Concept and practical set-up of CFR, FFR, IMR

Zsolt Piróth MDGottsegen 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

So, who do we believe?

Complaints of pt Non-invasive tests

Courtesy of Attila Kónyi, MD

The ideal parameterReflects

• 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

Circulation 1995; 92: 39-46

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.

Assumptions:

1. Resistances are constant and minimal

2. CVP is negligibleE = mc2

• Mathematics of FFRmyo

Characteristics of FFRmyo

NHJ Pijls, B de Bruyne (eds): Coronary Pressure

• 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

Specificity: 100%

Sensitivity: 90%

Evaluating FFRmyo

Practical assets of FFRmyo

NHJ Pijls, B de Bruyne (eds): Coronary Pressure

• 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

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 PCI of the LAD

Tecnic 3,0x15 mm

ZI

RAO cranial AP

Should we intervene?Courage trial

NEJM 2007; 356: 1503-1516

Importance of ischemiaCourage 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

CFRCFR

FFRFFR IMRIMR

Epicardial ArteryEpicardial Artery MicrovasculatureMicrovasculature

One word on CFR

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:• 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

IMR = Pd x Th = 78 x 0,12 = 9,36

Measurement of IMR