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Concept and practical set-up of
CFR, FFR, IMR
Zsolt Piróth MD
Gottsegen György Hungarian Institute of Cardiology
We all love coronary angiography, but
– Intermediate lesions (30-70%)
– Ostial lesions
– Left main coronary artery disease
– Diffusely diseased vessels
– Complex lesions
– Sequental lesions
– Loose relationship between angiography and prognosis
– Even best flat panel has resolution limited to 3 line pairs
per mm, i. e. 9 line pairs or 9 pixels for a 3 mm vessel
– Coronary arteries are notoriously hard to image sharply:
they are small and mobile.
Limitations of coronary angiography
Circulation 1995; 92: 2333-42
What else than morphology?
What kind of a physiologic parameter truly reflects the
impact of a stenosis?
• Blood flow? – no meaning w/o the extent of
perfusion area
• Flow derived parameters? – dependent on perfusion
pressure
• Transstenotic gradient? – coronary blood flow is
often not representative of myocardial flow
Complaints of pt
Non-invasive tests
So, who do we believe?
Courtesy of Attila Kónyi, MD
The ideal parameter
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Reflects
Severity of the stenosis in
the subepicardial
coronary artery (PCI)
Amount of myocardium
perfused by the diseased
vessel
Full myocardial perfusion,
including collaterals
Inducible ischemia
FFR
FFRmyo
Circulation 1993; 87: 1354-67
Definition of FFRmyo
FFRmyo … is defined as the ratio of maximal
achievable flow in the myocardium supplied
by the stenotic vessel to the maximal
achievable flow in the same territory in the
hypothetical case that the vessel were
normal.
Circulation 1995; 92: 39-46
• Mathematics of FFRmyo
Assumptions:
1.
Resistances are constant and minimal
2.
CVP is negligible
E = mc2
Characteristics of FFRmyo
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Specific index of the lesion in the subepicardial vessel
„Pullback curve” conveys unparalelled spatial resolution
Independent form HR, BP and contractility
Normal value is 1,0 always and in all coronaries
Well defined cut-off value: (0,75 - ) 0,80
Reflects collaterals
Accounts for the amount of myocardium perfused by the
vessel
• Applicable both in single vessel disease and MVD (no need
for normal reference vessel)
• Measurement is simple, safe and possible in 99% of cases
NHJ Pijls, B de Bruyne (eds): Coronary Pressure
Evaluating FFRmyo
Sensitivity: 90%
Specificity: 100%
Practical assets of FFRmyo
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Helpful in the indication of PCI
Helps to avoid unnecessary interventions
Identifies the „culprit lesion”
Quality control of PCI, giving some prognostic
implications
• Highly reproducible
• Relatively cheap, easy to perform, steep learning
curve
NHJ Pijls, B de Bruyne (eds): Coronary Pressure
Practice of measuring FFRmyo
– Standard preparation for PCI (TF/TR, venous access, anticoagulation, optimal
GC, Y-connector)
– Set-up of Radi Analyzer® / Ilumien® / Quantien ®
– Flush PW, connect to interface then calibrate
– Zero aortic pressure signal
– Equalize pressure signals (Pa and Pd) when PW sensor is at the tip of the GC
/preferably in the aorta/
– Advance PW across the stenosis
– Induce MAXIMAL hyperemia (do not forget Ngl!)
– Measure FFR, perform pullback recording if necessary
– Perform PCI if indicated /possibility of measuring Pw, may not need any other
guidewire/
– Check post PCI FFR, perform pullback recording if necessary
– After pulling back the PW to the tip of the GC verify absence of pressure drift
Some practical tips
– Incorporate Analyzer into cath lab equipment (no
nuisance to measure anymore)
– Perform measurement systematically, step-by-step
– Do it always the same way
– Act according to the result (do not discredit your own
measurement)
– Make your coworkers understand what you are doing
(assistants, surgeons...)
– If possible, get access to adenosine infusion for i. v.
administration
FFR in critical anatomy
• ZI (Mrs. Tough MI Pt)
– 53-year-old lady
– Hx: hypertension, type II diabetes mellitus, s/p
nephrectomy
– March 4, 2006: anterior STEMI (3 hrs)
– Coronary angiography
– Echo: LVH, good LVF, anterior akinesis w/o thinning
ZI
RCA
Tecnic 3,0x15 mm
PCI of the LAD
ZI
RAO cranial
AP
Should we intervene?
Courage trial
NEJM 2007; 356: 1503-1516
Importance of ischemia
Courage trial: 314 pt w/NPS
Circulation 2008; 117: 1283- 1291
ZI: Left coronary artery
140 μg/kg/min iv adenosine
ZI: Right coronary artery
140 μg/kg/min iv adenosine
ZI
• No further treatment
• Pt continues to be symptom-free
Pull-back recording
– By inducing long-lasting hyperemia, one may slowly pull
the PW back under fluoroscopy and determine how
different segments of the vessel (lesions) contribute to
the resistance to flow.
– By doing this, we are offered a lesion-specific index of
ischemia
• By contrast, exercise ECG can be considered patient-specific
(unable to determine ischemia localization), SPECT can be held
vessel-specific.
– If an ischemic FFR value is obtained, and
revascularisation is performed, FFR should be
remeasured thereafter, because fixing one lesion may
unmask the physiological significance of another.
Two compartments
Epicardial Artery
Microvasculature
FFR
IMR
CFR
One word on CFR
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General principle of coronary thermodilution: F= V/Tmn
Since CFR= Fhyp/Fbas
CFR= Tmnbas/Tmnhyp
PW sensor acts as distal thermistor, PW shaft proximal thermistor
Mean transit times measured by 3 brisk injections of 3 ml saline
Issues with CFR:
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Highly dependent on resting flow
Not specific for epicardial stenosis
Normal value not clearly defined
Distance of the sensor from GC tip is important
Large sidebranches just proximal to distal stenosis
GC position crucial (stable but not too deep)
IMR
R= Pd-Pv/flow
– Since Flow ≈ 1/Tmn
IMR= Pd/(1/Tmn)
IMR= Pd x Tmn at maximal hyperemia
– Practical set-up identical to measuring simultaneous FFR and
CFRthermo
– Limitations:
• Somewhat dependent on distance of PW down the vessel
• Clinical value not established
Measurement of IMR
IMR = Pd x Th = 78 x 0,12 = 9,36