Cardiac ischemia is a situation in which the flow of oxygen-rich blood to the heart muscle is impeded, resulting in inadequate oxygenation of the heart. The most common cause of cardiac ischemia is plaque buildup in the arteries due to the long-term effects of coronary artery disease. This plaque buildup narrows the arteries to the point where the amount of blood flowing through the arteries is not enough to supply oxygen-rich blood to the heart, especially during times of physical exertion or emotional stress.
The lack of oxygen is often temporary, and symptoms can include a type of chest pain, pressure or discomfort called angina. These episodes may last anywhere from 2 to 20 minutes. However, many episodes of ischemia do not have any associated symptoms (silent ischemia).
Lengthy episodes of cardiac ischemia can be a sign of a heart attack. A heart attack occurs when a blood clot blocks the flow of blood to the heart muscle. It can occur in an artery already narrowed by plaque (atherosclerosis), or a heart attack can occur after a blood clot breaks off from its original site and travels through the arteries. The blockage causes a sudden and possibly complete interruption of oxygen-rich blood flow, and the resulting heart attack could cause permanent damage and scarring to the portion of the heart muscle supplied by the blocked artery. Prevention and treatment are related to modifying the underlying factors that promote the development of atherosclerosis and blood clot formation.
About cardiac ischemia
Ischemia describes a situation in which the flow of oxygen-rich blood is restricted. It can occur in many areas of the body. Reduced blood flow to the brain, for example, is called cerebral ischemia, which can lead to a “mini-stroke” (transient ischemic attack) or full ischemic stroke. Ischemia in the liver and kidneys are called hepatic ischemia and renal ischemia, respectively. In the legs ischemia can cause pain when walking (claudication) or even more severe problems such as gangrene and tissue death (necrosis).
Cardiac ischemia refers to reduced blood flow to arteries around the heart (coronary arteries), usually the result of the buildup of plaque (atherosclerosis). In many cases, ischemia has no symptoms (silent ischemia). In these patients, it is important to identify the ischemia before a major heart-related health concern, such as heart attack or sudden cardiac death, occurs. The American Heart Association estimates that between three and four million Americans have silent cardiac ischemia.
Other patients experience a kind of chest discomfort or pain (called angina) with their ischemia. Episodes of angina may last between 2 and 20 minutes. The discomfort or pain is often described as “crushing” or “heaviness.”
Minor episodes of cardiac ischemia tend to cause little long-term damage to the heart, but there may be serious side effects in some patients:
They can cause abnormal heart rhythms (arrhythmias), which can lead to either syncope (fainting) or cardiac arrest (the abrupt inability of the heart to pump blood) and sudden cardiac death.
Severe or lengthy episodes can trigger a heart attack.
The collective effects of minor episodes of cardiac ischemia can potentially lead to a weakening of the heart muscle (cardiomyopathy).
Because of the potentially harmful effects of cardiac ischemia, researchers have thoroughly investigated both its symptoms and available strategies for diagnosing, treating and preventing it.
Signs and symptoms of cardiac ischemia
Some people have painful symptoms of cardiac ischemia, and others have no symptoms at all (silent ischemia). People who feel pain, pressure or discomfort from cardiac ischemia have an angina attack. Angina is the primary symptom of coronary artery disease(CAD). According to the American Heart Association, rouhgly 20 percent of patients who have a heart attack experience angina before the attack. Angina may feel like a squeezing vise or crushing pressure deep in the chest behind the breastbone (sternum) and may also be felt in the shoulders, arms, back, neck or jaw. In women, angina may be experienced as abdominal pain or inconsistent chest pain that does not fit the classic model of heart-related chest pain.
Translated literally, the term “angina pectoris” means “a choking sensation of the chest.” The pain of an angina attack can be a warning sign of a more dangerous underlying cause and should be taken seriously by patients, especially if it worsens or starts to happen more often. Angina that occurs at irregular times, without provocation (e.g., physical exertion) is known as unstable angina. This is considered a major warning sign of a heart attack, and any person experiencing unstable angina should consult a physician at the earliest possible opportunity.
It is important to also note that most chest pain reported to physicians is not cardiac ischemia, but due to some other cause (e.g., muscle pain, gastrointestinal issues). However, when chest pain is reported, physicians first will attempt to exclude cardiac problems.
Conversely, not all people with cardiac ischemia suffer from angina. According to the American Heart Association, as many as 4 million people in the United States suffer from cardiac ischemia without symptoms (silent ischemia). In fact, studies have shown that silent ischemia is the most common manifestation of coronary heart disease, accounting for about 80 percent of ischemic episodes.
Ischemia, whether silent or symptomatic, is associated with increased risk for heart attack and other serious cardiac events. In people with silent ischemia, the first indication of heart trouble is frequently a major heart attack. Thus, it is the goal of physicians to identify as many cases of silent ischemia as possible, through screening and careful attention to known risk factors for heart disease. Studies have demonstrated that silent ischemia can be more common among certain ethnic or racial groups. For example, recent reports find that Asian Americans, in comparison to white Americans, experience significantly fewer episodes of ischemic chest pain. Other symptoms, however, occur more frequently, such as shortness of breath, fatigue and palpitations.
Diagnosis methods for cardiac ischemia
A diagnosis of cardiac ischemia depends on whether it is symptomatic (with angina) or not (silent ischemia). Bouts of angina, coupled with the presence of risk factors for heart disease, may lead a physician to order tests to detect blockage in the coronary arteries. However, the diagnosis of silent ischemia is open to some debate. The medical community is working toward identifying the greatest number of people with silent ischemia by using widely available and financially feasible tests.
Widespread screening for cardiac ischemia among people with a low coronary risk profile is not recommended. However, there is some debate about the effectiveness of screening people at the higher end of the coronary risk profile. In general, screening of asymptomatic people (those who show no symptoms) is suggested for those with jobs linked to public safety (e.g., airline pilots), or for men over 40 and women over 50 with multiple risk factors, especially if they are about to start a vigorous exercise program.
Tests that may be used to diagnose cardiac ischemia include:
An electrocardiogram (EKG or ECG). Standard EKGs are noninvasive, quick, safe, painless and inexpensive tests that are routinely done if a heart condition is suspected. An EKG records the heart’s electrical activity as a graph or series of wave lines on a moving strip of paper. However, an EKG can only detect cardiac ischemia if an episode just happens to occur during the few minutes when the EKG is being done.
Exercise stress test. This is the most widely used screening test to detect silent ischemia. The test uses an EKG, but with the patient exercising in a controlled manner on a treadmill or stationary bicycle at varied speeds and elevations. The response of the heart under physical exertion can be measured and evaluated, often with the use of an echocardiogram.
Alternatively, a pharmacological stress test may be recommended for patients who are unable to perform physical activity. A drug such as dobutamine or adenosine is given to the patient, causing the heart to react as if the person were exercising, though the patient is actually at rest. Some drugs increase the heart rate, and other drugs increase blood flow by causing the coronary arteries to widen.
Either of these tests can be combined with a nuclear stress test, which includes an additional component that produces images of the heart. These images are particularly clear because they show contrasts between light and dark spots. The contrasts reveal any scarring or reductions in blood flow that occurred before, during or after exertion.
Holter monitor. A continuous EKG is temporarily attached to an ambulatory (freely moving) patient for a 24-hour period. This test can detect or diagnose abnormal heartbeats (arrhythmias), as well as episodes of cardiac ischemia. It can also help to evaluate the effectiveness of any medications, especially antiarrhythmics, that the patient may be taking. For longer term monitoring, patients may be outfitted with an event recorder that is activated by the patient only when a cardiac abnormality is detected. The results of these episodes are saved by the recorder so they can be evaluated at a later date by a physician.
Computed tomography arteriography (CT-A). This is a relatively new technique that uses a scanner to generate pictures of the carotid arteries, which lie in the neck and supply oxygen-rich blood to the brain. This is nearly identical to a carotid angiogram except that the contrast medium is put into the veins instead of the arteries and therefore has a lower risk of complications. This has become the primary test in some locations and is very likely to have a much more prominent role in the future as a result of the high reliability and availability of CT scanners in the United States.
One diagnostic aid is a relatively new blood test that measures blood levels of the protein albumin, which rises as a result of a heart attack. Approved by the U.S. Food and Drug Administration in February 2003, the test helps physicians further distinguish between chest pain and heart attack. Use of the test is recommended along with an electrocardiogram and an evaluation of cardiac enzyme levels.
Experimental diagnostic tests that use a type of nuclear imaging have shown success at revealing heart damage up to 30 hours after an interruption of blood flow has occurred. These tests may one day be used to diagnose cardiac ischemia.
Treatment options for cardiac ischemia
Because cardiac ischemia is due to the heart not getting enough oxygen, one treatment option involves reducing the heart’s need for oxygen or improving its utilization of available oxygen. This may include taking medications that slow the heart rate, reduce blood pressure and relax the blood vessels. Drugs used to accomplish these goals include ACE inhibitors, beta blockers, calcium channel blockers and nitrates. Aspirin and other antiplatelets may be prescribed to decrease the chance of a blood clot forming in the narrowed artery (which could trigger a heart attack). Exercise and/or stress management techniques may be helpful as well.
In some cases, physicians may choose to treat underlying factors that can lead to cardiac ischemia, such as hypertension, anemia and hyperthyroidism.
If noninvasive techniques are not successful, more invasive techniques such as a balloon angioplasty or bypass surgery may be recommended to clear the blockage in the coronary arteries, thus increasing blood flow to the heart. The development of drug-coated (drug eluting) stents has helped to reduce the rates of re-narrowing (restenosis) following angioplasty. Advances in treatment have also resulted in the increased use of off-pump bypass surgery. About 20 percent of coronary artery bypass surgeries are currently performed without use of the heart-lung bypass machine.
Prevention methods for cardiac ischemia
Because cardiac ischemia is usually caused by “hardening of the arteries” (atherosclerosis) associated with coronary artery disease, prevention involves understanding the risk factors associated with those conditions. People can then work to either avoid or reduce those risk factors, or to manage any unavoidable risk factors with the help of their physician.
Controllable risk factors associated with hardening of the arteries and coronary artery disease include:
Eating a diet that is high in fats and oils and cholesterol
Inadequate control of diabetes
Inadequate control of high blood pressure (hypertension)
Smoking any tobacco products (e.g., cigarettes, cigars, pipes)
Sedentary lifestyle (not exercising)
Obesity(body mass index [BMI] of 30 or greater)
Stress (which increases heart rate and blood pressure)
Until recently, hormone replacement therapy (HRT) was commonly prescribed to peri- and postmenopausal women to reduce their risk of heart attack. However, a large-scale study called the Women's Health Initiative showed that HRT was actually associated with increased risk of heart attack, stroke and other conditions. As a result, HRT is no longer prescribed for the primary purpose of increasing cardiac health.
Questions for your doctor on cardiac ischemia
Preparing questions in advance can help patients to have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions about cardiac ischemia:
Is it normal to experience chest pain while exercising if I have cardiac ischemia?
Can cardiac ischemia cause a heart attack?
Is shortness of breath a symptom of cardiac ischemia?
Is there a cure for cardiac ischemia?
Will I need surgery?
Will it help if I lose weight?
Should I alter my diet?
Can I continue to take my current medications?
What kind of changes in angina are dangerous?
If we treat the cause of my angina, will it reduce my chances of having a heart attack?
