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Blood flows to heart muscle first through large arteries (the coronary arteries) and then through a branching network of smaller blood vessels. The symptoms of heart disease, in men or women, often result from cholesterol-filled plaques that can slow and completely block the flow of blood to the heart muscle. This type of heart disease, which has been recognized for a century, can be seen with tests such as coronary angiograms (or arteriograms) and, less well, with noninvasive tests such as special CT and MRI scans.

In just the past decade, researchers have learned that many women with chest pain and other symptoms of heart disease have a condition called coronary microvascular disease, which affects the heart's smallest arteries. This fundamentally different form of heart disease is as common and as costly as all female-specific cancers combined, affecting as many as 3 million American women. It affects men, too, but not nearly as often.

Coronary microvascular disease was discovered only recently because, until now, it was not possible to "see" the heart's smallest arteries, which are invisible on a standard angiogram. When microvascular disease occurs, these arteries lose their ability to relax and dilate to increase blood flow to the heart muscle. That's a problem because these tiny tributaries are the ones that must respond most readily when hardworking heart muscle needs more blood. Their inability to dilate on demand limits blood flow to the heart muscle as surely as blockages in larger arteries and causes the same set of symptoms.

Many doctors have not yet heard about coronary microvascular disease. Currently, the most definitive test involves measuring coronary-artery flow reserve or coronary reactivity. It involves threading an ultrathin wire with blood-flow sensors at the tip deep into a coronary artery. Blood flow in the artery is then measured before and after injections of one or more medications that should cause the microvessels to dilate. An alternative, noninvasive way of detecting microvascular disease is with cardiac MRI. This scan measures the amount of blood flowing into the heart muscle before and after the heart is infused with a drug that dilates the microvessels. As with the coronary-reactivity test, if blood flow does not increase, there is disease of the microvessels.

If you are a woman with recurrent chest pain or discomfort, shortness of breath, unexplainable exhaustion and depression, you may need special evaluation even if you have clear arteries on an angiogram. If your doctor says there's nothing wrong, ask for a second opinion at one of a growing number of women's cardiovascular-care centers. You may have coronary microvascular disease.
--Patrick J. Skerrett, Editor of the Harvard Heart Letter, and Jane A. Leopold, M.D., Assistant Professor of Medicine at Harvard Medical school. For more information go to Health.Harvard.Edu/Newsweek.

© 2008