Fractional Flow Reserve
Encyclopedia
Fractional flow reserve is a technique used in coronary catheterization
to measure pressure differences across a coronary artery stenosis
(narrowing, usually due to atherosclerosis
) to determine the likelihood that the stenosis impedes oxygen delivery to the heart muscle (myocardial ischemia
).
Fractional flow reserve is defined as the pressure behind (distal to) a stenosis relative to the pressure before the stenosis. The result is an absolute number; an FFR of 0.50 means that a given stenosis causes a 50% drop in blood pressure
. 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.
(groin) or radial arteries (wrist) using a sheath and guidewire. FFR uses a small sensor
on the tip of the wire (commonly a transducer) to measure pressure, temperature and flow to determine the exact severity of the lesion. This is done during maximal blood flow (hyperemia), which can be induced by injecting products such as adenosine or papaverine
. A pullback of the pressure wire is performed, and pressures are recorded across the vessel.
There is no absolute cut-off point at which FFR becomes abnormal; rather, there is a smooth transition, with a large grey zone of insecurity. In clinical trials however, a cut-off point of 0.75 to 0.80 has been used; higher values indicate a non-significant stenosis, whereas lower values indicate a significant lesion.
or CT coronarography. 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.
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.
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
ing. In this test, physical exercise or intravenous medication is used to increase the workload and oxygen demand of the heart muscle, and ischemia is detected using ECG
changes or nuclear imaging.
with drug eluting stent 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
, and repeat revascularization
were lower in the FFR group (13.2% versus 18.3%). There also was a non-significant higher number of patients of residual angina sufferers (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).
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 purposes....
to measure pressure differences across a coronary artery stenosis
Stenosis
A stenosis is an abnormal narrowing in a blood vessel or other tubular organ or structure.It is also sometimes called a stricture ....
(narrowing, usually due to atherosclerosis
Atherosclerosis
Atherosclerosis is a condition in which an artery wall thickens as a result of the accumulation of fatty materials such as cholesterol...
) to determine the likelihood that the stenosis impedes oxygen delivery to the heart muscle (myocardial ischemia
Ischemia
In medicine, ischemia is a restriction in blood supply, generally due to factors in the blood vessels, with resultant damage or dysfunction of tissue. It may also be spelled ischaemia or ischæmia...
).
Fractional flow reserve is defined as the pressure behind (distal to) a stenosis relative to the pressure before the stenosis. The result is an absolute number; an FFR of 0.50 means that a given stenosis causes a 50% drop in blood pressure
Blood pressure
Blood pressure is the pressure exerted by circulating blood upon the walls of blood vessels, and is one of the principal vital signs. When used without further specification, "blood pressure" usually refers to the arterial pressure of the systemic circulation. During each heartbeat, BP varies...
. 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 is inserted into the femoralFemoral
Femoral can refer to:* Femoral artery* Femoral vein* Femur* Femoral triangle* Femoral nerve...
(groin) or radial arteries (wrist) using a sheath and guidewire. FFR uses a small sensor
Sensor
A sensor is a device that measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument. For example, a mercury-in-glass thermometer converts the measured temperature into expansion and contraction of a liquid which can be read on a calibrated...
on the tip of the wire (commonly a transducer) to measure pressure, temperature and flow to determine the exact severity of the lesion. This is done during maximal blood flow (hyperemia), which can be induced by injecting products such as adenosine or papaverine
Papaverine
Papaverine is an opium alkaloid antispasmodic drug, used primarily in the treatment of visceral spasm, vasospasm , and occasionally in the treatment of erectile dysfunction...
. A pullback of the pressure wire is performed, and pressures are recorded across the vessel.
There is no absolute cut-off point at which FFR becomes abnormal; rather, there is a smooth transition, with a large grey zone of insecurity. In clinical trials however, a cut-off point of 0.75 to 0.80 has been used; higher values indicate a non-significant stenosis, whereas lower values indicate a significant lesion.
Rationale
The decision to perform a PCI is usually based on angiographic results alone. Angiography 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 provides 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 ultrasoundIntravascular ultrasound
Intravascular ultrasound 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 catheter is attached to computerized ultrasound equipment...
or CT coronarography. 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.
Other techniques can also provide information which FFR cannot. Intravascular ultrasound, for example, can provide information on plaque vulnerability
Vulnerable plaque
A vulnerable plaque is a kind of atheromatous plaque – a collection of white blood cells and lipids in the wall of an artery - that is particularly unstable and prone to produce sudden major problems, such as a heart attack or stroke.In many cases, a vulnerable plaque has a thin fibrous cap and a...
, whereas FFR measures are only determined by plaque thickness.
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
Cardiac stress test
Cardiac stress test is a test used in medicine and cardiology to measure the heart's ability to respond to external stress in a controlled clinical environment....
ing. In this test, physical exercise or intravenous medication is used to increase the workload and oxygen demand of the heart muscle, and ischemia is detected using ECG
Electrocardiogram
Electrocardiography is a transthoracic interpretation of the electrical activity of the heart over a period of time, as detected by electrodes attached to the outer surface of the skin and recorded by a device external to the body...
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 those patients with a stenosis with a FFR of less than 0.75, outcome was significantly worse. In patients with a FFR of 0.75 or more however, stenting did not influence outcomes. This suggests that FFR is a useful tool to gauge decision-making in this setting.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 interventionPercutaneous coronary intervention
Percutaneous coronary intervention , commonly known as coronary angioplasty or simply angioplasty, is one therapeutic procedure used to treat the stenotic coronary arteries of the heart found in coronary heart disease. These stenotic segments are due to the build up of cholesterol-laden plaques...
with drug eluting stent 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
Myocardial infarction
Myocardial infarction or acute myocardial infarction , commonly known as a heart attack, results from the interruption of blood supply to a part of the heart, causing heart cells to die...
, and repeat revascularization
Revascularization
Revascularization is "a surgical procedure for the provision of a new, additional, or augmented blood supply to a body part or organ." The term derives from the prefix re-, in this case meaning "restoration" and vasculature, which refers to the circulatory structures of an organ.Revascularization...
were lower in the FFR group (13.2% versus 18.3%). There also was a non-significant higher number of patients of residual angina sufferers (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).
External links
- Angioplasty.Org, Fractional Flow Reserve: An Overview
- Angioplasty.Org, Interview with Nico H. J. Pijls, MD, PhD about the FAME Study and Fractional Flow Reserve