Fractional Flow Reserve

Fractional Flow Reserve

Interventional Conference

Fundamentals

• Supply and Demand Equation of normal coronary physiology:

– Myocardial Flow will increase to meet demand and is influenced by:

• Heart Rate• LV wall stress• Contractility

Fundamentals

• Sources of perfusion of a vessel:– Epicardial – Myocardial – Collaterals

As per equation stenosis physiology is very flow dependent

• Doppler guidewire sends out 12-15MHz signal reflecting off moving Red Cells

• Measures velocities rather than actual flow – changes in vessel diameter therefore become important

Coronary Flow Reserve

Adenosine given

CFR Definition:

Coronary Flow Reserve

=

Ratio of maximal Flow / resting Flow

Hyperemic to Resting flow ratio and normally greater > 2

CFR

• Normal CFR implies that resistances across epicardial vessels and

microcirculation are low (normal)

• An abnormal CFR is therefore unable to distinguish microvascular impedance to

epicardial impedance due to atherosclerotic disease

Relative Coronary Flow Reserve

Ratio of 2 CFR = One in a target vessel/One in a normal vessel

Assumes basal flow is similar and therefore eliminates effect of the microcirculation

Also derived by separate doppler measurements

Assumes normal vessel is truly “normal”, therefore clinically not very useful

Intra-Coronary FFR

• Lesions produce energy loss by friction, separation and turbulance

• Energy is taken out as heat and pressure loss occurs

FFR=

Maximal Flow in Target artery / Flow in the same artery before the stenosis

Derived by pressure distal to the stenosis and aorta at the time of maximal hyperemia induced by adenosine

FFR differs from CFR in 3 ways

FFR is unaffected by changing the basal flow parameters

FFR is unaffected by systemic pressure

Hypertension decreases CFR

FFR is unaffected by hemodynamics

Increased contractility increases CFR

Tachycardia will increase CFR

Drugs used to induce hyperemia

Drug Dose Onset ½ Life Side E.

Papaverine IC

15mg LCA

10mg RCA

30 – 60 s 2 min QT prolong

TdP

Adenosine

IV

140mcg/kg/min

60 - 120 s 1 – 2 min Hypotension

CP

Avoid in asthma

Adenosine

IC

>30 LCA

24-36 RCA

5 – 10s 0.5 – 1 min AV Block in dominant artery

Repeated in escalating doses

Dobutamine

IV

20 - 40 g/kg/min

60 -120 s 3 – 5 min Tachycardia

Elev. BP

Nitroprusside IC

0.3-0.9 g/kg 20 s 1 min Dec. BP

FFR vs. IVUS vs. Spect

Conclusion

• FFR is comparable to IVUS and SPECT imaging

• FFR < 0.75: – Specificity 100%– Sensitivity 88%– PPV 100%– Accuracy 93%

Radi Wire

Handling characteristic almost similar to standard guidewires

Compatible with monorail balloon catheter systems

Intermediate lesions with Normal FFR

Importance of lesion assessment

Mild Angiographic disease with positive FFR

Angiographically unremarkable LAD in patient with angina

Area with significant FFR reduction identified with pressure wire assessment

Serial Stenosis and Diffuse Disease

Multiple sequential lesions:

Can be assessed by a gradual pull back and guide intervention

Illustrated are a significant step up at the distal and proximal stenosis

Mibi Spect is usually unable to differentiate between severe stenosis in a single vessel

Multivessel Disease

• Number of small studies examined tailored approach selective PCI for hemodynamically significant stenosis + medical therapy vs. CABG

• After 2 years follow up no difference in event free survival with decreased repeat revascularization compared to standard trials

Considerations

FFR = 0.94

FFR with ostial lesions

• No indication for stenting for ostial lesions with normal FFR

• Many case reports on FFR measurements in jailed sidebranches after bifurcation stenting

• No studies on the validity of FFR in this lesion subset

FFR for Stent Deployment

-FFR does not help with stent implantation is because the stent implantation relies on the anatomic structures surrounding the stent.

-However, FFR does provide prognosis and can identify gross under deployment in many patients.