What is Syndrome X?
Syndrome X describes chest pain ( angina) in people who do not show signs of blockages in the arteries of their heart ( coronary arteries) after an angiogram, or X-ray of these arteries. It is not clear what causes Syndrome X, but there are several theories. Syndrome X patients do not seem to have a higher risk of dying early or having a heart attack, but they often continue to suffer from chest pain even after treatment.
Syndrome X is more common in women than men: about 70% of patients are women who are approaching or have already gone through menopause.1 In the WISE study of 936 women undergoing cardiac catheterization for chest pain, 60% did not have a major blockages in the arteries of their heart. Some of the women in this study may have had chest pain that was not heart-related.
How does Syndrome X differ from other types of chest pain?
Syndrome X is different from stable angina because an angiogram from a stable angina patient will show major blockages or narrowing in the coronary arteries. People with stable angina also typically experience chest pain during exertion that is alleviated with rest. The chest pain associated with Syndrome X is less predictable and can occur during exercise or at rest. Syndrome X patients may experience chest pain more often, more intensely, and for longer periods than people with stable angina. In addition, a medication called nitroglycerin usually relieves chest pain in stable angina patients, but often does not work in people with Syndrome X.
Strictly speaking, Syndrome X is a type of unstable angina because the pain may occur at rest; however, people are usually diagnosed with unstable angina as opposed to Syndrome X when they have major narrowing or blockages in the arteries of the heart, putting them at increased risk of having a heart attack or dying from heart disease.
You should not confuse Syndrome X with the metabolic syndrome, which used to be called Metabolic Syndrome X. The metabolic syndrome refers to a grouping of certain heart disease risk factors (including a large waistline and higher than normal blood sugar or blood pressure) in one person.
What causes Syndrome X?
No one knows exactly what causes Syndrome X and it is unlikely to have a single cause. Two factors that may be involved are lack of blood flow caused by microvascular dysfunctionand enhanced pain perception.
The term “microvascular” refers to very small blood vessels and, in this case, very small arteries of the heart. The major arteries of the heart are spaghetti-thin, but these tiny arteries are smaller still. When these tiny blood vessels narrow, oxygen cannot reach some areas of the heart muscle, which can cause chest pain. Restricted blood flow to the heart is called myocardial ischemia; myocardial refers to the heart muscle and ischemia is a combination of the Greek words for “restrain” and “blood.” About 50% of women with Syndrome X have evidence of microvascular dysfunction,2 but only about 20% to 25% show signs of restricted blood flow to the heart, suggesting that there are other factors involved.1, 3 Syndrome X patients generally have good survival rates whereas people with true myocardial ischemia are at increased risk of having a heart attack or dying from heart disease.
Studies have also shown that people with Syndrome X have enhanced pain perception, meaning they feel chest pain more intensely than the average person.4-6 It is not known whether Syndrome X patients feel all types of pain more intensely or only chest pain.
Why are women more likely than men to have Syndrome X?
It is not completely clear why women are more likely than men to suffer from Syndrome X; however, hormones and other risk factors unique to women may play a role.
Women’s blood vessels are exposed to changing levels of estrogen throughout their lives, first during regular menstrual cycles and later during and after menopause as estrogen levels decline with age. Estrogen affects how blood vessels narrow and widen and how they respond to injury, so changes in estrogen levels mean changes in the behavior of the blood vessels. Women’s vessels may be “programmed” for more changes than men’s vessels, which could increase the risk of having problems in the lining of the arteries ( endothelium) and the smooth muscles in the walls of the arteries. Many women in the WISE study had evidence of damage to the smooth muscle in the small arteries. In addition to changing hormone levels, there are several other risk conditions for blood vessel problems that are unique to women, such as preeclampsia (a problem caused by high blood pressure during pregnancy) and delivering a low-birthweight baby.