|
If you live in a reasonably large American
city, you've no doubt heard the commercials.
Forty-two-year-old Henry is putting on a clown
costume, getting ready for his son's 5th birthday party, and counting
his blessings. He knows just how lucky he is to be doing the Bozo
thing instead of pushing up daisies. And if it hadn't been for the
Ultrafast CT scan, pushing up daisies is exactly where Henry would
be. "And to think," he muses, attaching his large red
nose, "on the day before I had my convenient and painless [insert
brand name here] heart scan that showed I was about to have a massive
heart attack, my doctor had given me a clean bill of health. Thanks
to [insert brand name here], I was able to get treatment in time."
Then the announcer comes on and says, "And
how do you feel? Are you sure? Like Henry here, you could be sitting
on a silent time bomb, and your next breath may be your last. So
maybe you should schedule a [insert brand name here] Ultrafast CT
scan, and like Henry, spend your child's next birthday at Chucky
Cheese's instead of Forest Lawn. Call today." Then the announcer
gives the address and number of - not an obscure office in a failing
strip mall - but a highly respected local hospital.
What gives here? Is the Ultrafast CT
scan some sort of fringe medical procedure, as suggested by the
cheesy commercials featuring heart rending vignettes, or is it a
legitimate and valuable diagnostic tool, as suggested by its university
hospital venue?
As it turns out, the cardiology community
has been just as schizophrenic about Ultrafast CT scans as have
been the commercials. While many cardiologists swear by them, many
others consider them a waste of time and money, and a grave risk
to the credibility of the profession.
In this article, we will examine, as dispassionately
as possible, the Ultrafast CT scan. We'll consider whether it is
merely another heart test, or whether it really is a uniquely valuable
tool that predicts dangerous cardiac events before they occur. And
we will try to answer the question: should you have one?
What is the Ultrafast CT scan?
CT scans have been in wide clinical use for
more than 25 years. CT scans arose when standard x-rays met the
power of the computer. X-ray images were computer-processed to give
pictures of a quality scarcely imagined before the 1970's. Since
their advent, CT scans have become a gold standard for imaging many
of the body's internal organs.
But CT scans have never been particularly
useful for imaging the heart. This is for one simple reason: the
heart moves. Since CT scanners take several minutes to acquire the
image, anything that moves during this time becomes blurred. And
the coronary arteries, riding as they do on the surface of the heart
muscle, are invariably blurred into oblivion.
Imagine trying to photograph a man running
on a treadmill with a camera that requires an exposure time of 10
minutes, and imagine that your assignment is to use the photograph
to document whether he's wearing Nikes or Reeboks. While the picture
you take may show a fairly clear image of the torso of the runner
(since its movement is relatively limited), the man's arms, legs,
and especially his feet, would come out a hopeless blur.
But now suppose you could somehow rig up your
camera so that it would repeatedly expose the film, but only during
the brief moments that the runner's right foot was just beginning
to touch the surface of the treadmill. The camera, it might be said,
would be "gated" so that only one brief portion of the
"running cycle" would be caught on film. The resultant
image would very likely show the right foot in a fair amount of
detail, since it would be in nearly the same position each time
the film was exposed. And detecting either the Nike or Reebok logo
would be a cinch.
This is how the Ultrafast CT scan works. The
CT camera uses the patient's ECG to "gate" the CT exposure,
so that the heart is imaged only during a particular moment within
the "cardiac cycle," when it is always in nearly the same
position. Gating the CT scan reduces and almost eliminates the blurring
produced by cardiac motion. And now, suddenly, the coronary arteries
can be seen with much higher resolution than with a standard CT
scan.
With current technology, even gating the image
does not render the coronary arteries visible nearly to the extent
of, say, a cardiac catheterization. The Ultrafast CT scan does not
tell us directly, therefore, whether there are significant blockages
in the coronary arteries. What it does tell us, with a high degree
of accuracy, is whether the coronary arteries contain deposits of
calcium.
Calcium, for all practical purposes, does
not occur in normal coronary arteries. Calcium deposits are a strong
marker for the presence of atherosclerosis, i.e., coronary artery
plaques, the lesions that cause narrowing of the coronary arteries,
and ultimately lead to heart attacks. If there is calcium in the
coronary arteries, then, you can be pretty sure there is also atherosclerosis.
Further testing - usually by means of a cardiac catheterization
- might then be indicated to measure the extent of the disease,
and to decide on the best way to treat it.
So it all makes perfect sense. Use the Ultrafast
CT scan as a completely safe, painless, and non-invasive screening
test to check for the presence of coronary artery calcification.
If it's present, then you know there's at least some degree of coronary
artery disease, and more invasive procedures can be elected. What
could be simpler?
Why it's not that simple
For one reason, nothing
is ever that simple.
For another, the presence of at least some
coronary artery calcification in Americans over the age of 25 or
30 is so frequent that the mere presence or absence of calcification
on the Ultrafast CT is not a valuable screening tool. (If you were
going by the mere presence of coronary artery calcium, you might
as well skip the Ultrafast CT and just catheterize everybody.)
This means that there has to be a method of
scoring the coronary artery calcium. And here's where it gets tricky.
Whatever scoring system you may devise, the
point would be to identify a "cutoff" score above which
significant blockages in the coronary arteries are quite likely,
and below which significant blockages are quite unlikely. Then you
could send for catheterization those patients whose scores are above
the cutoff.
As it turns out, this generic problem is a
very common one in medicine, one that has been solved hundreds of
times. Whenever you are measuring something that yields a range
of values - like serum glucose, for instance, or cholesterol levels
- you have to determine a "normal" range and an "abnormal"
range. To solve this problem, you simply measure the values in people
who are normal and in people who have the disease state the measurement
is meant to detect. Many times, a "cutoff" value will
quickly suggest itself.
That method, of course, has been tried with
the Ultrafast CT scan. Patients who were having heart catheterizations
anyway were given the Ultrafast CT scan as well, and the results
of the catheterization were compared to the results of the Ultrafast
CT. And as it turned out, patients who had lots of calcium tended
to have a lot of coronary artery disease, while patients without
a lot of calcium tended to have much less coronary artery disease.
And that was very good.
The problem came when researchers tried to
come up with a cutoff calcium score that effectively separated patients
with significant coronary artery disease from patients with no significant
disease. It turned out that no cutoff can do that cleanly. A few
patients with very little in the way of calcium have significant
blockages in their coronary arteries. (These patients are said to
have "false negative" Ultrafast CT scans).
But more importantly, many patients with a
lot of calcium on the Ultrafast CT turn out to have very little
in the way of coronary artery blockages. (These patients have "false
positive" Ultrafast CT scans.) So when researchers select the
cutoff point that is supposed to separate those with significant
blockages from those without significant blockages, they have no
choice but to decide whether to err on the side of false positives,
or false negatives. Because no matter what value they choose, they're
going to wind up with a lot of one or a lot of the other (or, if
they make a particularly bad choice, with a lot of both.)
Since the Ultrafast CT is a test designed
to screen for coronary artery disease, it would not be very useful
if a lot of patients with significant blockages were missed. Doctors
obviously want the test to be highly sensitive in picking out nearly
all patients with significant blockages. This means that the cutoff
values that are generally used with the Ultrafast CT have been chosen
to err on the side of false positives. (Again, this means that patients
receiving a "good" result are very unlikely to have significant
coronary artery disease, while those who receive a "bad"
result may or may not have significant disease.)
So if we elect to use the Ultrafast CT scan
as a screening procedure, we therefore accept - by definition -
the fact that many patients with "bad" calcium scores
will turn out to have no significant blockages in their coronary
arteries. There's nothing inherently wrong with using the Ultrafast
CT as a screening tool, in other words, as long as we accept this
proviso.
So Why All The Passion?
There are a lot of equivocal screening tests
used in cardiology, but none but the Ultrafast CT scan have engendered
TV and radio commercials imploring the public not to miss the opportunity
to be screened. And few save the Ultrafast CT have caused legions
of opposing cardiologists to hasten to the airwaves to publicly
deplore their use, or professional societies to rush "position
papers" into print in an attempt to adjudicate the differences
in opinion before the two sides come to blows.
To understand why the Ultrafast CT scan -
of all cardiac screening tests - is so controversial, one simply
has to (to coin a phrase) follow the money.
It costs about $2 million to buy the machine
that does Ultrafast CT scans. Especially in today's health care
environment, with hospitals and HMOs going bankrupt every day, that's
a lot of money. Furthermore, most insurance companies, after reviewing
the available data on Ultrafast CT scans (and noting the high proportion
of false positive tests), have elected not to pay for the test.
As a consequence, most hospitals have quite reasonably elected not
to spend a huge wad of money to buy a device that performs (yet
another) non-invasive cardiac screening test, one that is, to boot,
non-reimbursable.
But look what the hospitals that have purchased
Ultrafast CT scanners have figured out: If you buy it (and invest
in the appropriate advertising,) They Will Come. And furthermore,
if you position it effectively (and nobody wants to miss their kid's
birthday,) They Will Pay Cash.
Think of it. Payment in advance, major cards
accepted. No paperwork. No pre-certification. No wrangling 8 - 12
months to collect an average of 45% of the amount billed. The best
thing that ever happened, many hospitals are finding, was when insurance
companies refused to pay for the test. Suddenly, the Ultrafast CT
scanner was no longer bogged down within the traditional health
care system; suddenly, it was in the wonderful, wild free market.
There's more. There's
a Dirty Little Secret in cardiology that has to do with non-invasive
tests. Every time a new non-invasive heart test is invented,
it is hailed as bringing us one step closer to the day when invasive
tests will no longer be necessary. And yet, as time goes by and
the new non-invasive test comes into common use, more and more invasive
tests end up being performed. This is not a mysterious or inexplicable
result. It is entirely predictable.
And that's the Dirty Little Secret. To wit:
every new non-invasive test creates a brand new category of "false
positive" results that need to be followed up by performing
an invasive test. Therefore, each time a new non-invasive test
comes into use, the need to perform invasive procedures increases.
For Ultrafast CT scans, this truism applies
in spades, because, as we have seen, a cutoff calcium score has
been selected that guarantees a significant proportion of falsely
positive tests.
So cardiologists lucky enough to work in hospitals
that were "early adopters" of Ultrafast CT scanners, and
that advertised them sufficiently, found that their catheterization
volume increased significantly. They learned to like the Ultrafast
CT scan very much, and found themselves willing to appear in commercials
promoting this effective screening tool. Cardiologists in neighboring
hospitals, feeling the impact of paying customers being siphoned
off by (and being catheterized at) rival institutions, tended to
react rather passionately and publicly themselves, but in the opposite
direction.
The next thing you
know, you've got a controversy on your hands.
Beyond the passion
Early adopters of the Ultrafast CT scan, by
blitzing the airwaves with commercials of dubious taste, tended
to poison the waters for a sober, scientific assessment of the efficacy
of this test as a screening tool. But as time has gone by, the publication
of several scientific studies has tended to bring the discussions
regarding the usefulness of the Ultrafast CT to a somewhat higher
plane.
In summary, these studies have shown what
one might expect: the Ultrafast CT scan is effective in identifying
individuals who are likely to have significant coronary artery disease.
And while it is often stressed that a "normal" Ultrafast
CT scan does not rule out the possibility of coronary artery disease
(and so people with good Ultrafast CT results should not take up
smoking, eating, drinking, and being merry), by far the bigger "problem"
is that almost half the patients with a positive scan turn out not
to have significant coronary artery blockages.
Some have said that this latter problem is
a blessing in disguise, since the presence of calcium on the coronary
arteries is a powerful motivator for patients to adopt healthier
lifestyles. The calcium means, after all, that they really do have
coronary artery disease - it just hasn't progressed enough to cause
serious problems - yet.
Furthermore, slow but steady progress is being
made in deciphering which populations of patients may benefit the
most from Ultrafast CT scans. Not surprisingly, it is the patients
who have either symptoms suggestive of coronary artery disease,
or important risk factors for the disease, who seem to be the best
groups to test. These patients tend to have a high probability of
having coronary disease even before the test. This means that a
positive Ultrafast CT scan is much more likely to be truly positive
in these patients than in a lower risk population.
In any case, over the past year or two, because
discussions within the cardiology community over the Ultrafast CT
scan have come to be based more on data and less on feelings, those
discussions have become much less polarized, and much more objective.
On July 1, 2000, the American Heart Association
and the American College of Cardiology released an updated "expert
consensus" on the Ultrafast CT scan. The authors of this report
included both strong proponents of the Ultrafast CT scan, and skeptics.
The authors reviewed all the available published studies, and concluded
the following (note that in this statement the Ultrafast CT scan
is referred to as the electron beam CT scan, or the EBCT):
"Although preliminary data are intriguing
with respect to risk prediction in the asymptomatic patient, available
data are insufficient to support recommending EBCT to asymptomatic
members of the general public or for routine clinical use. Further
studies are enthusiastically recommended for determining the additive
predictive effect of the calcium score in patients with intermediate
risk, particularly in the elderly. The use of EBCT in selected asymptomatic
patients can be justified when performed in the context of a medical
assessment only after the more standard cardiac risk assessment
is considered insufficient by the physician to direct further therapy
plans."
In other words, the joint statement concluded
that routine use of the Ultrafast CT for screening members of the
general public who do not have symptoms of coronary artery disease
cannot yet be justified by the available data. The bone that was
thrown to proponents of the Ultrafast CT scan was an "enthusiastic
recommendation" for further study. While not really satisfying
to anybody, such a statement is felt to be a step forward from the
fervent endorsements and the angry denunciations of a few years
ago. We still do not know exactly what to do with Ultrafast CT scans,
but at least we can be collegial about it.
So should you have a Ultrafast
CT scan?
As with every medical
decision, it depends.
The easiest answer would be to simply endorse
the expert consensus of the AHA and ACC (which, in fact, I agree
with in all its particulars), and say no, don't get one until better
data is available. But that would leave you watching all those commercials
featuring Henry, and wondering, after all, wouldn't it be ok to
get yourself checked?
And while we're all waiting for more data,
heart disease is still the number one killer in the U.S., and while
many victims have plenty of warning and plenty of opportunity for
early medical intervention, the fact remains that for a substantial
minority of individuals (several hundred thousand a year), sudden
death is the very first sign that anything is wrong. So it is very
reasonable for Americans to wonder about the state of their coronary
arteries, even if they're feeling entirely well.
It is surely logical to consider having a
test, one you can schedule and pay for yourself, that is very good
at detecting the presence of coronary artery disease - even if that
test can't tell you the severity of the disease.
It's just that, if you decide to have the
Ultrafast CT scan, you had better understand its drawbacks as well
as its advantages. Its major advantages are that, if the test is
negative, the probability that you have significant coronary artery
disease is very small; and that if you do have significant coronary
artery disease, the Ultrafast CT will very likely be positive.
Its major disadvantage is that even if you
do not have significant coronary disease, the test is also reasonably
likely to be positive. And that means you may receive a heart catheterization
you don't really need. Whether that is a minor inconvenience or
a very bad thing depends almost entirely on your feelings as an
individual. (I'm not taking insurance companies into account here.
They would, I suspect, always consider it a very bad thing to have
to pay for catheterizations that were not necessary.)
If used appropriately, in individuals who
are motivated to know with a high degree of certainty the state
of their coronary arteries, and who are willing to pay the price
of a potentially unnecessary catheterization to get that information,
the Ultrafast CT can be very useful and very gratifying.
So the Ultrafast CT scan may be for you, but
don't decide by listening to cheesy commercials or to panicked naysayers.
Decide by considering: with how much certainty do you need to know
about your coronary arteries? If you have a lot of risk factors,
you would be quite justified in wanting to pursue the answer vigorously.
On the other hand, if you are a young person with few risk factors,
in whom a "positive" test is particularly likely to be
a "false positive," the Ultrafast CT scan would make far
less sense.
Either way, since many doctors are still not
being very objective on this matter, it would be to your benefit
to keep yourself on an even keel, to consider all the available
information objectively and dispassionately, and to make your own
decision.
Links
Commercials for the
Ultrafast CT scan are not limited to TV and radio. Here are a few
sites that are essentially advertisements for the Ultrafast CT.
Esthetics on these sites vary from the tasteful to the garish.
Imatron's
site
Another commercial site, less garish, with on-line images of Ultrafast
CT scans
Article
from Better Homes and Gardens
Another form of advertising is to disguise the ad as journalism
Heartinfo.com
on Ultrafast CT scanning
You have to look carefully to see that this apparently scholarly
and objective on-line piece actually comes from Imatron, Inc. Every
claim stated as fact on this page is in dispute (see the AHA/ACC
statement, below).
Here are some links
that present data on the Ultrafast CT scan somewhat more objectively.
The
ACC/AHA Consensus Statement
The summation of the latest expert consensus on Ultrafast CT scanning,
from July, 2000
Richard N. Fogoros, MD (DrRich)
Heart Disease Guide at About, Inc.
www.heartdisease.about.com
Originally published on About.com's
Heart Disease Website - 8/15/2000
| 