What
is FFR?
Fractional Flow Reserve, or FFR, is a guide wire-based procedure
that can accurately measure blood pressure and flow through a specific
part of the coronary artery. FFR is done through a standard diagnostic
catheter at the time of a coronary angiogram (a.k.a. cardiac catheterization).
The measurement of Fractional Flow
Reserve has been shown useful in assessing whether or not to perform
angioplasty or stenting on "intermediate" blockages.
The
point of opening up narrowings or
blockages in
the coronary arteries is to increase blood flow to the heart.
But a number of studies have shown that if a "functional measurement",
such as Fractional Flow Reserve, shows that the flow is not significantly
obstructed,
the blockage or lesion does not need to be revascularized (angioplasty) and
the patient can be treated safely with medical therapy
How Can FFR Affect Treatment of the Patient?
For
example, a lesion measures 50% on the coronary angiogram. The patient
hasn't
experienced
symptoms,
like angina or chest pain. Nonetheless the lesion can be seen clearly
on the TV monitor in the cath lab. The cardiologist (and patient)
may
be tempted to stent the lesion (a.k.a. the stenosis) for any number
of reasons. After all, there's a blockage there -- why not take
care of it?
This
reaction has been referred to in the medical literature as the
"oculo-stenotic reflex" -- you see a stenosis, so you open it
up and stent it.
However, a few minutes of measurement with a special guide wire
may reveal that an intervention won't have a significant impact
on this particular blockage. Being able to better select cases
not only saves health care costs, but contributes to more appropriate
patient care.
Recent studies, such as the COURAGE trial, have
re-emphasized what all current medical guidelines recommend: that
for low risk patients, even those experiencing angina,
optimal
medical
therapy should be the initial treatment. For those patients whose
disease progresses, or for whom chest pain is not alleviated, revascularization,
either through angioplasty and stenting or surgery, should be performed.
Fractional Flow Reserve can be a significant tool to help physicians
in deciding whether to intervene or not.
Furthermore, studies such as DEFER, or published
in the European Heart Journal, show
that patients who have been screened out of angioplasty by using
FFR have not experienced an increase in adverse outcomes. And in
these studies, two-thirds of the patients were judged not to
need an intervention with balloons or stents.
ComboMap® Pressure
and Flow System image,
courtesy Volcano Corporation
How Does Fractional
Flow Reserve Work?
A very thin guide wire is inserted through a
standard 4F or 5F diagnostic catheter during an angiogram. Because
of the smaller size catheter necessary, this can be done as an
outpatient procedure.
The special guide wire crosses the lesion and
is able to measure the flow and pressure of the blood. Results
are displayed on a special monitor (left) along with the "FFR value".
Studies have shown that an FFR value less than 0.75 or 0.80 corresponds
to inducible ischemia, and most likely will require interventional
treatment. Blockages that score above this threshold can be safely
and adequately treated by medical therapy without the need for
angioplasty.
Is Fractional Flow Reserve a New Technology?
The concept of measuring the blood flow across a blocked area or
stenosis is as old as coronary angioplasty itself. The first
balloon catheters invented by Dr. Andreas Gruentzig included
a a special lumen (or channel) to measure pressures at the proximal
and distal ends. The waveforms were then displayed on a monitor
in
the cath
lab. The greater the distance between the two pressures, the
greater the blockage. Dr. Gruentzig would inflate the balloon
several times, until he was able to get the two pressures close
to each other, indicating that the blockage was now sufficiently
open.
But to read the pressures, the balloon
needed an extra lumen, which made the balloon too large to get through
very tight lesions or into smaller arteries. Lower profile balloons
were invented, but they could not measure pressures,
so this concept of measuring pressures virtually disappeared, to the
chagrin of a number of cardiologists.
Today, however,
newer devices that use Doppler and other technologies allow these
measurements using only a .014" guide
wire -- no balloon needed.
