64-Slice CT Heart Scan Gets High Marks As Test for Blocked Arteries
Drs.
Joao Lima and Julie Miller of
Johns Hopkins Medical Center
discuss the results of the CorE 64 Study and future applications
for 64-slice CT angiography in the detection of coronary
artery
disease
November 5, 2007 -- A study by an international
team of cardiac imaging specialists, led by researchers at
Johns Hopkins, concludes that sophisticated computed tomography
(CT) scans of the heart and its surrounding arteries are almost
as reliable and accurate as more invasive procedures to check
for blockages.
Researchers say the newer, 64-slice CT
scans, first introduced in the United States in 2005 and
initially tested at Johns
Hopkins, won't replace the need for inspecting arteries by
cardiac catheterization, also known as coronary angiography,
but the scans will help cardiologists more quickly rule out
those who can skip the more invasive procedures. Studies
suggest that as much as 25 percent of the 1.3 million cardiac
catheterizations performed each year in the United States
may be unnecessary.
The latest study, using Toshiba's Aquilion
64 CFX multislice CT scanner, also showed that early detection
with 64-CT
is
a good predictor of who will need angioplasty or coronary bypass
surgery to open up new blood supply routes to the heart.
Results showed that on average 91 percent of patients with blockages
were detected by 64-CT and that the scans were able to diagnose 83
percent of patients without blockages. This reliability, researchers
say, allows them to accurately identify patients who need angioplasty
or bypass surgery. More than a quarter million Americans undergo
coronary bypass surgery each year.
In the study, investigators selected 291 men and women over the
age of 40 who were already scheduled to have cardiac catheterization
to check for blocked arteries. Each underwent a 64-CT scan prior
to catheterization. Participants were then monitored through regular
check-ups to identify who developed or did not develop coronary artery
disease and who required subsequent bypass surgery or did not need
surgery.
After the first year of monitoring, to continue annually until 2009,
researchers found that results from 64-CT scans matched up 90 percent
of the time with results from invasive catheterization in detecting
patients with blockages.
In other measures, researchers found that 64-CT scans were 83 percent
to 90 percent accurate, while tests using older, 16-CT scans were
in some instances only 20 percent to 30 percent as precise.
"This study is the first step to realizing the full potential
of CT imaging in predicting coronary artery disease, and these scans
complement the arsenal of diagnostic tests available to physicians
to prevent heart attacks," says cardiologist Julie Miller, M.D.,
who led the study at Johns Hopkins.
The new study also suggests that the new scanners, four times quicker
than the more widely used 16-CT, may be a good alternative to cardiac
stress testing, which evaluates heart function by measuring the effects
of hard exercising. Exercise stress testing enerally cannot safely
be performed on the weak and elderly.
"Use of 64-CT scans will dramatically improve our ability to
detect and treat people with suspected coronary disease and chest
pain much earlier in their disease," says cardiologist João
Lima, M.D., senior investigator to the team whose findings will be
presented Nov. 5 at the American Heart Association's (AHA) annual
Scientific Sessions in Orlando, Fla. "Cardiac catheterization
is still the gold standard for evaluating clogged arteries, but our
results show that this test could easily be the best backup or alternative."
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. In CT imaging, computer-driven machinery
passes X-rays through the body, producing digitized signals or "slices" that
are detected and reconstructed for a precise picture.
Blocked arteries are the most frequent trigger
of heart attack, says Lima, an associate professor
of medicine and radiology at the Johns Hopkins University School
of Medicine and its Heart Institute. The latest estimates from the
AHA show that one in five deaths in the United States each year is
due to coronary heart disease (653,000 deaths in 2004), including
157,000 who die from heart attack.
Miller, an assistant professor at Johns Hopkins,
says 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 ranging in diameter from 2 millimeters to
4.5 millimeters, and to calculate the amount of calcium buildup in
the arteries, also a predictor of the degree of blockage, "but
now we have a more-advanced test that actually measures the amount
and volume of blockage present."
She says older scanners were not as powerful, either, unable to
image as much as 25 percent of the smaller blood vessels that branch
out from the heart's main arteries. However, the 64-CT scanner picks
up as much as 98 percent of the heart's arterial network (and lacks
good images for only 2 percent.)
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.
The advanced CT scanners, she says, produce pictures
within five to 10 seconds, while cardiac
catheterization, which also checks the function of heart valves and
muscle, takes between 30 minutes and 45 minutes to perform, and requires
almost an hour for recovery. Potential complications from the invasive
procedure include infection, heart attack and stroke, but they are
rare.
"And we no longer need to wait until a patient is stabilized
before performing this diagnostic test, as no anesthetic is needed
for CT scanning," says Miller.
According to researchers, nearly 5,000 64-CT scanners
are installed worldwide, and about four-fifths of the centers are
equipped to perform
and read cardiac CTs. Miller notes that special training and certification
are required by technicians and physicians to accurately perform,
interpret and read 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 CFX multislice
CT scanner, manufactured by Toshiba. Similar devices also are manufactured
by Siemens and General Electric. Each machine costs between $1.5
million and $2 million. A single test costs approximately $700.
Toshiba also provided funding support for the study, called CORE-64,
short for Coronary Artery Evaluation using 64-row Multidetector Computed
Tomography.
In CT imaging, each X-ray measurement lasts
just a fraction of a second and represents a "slice" of
an organ or tissue. The greater the number of detectors - the device
being used in this
study has a total of 64 - the better the picture resolution. A computer
then uses these slices to reconstruct highly detailed, 3-D images
of the heart and surrounding arteries. In cardiac imaging, a patient
is injected with a contrast solution to increase the visual detail.
Besides Lima and Miller, other Johns Hopkins researchers
involved in this study were Armin
Zadeh, M.D.; Ilan Gottlieb, M.D.: Edward Shapiro, M.D.: Albert Lardo,
Ph.D.; David Bush, M.D.; Christopher Cox, Ph.D.; and Jeffrey Brinker,
M.D. Additional investigators included Carolos E. Rochitte, from
the University of Sao Paolo in Brazil; Marc Dewey, from Humbolt University
in
Charite, Germany; Hiroyuki Niinuma, from Iwate Medical University
in Japan; Narinder Paul, from the University ofToronto in Canada;
Melvin Clouse, from Beth Israel Deaconess Hospital in Boston, Mass.;
John Hoe, from Mount Elizabeth Hospital of Singapore; and Albert
de Roos, from Leiden University in the Netherlands.
(Source: Johns Hopkins Medical Center with
additional reporting by Angioplasty.Org)