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Imaging
Imaging Techniques for the Assessment of Coronary Flow Reserve
a report by
Mario Petretta,
1
Pierluigi Costanzo
1
and Alberto Cuocolo
2
1. Department of Clinical Medicine, Cardiovascular and Immunological Sciences;
2. Department of Biomorphological and Functional Sciences, University of Naples Federico II
Myocardial blood flow (MBF) must respond to changes in metabolic ventricular (LV) hypertrophy, diabetes mellitus or myocardial infarction
conditions and oxygen requests to meet the needs of myocytes, and will affect the CFVR value, independent of epicardial coronary artery
autoregulation plays a mayor role in the control of coronary disease (CAD).
18
Limitations of Doppler-tipped guidewire assessment
circulation.
1–3
It has been demonstrated that, as a coronary artery is of CFVR include the technical difficulty in obtaining reliable Doppler
progressively narrowed, resting flow does not change at first, but ultrasound scanning envelopes, variability in measurement with
maximal flow (achieved by injecting a vasodilator) decreases haemodynamic changes and significant overlap between normal and
progressively.
4,5
Coronary flow reserve (CFR) is the term used to abnormal measurements.
25,26
describe the amount of additional blood flow that can be supplied
to the heart above baseline blood flow. The absence of CFR implies Pressure-derived Method
maximal vasodilatation of the resistance vessels at rest and an inability With this method, CRF can be evaluated by using pressure-tipped
to further increase MBF. catheters that are small enough to pass coronary lesions. The use of
side-hole catheters is possible, but only if intravenous rather than
Different terms are used to describe CFR.
6,7
Absolute flow reserve is intracoronary vasodilators are used.
14,27
Two types of flow reserve,
the ratio of blood flow in a stenotic artery during maximal hyperaemia namely coronary FFR and myocardial FFR, can be estimated.
to blood flow in the same artery under resting conditions.
8,9
The Myocardial FFR is defined as the maximal flow in the myocardium
invasive Doppler-based technique, which measures coronary blood supplied by the stenotic artery, divided by the theoretical normal
velocity at rest and during hyperaemia, and positron emission maximal flow in the same region distribution in the absence of
tomography (PET), which measures absolute MBF at rest and during stenosis. Coronary FFR is defined as the maximal flow through
hyperaemia, are good examples of absolute CFR measurements. the stenosis divided by the maximal flow in the same artery without
Relative flow reserve is the ratio of hyperaemic flow in a stenotic artery stenosis, excluding collateral blood flow. The difference between
to hyperaemic flow in a normal artery.
10,11
Myocardial perfusion myocardial FFR and coronary FFR yields collateral FFR, the fractional
imaging by single-photon-emission computed tomography (SPECT) is collateral flow.
28
In an attempt to overcome the intrinsic limitations of
based on this concept of demonstrating ischaemia and identifying coronary reserve assessment by invasive techniques, technical
significant coronary artery stenosis. Fractional flow reserve (FFR) is a
term used to describe the ratio of the maximum achievable flow in
Mario Petretta is a Professor of Internal Medicine in the
the presence of a stenosis to the theoretical maximum flow in the
Department of Clinical Medicine at the University of Naples
same artery if it were normal.
12,13
This is the basis of the pressure- Federico II. He has authored many scientific publications, books
derived method that is the invasive method of choice for determining
and book chapters and has participated in many national and
international scientific meetings as a speaker. Professor
the significance of a stenosis of moderate severity.
14
It must be noted
Petretta is a member of several scientific societies and is a
that several factors influence CFR measurement, including the
referee for several scientific journals.
ability to achieve maximal coronary vasodilatation, heart rate and
myocardial contractility, right atrial pressure, serial coronary stenosis,
Pierluigi Costanzo is a Pre-doctoral Fellow in the Department
coronary resistance and coronary collateral circulation.
15–21
Each of
of Clinical Medicine of the University of Naples Federico II.
these factors has a different impact according to the method used for
He has written several scientific publications and
CFR evaluation.
participated in various national and international scientific
meetings as a speaker.
Intracoronary Doppler Ultrasound
Doppler guidewires make it possible to calculate coronary flow velocity
reserve (CFVR), which is the ratio between intracoronary
Alberto Cuocolo is a Professor of Diagnostic Imaging,
mean velocity under baseline conditions and after pharmacological
Director of the Specialisation School in Nuclear Medicine and
induction of maximum hyperaemia.
6
As blood velocity is proportional Chief of the Cardiac Imaging Clinical Centre at the University
to flow for a constant vessel area, CFVR may be calculated from the
of Naples Federico II. He is also President of the European
Association of Nuclear Medicine (EANM). Professor Cuocolo
hyperaemic flow divided by resting blood velocity in a vessel.
22,23
In
has authored over 200 publications and served on numerous
humans, a cut-off value of <2.0 was found to define a significant
Editorial Boards, and holds several positions in national and
international scientific organisations.
stenosis.
24
CFVR reflects the combined impact of epicardial and
microvascular resistance on limiting hyperaemic flow. Conditions
E:
cuocolo@unina.it
affecting myocardial or microvascular properties such as age, left
© TOUCH BRIEFINGS 2008 37
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