE3 at 24 months (trial prematurely stopped at 7-month follow-up) | ≤0.80 | • FFR guided PCI + OMT: 0.68 ± 0.10 • OMT alone: 0.68 ± 0.15 | FFR guided PCI + OMT reduces ischaemic outcomes compared with OMT alone |
Total | 2550 | 2054 | ||||||
ACS: acute coronary syndrome; CAD: coronary artery disease; FFR: fractional flow reserve; MACE: major adverse cardiac events; OMT: optimal medical treatment; PCI: percutaneous coronary intervention. 1 Composite of all-cause mortality, myocardial infarction, CABG, coronary angioplasty, and any procedure-related complication necessitating major intervention or prolonged hospital stay. 2 Composite of death, myocardial infarction, and any repeat revascularisation. 3 Composite of death from any cause, non-fatal myocardial infarction, or unplanned hospitalisation leading to urgent revascularisation. |
Table 3: Summary of pivotal iFR patient outcome trials. | |||||||||||
Trial | Study population (n) | Patients in the coronary physiology-guided group (n) | Mean FFR value | Mean IFR value | Patients deferred by FFR (n, % total assessed) | Patients deferred by IFR (n, % total assessed) | MACE rate in the FFR arm (%) | MACE rate in the IFR arm (%) | Hazard ratio (95% confidence interval) | p-value for superiority | p-value for noninferiority |
DEFINE-FLAIR [29] | 2492 | 2492 | 0.83 ± 0.09 (n = 1250) | 0.91 ± 0.09 (n = 1242) | 583 (46.6) | 652 (52.5) | 7.0 | 6.8 | 0.95 (0.68–1.33) | 0.78 | <0.001 |
iFR-SWEDEHEART [30] | 2037 | 2037 | 0.82 ± 0.10 (n = 1019) | 0.91 ± 0.10 (n = 1018) | 438 (43.5) | 476 (46.7) | 6.1 | 6.7 | 1.12 (0.79–1.58) | 0.53 | 0.007 |
Total | 4529 | 4529 | |||||||||
FFR: fractional flow reserve; iFR: instantaneous wave-free ratio; MACE: major adverse cardiac events, defined as a composite of death from any cause, non-fatal myocardial infarction, or unplanned revascularisation, at 12 months. |
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