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.