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Letter to New York Times

Posted Jul 03 2008 6:14am
All right. I sent a Letter to the Editor to the New York Times. No word from them; it's no longer news.

So here is what I tried to convey.

While the authors overall did a credible job of talking to my colleagues and laying out the issues, they made the crucial and boneheaded mistake of confusing CT heart scans with CT coronary angiograms. Sadly, many people who may have been considering having a simple screening heart scan may be scared away by the confused authors, Alexn Berenson and Reed Abelson.

They do correctly point out that, while CT coronary angiograms are fascinating examples of technology and a way of visualizing coronary arteries, this test all too often is being subverted into the "let's make money from high-tech testing" medical model. It's also a test that frequently leads to the "real" test, heart catheterization, since the "time bomb" you have in your arteries might "need" a stent.

CT coronary angiograms are also virtually useless for purposes of tracking disease, since they are not longitudinally (along the length of the artery) quantitative, nor should anyone be exposed to this much radiation repeatedly.

A simple heart scan, on the hand, provides a longitudinal summation of coronary plaque volume. Radiation exposure is sufficiently low that repeated scanning can be performed for purposes of tracking . . .yes, track your plaque.

Poorly-informed reporters can do a lot of damage. As always, you and I must dig a little deeper for the truth.

Dear Editor,

Re:Weighing the Costs of a CT Scan’s Look Inside the Heart

The Times featured an article on June 29th that discussed rapidly expanding use of CT scans for the heart:

Weighing the Costs of a CT Scan’s Look Inside the Heart.

The authors, Alex Berenson and Reed Abelson, stated that CT heart scans “expose patients to large doses of radiation, equivalent to at least several hundred X-rays, creating a small but real cancer risk.”

I’d like to offer a clarification.

Though the authors discuss both CT heart scans and CT coronary angiograms, they confuse the two and use the terms interchangeably.

A heart scan is a simple screening test for coronary atherosclerotic plaque. It detects the presence of calcium in the heart’s arteries, provided as a “score.” (Because calcium occupies 20% of total plaque volume, knowing the amount of calcium tells you how much total coronary plaque is present by applying this simple proportion.) Just having a high score should not prompt heart procedures, since people undergoing simple screening heart scans are without symptoms. However, a stress test may yield some useful information.

On present-day CT devices, heart scans expose a patient to 0.4 mSv of radiation on an electron-beam, or EBT, device, and on up to 1.2 mSv on a 64-slice multi-detector, or MDCT, device, compared to 0.1 mSv during a standard chest x-ray. CT heart scans are therefore performed with about the same quantity of radiation as a mammogram done to screen women for breast cancer, or about the equivalent of four chest x-rays on an EBT scanner, up to 12 chest-xrays on a MDCT scanner.

CT coronary angiograms, while performed on the same devices as heart scans, require x-ray dye to fill the contours of the coronary arteries. It also requires up to several hundred times more radiation. While new engineering innovations are being introduced that promise to reduce this exposure, the current devices being used today do indeed require a radiation dose equivalent to 100 to 400 chest x-rays (usually in the range of 10-15 mSv), a value that equals or exceeds that obtained during a conventional heart catheterization.

While heart scans are most useful to detect and quantify plaque that can help determine the intensity of a heart disease prevention program, CT coronary angiograms are generally used as prelude to hospital procedures like catheterizations, stents and bypass surgery. That’s because they are performed to look for (or rule out) “severe” blockages.

CT heart scans and CT coronary angiography are therefore two different tests that yield two different kinds of information, and yield two entirely different levels of radiation exposure.

This confusion from a major and respected media outlet like the New York Times is unfortunate, because it could persuade millions of people who otherwise could benefit from simple heart scans to avoid them because of misleading information on radiation exposure of a different test.

Thank you.

William Davis, MD
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