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What is coronary microvascular disease (MVD)?

Coronary microvascular disease (MVD) is a heart disease that affects the smallest arteries that nourish the heart. It differs from traditional coronary heart disease (CHD), also called coronary artery disease. In CHD, a fatty substance called plaque builds up in the large coronary arteries. This deposition can lead to blockages that reduce or block the flow of oxygen-rich blood to the heart muscle.

Coronary MVD, however, affects the heart's smallest arteries, perhaps due to inflammation or even hormone changes. Studies have shown that women are more likely than men to have coronary MVD. Many researchers think that a drop in estrogen levels during menopause, combined with traditional risk factors for heart disease, can promote coronary MVD.

Standard tests for coronary heart disease (CHD) are not designed to detect another type of heart disease, coronary microvascular disease (MVD). MVD mainly affects women and is not as well understood as CHD. Standard test results for women may show that they are at low risk for heart disease, even if they have coronary MVD. Research is ongoing to learn more about coronary MVD and its causes.

Also known as cardiac syndrome X or small vessel disease, microvascular disease is a disease of the finer blood vessels and is characterized by chest pain or ischemia without evidence of blockage in the large coronary arteries. Women are at higher risk than men for this condition. Microvascular disease may be caused when the small blood vessels in the heart don't expand enough due to abnormalities in the function of the endothelium (the layer of cells lining blood vessels). Postmenopausal women and women who have had surgical menopause are at risk for experiencing symptoms of microvascular disease because their declining estrogen levels may affect the small blood vessels in their hearts.

Because this condition is a small vessel disease, it can't be seen on an angiogram (an X-ray with dye that identifies blockages in the larger blood vessels). Special imaging tests, such as PET scanning or MRI, may help with the diagnosis in the future. Today, however, microvascular disease is often a diagnosis of exclusion -- meaning you may be diagnosed with this condition after tests provide no other cause for the chest pain. The same tests done to diagnose coronary artery disease, such as an electrocardiogram, echocardiogram or coronary angiogram, are usually used to diagnose microvascular disease. In addition, special chemical tests of the coronary blood vessels can be done at the time of the angiogram. Most women with microvascular disease have at least one risk factor for coronary heart disease (CHD), but it can occur in women who are otherwise healthy.

Medications commonly used to treat CHD conditions may help to relieve pain caused by microvascular disease. Symptoms can be debilitating and new data suggests that if left untreated, women with microvascular disease do not have as favorable a prognosis as previously believed. Their risk factors should be managed as aggressively as someone who has CHD.

As many as 30 percent of women with angina (chest pain) have "clear" angiograms. In the past, these women were likely to be told they had a condition known as "cardiac syndrome X" and reassured that their symptoms were nothing to worry about. However, research determined that syndrome X is actually a form of heart disease called coronary microvascular dysfunction, which isn't detected by standard diagnostic procedures. Microvascular disease is also thought to be responsible for other, less dramatic symptoms like fatigue, diffuse chest discomfort and shortness of breath.

Microvascular disease went undetected for so long because it is sneakier than coronary artery disease. It is thought to be more common in women because of two factors—females have smaller blood vessels and a higher rate of inflammation. In coronary artery disease, vessels are narrowed or obstructed by discrete deposits of atherosclerotic plaque that jut into the open passage through which blood flows or burrow into vessel walls. In microvascular disease, inflammation sets the stage for plaque, which is laid down uniformly, like plaster; the vessels aren't obstructed, just narrowed and stiffened. They can't dilate to increase blood flow in response to the body's demands. Like plaster, microvascular plaque tends to erode rather than rupture. The body's efforts to repair the erosion perpetuate the inflammatory cycle and spur the formation of tiny blood clots, a possible trigger for heart attacks in women with microvascular disease.

Microvascular disease is a disease of the smallest blood vessels, such as those found in the eyes, nerves and kidneys. The walls of the vessels become abnormally thick but weak. Then they bleed, leak protein and slow the flow of blood to the cells.

Coronary microvascular disease (MVD) affects the heart's smallest coronary arteries. Coronary MVD occurs in the heart's tiny arteries when:

  • Plaque forms in the arteries. Plaque is made up of fat, cholesterol, calcium and other substances found in the blood. It narrows the coronary arteries and reduces blood flow to the heart muscle. As a result, the heart doesn't get the oxygen it needs. This is known as ischemic heart disease, or heart disease. In coronary MVD, plaque can scatter, spread out evenly or build up into blockages in the tiny coronary arteries.
  • The arteries spasm (tighten). Spasms of the small coronary arteries also can prevent enough oxygen-rich blood from moving through the arteries. This too can cause ischemic heart disease.
  • The walls of the arteries are damaged or diseased. Changes in the arteries' cells and the surrounding muscle tissues may, over time, damage the arteries' walls.

Coronary MVD is a new concept. It's different from traditional coronary artery disease (CAD). In CAD, plaque builds up in the heart's large arteries. This buildup can lead to blockages that limit or prevent oxygen-rich blood from reaching the heart muscle.

In coronary MVD, however, the heart's smallest arteries are affected. Plaque doesn't always create blockages as it does in CAD. For this reason, coronary MVD also is called non obstructive CAD.

No one knows whether coronary MVD is the same as MVD linked to other diseases, such as diabetes.

This answer from the National Heart, Lung and Blood Institute has been reviewed and/or edited by Dr. William D. Knopf.

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