WASHINGTON (AP) — Millions of people with chest pain enter emergency room limbo, spending up to 24 hours waiting for tests to tell if a heart attack really is brewing or if it's something less dire. A computerized heart scan may start easing the wait, giving doctors a faster picture of clogged arteries to help determine who can go home — within just four hours — and who needs more care. If these souped-up CT scans pan out — and major studies of several thousand chest-pain sufferers are to begin soon — they may do more than send the worried well home faster.

"To be able to show the patient what's going on in their arteries is very powerful," says Dr. James Goldstein of William Beaumont Hospital in Royal Oak, Mich.

He's finding that the 3-D pictures of gunk-filled arteries can motivate patients to change their heart-risky behaviors better than lecturing them about high blood pressure or cholesterol.

On the other side, when arteries look clean, "you can say the chance that this patient would have any cardiac event in the next five years will be very, very low," adds Dr. Udo Hoffmann of Massachusetts General Hospital. "If they come back a week later with chest pain, you know it's not the heart."

Sudden chest pain sends about 6 million people to U.S. emergency rooms every year. It's the most common symptom of a heart attack, but a maddening symptom, too — because half the time it signals something other than heart disease, and telling the difference can be tough.

The dilemma starts with describing the pain. The classic "elephant on my chest" sensation isn't what everyone experiences. Some feel not pain but a tightening of the chest. Others feel pain in the arm, neck or jaw. Some people say it felt like they had a toothache before their heart attack; others felt nausea.

"Trying to sort out whether there's a life-threatening heart problem based on symptoms alone is difficult," explains Goldstein. "Sometimes it seems obvious, and you're wrong. Sometimes the symptoms are unimpressive, and you're wrong. The implications of missing the diagnosis are disastrous."

An electrocardiogram, or EKG, sometimes catches a heart attack in progress, or an artery so unstable that one's imminent.

But at least half the time, early tests are inconclusive and patients are admitted to the hospital for repeat EKGs, blood tests and other checks that can last 24 hours — and eventually rule out a heart attack two-thirds of the time. Patient anxiety aside, the tab for all that testing surpasses $10 billion annually.

Worse are those whose heart attacks are missed, between 2 percent and 8 percent of patients who are sent home too soon.

Cardiac catheterization — threading a probe up into the heart to view the inside of arteries — or stressing the heart with exercise can provide a faster answer, but both are risky so doctors until now have stuck with the wait-and-see approach.

Enter CT angiography. Doctors inject patients with a dye to illuminate artery walls. Then newer machines called 64-slice CT scanners use computerized X-rays to measure both rock-like calcium and soft fatty blockages inside arteries. Within 30 minutes, the 3-D images can show if arteries are narrowed, and how much.

Beaumont researchers studied 197 chest pain sufferers considered at low risk of a heart attack, giving half the souped-up CT scan. The noninvasive test either ruled in or ruled out heart disease in 75 percent, helping to decide who really needed to be hospitalized 11 hours faster than with routine testing, researchers report in this week's Journal of the American College of Cardiology.

Don't reserve the souped-up CTs for low-risk patients, says Mass General's Hoffmann. He tested the scans in 103 patients, 14 of whom had either a full heart attack or a dangerous condition called unstable angina. The CT scans correctly spotted blocked arteries in those patients, and correctly cleared others who had no or minimal clogs, he reported last fall in the journal Circulation.

So who should get the scans? Hoffmann and the Beaumont group both are preparing larger studies to try to settle that, and to tell if CT angiography improves patients' outcomes or just speeds the diagnosis.

Finding clean arteries or very blocked ones makes for an easy diagnosis. But if the clog is medium-sized, is it causing the chest pain and does it need immediate treatment? A CT alone won't be enough to tell, notes Hoffmann.

Nor is even this noninvasive test risk-free. CT scans do involve radiation, and the injectible dye isn't for people with kidney disease.

While some hospitals already are using the CTs to diagnose chest pain, "most physicians at this time are not familiar with a cardiac CT and what it means," Hoffmann cautions.

For now, just insisting on a thorough check may be the best consumer advice. A disturbing new study of more than 7,000 emergency room visits found blacks and women were less likely to get even that first-step EKG than other chest-pain sufferers. The study couldn't explain the disparity, but lead researcher Liliana Pezzin of the Medical College of Wisconsin suspects harried workers in overcrowded ERs were too quick to assume another cause.

"Be your own advocate," Pezzin says. "Say, 'I need to be tested.'"