Reception still fuzzy for fast CT scans of the heart

As technology for seeing into the heart improves, how the machines will be used is still up in the air.

Machines that peer into the body, such as the familiar x-ray and the alphabet soup of CT, MRI, PET, and SPECT scanners, can make incredibly detailed pictures of tissues that sit still when you do. Their renderings of the ever-beating heart, though, come out blurry. It’s akin to what happens when you try to photograph a fast-moving grandchild in low light with a slow camera.

Modifications that speed up these machines are inching closer to a longstanding dream for many cardiologists: crystal-clear images of the beating heart taken from outside the body.

Traditional angiograms do a great job of this, but they require working inside the body. A doctor must insert a slender tube called a catheter into an artery in the groin or arm and gently maneuver it into the coronary arteries. Once the catheter is in place, it releases a dye (properly called contrast) that makes blood flowing through the artery visible on an x-ray. This procedure definitely shows if an obstruction is clogging or blocking a blood vessel, which can be fixed right then with a stent.

Not everyone has a blockage that needs to be opened. And traditional angiograms carry a low but real risk of complications such as a punctured blood vessel, hard-to-control bleeding, stroke, heart attack, kidney problems, and even death.

Souped-up CT (computed tomography) scanners nearly rival the clarity and detail of angiograms without physically invading the body. Called multidetector CT scanners, these machines use multiple x-ray sources and detectors to take many simultaneous pictures of small “slices” of the heart. From these pictures, a computer constructs a three-dimensional image of the heart and the arteries that feed it. The latest machines divide the heart into 64 or 128 slices. The more slices, the shorter the scanning time and the sharper the image will be.

Multidetector CT scans illuminate cholesterol-filled atherosclerotic plaques that bulge inward — the ones that limit blood flow and cause chest pain with stress or exertion. They can also spot plaques that bulge outward, which are often the cause of heart attacks and strokes.

Multidetector CT scans take only a few minutes to perform and cost a few hundred dollars, compared to a few thousand for an angiogram. Like angiograms, these tests depend on a dye infused into the circulation, which limits their use in people with kidney disease. A beta blocker must also be given to slow the heartbeat.

Multidetector CTs aren’t ready to challenge angiograms as the standard for diagnosing narrowed or blocked coronary arteries because there haven’t been enough large, long-term studies. That’s not a bad thing — the slow evolution of the technology is giving the medical community time to figure out when, where, and in whom to use it.

Emergency aid
Some physicians see a promising use in the emergency room. Each year, more than six million Americans are rushed to the hospital with chest pain. Based on just the patient’s story, an electrocardiogram, and blood tests for enzymes that can show heart muscle damage, doctors must decide whether a heart attack is occurring. More than half the time, the pain comes from something other than the heart, and the tests don’t always scream out heart attack in progress even when there is one. The next step is often an angiogram.

A CT scan of the heart could do the same thing in less time. Studies published in February and April 2007, one from Michigan and one from Israel, show that multidetector CT scanners are very good at identifying artery-blocking plaque or clots as the source of chest pain or excluding them as a cause. But the machines aren’t yet perfect, and some people must still have an angiogram to get a definitive diagnosis.

“These findings suggest that coronary CT imaging may help quickly identify patients who are not having heart attacks and who can be sent home faster and without unnecessary testing,” says Dr. Udo Hoffmann, who codirects the cardiac imaging program at Harvard-affiliated Massachusetts General Hospital. His team published a study in 2006 supporting the use of multidetector CTs to quickly determine if heart disease is the cause of chest pain.

Hazy reception
What’s not to like about multidetector CT scans? Critics worry that the machines are so convenient that doctors might lean too heavily on them to learn what is wrong with patients’ hearts. The sizable radiation dose from a cardiac CT scan is justified if the scan offers truly helpful information, but not if it is done just to see what’s going on. Finally, these scans find partial blockages that some patients will want to “fix” with angioplasty or bypass surgery, which doesn’t do anything to treat the underlying disease.

Those uncertainties mean that cardiac CT scanners aren’t quite ready for routine use and certainly shouldn’t be used to satisfy your curiosity about the state of your heart. As the technology improves, though, the odds are high that these scanners will rival angiograms, and may even eclipse them, for diagnosing heart disease.