Fractional flow reserve (FFR) is a diagnostic technique used in
coronary catheterization
A coronary catheterization is a minimally invasive procedure to access the coronary circulation and blood filled chambers of the heart using a catheter. It is performed for both diagnostic and interventional (treatment) purposes.
Coronary cathet ...
. FFR measures pressure differences across a
coronary artery
The coronary arteries are the arterial blood vessels of coronary circulation, which transport oxygenated blood to the heart muscle. The heart requires a continuous supply of oxygen to function and survive, much like any other tissue or organ of ...
stenosis
Stenosis () is the abnormal narrowing of a blood vessel or other tubular organ or structure such as foramina and canals. It is also sometimes called a stricture (as in urethral stricture).
''Stricture'' as a term is usually used when narrowing ...
(narrowing, usually due to
atherosclerosis
Atherosclerosis is a pattern of the disease arteriosclerosis, characterized by development of abnormalities called lesions in walls of arteries. This is a chronic inflammatory disease involving many different cell types and is driven by eleva ...
) to determine the likelihood that the stenosis impedes oxygen delivery to the heart muscle (
myocardial
Cardiac muscle (also called heart muscle or myocardium) is one of three types of vertebrate muscle tissues, the others being skeletal muscle and smooth muscle. It is an involuntary, striated muscle that constitutes the main tissue of the wall of ...
ischemia
Ischemia or ischaemia is a restriction in blood supply to any tissue, muscle group, or organ of the body, causing a shortage of oxygen that is needed for cellular metabolism (to keep tissue alive). Ischemia is generally caused by problems ...
).
Fractional flow reserve is defined as the pressure after (distal to) a stenosis relative to the pressure before the stenosis.
The result is an absolute number; an FFR of 0.80 means that a given stenosis causes a 20% drop in
blood pressure
Blood pressure (BP) is the pressure of Circulatory system, circulating blood against the walls of blood vessels. Most of this pressure results from the heart pumping blood through the circulatory system. When used without qualification, the term ...
. In other words, FFR expresses the maximal flow down a vessel in the presence of a stenosis compared to the maximal flow in the hypothetical absence of the stenosis.
Procedure
During coronary catheterization, a
catheter
In medicine, a catheter ( ) is a thin tubing (material), tube made from medical grade materials serving a broad range of functions. Catheters are medical devices that can be inserted in the body to treat diseases or perform a surgical procedure. ...
is inserted into the
femoral (groin) or
radial arteries (wrist) using a sheath and guidewire. FFR uses a small sensor on the tip of the wire (commonly a
transducer
A transducer is a device that Energy transformation, converts energy from one form to another. Usually a transducer converts a signal in one form of energy to a signal in another.
Transducers are often employed at the boundaries of automation, M ...
) to measure pressure, temperature and flow to determine the exact severity of the
lesion
A lesion is any damage or abnormal change in the tissue of an organism, usually caused by injury or diseases. The term ''Lesion'' is derived from the Latin meaning "injury". Lesions may occur in both plants and animals.
Types
There is no de ...
. This is done during maximal blood flow (
hyperemia
Hyperaemia (also hyperemia) is the increase of blood flow to different tissues in the body. It can have medical implications but is also a regulatory response, allowing change in blood supply to different tissues through vasodilation (widenin ...
), which can be induced by injecting products such as
adenosine
Adenosine (symbol A) is an organic compound that occurs widely in nature in the form of diverse derivatives. The molecule consists of an adenine attached to a ribose via a β-N9- glycosidic bond. Adenosine is one of the four nucleoside build ...
or
papaverine
Papaverine (Latin '' papaver'', "poppy") is an opium alkaloid antispasmodic drug, used primarily in the treatment of visceral spasms and vasospasms (especially those involving the intestines, heart, or brain), occasionally in the treatment of ...
. A pullback of the pressure wire is performed, and pressures are recorded across the vessel.
When interpreting FFR measurements, higher values indicate a non-significant stenosis, whereas lower values indicate a significant lesion. There is no absolute cut-off point at which an FFR measurement is considered abnormal. However, reviews of clinical trials show a cut-off range between 0.75 and 0.80 has been used when determining significance.
Equation
Fractional flow reserve (FFR) is the ratio of maximum blood flow distal to a stenotic lesion to normal maximum flow in the same vessel. It is calculated using the pressure ratio
where
is the pressure distal to the lesion, and
is the pressure proximal to the lesion.
Rationale
The decision to perform a
percutaneous coronary intervention
Percutaneous coronary intervention (PCI) is a minimally invasive non-surgical procedure used to treat stenosis, narrowing of the coronary artery, coronary arteries of the heart found in coronary artery disease. The procedure is used to place and ...
(PCI) is usually based on angiographic results alone.
Angiography
Angiography or arteriography is a medical imaging technique used to visualize the inside, or lumen, of blood vessels and organs of the body, with particular interest in the arteries, veins, and the heart chambers. Modern angiography is perfo ...
can be used for the visual evaluation of the inner diameter of a vessel. In ischemic heart disease, deciding which narrowing is the culprit lesion is not always clear-cut. Fractional flow reserve can provide a functional evaluation by measuring the pressure decline caused by a vessel narrowing.
Advantages and disadvantages
FFR has certain advantages over other techniques to evaluate narrowed coronary arteries, such as coronary angiography,
intravascular ultrasound
Intravascular ultrasound (IVUS) or intravascular echocardiography is a medical imaging methodology using a specially designed catheter with a miniaturized ultrasound probe attached to the distal end of the catheter. The proximal end of the cathe ...
or
CT coronary angiography. For example, FFR takes into account collateral flow, which can render an anatomical blockage functionally unimportant. Also, standard angiography can underestimate or overestimate narrowing, because it only visualizes contrast inside a vessel. Finally, when compared to other indices of vessel narrowing, FFR seems to be less vulnerable to variability between patients.
Other techniques can also provide information which FFR cannot. Intravascular ultrasound, for example, can provide information on
plaque vulnerability, whereas FFR measures are only determined by plaque thickness. There are newly developed technologies that can assess both plaque vulnerability and FFR from CT by measuring the vasodilitative capacity of the arterial wall.
FFR allows real-time estimation of the effects of a narrowed vessel, and allows for simultaneous treatment with balloon dilatation and stenting. On the other hand, FFR is an
invasive procedure for which non-invasive (less drastic) alternatives exist, such as
cardiac stress test
A cardiac stress test is a cardiological examination that evaluates the cardiovascular system's response to external stress within a controlled clinical setting. This stress response can be induced through physical exercise (usually a treadmill) o ...
ing. In this test, physical exercise or intravenous medication (adenosine/dobutamine) is used to increase the workload and oxygen demand of the heart muscle, and ischemia is detected using
ECG
Electrocardiography is the process of producing an electrocardiogram (ECG or EKG), a recording of the heart's electrical activity through repeated cardiac cycles.
It is an electrogram of the heart which is a graph of voltage versus time of ...
changes or
nuclear imaging.
DEFER study
In the DEFER study, fractional flow reserve was used to determine the need for stenting in patients with intermediate single vessel disease. In stenosis patients with an FFR of less than 0.75, outcomes were significantly worse. In patients with an FFR of 0.75 or more however, stenting did not influence outcomes.
FAME study
The ''Fractional Flow Reserve versus Angiography for Multivessel Evaluation'' (FAME) study evaluated the role of FFR in patients with multivessel coronary artery disease.
In 20 centers in Europe and the United States, 1005 patients undergoing
percutaneous coronary intervention
Percutaneous coronary intervention (PCI) is a minimally invasive non-surgical procedure used to treat stenosis, narrowing of the coronary artery, coronary arteries of the heart found in coronary artery disease. The procedure is used to place and ...
with
drug eluting stent
A drug-eluting stent (DES) is a tube made of a mesh-like material used to treat narrowed arteries in medical procedures both mechanically (by providing a supporting scaffold inside the artery) and pharmacologically (by slowly releasing a phar ...
implantation were randomized to intervention based on angiography or based on fractional flow reserve in addition to angiography. In the angiography arm of the study, all suspicious-looking lesions were stented. In the FFR arm, only angiographically suspicious lesions with an FFR of 0.80 or less were stented.
In the patients whose care was guided by FFR, fewer stents were used (2.7±1.2 and 1.9±1.3, respectively). After one year, the primary endpoint of death, nonfatal
myocardial infarction
A myocardial infarction (MI), commonly known as a heart attack, occurs when Ischemia, blood flow decreases or stops in one of the coronary arteries of the heart, causing infarction (tissue death) to the heart muscle. The most common symptom ...
, and repeat
revascularization
In medical and surgical therapy, revascularization is the restoration of perfusion to a body part or organ that has had ischemia. It is typically accomplished by surgical means. Vascular bypass and angioplasty are the two primary means of r ...
were lower in the FFR group (13.2% versus 18.3%), largely attributable to fewer stenting procedures and their associated complications. There also was a non-significant higher number of patients with residual
angina
Angina, also known as angina pectoris, is chest pain or pressure, usually caused by insufficient blood flow to the heart muscle (myocardium). It is most commonly a symptom of coronary artery disease.
Angina is typically the result of parti ...
(81% versus 78%). In the FFR group, hospital stay was slightly shorter (3.4 vs 3.7 days) and procedural costs were less ($5,332 vs $6,007). FFR did not prolong procedure (around 70 minutes in both groups).
References
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Cardiology