A study by an international team of cardiac imaging
specialists, led by researchers at Johns
Hopkins, concludes that sophisticated computed tomography 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, 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 many as 25 percent
of the 1.3 million cardiac catheterizations performed each year
in the United States may be
unnecessary.
The latest study 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 checkups 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," said cardiologist Julie Miller, 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
generally cannot be performed
safely 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," said
cardiologist Joao Lima,
senior investigator to the team whose findings were presented
Nov. 5 at the American Heart
Association's 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, said 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 American Heart
Association 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 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 said, 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 that 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 30 to 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," Miller
said.
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 are manufactured by Siemens and
General Electric. Each machine costs
between $1.5 million and $2 million. A single test costs
approximately $700.
Toshiba provided funding support for the study, called
CORE-64, short 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.
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