Heart Disease in Women Symptoms and Prevention

Heart disease in women facts

  • Heart disease is the leading cause of death among women.
  • Most women have at least one risk factor for heart disease.
  • Heart attack symptoms can be different for women than for men.
  • Younger women with heart disease are more likely to die than men of the same age with heart disease. It is especially important for women and their doctors to be aware of early risk detection for primary prevention.
  • Despite being the #1 killer, only 13% of women surveyed by the American Heart Association (AHA) thought heart disease was their biggest health risk. Awareness may be a barrier to timely assessment and treatment.
  • Cardiovascular disease (CVD) can be prevented and reversed with lifestyle changes.

What is cardiovascular disease (CVD)?
Cardiovascular disease includes a large number of unique conditions that can affect not only the heart but also the blood vessels throughout the body including those in the brain (stroke) and extremities (peripheral artery disease). Within the heart, disease can affect the physical structure including the valves (for example, congenital mitral valve prolapse or rheumatic heart disease caused by strep infections) or the muscle wall (for example, cardiomyopathy or congestive heart failure). Cardiovascular disease also includes conditions of vascular function (for example, endothelial dysfunction, angina, or hypertension), inflammation (for example, endo- or myocarditis), or the electrical regulation of the heartbeat (for example, arrhythmia or atrial fibrillation). 

What is atherosclerosis?
One type of cardiovascular disease includes physical blockages that can stop blood flow in the coronary vessels and cause ischemia of the heart muscle. When this is severe and sudden, this is what is commonly referred to as myocardial infarction or a "heart attack." However, years of coronary artery disease typically precede the attack with gradual narrowing and blocking of the blood vessels. The blockages are formed by lipid or cholesterol deposits that cause inflammation and form plaques. These plaques calcify, block the vessels, and limit blood flow to the heart muscle. This process is called atherosclerosis. The plaques can also rupture, releasing a thrombus or clot that can block blood flow downstream and cause ischemia (decreased oxygen delivery to tissues) elsewhere in the heart or brain.

Because the body was not designed to have high levels of cholesterol (specifically LDL) in the blood, immune cells called macrophages move it into the blood vessel walls to get it out of the circulation. In this process, it becomes oxidized, and this is what triggers the inflammatory process. The macrophages become overwhelmed with the oxidized LDL, try to engulf it, becoming "foam cells." These foam cells trigger the need for further "clean up," and the body tries to sequester the unhealthy foam cells and forms a hard plaque around it. These plaques cause further inflammation within the tissue of the artery wall; this is how atherosclerosis progresses.

There are differences between how atherosclerosis develops in men and women. In general, women are more likely to have plaque formation in a single coronary vessel and in smaller blood vessels. Overall, atherosclerosis or obstructive cardiovascular disease is a less common form of heart disease among women, although when plaques do form, the plaques are comprised of lipid-filled foam cells, which are both more easily treated and reversed. However, the plaques in women are more likely to rupture than atherosclerotic plaques in men.

What are the statistics for heart disease in women?
One in 3 women die of cardiovascular disease, compared to 1 in 31 women who die of breast cancer. While the actual numbers of deaths from heart disease have declined among both men and women, more women die of cardiovascular disease each year than men. In fact, rates of heart disease among younger women (aged 35 to 54) are actually increasing, a trend thought to be attributable to obesity. Rates of heart disease are higher among black women and Hispanic women compared to non-Hispanic Caucasian and Asian women.

Cardiovascular disease is the leading cause of death among women. On average, women develop cardiovascular disease, on average, about 10 years later than men. It is thought that this difference is at least partially due to protective hormonal effects because women's risk increases after menopause. Women who undergo early menopause, either due to surgical removal of their ovaries or premature ovarian failure, have similar rates of cardiovascular disease as age-matched men. Most women have one or more risk factors for cardiovascular disease.

What are the gender differences?
There are notable differences in the types of heart disease that affect men and women. Differences exist in the underlying mechanisms of their heart disease, the symptoms that they present, and the types of complications they experience. There are also differences in the comprehensiveness of the medical care men and women receive and the general awareness of the magnitude of women's cardiovascular risk compared to that of men.

Researchers who study the gender differences in cardiovascular disease often focus on the protective role of estrogen. Estrogen has numerous effects on vascular tissue. It relaxes blood vessels, lowering blood pressure (pre-menopausally). Estrogen blunts the effects of stress hormones (catecholamines) which are vasoactive and cause blood vessel constriction, especially in times of stress. Estrogen is also a natural antioxidant. However, estrogen also promotes blood coagulation, which isn't helpful. This is why women who use oral contraceptives are at an increased risk of thrombotic events (blood clots). The use of hormone replacement therapy containing conjugated equine estrogens, once thought to protect women against cardiovascular disease, is now known to increase CVD.

Several types of heart disease are more common in women than in men: stroke, hypertension, endothelial dysfunction, and congestive heart failure. Because the presentation of these diseases is often less symptomatic, both women and their doctors benefit from efforts to increase awareness and practice prevention to reduce cardiovascular disease.

While men and women have similar rates of hospitalization due to heart disease, women tend to have longer hospital stays, receive less of the recommended assessment and treatment, and experience greater long-term disability. Women are less likely to return to work following a CVD-related hospital admission and have lower health-related quality of life following an event. These are important reasons for women to be well educated about what they can do to prevent heart disease and the types of treatment that should be recommended if they do have heart disease. With this knowledge, women can advocate for their own best health care.

What are heart disease risk factors for women?
Many of the risk factors for cardiovascular disease are lifestyle behaviors. Diet, exercise, tobacco use, alcohol consumption, overweight, psychosocial stress, and depression are all significant risk factors. The good news is that these factors are largely modifiable.

Medical conditions such as obesity, diabetes, hypertension, and high cholesterol also increase women's risk of heart disease. Women are more likely than men to have multiple risk factors. Women also have higher risks of mortality (death) when they have multiple conditions; for example, women with diabetes have an increased risk of dying of cardiovascular disease compared to men with diabetes. Additional risk factors specific to women include oral contraceptive use, hormone replacement therapy, and history of preeclampsia or gestational diabetes during pregnancy.

Risk factors are very common in women and, in fact, women are also less likely to experience a heart attack or present with symptoms without at least one traditional risk factor. This suggests that if women and their doctors pay attention and treat early risk factors, heart attacks could be avoided.

Many risk factors can be easily identified through routine testing and review of lifestyle habits. Unfortunately, women are less likely to receive a comprehensive evaluation, even when they present to their doctor or hospital with symptoms. While simply improving the rates of basic assessment to equal the frequency of evaluation in men will improve CVD detection and prevention for women, in order to most accurately assess risk in women, different factors should considered in addition to the traditional markers of risk. This is because of the differences in the underlying types of CVD that affect women, and thus testing and screening should seek to identify those types of cardiovascular disease that a woman is most likely to have. 

Lifestyle
Dietary risk factors specifically include overconsumption of unhealthy fats (saturated fat and trans fatty acids) and underconsumption of good fats (mono unsaturated fats, omega-3 fatty acids) and fruits and vegetables (see below for information on what to eat to prevent and reverse CVD). Alcohol intake, greater than 1 drink per day for women, is also a risk factor.

Exercise is also a significant factor; women who are at less than 85% of their age-predicted exercise capacity have twice the risk of mortality compared to women who achieve an appropriate exercise capacity. For example, a 60-year-old woman should be able to achieve 85% of her target heart rate (136 bpm) during a vigorous exercise session and should be able to recover her heart rate down to at least 124 bpm within 1 minute. If she cannot, she is below her predicted exercise capacity and at increased risk. (See below for information on how much activity is necessary to prevent and reverse CVD).

Smoking is a substantial risk factor. Among women who experience a myocardial infarction under the age of 50, 60% are attributable to smoking. Additionally, exposure to secondhand smoke and environmental particulate (such as pollution) are known risk factors. Women who smoke should seek help to quit.

Psychosocial risk factors were first measured and quantified by the INTERHEART study, a large international study of CVD risk factors among men and women. Stress is a known risk factor and can stem from work, home, emotional distress, pain, lack of control, social isolation, or lack of support. While epidemiologists classically described marriage as a heart protective factor, this benefit is only seen for men; no differences in heart disease have been observed among married and non-married women. Depression is more prevalent in women and is a significant risk factor for both genders. Depression appears to directly increase CVD risk and also impacts women's success in adopting and sticking with healthy lifestyle behaviors. (See below for information on how to reduce stress-related CVD risk factors).

Personality traits can also contribute to CVD risk. Research has shown that Type A personality characteristics, such as competitive ambition, time urgency, and hostility all increase rates of CVD. A high locus of control or sense of being able to handle things is protective. Other factors, such as negative emotional states, having a fighting spirit, stoic acceptance or fatalism, or active coping mechanisms demonstrate a more complicated relationship with heart disease, likely modified by the other risk factors discussed previously.

Being overweight or obese is also a CVD risk factor. Women with a BMI greater than 25 are at increased risk both for CVD specifically and for other conditions such as high blood pressure and diabetes that indirectly increase heart disease risk. The good news is that as women adopt healthier lifestyle behaviors and lose even 5% of their excess weight, they measurably reduce their disease risk. 

Clinical measures and biomarkers of risk
Cholesterol, hypertension, high-sensitivity C-reactive protein (hs-CRP) and other lab tests have classically been termed risk factors but they are more accurately described as signs of preclinical or asymptomatic disease.

Lipids are important traditional risk factors for men and women, yet there are gender differences. While total cholesterol (TC) and low-density lipoprotein (LDL) cannot be ignored, among women low high-density lipoprotein (HDL) or "good" cholesterol and high triglycerides (TG) are more significant than LDL and TC alone. Elevated triglycerides can reflect fatty acid metabolism secondary to high dietary carbohydrate and low dietary omega-3 intake and thus are modifiable with diet or supplemental omega-3 fatty acids. Family history and genetics also play a role in cholesterol biomarkers.

Hypertension is an independent risk factor for CVD and increases risk for stroke dramatically. High blood pressure is defined as a systolic blood pressure greater than 140 mmHg and/or a diastolic pressure greater than 90 mmHg. High blood pressure puts stress on the vasculature, increasing the risk of rupture (hemorrhagic stroke) or ischemia. Stress, obesity, family history, and sodium intake all affect blood pressure. For every 20 mm increase in systolic or 10 mm in diastolic blood pressure, CVD risk doubles (for women aged 40 to 89). Preeclampsia, a condition of high blood pressure in pregnancy, doubles the risk for cardiovascular events over the 5 to 15 years after pregnancy.

Inflammation is at the root of atherosclerosis and most forms of cardiovascular disease. There are many biomarkers of inflammation that can help doctors differentiate the origin of the inflammation (such as whether it is coming from the inner lining of the arteries or from immune cell activity). American Heart Association guidelines recommend testing biomarkers of inflammation when the level of risk is uncertain. Because of the differences in the origins of heart disease in women, understanding inflammation and the resulting oxidative stress is important.

Inflammation can be measured with high-sensitivity C-reactive protein (hs-CRP). Several studies have demonstrated that hs-CRP is an independent risk factor for heart disease. That is, it adds information about someone's risk in addition to the information provided by cholesterol measurement, blood pressure, or any of the other risk factors that have been discussed. Increased hs-CRP may indicate a doubling of risk that can be identified only if this biomarker is measured. Other biomarkers of inflammation exist and can add precision to the doctor's assessment of where the source of inflammation is located; these are discussed in the laboratory testing section of this article.

How is heart disease risk calculated?
Risk classification has historically been calculated using the Framingham Risk Score. Based on the presence of risk factors, the likelihood of having a cardiovascular event within the next 10 years can be calculated and thus doctors can compute "how worried" they should be about someone at risk for a cardiovascular event. However, the Framingham score underestimates risk among women and is limited in estimating only the likelihood of coronary artery disease, not all forms of cardiovascular disease. Because of this, an alternative tool, the Reynolds risk score, may be more appropriate for women. Risk can be calculated at www.ReynoldsRiskScore.org (see table for risk factors included in the calculation). The table shows the factors considered in determining the risk score with each method.

What causes heart disease in women?
Much of heart disease is asymptomatic, meaning it does not cause symptoms. Thus it is particularly important for health care professionals to recognize risk factors, for women to be screened, and for everyone to follow lifestyle patterns known to prevent disease.

Heart disease results when the risk factors discussed previously cause maladaptive changes in the heart and blood vessels. For example, chronic high blood pressure increases the stress on the blood vessels and increases the turbulence of blood flow which leads to vascular inflammation and plaque deposits. A clot or narrowed artery prevents oxygen-rich blood from reaching the muscle downstream, leading to ischemia or damage to the heart muscle. Weak or damaged heart muscle cannot pump efficiently which leads to an enlarged, inefficient heart or congestive heart failure. Electrical signals don't pass through damaged tissue very well either, leading to arrhythmias. When any of these conditions occur due to the presence of risk factors, disease is likely to progress, although the specific patterns differ among men and women.

Women are less likely than men to have obstructive or ischemic causes of heart disease. In women, when they do experience ischemic heart disease, it is more likely to affect small vessels. CVD in women is more likely to involve microvascular disease, inflammation and endothelial dysfunction, and congestive heart failure. In these conditions, small blood vessels and the linings of the vessels are affected. This is often asymptomatic, but over time it can lead to angina, vasospasm (spasm of the coronary arteries), stroke, and many of the other forms of heart disease that have been discussed. Women also have more coagulative disorders, possibly due to the role of estrogen.

What are the signs and symptoms of heart disease in women?
Signs include hypertension, angina, edema (fluid accumulation in tissues), palpitations, and vague symptoms that are often confused with indigestion or musculoskeletal pain. Overall symptoms get worse with exertion and improve with rest. Women are more likely than men to experience unstable angina (chest pain or sensations that occur irregularly and unpredictably).

Some women experience classic angina symptoms such as chest pain or pressure but more commonly, women experience:
  • chest tightness
  • squeezing
  • burning
  • sense of discomfort

While the pain is often described as coming from behind the chest bone, women are more likely than men to experience discomfort in the arms, neck, jaw, throat or back.

Women often have a hard time determining where the pain is exactly coming from.

It may be accompanied by:
  • nausea or indigestion
  • sweating
  • lightheadedness
  • fatigue

Symptoms of coronary artery disease or angina typically occur at times of exertion such as during exercise, like rushing for a plane. However, for women, it is also often triggered by high stress, including mental or emotional stress, during activities of daily living, or even at times of rest.

Unfortunately women are less likely to seek help if symptomatic. When they do seek help, they are less likely to get stress tests. When abnormal stress tests are reported, they are less likely to get angiography. Any chest pain that doesn't resolve with a few minutes of rest, or chest pain that recurs, needs to be evaluated.

Congestive heart failure is also a more common type of heart disease among women compared to men. Heart failure is when the heart muscle is not strong enough to pump efficiently. Symptoms and signs of heart failure can include:
  1. swelling in the legs or abdomen (edema)
  2. fatigue
  3. high blood pressure
  4. shortness of breath

Heart failure is the leading cause of hospital admission globally, and the proportion of admissions that are women continues to increase. If women notice these symptoms, they should seek evaluation.

What are the signs and symptoms of a heart attack in women?
Highly concerning is a recent national survey by the American Heart Association that reported that only 53% of women said the first thing they would do if they thought they were having a heart attack was to call 9-1-1! On average, women have a 4-hour delay in seeking treatment when they are having a heart attack. A time delay of 4 hours can mean the difference between getting life-saving treatment or not.

Heart attack symptoms can be similar to the symptoms women experience with angina, but they do not resolve with rest. Chest pain and pain radiating into the left arm are classic, but lesser known symptoms can include:
  • chest pressure
  • suffocating feeling
  • shortness of breath
  • shoulder blade discomfort
  • sense of dread
  • unusual back pain
  • jaw, head, or neck pain
  • nausea
  • an intuitive feeling that something just isn't right

Don't ignore these symptoms in yourself or in a woman you love!

What are the signs and symptoms of stroke?
Strokes are sometimes called brain attacks because the causes are very similar to the causes of heart attack -- a clot in or rupture of a blood vessel and damage to the tissue downstream from the site of injury. In the case of a stroke, the symptoms depend on what part of the brain is affected; thus strokes can affect speech, hearing, vision, movement, sensations, or other functions. Common stroke symptoms begin quite suddenly and can include:
  • numbness or weakness in one limb, part of the face, or other region, especially if it is one-sided
  • seeing double or blurring vision
  • difficulty speaking, finding words, or understanding language
  • loss of balance, dizziness, vertigo, difficulty walking
  • sudden, severe headache

Women also report unique symptoms:
  • sudden hiccups
  • sudden general weakness
  • sudden sweating
  • sudden anxiety and fear

The American Stroke Association has initiated the F-A-S-T campaign to help people identify possible stroke and call 9-1-1 quickly. F-A-S-T stands for:
  1. Face: Ask the person to smile and look for drooping on one side.
  2. Arms: Ask the person to raise their arms and look for weakness or drifting on one side.
  3. Speech: Ask the person to repeat a simple sentence and listen for slurring or inappropriate answers.
  4. Time: If any of these symptoms are present call 9-1-1 immediately as rapid administration of medicine can make a difference for some types of stroke.

How is heart disease in women diagnosed?
Women are less likely to get thorough cardiac assessment or treatment when they present to their doctors or hospital for care, so it is especially important for women to understand what may be involved in evaluation so they can be advocates for themselves. As discussed previously, women can evaluate their own risk factors using the Reynolds Risk Score. This tool is more sensitive in catching heart disease in women. Women can complete their own scores and bring their results to their doctor.

Evaluation of CVD may include the following tests:
  • EKG or ECG (electrocardiogram): This test measures the electrical activity of the heart. From the patterns of conductivity, different conditions can be diagnosed. For women, it is important to know that while there are some gender-specific differences in reading ECG results, the differences are small. It is important to be tested if you have risk factors, even if you are asymptomatic.
  • Stress-ECG or exercise-ECG: This is perhaps the most important test for women at risk of CVD. During this test, the woman is connected to the ECG lead wires as she would be for a regular ECG but she is asked to walk and/or run on a treadmill per a timed protocol. Heart rate and blood pressure are also measured. It is noteworthy that, in the past, stress tests were thought to be less accurate in women because many women had difficulty achieving the exercise thresholds and thus had "invalid" tests. However, there is significant diagnostic information in measuring the level to which a woman can exert herself on the treadmill. If she is unable to reach 85% of her age-predicted exercise capacity it is known that she is already at a 2-fold increased risk of heart attack regardless of additional ECG findings. AHA/ACC guidelines state that ECG AND stress testing should be performed as initial screening in asymptomatic women.
  • Endothelial testing (EndoPat): This non-invasive test helps diagnose early heart disease in the lining of the blood vessels -- the endothelium. Normal endothelial function protects the blood vessels from developing atherosclerosis. In this test, detectors are placed on the finger tips and a blood pressure cuff occludes blood flow to the arm for a few minutes. When the cuff is released, it measures how the blood vessels respond to the reperfusion. This test is highly useful in detecting early coronary artery disease (CAD) and is especially relevant to women because women have higher rates of endothelial dysfunction and microvascular disease.
  • Ankle-brachial Index (ABI): This is a test performed with a blood pressure cuff around the ankle and around the arm. The differences in blood pressure at the two sites are compared both before and after mild exercise. Results diagnose peripheral artery disease.
Imaging studies
Imaging studies provide information on blood flow in addition to the size and function of the heart muscle. Image-assisted stress tests such as a stress echocardiogram or single photon emission computed tomography (SPECT) provide more diagnostic detail than static tests. Because women tend to have coronary artery disease that affects only one vessel, it may be harder to detect cardiovascular disease in women with imaging tests.

  • Echocardiograms: These tests provide images of the structure and function of the heart. The echocardiogram (often called a stress echo test) is an ultrasound examination and does not involve radiation. Stress echo is the most sensitive test for women, but there are a few limitations; breast tissue can make visualization of the coronary vessels difficult, decreasing sensitivity. Like any stress test, obese or de-conditioned women may have difficulty reaching the exercise thresholds for diagnostic specificity. From an echocardiogram we can learn:
  1. The size of the heart's chambers
  2. The strength of the heart muscle called ejection fraction or EF
  3. The function of the heart valves (Heart valves can be too tight, called stenotic; or leaky, called regurgitation.)
  4. Has the heart muscle been damaged from a heart attack?
  5. What are the pressures inside the heart?
  • Nuclear imaging: Myocardial Perfusion Imaging tests use radioactive tracers in the bloodstream and X-rays to see with a high degree of detail the flow of blood through the arteries and thus identification of plaques that prevent normal blood flow. This can be done during exercise or at rest using a medication to simulate exercise. It can also be done during symptoms of a heart attack or acute coronary syndrome to determine if the woman is having a heart attack, or during asymptomatic times to determine the degree of narrowing of the vessels. Because women tend to be more asymptomatic at rest and develop symptoms under stress, it is thought that myocardial perfusion imaging is particularly of value in diagnosing women with coronary artery disease (CAD). Single Photon Emission Computed Tomography (SPECT) or Positron Emission Tomography (PET) imaging can both be used in cardiac perfusion studies with a variety of tracers. They include technetium, thallium, and more recently rubidium. Rubidium is the most sensitive and specific for determining blood flow to the heart muscle. The rubidium test is performed in a PET scanner.
  • Electron beam CT (EBCT) test: Coronary calcium scores (CAC) can be calculated from an EBCT test. This more detailed study measures the amount of calcified plaque in the vessels. CAC has been shown to be an independent predictor of CAD beyond other risk factors. It has also been shown that CAC adds to the sensitivity of SPECT results alone. CAC testing is useful in identifying early atherosclerosis, at a stage when patients can make lifestyle changes to prevent a heart attack.
Invasive testing
Cardiac catheterization/coronary angiogram is the most accurate way CAD can be evaluated; however, it is an invasive test with some risk. In this test, a small tube is threaded through the arteries to the heart where a small amount of dye is released and viewed with X-ray. The person is sedated and local anesthetic is used. From this test, doctors can determine how well blood is flowing through the arteries in the heart wall. One of the advantages of a coronary angiogram is that therapeutic procedures (an angioplasty) can be immediately performed when a blockage is found (more on this below).

Laboratory testing
  • Cholesterol tests are still the most useful tool to identify risk; if you only do one thing to measure your risk of cardiovascular disease, have your lipids tested. A lipid panel includes total cholesterol (TC), HDL cholesterol, LDL cholesterol, and triglycerides (TG). Research shows that low HDL and high TG may be more significant in women than LDL and TC. The total cholesterol:HDL ratio is an important summary of risk and it should be less than 3.5. HDL particles represent healthy processing of lipid. LDL particles tell doctors about lipids that will ultimately need to be stored in tissues, such as blood vessel walls.
  • However, cholesterol isn't simply high density or low density, it is every size and concentration in between (see below). Advanced lipid tests look at these subfractions of lipids in more detail. These tests measure additional properties of lipoproteins such as their size, density, particle number, or concentration. Lipid sub-fraction testing is useful when standard lipid tests do not clearly show if a person is at moderate risk or well protected. They are also useful to guide treatment, such as providing feedback on how successful diet and exercise changes have been.
  • High-sensitive C-reactive protein (hs-CRP) has been found to be a better predictor of CVD in women, independent of other biomarkers. It is a marker of inflammation, although it is not specific to cardiac tissue. Many experts suggest that hs-CRP be added to routine lab testing for women at risk for and with CVD.
  • Other biomarkers of inflammation range from the non-specific (fibrinogen, white blood cell count) to the specific. For example, lipoprotein-associated phospholipase-A2 or Lp-PLA2, is a measure of inflammation within the plaques in the wall of the artery. Myeloperoxidase is a measure of the inflammatory response in the lumen of the artery and tells doctors about the immune response to "clean up" unstable plaques; however, it can also be elevated in other inflammatory conditions such as autoimmune disease. The biomarker called F2-isoprostane is not only a marker of inflammation (oxidative stress specifically), it is a chemical signal that triggers vasoconstriction which can cause further cardiovascular problems. Chemical signals called cytokines can also be measured. A few specific cytokines have been shown to independently add information about the risk of dying from cardiovascular disease. Those called tumor necrosis factor receptor-II (TNF-II), interleukin-6 (IL-6), and intercellular adhesion molecule-1 (ICAM-1) add precision to the doctor's assessment of risk of dying in men and women with cardiovascular disease.
When a woman is suspected of having a heart attack, additional tests are run in the hospital to determine if her heart tissue has been damaged. These tests include:
  • creatine kinase isoenzyme MB (CK-MB) levels
  • cardiac troponin levels
  • myoglobin levels
B-type natriuretic peptide (BNP)
Cardiac biomarkers like BNP and CRP are better predictors of ischemic events in women as opposed to the routinely checked CKMB and troponins, which do not rise to such high levels in women as in men. Some cardiovascular specialty labs are also running highly sensitive tests that measure very small amounts of these same substances, and some doctors are using these in hope of detecting very mild ischemia and heart muscle damage that precedes a full heart attack.