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USC study shows MRI may uncover causes of mysterious chest pain

A new noninvasive test shows potential for helping women with unexplained chest pain, according to a study by Keck School of Medicine researchers and colleagues from around the country. The test points out those women whose hearts are deprived of oxygen—even when standard tests show no coronary artery disease.

Women often seek medical help for chest pain, sometimes undergoing coronary angiography. But in almost half of all such women, coronary artery disease is not found. Blockages in the smaller, slender arteries that feed the heart muscle—blockages that cannot be spotted on standard tests—might be at fault, the researchers reported in the June 22 issue of Circulation.

“We have seen that many of these women are admitted to the hospital for chest pain, and undergo angiography to look for coronary artery disease, yet no such disease is found,” said Gerald M. Pohost, chief of the division of cardiovascular medicine at the Keck School and corresponding and senior author on the study. “Our results indicate that in many of these women, something is keeping the heart from getting the oxygen it needs. We suspect microvascular dysfunction or disease.”

Coronary artery disease, or CAD, claims more lives in the United States, Europe and other developed regions than any other disease. Prompted by symptoms such as chest pain, or angina, more than a half million U.S. women underwent coronary angiography to look for CAD in 2001.

Yet almost half of all women with chest pain who undergo coronary angiography are found to have no significant CAD, posing a puzzle for physicians.

CAD is a disease of the arteries that supply blood to the heart muscle. Over time, as fatty material collects in the vessels that supply the heart, the artery walls thicken and narrow the space where blood can flow, depriving heart tissue of oxygen.

The study was a part of the Women’s Ischemia Syndrome Evaluation, or WISE, study. WISE is a four-center study sponsored by the National Heart, Lung and Blood Institute of the National Institutes of Health. The study evaluated women undergoing coronary angiography for chest pain or suspected myocardial ischemia.

The researchers compared 352 women with CAD to 74 other women without it. These CAD-free women underwent an imaging scan called phosphorus-31 nuclear magnetic resonance spectroscopy, which is done completely from outside the body.

The technique simply required that women squeeze a handgrip while lying inside an MRI unit. Nuclear magnetic resonance spectroscopy technology enabled the investigators to measure levels of two phosphates found in heart tissue, once while women were at rest and again while they were squeezing the handgrip (experiencing physical stress). Investigators then compared the before-and-after levels of the two phosphates.

Researchers saw that the ratio of the two phosphates, phosphocreatine and ATP— called high-energy phosphates since they supply the energy source for heart contraction—decreased significantly in 14 of the 74 CAD-free women when they squeezed the handgrip. A big drop in the ratio is abnormal and a sign that heart tissue is not getting enough blood.

Investigators wanted to see whether the abnormal results were linked to women’s cardiovascular health. Over the next three years, they tracked how many of the women experienced a cardiovascular event such as a heart attack, stroke or hospitalization for a blood clot or unstable angina.

They found that 87 percent of the CAD-free women with normal magnetic resonance spectroscopy results stayed free of cardiovascular events.

But 43 percent of the CAD-free women with abnormal magnetic resonance spectroscopy results had events.

That is not much better than the women who had been diagnosed with CAD: 48 percent of them had cardiovascular events during that time period.

Most of the events were hospitalizations due to unstable angina, and many of the women with abnormal magnetic resonance spectroscopy results experienced repeated coronary angiography procedures to find the cause of the angina during the three-year follow-up.

Health care for CAD-free women with abnormal results cost more than twice that of the other CAD-free women over the three years.

In the clinic, Pohost and fellow cardiologists use standard angina therapies to treat chest pain in these CAD-free women, he said.

The study suggests that magnetic resonance spectroscopy could be widely used to evaluate women complaining of chest pain, and even may reduce the number of women undergoing repeated coronary angiography procedures.

Nuclear magnetic resonance spectroscopy is available only at a few select institutes and academic medical centers.

At USC University Hospital, cardiologists can evaluate patients suspected of having microvascular disease by using a new MRI scanner that is twice as powerful as its predecessors.

On its lower level, the hospital now has two new General Electric 3 Tesla MRI systems, which produce highly precise images. One of the scanners is exclusively dedicated to cardiac patients.

—Alicia Di Rado

USC study shows MRI may uncover causes of mysterious chest pain

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