In a development that researchers say is likely to
quell concerns about the value of costly
computed tomography scans to diagnose coronary artery
blockages, an international team led by
researchers at Johns Hopkins reports solid evidence that
the newer, more powerful 64-CT scans can
easily and correctly identify people with major blood
vessel disease and are nearly as accurate as
invasive coronary angiography.
Reporting in the New England Journal of
Medicine online Nov. 26, researchers at nine medical
centers say that the faster 64-CT scans were 93 percent as
precise as invasive conventional imaging,
better known as cardiac catheterization, and virtually 100
percent accurate in detecting people with
at least one artery dangerously clogged by the buildup of
cholesterol and plaque.
Comparison of CT and catheterization results also
showed for the first time that they were
equally useful in patients with heart attack symptoms, such
as chest pain and shortness of breath, for
predicting the need for cardiac bypass surgery or
angioplasty to restore blood flow. The CT scans
accurately predicted 84 percent of invasive procedures
performed, and catheterization predicted 82
percent. More than a quarter-million Americans undergo
coronary bypass surgery each year, and
another 1.2 million people undergo angioplasty.
Announcement of the latest findings was timed to
coincide with the annual meeting of the
Radiological Society of North America, after initial
results were reported last year at an annual
meeting of cardiologists.
Senior study investigator and Johns Hopkins
cardiologist Joao Lima says that 64-CT scans are
not a substitute for catheterization, but the scans, which
take between five and 10 seconds to
perform, are "an alternative diagnostic tool" physicians
can use to "rule in or rule out" coronary
blockages when other, more indirect tests for reduced blood
flow, such as cardiac stress testing, are
unclear or unsafe for a patient.
Cardiac catheterization, which also checks the
function of heart valves and muscle, takes
longer — between 30 and 45 minutes to perform, with
more than an hour for recovery. Potential
complications from the invasive procedure, although rare,
include infection, heart attack and stroke.
Lima, a professor of
medicine and
radiology at the Johns Hopkins University School of
Medicine and
its Heart and
Vascular Institute, says the 64-CT scans, introduced to
the United States and tested at
Johns Hopkins in 2005, could reduce by as much as one-fifth
the 1.3 million cardiac catheterizations
performed each year nationwide that show no blockages.
CT scans for heart disease, although not yet covered
by many private health plans, could also
serve as an alternative to cardiac stress testing, which
generally cannot be performed safely on the
weak and elderly because the test uses hard exercise to
speed up blood flow and measure heart
function.
Lima says that previous research had shown that older,
less powerful 16-CT scans were only a
quarter to a third as precise as the newer tests, "fueling
much-heated debate as to whether or not
use of the technology could ever be justified.
"But our latest findings weigh heavily in favor of the
more advanced 64-CT scans," he said,
citing additional study results showing that the scans
could pinpoint with 91 percent certainty the
precise artery blocked. At four times the strength of the
more widely available 16-CT scanner, the
64-CT scans, Lima said, "provided our first real view of
the whole picture of what is going on in the
artery, precisely where the blockage is, even if it is only
partially obstructed."
Lead study investigator and interventional
cardiologist Julie Miller says that the advanced
scanners are so good that physicians can for the first time
measure blockages in blood vessels as small
as 1.5 millimeters in diameter. Older 16-CT scanners, she
says, are best suited for looking inside
bigger arteries, those greater in diameter than 2
millimeters.
Each of the 291 men and women, all over the age of 40,
selected to participate in the new study
was already scheduled to have cardiac catheterization to
check for blocked arteries. Every
participant had a 64-CT scan prior to catheterization and
was then monitored through regular check-
ups, starting in 2005 and set to continue through 2009, to
identify who developed or did not develop
any heart problems, who required subsequent bypass surgery
or angioplasty and who did not need any
procedure.
Researchers found that 90 percent of the patients
without any major blockages were correctly
diagnosed with 64-CT scans.
The disadvantages of using 64-CT scans, Miller says,
are radiation exposure and the rare
potential in some people to have an allergic reaction or to
develop kidney problems resulting from the
contrast dyes injected into the body to enhance the
images.
"CT technology has come a long way in the last
decade," said Miller, the leader of angiographic
research and an assistant professor at Johns Hopkins. She
cites improvements that cut the average
amount of radiation exposure and time required for a CT
scan to less than 20 millisieverts with 16-CT
scanners (which took about 12 seconds to perform), on
average, to less than 15 millisieverts with 64-
CT devices (at close to six seconds) and less than 6
millisieverts with the 320-CT (at less than a
second.)
She says that the cost of the newer CT scans —
approximately $700 — compares favorably with
that of current nuclear stress testing for reduced blood
flow, in which radioactive dyes are used to
detect arterial clogs, at nearly $1,000.
In cardiac catheterization, a thin tube is threaded
into a blood vessel in the groin area to the
heart's arteries, where a dye is released to produce a
clear X-ray image of the beating heart and its
arterial blood supply. The procedure usually costs in
excess of $1,500.
In CT imaging, computer-driven machinery passes X-rays
through the body, producing digitized
signals from multiple angles that are detected and
reconstructed for a precise picture.
Miller points out that early detection of blockages is
critical to pre-empting a heart attack,
allowing time for drug therapy, angioplasty or heart bypass
surgery to be used to keep arteries open.
In coronary artery disease, hardened bits of fat and dead
tissue, called plaque, build up along the
inside wall of the blood vessels, impeding the body's
natural blood flow and leaving the narrowed
opening more vulnerable to formation of blood clots.
Lima says that the team's next steps are head-to-head
comparison studies using either CT or
nuclear stress testing, which gauges reduced blood flow in
parts of the heart to reveal clogging
arteries. Included in the next analysis will be scans
performed using an even more advanced scanner,
the 320-CT. The latest imaging device was also tested at
Johns Hopkins, in 2006, and it can obtain
images in less than a second, with significant reductions
in radiation exposure.
According to researchers, nearly 5,000 64-CT scanners
are installed worldwide, but not all the
centers where they're located are equipped to perform and
read cardiac CTs. Miller notes that special
training and certification are required for technicians and
physicians to accurately perform, read and
interpret the scanned images. The American Heart
Association and the American College of Cardiology
Foundation in 2005 jointly established training
guidelines.
The CT scanner used in the study was an Aquilion 64
multidetector CT scanner, manufactured
by Toshiba. Similar devices are manufactured by Siemens,
Phillips and General Electric. Toshiba
provided funding support for the study, called CORE-64 for
Coronary Artery Evaluation using 64-row
Multidetector Computed Tomography.
In addition to Lima and Miller, Johns Hopkins
researchers involved in this study were Armin
Zadeh, Ilan Gottlieb, Edward Shapiro, Albert Lardo, David
Bush, Christopher Cox and Jeffrey Brinker.