What Is Coronary Microvascular Disease?

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

• Plaque (plak) forms in the arteries. Plaque is made up of fat, cholesterol (ko-LES-ter-ol), 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 (is-KE-mik) 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 nonobstructive CAD.

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

Overview

Death rates from heart disease have dropped quite a bit in the last 30 years. This is due to improved treatments for conditions such as blocked coronary arteries, heart attack, and heart failure.

However, death rates haven't improved as much in women as they have in men. Heart disease in men and women may differ. Many researchers think that a drop in estrogen levels in women at menopause combined with traditional risk factors for heart disease causes coronary MVD. Therefore, coronary MVD is being studied as a possible cause of heart disease in women.

Diagnosing coronary MVD has been a challenge for doctors. Most of the research on heart disease has been done on men.

Standard tests used to diagnose heart disease have been useful in finding blockages in the coronary arteries. However, these same tests used in women with symptoms of heart disease—such as chest pain—often show that they have "clear" arteries.

This is because standard tests for CAD don't always detect coronary MVD in women. Standard tests look for blockages that affect blood flow in the large coronary arteries. However, these tests can't detect plaque that forms, scatters, or builds up in the smallest coronary arteries.

The standard tests also can't detect when the arteries spasm (tighten) or when the walls of the arteries are damaged or diseased.

As a result, women are often thought to be at low risk for heart disease.

Outlook

Coronary MVD is thought to affect up to 3 million women with heart disease in the United States.

Most of the information known about coronary MVD comes from the National Heart, Lung, and Blood Institute's WISE study (Women's Ischemia Syndrome Evaluation). The WISE study began in 1996. Its goal was to learn more about how heart disease develops in women.

The role of hormones in heart disease has been studied, as well as how to improve the diagnosis of coronary MVD. Further studies are under way to learn more about the disease, how to treat it, and its outcomes.

September 2007