CARDIOLOGY PATIENT PAGE Introduction to Noninvasive Cardiac Imaging Ron Blankstein, MD Noninvasive cardiac imaging refers to a combination of methods that can be used to obtain images related to the structure and function of the heart. As opposed to invasive techniques, which require catheters to be inserted into the heart, noninvasive tests are easier to perform, are safe, and can be used to detect various heart conditions, ranging from plaque in the arteries that supply the heart muscle (known as coronary artery disease) to abnormalities that impair the ability of the heart to pump blood. As a result of technological advances, the number of available noninvasive cardiac tests that physicians can order has increased substantially over the last decade (the Figure). Although these tests have improved physicians abilities to diagnose and treat heart disease, it is important to understand that not all individuals benefit from noninvasive cardiac imaging. Therefore, these tests should be ordered only at the advice of a physician and should be considered only if the information provided would influence subsequent treatment with medications, procedures, or lifestyle interventions. When Is Noninvasive Cardiac Imaging Used? The goal of cardiac testing may include any of the following: (1) to identify or exclude various forms of heart disease as a reason for a person s symptoms, (2) to establish the risk of developing future heart disease such as a heart attack, and (3) to decide on the need for additional medical therapies and procedures. For instance, in patients with coronary artery disease, the results of imaging tests could be used for selecting between procedures such as placing stents in the arteries of the heart or performing bypass surgery versus pursuing aggressive treatment with medications. Do I Need a Cardiac Imaging Test? Although some cardiac imaging tests can be used to evaluate the risk of individuals who do not have any symptoms, the majority of tests are performed to evaluate the cause of symptoms that may be attributable to cardiovascular disease (Table 1). It is important to know that although some individuals with narrowing in the coronary arteries may experience chest discomfort or shortness of breath most often during physical activity such symptoms can be caused by other reasons that are not related to heart disease. Table 2 lists questions about cardiac imaging tests that you should discuss with your physician. What Are the Different Types of Cardiac Imaging Tests Available? Table 3 provides an overview of the available noninvasive cardiac tests that your physician may order. Although different types of tests may be used to evaluate different disorders, several different testing options may be suitable for evaluating the same condition. Therefore, if testing is needed, it is important for your doctor to choose the test that she or he feels is the most appropriate for your clinical condition. How Will My Physician Choose Among These Tests? The choice of test type will depend on the type of heart disease being evaluated and your medical history. For instance, individuals who already have known coronary artery disease may require a test that iden- The information contained in this Circulation Cardiology Patient Page is not a substitute for medical advice, and the American Heart Association recommends consultation with your doctor or healthcare professional. From the Noninvasive Cardiovascular Imaging Program, Departments of Medicine (Cardiovascular Division) and Radiology, Brigham and Women s Hospital, Harvard Medical School, Boston, MA. Correspondence to Ron Blankstein, MD, FACC, Noninvasive Cardiovascular Imaging Program, Department of Medicine (Cardiovascular Division) and Department of Radiology, Brigham and Women s Hospital, 75 Francis St, Room Shapiro 5096, Boston, MA 02115. E-mail rblankstein@partners.org (Circulation. 2012;125:e267-e271.) 2012 American Heart Association, Inc. Circulation is available at http://circ.ahajournals.org DOI: 10.1161/CIRCULATIONAHA.110.017665 e267
e268 Circulation January 24, 2012 Figure. Example of images/data typically provided by various noninvasive cardiac tests. CT indicates computed tomography; MRI, magnetic resonance imaging. tifies abnormalities in blood flow under rest and stress conditions. On the other hand, in lower-risk patients, exercise treadmill testing or cardiac computed tomography can be considered (see Table 3 for details). Because not all tests are available in all Table 1. Symptoms That May Require Testing Chest discomfort Jaw, left shoulder, or left arm pain Shortness of breath Lightheadedness/dizziness Fatigue Table 2. Questions to Discuss With Your Physician What is the procedure that I will be having? Do I need this test? Do I have any alternatives? Could the results of this test affect how I am being treated? Will I be required to exercise during this test? Are there any medications which I should stop taking before the test? centers and different facilities may have different areas of expertise, your doctor should choose a test that your local hospital or clinic has sufficient experience in performing and interpreting. Most computed tomography examinations and some magnetic resonance imaging examinations require the use of intravenous contrast administration. Use of such contrast should be avoided in patients with abnormal kidney function (If needed, kidney function can be determined with a blood test). Furthermore, patients who are overweight may have lower image quality for some types of tests (stress echocardiogram, nuclear single-photon emission computed tomography) and may benefit from alternative techniques (eg,
Blankstein Introduction to Noninvasive Cardiac Imaging e269 Table 3. Overview of Noninvasive Cardiac Imaging Tests Type of Cardiac Testing What Does This Test Show? This Test Is Not Recommended for What Are the Most Common Conditions That This Test Evaluates? Patient Preparation/ Considerations Echocardiogram (during rest conditions) An ultrasound of the heart is performed by trained technicians and allows doctors to evaluate the pumping function of the heart and the function of the heart valves. Doctors can learn information about the size of the chambers, the thickness of the heart muscle, and whether there is fluid around the lining of the heart Evaluation of coronary artery disease (the arteries of the heart are not seen during this test) Reduced heart pumping function or heart failure Damage after a heart attack Disease involving the heart valves No preparation is required This test is widely available Exercise treadmill testing (without imaging) An exercise treadmill testing is performed by an exercise physiologist and provides doctors with information regarding the heart rate, blood pressure, symptoms, and electrocardiogram changes (ie, electric activity of the heart) that occur during or after exercise. This information may be used to identify the likelihood of plaques that limit the blood flow to the heart muscle during exercise Individuals who are unable to walk on a treadmill Individuals who do not have any symptoms Individuals with pacemakers or who have certain ECG abnormalities This test will not identify the presence of small plaques that do not limit blood flow Wear comfortable clothes/shoes to exercise This test is widely available Avoid eating before test Coronary artery calcium scoring scan Nuclear stress test A calcium scan is a computed tomography of the heart that detects whether there are plaques that contain calcium involving the arteries of the heart. This test does not use any intravenous contrast In selected individuals without known coronary artery disease, the presence/amount of plaque can be used to determine future risk of cardiovascular events such as heart attacks A nuclear stress test provides images of the blood flow to the heart muscle both under resting conditions and during stress (this can be accomplished with either exercise or medications). This test can be used to detect abnormal blood flow to the heart muscle from blockages or narrowing in the coronary arteries and the presence of prior heart attacks Not useful for individuals with known coronary artery disease or who are already at high risk Not performed for the evaluation of symptoms Not recommended for individuals 40yofage Patients with severe obesity may have limited images Determine future risk of cardiovascular disease among individuals who have no symptoms Useful only if the results of the test could influence treatment decisions No preparation is required You will need to hold your breath for 10 s Avoid products containing caffeine for 24 h before the test (Continued)
e270 Circulation January 24, 2012 Table 3. Continued Type of Cardiac Testing Cardiac computed tomography Cardiac magnetic resonance imaging What Does This Test Show? Technical note: There are 2 types of nuclear stress tests. The most commonly available test is single-photon emission computed tomography, although some centers may use positron emission tomography. Positron emission tomography has limited availability but may provide improved images, particularly in obese patients A cardiac computed tomography can be used to evaluate for the presence of plaque within the wall of coronary arteries. When plaque is present, cardiac computed tomography can be used to estimate the severity of narrowing of the coronary artery Cardiac computed tomography is most effective at excluding the presence of coronary artery disease. In other words, if your computed tomography scan shows no plaque or narrowing, it is extremely unlikely that your symptoms are related to coronary artery disease. On the other hand, the presence of plaque and narrowing of the arteries is not always associated with abnormalities of blood flow and may therefore not be related to your symptoms A cardiac magnetic resonance imaging test can be used to evaluate for many forms of heart disease, including heart muscle dysfunction, cardiac masses, and many other rare cardiac disorders. During a cardiac magnetic resonance imaging, a stress test (using medications) can be performed by imaging the blood flow to the heart under rest and stress conditions This Test Is Not Recommended for This test will not identify the presence of plaques that do not limit blood flow Routine evaluation of individuals who do not have any symptoms Individuals who have a high likelihood of disease (older age, eg 75yof age, and/or the presence of multiple risk factors such as high blood pressure, diabetes mellitus, elevated cholesterol, or smoking) Evaluation of narrowing inside coronary stents (except for very large stents) Individuals with fast or irregular heart rate Individuals who have abnormal kidney function Patients with certain implanted metallic objects (most pacemakers, all defibrillators) cannot undergo magnetic resonance imaging Patients with severe kidney function abnormalities may not be able to receive gadolinium (special contrast used during most cardiac magnetic resonance imaging examinations) What Are the Most Common Conditions That This Test Evaluates? Symptoms in patients with known coronary artery disease (prior stents or bypass surgery) Evaluation of bypass grafts in patients with prior cardiac surgery Evaluation before ablation procedures (see Table 1) Cause of heart muscle disease (cardiomyopathy) Evaluation after heart attack Evaluation before ablation procedures Patient Preparation/ Considerations Wear comfortable clothes/shoes to exercise You may be given medication to lower your heart rate You should not have this test if you are pregnant or are allergic to intravenous contrast dye If you have severe claustrophobia, this test may not be possible (Although in some cases, use of medications to relax you may help) If a stress test will be performed, avoid products containing caffeine for 24 h before the test This examination has limited availability and is performed only in specialized centers Coronary artery disease means deposition of plaques in the arteries that supply the heart muscle with blood. Patients with prior heart attacks, bypass surgery, or stents are all considered to have coronary artery disease.
Blankstein Introduction to Noninvasive Cardiac Imaging e271 cardiac magnetic resonance imaging, nuclear positron emission tomography) if available. Table 4. Typical Radiation Exposure Associated With Cardiac Imaging Tests Relative to Naturally Occurring Background Radiation Exposure Test Type Naturally occurring annual background radiation exposure for a person living in the United States ( 3 msv) Coronary artery calcium score Cardiac computed tomography angiography Nuclear stress test (single-photon emission computed tomography) 1 Exposure (Relative to Row 1) 1 0.5 1 4 3 4 Exercise treadmill testing 0 (with no imaging) Cardiac magnetic resonance 0 imaging/echocardiogram Note that the above estimates are based on typical estimates using the most commonly performed techniques; actual exposure may vary between individuals and among different centers. What Are the Risks of Testing? The majority of cardiac imaging tests are extremely safe. During tests that use exercise or medications that simulate the effects of exercise, the chance of having a heart attack or dying as a result of the test is less than 1 in 10 000. Tests that use a radioactive medication (nuclear cardiology) or x-rays (computed tomography) are associated with a small exposure to radiation. Table 4 provides a comparison of the radiation dose of commonly used cardiac imaging tests relative to nonmedical exposure from background radiation. Although there is no direct evidence linking the small amounts of radiation used in imaging tests to the development of cancer, given the known harmful effects of larger amounts of radiation, it is prudent to limit unnecessary exposure to radiation, particularly in younger individuals because they may be more susceptible to the potential harmful effects of radiation. It is important to understand that for the majority of patients who require cardiovascular testing, the benefit of these tests far outweighs the small amount of risk. If you have questions about the benefits and risks of the examination, it is always best to talk with your doctor. Before your test, technicians and/or physicians specializing in imaging may also be able to provide you with more information about your specific test. Acknowledgment The author acknowledges Erin West, chief exercise physiologist, Brigham and Women s Hospital. None. Disclosures Reference 1. Fazel R, Dilsizian V, Einstein AJ, Ficaro EP, Henzlova M, Shaw LJ. Strategies for defining an optimal risk-benefit ratio for stress myocardial perfusion spect. J Nucl Cardiol. 2011;18:385 392.