Coronary heart disease costs the United States $108.9 billion each year.1 Between

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1 Cover Cardiac Diagnostic Testing: What Bedside Nurses Need to Know LUPE M. RAMOS, MSN, NP-C, ACNP Coronary artery disease affects more than persons annually and continues to be a leading cause of death in the United States. Recently, the number of available noninvasive cardiac diagnostic tests has increased substantially. Nurses should be knowledgeable about available noninvasive cardiac diagnostic testing. The common noninvasive cardiac diagnostic testing procedures used to diagnose coronary heart disease are transthoracic echocardiography, stress testing (exercise, pharmacological, and nuclear), multidetector computed tomography, coronary artery calcium scoring (with electron beam computed tomography or computed tomographic angiography), and cardiac magnetic resonance imaging. Objectives include (1) describing available methods for noninvasive assessment of coronary artery disease, (2) identifying which populations each test is most appropriate for, (3) discussing advantages and limitations of each method of testing, (4) identifying nursing considerations when caring for patients undergoing various methods of testing, and (5) describing outcome findings of various methods. (Critical Care Nurse. 2014; 34[3]:16-28) Coronary heart disease costs the United States $108.9 billion each year.1 Between 1999 and 2009, rates for death due to cardiovascular disease declined, yet coronary heart disease continues to be the leading cause of death in the United States, with 1 American experiencing a coronary event every 34 seconds. 2 Of those persons who die suddenly of coronary heart disease, 50% of men and 64% of women have had no previous signs or symptoms. 2 Accurate assessment and risk stratification of patients with coronary heart disease are crucial in identifying patients at greatest risk for coronary events. Thus, clinicians must be knowledgeable about the many forms of cardiac diagnostic testing available. Although considered the gold standard for visualization of coronary heart disease, coronary angio - graphy is invasive and expensive and involves a risk for acute myocardial infarction, stroke, arrhythmias, CNE Continuing Nursing Education This article has been designated for CNE credit. A closed-book, multiple-choice examination follows this article, which tests your knowledge of the following objectives: 1. Discuss common noninvasive cardiac diagnostic tests 2. Interpret results of noninvasive cardiac diagnostic tests 3. Describe nursing considerations for care of patients undergoing noninvasive cardiac diagnostic testing 2014 American Association of Critical-Care Nurses doi: 16 CriticalCareNurse Vol 34, No. 3, JUNE

2 Risk category Low Moderate Moderately high High Table 1 Framingham risk category definitions a No. of risk factors present Presence of diabetes mellitus in a patient older than 40 years, peripheral arterial disease, or other coronary risk equivalent 10-Year absolute risk for coronary heart disease, % <10 < >20 a Based on information from the third report of the National Cholesterol Education Program (NCEP) expert panel on detection, evaluation, and treatment of high blood cholesterol in adults (Adult Treatment Panel III) final report. 9 and bleeding. 3 This imaging method is not considered a first-line diagnostic study in patients at low risk for heart disease. 4 Cardiac imaging studies are costly and when used inappropriately can be harmful to patients by exposing them to unnecessary radiation and medications. In addition, unprecedented outside scrutiny by patients, increased emphasis on transparency, and pay-for-performance policies have required clinicians to be even more judicious in choosing the most appropriate, least invasive test for a patient s condition. Appropriate use of cardiac procedures has received much attention recently in media coverage of cases in which patients underwent procedures that were deemed medically unnecessary. 5 In addition, a recent article 6 in the New England Journal of Medicine indicated that only one-third of patients at low risk for coronary heart disease who had elective diagnostic angiography had obstructive coronary artery disease. Because of these findings, the authors 6 concluded that better strategies for risk stratification are needed. In 2005 the American College of Cardiology Foundation began to develop appropriate use criteria. The goal was to assist cardiology professionals in deciding when and how often to do an imaging test or procedure. The ultimate goal is to improve patient care and health outcomes in a cost-effective manner. 4,7 Adoption of appropriate use criteria has been somewhat slow because of confusion over the method with which the criteria were formulated, application of the criteria to clinical care, and use of the labels uncertain and inappropriate in describing indications for testing. 8 Clinicians are hopeful, however, that new terminology published in 2013 will lead to increased use of appropriate use criteria. 8 Because of the numerous advances and improvements in cardiac imaging, nurses should know about the vast array of diagnostic testing that a patient may undergo. Nurses play a key role in the safe administration of these tests by educating patients about the indication for testing and explaining the results. In this article, I review common noninvasive cardiac diagnostic tests, specifically those used in diagnosing coronary heart disease. Emphasis is placed on how each test is administered, what information is provided by the results, and what nurses need to know when caring for patients who have the tests. Risk-Factor Assessment For patients who have never had a diagnosis of coronary heart disease, a risk stratification method such as the Framingham Risk Score is useful in identifying patients 10-year risk for a major coronary event. 9 The Framingham Risk Score is based on a patient s sex, level of total cholesterol, level of high-density lipoprotein, systolic blood pressure, history of cigarette smoking, and age. 9 Depending on the score, a patient is assigned to a low-, intermediate-, or high-risk category (Table 1). Author Lupe Ramos is a nurse practitioner in cardiac services at St Joseph Hospital in Orange, California. Corresponding author: Lupe Ramos, 1416 N Olive St, Santa Ana, CA ( lupe38@msn.com). To purchase electronic or print reprints, contact the American Association of Critical-Care Nurses, 101 Columbia, Aliso Viejo, CA Phone, (800) or (949) (ext 532); fax, (949) ; , reprints@aacn.org. CriticalCareNurse Vol 34, No. 3, JUNE

3 Intermediate risk may be further categorized as moderate and moderately high. 9,10 The Framingham Risk Score is useful in helping both patients and clinicians identify appropriate lifestyle modifications in an attempt at primary prevention of coronary heart disease. For patients in the intermediate- to high-risk categories, the concern is how to approach the patients about diagnostic testing. The American College of Cardiology Foundation and the American Heart Association have issued guidelines to assist clinicians in selecting tests. I address these guidelines in the subsequent sections. Methods of risk-factor assessment include advanced lipid assessment, level of C-reactive protein, carotid intima-media thickness, and ankle-brachial index; however, in this article, I focus on the noninvasive imaging studies most often used in practice. Transthoracic Echocardiography Echocardiography is one of the most frequently used noninvasive cardiovascular diagnostic tests. 11 The procedure provides high-quality imaging and hemodynamic data in a safe, quick, and painless manner and requires little preparation of patients (unless done by the transesophageal approach). The imaging can be done by using a transthoracic or a transesophageal probe that emits ultrasound waves directed at cardiac structures. In transthoracic echocardiography, a probe is placed externally over the chest wall. The Framingham Risk Score can help If they are both patients and clinicians identify able, patients appropriate lifestyle modifications to are asked to prevent coronary heart disease. lie on their left side for better visualization of cardiac structures. Continuous electrocardiographic (ECG) monitoring is used to time events to the cardiac cycle. Transducer gel is placed on the chest wall to facilitate ultrasound transmission. The sound waves are interpreted by the ultrasound machine to reconstruct images of the heart. 12 Transthoracic echocardiography is done with M-mode, and either 2- or 3-dimensional imaging. M-mode provides a 1-dimensional view and is used for fine measurements. Two-dimensional imaging is the standard mode and is used for cross-sections of the heart moving in real time. Three-dimensional imaging is becoming more common and offers the benefit of eliminating some of the artifacts associated with 2-dimensional imaging. Doppler imaging is used to assess the speed and direction of blood as Table 2 Definitions of sensitivity and specificity Sensitivity Specificity Can be thought of as a true-positive rate If the results of a test with high sensitivity for detection of a disease are negative, the disease almost certainly is not present Can be thought of as a true-negative rate If the results of a test with a high specificity for detection of a disease are positive, the disease almost certainly is present it moves through cardiac structures and is particularly useful for identifying the severity of valve disease, flow across a ventricular septal defect, and severity of pulmonary hypertension. 12 Transthoracic echocardiography is useful in assessing conditions such as dyspnea, syncope, angina without elevation in cardiac enzymes or changes in ECG findings, sustained ventricular or supraventricular tachycardia, suspected valve disease, and cerebrovascular events. 12 It is also used to evaluate ventricular systolic and diastolic function, abnormalities in regional wall motion, hemodynamic changes, and presence of pericardial effusions with or without cardiac tamponade. 12 Transthoracic echocardiography allows visualization of areas of hyperkinesia, hypokinesia, akinesia, and dys - kinesia and imaging of aneurysmal segments. 11 This procedure is an accurate diagnostic tool for detecting and localizing acute myocardial infarction and is helpful in detecting complications of acute myocardial infarction such as ventricular free wall rupture and rupture of the papillary muscle. 11 Normal motion of the left ventricular wall during an episode of acute chest pain usually indicates that no myocardial infarction has occurred. 3 Although useful for diagnosing impending myocardial infarction and for assessing left ventricular function in patients after myocardial infarction, resting echocardiography alone does not have high sensitivity or specificity for the diagnosis of coronary heart disease in patients who do not have ischemia or infarction 13 (Table 2). The guidelines of the American College of Cardiology Foundation and the American Heart Association for cardiovascular risk assessment recommend echocardiography for detection of left ventricular hypertrophy in adults who have no signs or symptoms of heart disease who have hypertension. 13 Echocardio - graphy is not routinely recommended for patients who do not have hypertension CriticalCareNurse Vol 34, No. 3, JUNE

4 Table 3 Contraindications to stress testing a Absolute Congestive heart failure Uncontrolled cardiac arrhythmias Severe aortic stenosis Unstable angina Myocardial infarction within the past 2 days Acute pulmonary embolus Myocarditis Severe pulmonary hypertension Aortic dissection a Based on information from Fletcher et al. 15 Relative Known obstruction of the left coronary artery Tachyarrythmias with uncontrolled ventricular rate Hypertrophic obstructive cardiomyopathy Hypertension greater than 200/110 mm Hg Acute illness such as anemia Electrolyte imbalance Uncontrolled hyperthyroidism Stress Testing Stress testing is one of the most commonly used methods of noninvasive assessment of coronary artery disease. Stress testing involves the use of exercise (for patients who are physically able) or drugs such as vasodilators and dobutamine (for patients who are physically unable to exercise) to increase myocardial demand and is used to determine the presence of ischemia. Assessment data are collected by using continuous ECG monitoring, echocardiography, nuclear imaging, or various combinations of these 3 methods. Exercise Stress Testing Strenuous exercise increases heart rate, stroke volume, and cardiac output and activates the sympathetic nervous system, resulting in vasoconstriction of most vasculature except that of the exercising muscle and cerebral and coronary vessels. 14 Release of norepinephrine and increased levels of renin result in increased cardiac contractility. During exercise, coronary blood flow increases. Obstructive coronary artery disease prohibits adequate coronary blood flow to the affected area of the myocardium and ischemia occurs. 15 Exercise stress testing is therefore a useful way to assess for evidence of myocardial ischemia and exercise capacity. Exercise stress testing often involves use of a treadmill or bicycle ergometer. 14 In order to participate in an exercise stress test, patients must be alert and oriented and have adequate coordination. Advanced age, poor functional Table 4 Indications for terminating exercise testing a Absolute Acute myocardial infarction Moderate to severe angina Symptomatic decrease in systolic blood pressure despite an increase in workload Arrhythmias such as second- or third-degree atrioventricular block, ventricular tachycardia, frequent premature ventricular contractions, atrial fibrillation with rapid ventricular response Signs of poor perfusion including pallor, cyanosis, or cold, clammy skin Severe dyspnea Ataxia, vertigo, visual or gait problems, or confusion Patient requests to stop a Based on information from Henzlova et al. 18 Relative Decrease in systolic blood pressure greater than 10 mm Hg from baseline blood pressure, despite an increase in workload, in the absence of signs and symptoms Increasing angina Hypertensive response (systolic blood pressure >260 mm Hg, diastolic blood pressure >115 mm Hg) Fatigue, shortness of breath, wheezing, leg cramps, or claudication capacity, poor balance, joint or back pain, and generalized deconditioning are typically contraindications to treadmill testing 16 ; in these instances, pharmacological testing may be used (Table 3). Before stress testing begins, Advanced Cardiac Life Support equipment should be on standby. Leads are placed on the patient for 12-lead ECG, and baseline values are obtained. Baseline vital signs are assessed along with the patient s history and list of medications. Medications such as digoxin, calcium channel blockers, and -blockers may produce ST-segment depression or prevent the patient from reaching the target heart rate. 15 If safe to do so, administration of these medications should be stopped 24 to 48 hours before the stress test is done. Nursing considerations before treadmill testing include explaining the procedure to the patient and informing him or her of what to expect during the test, including signs and symptoms that warrant termination of the test (Table 4) and possible complications. 15 Because of the risk for aspiration, patients should not take anything by mouth for 4 hours before the test, but they may take routine medications with small amounts of water. 15 Patients should wear comfortable clothing and shoes and must be able to walk briskly up an incline. The skin should be cleansed where the ECG electrodes will be CriticalCareNurse Vol 34, No. 3, JUNE

5 applied to ensure good contact. If pharmacological testing is being done, intravenous access is obtained, preferably in the antecubital fossa. Intravenous access is not required for treadmill testing done without use of vasodilators or dobutamine. Various protocols for exercise stress testing exist, but much of the reported data are based on the Bruce protocol. 17 With the Bruce protocol, both the speed and the grade of the treadmill are increased every 3 minutes through each of 7 stages, for a total of 21 minutes of exercise; the goal is to reach at least 85% of the target heart rate (220 minus age). 18 Three key parameters are monitored during an exercise stress test: the patient s subjective clinical response (eg, dyspnea, dizziness, chest pain), hemodynamic response (eg, tachyarrhythmia, bradyarrhythmia, or marked hypotension or hypertension), and ECG changes (horizontal or downsloping ST-segment depression >1 mm). 15 Continuous ECG monitoring is done throughout the testing and for 6 to 8 minutes after exercise is completed (or longer if the patient is symptomatic). 15 Echocardiography may be used as an adjunct to treadmill or pharmacological stress testing and is indicated for symptomatic patients who have abnormal ECG findings at rest, such as findings indicative of left bundle branch block, use of a pacemaker, left ventricular hypertrophy, or use of digoxin. 13 If echocardiography is used, echocardiography is done Adenosine is useful in pharmacological stress testing because it can increase at the start of blood flow in normal coronary arteries the stress testing and imme- with little or no change in the flow in stenotic arteries. diately after exercise is completed (preferably <1 minute). 15 In pharmacological stress tests, echocardiographic images are obtained at baseline, time of peak dobutamine infusion, and during recovery. 15 Echocardiographic evidence of segmental and global left ventricular dysfunction is indicative of ischemia. Exercise stress testing is useful for detecting obstructive coronary disease in patients at high risk for the disease and for risk stratification of patients after myocardial infarction. 18 It is also helpful in assessing risk in patients with chronic stable coronary artery disease and in patients at low risk for acute coronary syndrome who are not having active chest pain or heart failure. 18 Exercise stress testing is also sometimes used for preoperative evaluation of patients undergoing noncardiac surgery. 18 It is not recommended as a method of risk assessment in asymptomatic patients who have low or intermediate risk for a coronary event. 13 The mean sensitivity of exercise stress testing for detection of coronary artery disease is 68%, and the specificity is 77% (in a meta-analysis of a findings obtained predominantly in men). 15,19 If echocardiography is added, stress testing has a sensitivity of 81% and a specificity of 92%, and if nuclear imaging is added, it has a sensitivity of 88% and a specificity of 90%. 19 Compared with men, women have an increased risk for false-positives, with a sensitivity of 31% to 71% and a specificity of 66% to 78%. 19 The difference between the sexes may be due to more frequent ST-T wave changes in women at rest, lower ECG voltage, and hormone-related factors. 20 Pharmacological Stress Testing Pharmacological stress testing is indicated for patients who are unable to exercise on a treadmill. Cardiac vasodilators such as adenosine, dipyridamole, and regadenoson and the positive inotrope dobutamine are common agents used in pharmacological stress testing (Table 5). Adenosine Adenosine antagonizes -adrenergic receptors, resulting in vasodilatation and a decrease in heart rate. Adenosine is useful in pharmacological stress testing because it can increase blood flow in normal coronary arteries with little or no change in the flow in stenotic arteries. 15 Stenotic arteries visualized with adenosine and a radiopharmaceutical show less uptake of the radioactive drug than normal arteries do. 15 In addition to the nursing considerations associated with exercise stress testing mentioned earlier, nurses caring for a patient undergoing pharmacological stress testing must ensure that the patient has not had any theophylline or dipyridamole 48 hours before the test and no caffeine-containing products 24 hours before the test, because these drugs competitively block the effects of adenosine. 15 An intravenous catheter with a Y-connector is required for injection of the adenosine and the radiopharmaceutical. Typically the adenosine is administered intravenously via an infusion pump at a dose of 140 μg/kg per minute for 6 minutes. 21 A radiopharmaceutical such as thallous chloride Tl 201 is injected after the first 3 minutes of the adenosine infusion 21 (see section on nuclear testing). Patients may experience flushing, shortness of breath, nausea, and even chest pain that is not 20 CriticalCareNurse Vol 34, No. 3, JUNE

6 Medication Adenosine Dipyridamole Dobutamine Regadenoson Dose 140 μg/kg per minute for 6 minutes 0.14 mg/kg per minute for 4 minutes Initiated at 10 μg/kg per minute and increased every 3 minutes to a maximum dose of 50 μg/kg per minute until THR is achieved Single bolus of 400-μg, 10-second infusion Table 5 Pharmacological agents used in stress testing a Adverse effects Flushing, shortness of breath, nausea, chest pain Chest pain, ECG changes, headache, dizziness Feeling of shakiness, nausea Chest discomfort, headache, abdominal pain, flushing, dyspnea, dizziness Contraindications Second- or third-degree AVB, sick sinus syndrome without a pacemaker, ventricular tachycardia, bronchospastic disease Second- or third-degree AVB, bronchospastic disease Uncontrolled hypertension, atrial fibrillation, tachy - arrhythmias, recent myocardial infarction, unstable angina Second- or third-degree AVB, sick sinus syndrome without a pacemaker, broncho - spasm, SBP < 90 mm Hg Nursing considerations NPO after midnight Off theophylline for 48 hours Off caffeine for 24 hours Can cause hypotension Short half-life Has longer half-life than adenosine Give aminophylline mg slow IVP for 1-2 minutes if adverse reaction occurs NPO after midnight Off -blockers for 48 hours If severe adverse effects, may give short-acting -blocker Has a longer half-life than adenosine Has mild effect on blood pressure Off dipyridamole, aminophylline, or caffeine for 48 hours If severe reaction, can give aminophylline mg IVP for 1-2 minutes Abbreviations: AVB, atrioventricular block; ECG, electrocardiogram; IVP, intravenous bolus; NPO, nothing by mouth; SBP, systolic blood pressure; THR, target heart rate. a Adapted from Henzlova et al. 18 necessarily indicative of coronary heart disease. ECG recordings and blood pressure measurements are taken every minute during the testing and for 3 to 5 minutes during the recovery phase. Adenosine should be avoided in patients with bronchoconstrictive or bronchospastic lung disease because of the risk for bronchospasm. It also should not be given to patients who have second- or third-degree atrioventricular block, sick sinus syndrome, symptomatic bradycardia (except in patients with a functioning pacemaker), or ventricular tachycardia. Because adenosine has a short half-life, adverse signs and symptoms typically resolve shortly after the infusion has ended. 22 The sensitivity of adenosine stress testing with echocardiology for detecting coronary artery disease is 62% to 79%, and the specificity is 88% to 93%. 23 Because use of vasodilators does not require that a target heart rate be reached, vasodilators are useful in patients who have chronotropic incompetence (inability of the heart rate to increase with increased activity) or depend on a pacemaker. 16 Dipyridamole Dipyridamole (Persantine) is another vasodilator that may be used for stress nuclear imaging. It stimulates production of prostacyclin, a potent inhibitor of platelet aggregation and vasodilatation. It also inhibits uptake of adenosine and increases local concentrations of adenosine. 22 Dipyridamole is administered intravenously at 0.14 mg/kg per minute for 4 minutes. 22 A radiopharmaceutical is injected 3 to 5 minutes after the dipyridamole infusion. Like adenosine, dipyridamole should be avoided in patients with bronchospastic lung disease. Adverse effects include chest pain, ECG changes, headache, and dizziness. 22 Dipyridamole has a longer half-life than does adenosine, and adverse signs and symptoms may last for 15 to 30 minutes after the infusion is complete. 22 If an emergency occurs, aminophylline should be given slowly at a dose of 50 to 250 mg as an intravenous bolus 1 to 2 minutes. 24 Regadenoson Regadenoson (Lexiscan) is another drug that may be used for myocardial perfusion imaging. Some evidence 25 suggests that patients subjectively feel better after a regadenoson stress test than after an adenosine stress test. Regadenoson is more cardioselective for adenosine receptors than is adenosine and is administered as a single rapid bolus of 0.4 mg over 10 seconds and then CriticalCareNurse Vol 34, No. 3, JUNE

7 Receptor Table 6 Adrenergic receptors and associated therapeutic response Response Vasoconstriction, bronchoconstriction Vasoconstriction, platelet aggregation Increased contractility, increased heart rate Vasodilatation, bronchodilatation an immediate 5-mL bolus. 22 The radiopharmaceutical for imaging myocardial perfusion is administered 10 to 20 seconds after the bolus. 26 Regadenoson is contraindicated in patients with second- or third-degree heart block and in patients with sinus node dysfunction who do not have a functioning pacemaker. Use of dipyridamole should be stopped 48 hours before regadenoson is injected, and patients should not ingest any theophylline or caffeine-containing products for at least 12 hours before the stress test. Dobutamine Dobutamine is another pharmacological stressor useful in patients who are unable to physically exercise and have contraindications to use of vasodilators, such as chronic obstructive pulmonary disorder. Dobutamine is often used in conjunction with echocardiography but may also be used with nuclear imaging. Dobutamine is primarily a 1 -inotrope but also has some 2 - and 1 -agonist properties (Table 6). The drug increases heart rate and myocardial contractility, leading to Nuclear stress testing is useful for detecting increases in coronary artery disease in asymptomatic coronary adults with a strong family history of coronary artery disease or diabetes mellitus and myocar- blood flow and in adults who have a coronary artery dial oxygen calcium score >400. demand without causing bronchoconstriction as the vasodilators can. During pharmacological stress testing, dobutamine is infused intravenously at a rate of 10 μg/kg per minute and increased by 10 μg/kg per minute every 3 minutes to a maximum dose of 50 μg/kg per minute until the target heart rate is achieved. 27 A radiopharmaceutical may be injected once the target heart rate has been achieved. Patients may feel shaky or nauseated during dobutamine administration. Patients with uncontrolled hypertension, atrial fibrillation, or tachyarrhythmia should not receive dobutamine. 27 Atropine may be administered at a dose of 0.25 to 0.5 mg if the patient is having difficulty achieving the maximum heart rate. 27 Nuclear Stress Testing Both exercise and pharmacological stress testing can be used in combination with intravenous injection of a radiopharmaceutical such as thallous chloride Tl 201 or technetium sestamibi Tc 99m (Cardiolite). 22 These agents are distributed into the myocardial tissue proportionally to the flow of blood. In nuclear stress testing, also called myocardial perfusion imaging, a radiopharmaceutical is injected first, before peak exercise stress or peak pharmacological vasodilatation. Then 15 to 20 minutes later, a rest scan is done. After the rest scan, the stressing agent and a second injection of the radiopharmaceutical are injected. Then after 30 to 60 minutes, a stress scan is done for comparison with the rest scan. Vessels that dilate take up more of the radiopharmaceutical than do diseased vessels. This lack of uptake is known as a perfusion defect. A reversible perfusion defect indicates ischemia and will occur during stress but will normalize when the heart is at rest. 22 A nonreversible or fixed defect (evidence of decreased uptake of radiopharmaceutical on both rest and stress images) suggests a scar or hibernating myocardium. 22 Hibernating myocardium is defined as an area of dysfunctional myocardium that improves once perfusion is reestablished. Contraindications to nuclear stress testing include the general contraindications for any stress test and the medications mentioned earlier. Some scanners may have a weight requirement, making nuclear stress testing an inappropriate technique for patients who weigh more than 135 to 158 kg ( lb). Nuclear stress testing is useful for detecting coronary artery disease in asymptomatic adults with a strong family history of coronary artery disease or diabetes mellitus and in adults who have a coronary artery calcium (CAC) score greater than It has no benefit in asymptomatic patients who have low or intermediate risk for heart disease. 13 Computed Tomography Another method of noninvasive diagnostic testing is computed tomography (CT). Historically, CT techniques for visualizing coronary arteries have been difficult, because of the constant motion of the heart during the 22 CriticalCareNurse Vol 34, No. 3, JUNE

8 cardiac cycle and respiratory motion produced by the rising and falling diaphragm during inspiration and expiration. 28 With the advent of multidetector CT (MDCT), improvements in spatial and temporal resolution have improved visualization of the coronary arteries, making this imaging method more reliable for detecting coronary artery disease. 28 With MDCT, an arm with an x-ray tube located within a moveable platform (a gantry) rotates around a patient with 165-ms or faster imaging at 3.0-mm intervals. 29 X-rays are taken on a detector array and converted to images. 30 Each detector array consists of an alignment of narrow rows or channels. Most arrays have 64 or more rows. The greater the number of rows, the shorter are the scan time and duration of exposure to radiation. 30 MDCT testing is conducted during a single breath hold. 28 Patients cooperation and ability to understand and follow directions are paramount to the success of this method. ECG gating is used, and images are acquired solely during a specific part of the cardiac cycle. With MDCT, images are obtained during end systole and mid diastole when the heart motion is the least. 28 In an effort to improve image quality, -blockers or calcium channel blockers are often administered before the procedure to decrease heart rate and reduce or eliminate ectopy. Because of the adverse impact of motion on the quality of the images, patients with atrial fibrillation are not candidates for this imaging technique. 28 Sublingual nitroglycerin may also be given to dilate the coronary arteries and improve visualization. In order to avoid a risk for profound hypotension, nurses must ensure that patients have not used phosphodiesterase inhibitors (eg, sildenafil, tadalafil, and vardenafil) within the previous 24 hours. Pacer and implantable cardioverter defibrillator wires, artificial valves, and surgical clips can be a source of artifacts and can make the images uninterpretable. 31 CT can be used for CAC scoring and with angiography. CAC Scoring The atherosclerotic process involves deposition of calcium in the coronary arteries. Any calcium deposition in the coronary arteries is considered abnormal. CAC screening is useful as an adjunct method for predicting risk for coronary artery disease in asymptomatic patients beyond traditional risk-factor stratification. The 2010 guidelines 13 of the American College of Cardiology Foundation and the American Heart Association recommend CAC screening as a reasonable method for risk assessment in patients who are asymptomatic and have a 10% to 20% 10-year Framingham risk for a coronary event (intermediate risk). CAC screening may also be reasonable for patients who are at low to intermediate risk (6% to 10% 10-year risk for a coronary event). 13 According to the guidelines, patients who are asymptomatic and at low risk should not undergo CAC measurement for cardiovascular risk assessment. 13 Use of CAC scoring may be reasonable, however, in asymptomatic patients who are more than 40 years old and have diabetes mellitus (high risk). 13 Electron Beam CT One method of CAC screening includes electron beam CT (EBCT). In EBCT, an electron beam rotates around the patient who is supine on the table with the arms extended over the head or at the side. The beam is directed at a stationary tungsten target that lies beneath In EBCT, a computerized scoring algorithm is used to generate a calcium score, which provides a measurement of the area and density of the calcium deposition in the coronary tree. the patient. EBCT allows the acquisition of 1.5- to 3-mm sections with an exposure time of 50 to 100 ms during a single breath hold. No intravenous contrast material is used, and the patient does not need to avoid ingesting anything by mouth beforehand. The procedure requires approximately 10 to 15 minutes. Patients usually experience little to no discomfort, and the CT tube is typically much larger than that of a traditional magnetic resonance imaging (MRI) device, so claustrophobia is not much of a concern. Patients may be asked to remove metal objects near the chest, such as jewelry or underwire bras, because these objects may produce artifacts in the images. EBCT requires less radiation than does MDCT; however, radiation from CAC screening is associated with a small but measurable increase in the risk for cancer. 32 In EBCT, a computerized scoring algorithm is used to generate a calcium score, which provides a measurement of the area and density of the calcium deposition in the coronary tree. The most commonly used score is the Agatston score. Patients who have a score of 10 or less are considered at low risk. Scores of 11 to 399 indicate intermediate risk, and patients with a CAC score greater than 400 are at very high risk. 33 In a systematic review 33 CriticalCareNurse Vol 34, No. 3, JUNE

9 CASE STUDY Ms Whitney, a 37-year-old woman with a history of hypertension and hyperlipidemia, has her cardiovascular conditions medically managed by her primary care provider. Her blood pressure is currently 128/78 mm Hg; she is taking olmesartan 10 mg twice a day and nebivilol 5 mg/d. Her lipid profile is as follows: total cholesterol 170 mg/dl (4.40 mmol/l; desirable <100 [2.60]), triglycerides 128 mg/dl (1.45 mmol/l; desirable <150 [<1.69]), low-density lipoproteins 78 mg/dl (2.02 mmol/l; desirable <70 [<1.81]), and high-density lipoproteins 30 mg/dl (0.78 mmol/l; desirable >50 [>1.3] in women). She takes rosuvastatin 10 mg once a day and omega-3-acid ethyl esters (Lovaza) 1 g/d. Other medications include aspirin 81 mg/d and escitalopram 10 mg/d. Her body mass index (calculated as weight in kilograms divided by height in meters squared) is 23. She is physically active and does 45 minutes of aerobic exercise daily, does not smoke, and describes herself as a social drinker. She works as a pharmaceutical representative. She has a family history of coronary artery disease on her father s side, and she has a 42-year-old brother who has coronary calcification. Although she currently has no indications of coronary artery disease, she was referred for further evaluation because she was concerned about her risk for a heart attack. Ms Whitney had electron beam computed tomography through a heart and vascular screening program at her local hospital to determine her coronary artery calcium score. The score was greater than 2000, which is in the 99th percentile. The cardiologist recommended that Ms Whitney have treadmill stress echocardiography. During the stress test, she had exercise-induced hypokinesis of the distal anterior septal region, no ST-segment depression, and some vague chest discomfort. Ms Whitney later had coronary angiography. The findings indicated that she had nonobstructive coronary atherosclerosis with severe coronary calcification, although she had no evidence of obstructive disease. No percutaneous coronary intervention was indicated at this time. Medical therapy was maximized, and she was referred for advanced cholesterol assessment and endocrine screening because of the unusually high coronary calcification revealed by both electron beam computed tomography and angiography. of CAC screening with standard EBCT, the range of sensitivities for detecting coronary artery disease were 68% to 97%, and specificities were 52.6% to 94%. CT Angiography CAC scoring by EBCT and MDCT is limited: noncalcified plaque cannot be visualized, and the degree of luminal stenosis cannot be determined. CT angiography (CTA) is an excellent technique in which ECG gating and administration of intravenous contrast material are used to visualize and measure calcified areas of coronary plaque and luminal stenosis. 34 Although considered inferior to cardiac catheterization, CTA can provide visualization of small, tortuous arteries (as small as 1 mm in diameter). 34 Coronary CTA can provide valuable information on distribution, severity, morphology, and composition of coronary arterial plaque, along with prognostic information on the severity of both obstructive (>50% blockage) and nonobstructive (<50% blockage) disease. 28 Stenosis is usually reported as mild (<50% blockage), moderate (50%-60% blockage), and severe (>70% blockage). 35 CTA is also useful in evaluating patency of coronary bypass grafts, detecting coronary anomalies, evaluating coronary aneurysms and cardiac masses, and assessing complex congenital heart disease. 28 This method is considered superior to catheter angiography for imaging the aorta and pulmonary arteries. 34 CTA is less useful in evaluating patients who have received percutaneous stents because the stents can cause artifacts. 28 Most CTAs are performed with MDCT because of the high spatial and temporal resolution of the latter. 34 Patients undergoing CTA should have nothing by mouth for 3 hours before the study and should avoid ingesting caffeine 24 hours before the study because caffeine can elevate heart rate. Nurses should assess patients for adequate hydration because dehydration increases the risk for contrast-induced nephropathy (CIN). 35 Vital signs are assessed before the procedure, and a large-bore intravenous catheter is placed. Because iodinated contrast medium is administered via injection at a rate of 24 CriticalCareNurse Vol 34, No. 3, JUNE

10 5 ml/s, a 20-gauge or larger cannula should be placed in the cephalic or medial cubital vein. 35 The patient is positioned in the CT scanner with the arms above the head, and ECG leads are applied. Patients are asked to hold their breath at various intervals during the test, and during injection of the contrast medium, they may experience a sensation of flushing, warmth, or a metallic taste in the mouth. 22 Risks of CTA include allergic reactions (anaphylactic or idiosyncratic) and CIN because iodinated contrast medium is toxic to renal tubular cells. An allergic reaction is the most frequent form of a reaction to contrast material and may, on occasion, be fatal. 35 Patients at greater risk for reactions include those with asthma, a history of reaction to contrast material, and renal disease. 35 Patients who are more than 75 years old or who have congestive heart failure, diabetes, or multiple myeloma are at increased risk for CIN. 36 CIN is defined as an increase in the serum level of creatinine of at least 25% from baseline after administration of iodinated contrast material. 35 The incidence of CIN is 3.3% to 8% in patients without preexisting renal dysfunction. 36 Nurses who provide care for patients undergoing CTA should assess baseline renal function. Patients with a glomerular filtration rate greater than 60 ml/min per 1.73 m 2 are considered at low risk for CIN, those with a rate of 30 to 60 ml/min per 1.73 m 2 are considered at intermediate risk, and patients with a rate less than 30 ml/min per 1.73 m 2 are considered at high risk. 35 Patients at intermediate or greater risk should have nephrotoxic medications discontinued 2 days before CTA, and those considered at high risk should avoid iodinated contrast material altogether unless CTA is absolutely necessary. 35 All patients taking metformin should discontinue the medication on the day of the imaging and for 48 hours after the administration of contrast material because of the risk for lactic acidosis. 35 Patients should be assessed for adequate hydration, and oral intake of fluids should be encouraged within the 12 hours before CTA. Patients at greatest risk may benefit from intravenous hydration before the imaging. A reaction to contrast material within the preceding 24 hours is a relative contraindication to CTA. 35 After the procedure, patients should be advised to increase oral intake of fluids, or fluids may be administered intravenously. Follow-up measurements of serum creatinine should be obtained 48 hours after CTA for patients at intermediate or high risk for CIN. 35 One drawback to CTA is that patients must be in sinus rhythm. Intravenous -blockers may be administered to lower the patient s heart rate to less than 70/min but may be contraindicated in patients with asthma, severe aortic stenosis, second- or third-degree atrioventricular block, or severe left ventricular dysfunction. The degree of stenosis may be difficult to assess in heavily calcified vessels, and if marked blockage is detected, the patient will still have to undergo invasive coronary angiography for intervention. 37 The radiation dose associated with CTA is also higher than that associated with invasive coronary angiography. Compared with invasive coronary angiography, CTA has a 92% sensitivity and a 95% specificity. 28 Its high negative predictive value of 97% to 99% makes it a useful test for asymptomatic patients who have an intermediate Framingham Risk Score of 10% to 20%. 28 Coronary CTA is not recommended as a method of risk assessment in asymptomatic adults. 13 It is, however, reasonable to consider for patients with Contrast-induced nephropathy is defined as an increase in the serum level of creatinine of at least 25% from baseline after administration of iodinated contrast material. intermediate risk for coronary heart disease or for patients who are symptomatic or who have inconclusive results from pharmacological stress testing or are unable to undergo nuclear myocardial perfusion imaging or echocardiography. 13 Cardiac MRI In cardiac MRI, a static magnet, pulsed radiofrequency energy, and gradient magnetic fields are used to image the body. These studies can be performed with patients at rest or during the intravenous administration of a pharmacological stress agent such as dobutamine. Cardiac MRI may be useful for assessment or detection of dynamic cardiac anatomy and ventricular function, cardiomyopathies and fibrosis, myocardial ischemia and viability through the use of pharmacological agents, perfusion abnormalities at rest or during pharmacologically induced stress, cardiac masses or pericardial disease, valvular disease, and complex congenital and coronary anomalies. 38 It is not recommended for cardiovascular risk assessment in patients who do not have symptoms of coronary heart disease CriticalCareNurse Vol 34, No. 3, JUNE

11 Cardiac MRI has several advantages. 39 Patients are not exposed to ionizing radiation, radioactive isotopes, or iodinated contrast material unless the imaging is done in conjunction with a stress test. Images can be obtained without regard to a patient s body size. The imaging method can be used to assess cardiovascular anatomy and structure, determine myocardial viability, measure wall motion, visualize myocardial perfusion, and define the course and orientation of coronary arteries. Also, cardiac MRI has high temporal and spatial resolution. It is particularly useful in patients who have allergic reactions to contrast material or have chronic kidney disease in whom exposure to contrast material would be problematic. 40 Disadvantages include cost and lack of widespread availability; most cardiac MRI is done at specialized centers. Nursing considerations include assessment of patients for metal objects that are contraindicated in any MRI, such as neural stimulators, aneurysm clips, cochlear implants, metal fragments in the eye, and infusion pumps. Patients who have received coronary stents should not have MRI within the first 6 weeks after placement of the stent. Pacemakers, internal cardioverter defibrillators, and hemodynamic support devices such as intra-aortic balloon pumps or left ventricular assist devices are contraindications to MRI, although some newer versions of these devices are considered MRI compatible. Patients should remove all jewelry and hairpins. Tattoos may heat up slightly but are not considered contraindications to the imaging. 40 Intravenous access is required for infusion of the radiopharmaceutical. During the procedure, patients have continuous monitoring of ECG findings and vital signs, including oxygen saturation. Patients lie supine on a flat table in a tunnel-like apparatus. Because of the loud knocking noise made by the MRI scanner, patients wear headsets to protect their ears and may be given a mild anxiolytic. Patients can communicate via an intercom system and are asked to hold their breath for 10 to 20 seconds several times during the imaging. The procedure lasts 1 to 2 hours. Cardiac MRI may be especially difficult for patients who are claustrophobic. Conclusion Advances in noninvasive cardiac imaging techniques most likely will continue during the next several years. Although coronary angiography remains the gold standard for coronary artery assessment, newly emerging techniques most likely will begin to play a larger role in patient assessment and offer potential for increased accuracy and patient satisfaction in a noninvasive approach. Nurses must be knowledgeable about the various techniques available in order to offer patients education and guidance (Table 7 available online at CCN Financial Disclosures None reported. Now that you ve read the article, create or contribute to an online discussion about this topic using eletters. Just visit and select the article you want to comment on. In the full-text or PDF view of the article, click Responses in the middle column and then Submit a response. To learn more about cardiac monitoring, read National Survey of Cardiologists Standard of Practice for Continuous ST-Segment Monitoring by Sandau et al in the American Journal of Critical Care, March 2010;19: Available at References 1. 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