Revisiting Cardiac CT Angiograms

The New York Times published an extensive article on the CT angiogram (CTA) for the diagnosis of coronary disease and is a very worthwhile read. In the report, they describe the controversy between cardiologists surrounding these tests. But in their push to provide eye-catching content, they permitted a CT angiogram proponent, Dr. Harvey Hecht of The Lenox Hill Heart and Vascular Institute of New York, to show perfect 3D images of a normal CTA obtained in nice, slow, regular heart rhythm that peels away the rib structures and shows some of the coronary arteries, the inside surface of the heart, and heart valves as he narrates the video. It's like watching something from the "Undersea World of Jacque Cousteau." Yes, they are beautiful pictures and demonstrate the incredible capabilities of this technology. Gosh, who wouldn't want those beautiful pictures of their heart?

Thank you, NYT, for giving Dr. Hecht, and the entire CT proponents all they need to peddle their scans, after all, a picture is worth a thousand words, right?

But if you read the article carefully, those beautiful pictures come at a price: both for the patient and our economically-burdened healthcare system. Not only are they fairly expensive, but the risks of radiation to the patient are real. To the authors' credit, they made this point. But they also failed to explain that for women with generally smaller frames and greater levels of breast tissue, those risks of radiation are amplified. They also didn't show a flawed CTA in their online article sidebar: like one taken in atrial fibrillation (an irregular heart rhythm) or with lots of skipped heart beats - you see, those images aren't quite so clear. Because the heart is a moving organ, collection of the images must be precisely gated to the heart beat. In people with irregular heart rhythms, motion artifact is introduced, degrading the quality of the images obtained.

The authors also failed to show the images of a patient with a heavy coronary calcium score. Those CTA images sometimes don't turn out so well, either. All CT angiograms use iodinated contrast material injected rapidly through an intravenous line placed in the arm. Scanning begins a few seconds later, after the operators think the dye has reached the patient's coronary arteries (the circulation time is estimated). Once the contrast agent reaches the arteries, it causes the blood vessels and chambers of the heart to "stand out" from the surrounding walls of the heart and blood vessels. In the case of someone with too much calcium in the arteries, the native calcium also "stands out" and might shadow the actual ability of the contrast to define the lumen of the blood vessel. Also, things like stents, which are metallic, interfere the same way. Additionally, the contrast agents used might be harmful to a patient if they have compromised kidney function, so most people have a blood test to evaluate their kidney function before the test (yes, more money).

Certainly in complex congenital heart disease, here are few tests better than CTA to define to course of anomalous blood vessels. CTA has also been invaluable to electrophysiologists to image the left atrium and the pulmonary arteries to define the size, number, and orientation of vessels before left atrial catheter ablation procedures. Likewise, there might be a role to perform CTA to exclude coronary artery disease in the chest pain patient who presents to the Emergency Room. But as a screening test for the general population or even our "walking well" in the cardiology clinic, these scans have no role today, despite what others may suggest.

Despite this, the patient testimonial was telling:

Nonetheless, in February, Mr. Franks took a test called a calcium score, which measures the amount of calcified plaque in the arteries. The test, a less extensive form of scanning, revealed a moderate buildup of calcium in his arteries, a potential sign of heart disease.

So he decided to have a nuclear stress test. When that test showed no problem, the cardiologist who conducted it said he did not need more testing.

But Mr. Franks was still not satisfied. “I’m someone who wants to know,” he said.

After doing research on the Internet, he found Dr. Hecht, who recommended a CT angiogram. Dr. Hecht acknowledged that Mr. Franks probably did not have severe heart disease. But he said the scan would be valuable anyway because it might reassure him. And his insurance would cover the cost.

"If it's free, it's for me," right?

Boo rah.

But adding up this patient's cumulative radiation dose (10 mSV for the "Calcium Score" + 27.3 mSv for the thallium study + another 21.4 mSv for the CTA) gives him the equivalent of almost 3000 chest x-rays worth of radiation.

And then his cardiologist (Dr. Hecht) wanted to repeat the test every year "so he could see how quickly the plaque in Mr. Franks’s arteries was thickening" claiming "how do we know that our therapy is effective?"

Boo rah.

For the record, I know of no study demonstrating the safety, cost effectiveness, or the ability of CTA to document CAD progression year to year. Further, Hecht's own paper demonstrated that even with extensive cholesterol lowering, no change to plaque burden was documented. I also have never seen such documentation be able to predict a cardiac event of any type. But Dr. Hecht seems to feel insults to those questioning the utility of CTA are appropriate:

Cardiologists like Dr. Brindis (and Dr. Wes, it seems) hurt their patients by being overly conservative and setting unrealistic standards for the use of new technology, Dr. Hecht said.

“It’s incumbent on the community to dispense with the need for evidence-based medicine,” he said. “Thousands of people are dying unnecessarily.”

Hmmm. Dispense with need for evidenced-based medicine? I wonder what Dr. Hecht will say to his patient when the CTA scan shows a tumor mass one year.

-Wes

References: Nico R. Mollet, Filippo Cademartiri, Carlos A.G. van Mieghem, Giuseppe Runza, Eugène P. McFadden, Timo Baks, Patrick W. Serruys, Gabriel P. Krestin and Pim J. de Feyter. "High-Resolution Spiral Computed Tomography Coronary Arteriography in Patients Referred for Diagnostic Conventional Coronary Angiography." Circulation 2005; 112: 2318-2323.

Abelson R, "Heart Scans Still Covered my Medicare." New York Times 13 March 2008.

Addendum 29Jun2008 @ 1523: - the opposing view over at "The Voice in the Ear".