CE ARTICLE
Essentials of noninvasive cardiac stress testing Kelley M. Anderson, PhD, FNP (Assistant Professor, Nurse Practitioner)1,2 , Dorothy L. Murphy, MS, FNP (Nurse Practitioner, Clinical Instructor)1,2 , & Mimi Balaji, MS, FNP (Nurse Practitioner)3 1
School of Nursing and Health Studies, Georgetown University, Washington, DC Division of Cardiology, Medstar Georgetown University Hospital, Washington, DC 3 Student Health, American University, Washington, DC 2
Keywords Cardiovascular disease; cardiovascular risk; cardiac testing; advance practice nurse. Correspondence Kelley M. Anderson, PhD, FNP, School of Nursing and Health Studies, Georgetown University, Washington, DC 20057. Tel: 202-687-8135; Fax: 202-687-5553; E-mail: [email protected] Received: April 2013; accepted: September 2013 doi: 10.1002/2327-6924.12096 To obtain CE credit for this activity, go to www.aanp.org and click on the CE Center. Locate the listing for this article and complete the post-test. Follow the instructions to print your CE certificate. Disclosure
Abstract Purpose: To provide advanced practice nurses (APNs) with practice recommendations for noninvasive cardiac stress testing (NCST) to enhance diagnostic test selection and to improve the interpretation of the test results. Data sources: A review and synthesis of current scientific literature on noninvasive cardiac stress tests was conducted including a review of pertinent guidelines, indications, contraindications, procedures and findings of exercise, pharmacological, echocardiographic, and myocardial perfusion imaging studies. Conclusions: Noninvasive cardiac stress testing is an integral component in the care of men and women for the diagnosis, prognosis, and management of individuals at risk for cardiovascular conditions or with known histories of cardiovascular disorders. Implications for NPs: Cardiovascular disorders are common in our society. APNs care for a variety of individuals in the inpatient and outpatient settings that may require noninvasive cardiac stress tests for the evaluation of significant health histories and clinical presentations. An enhanced understanding of NCST improves test selection, preparation and education of patients, interpretation of test results, and implications for future patient care.
Dr. Anderson, Ms. Murphy, and Ms. Balaji have no conflicts of interest to report.
Noninvasive cardiac stress testing (NCST) is an integral component of the diagnosis, prognosis, and management of cardiovascular disease (CVD). According to the American Heart Association (Go et al., 2013) heart disease and stroke statistics, CVD is prevalent in the United States (U.S.), affecting nearly 83.6 million Americans or more than one in three adults (Go et al., 2013). Furthermore, it is estimated that by 2030, 40.8% of the U.S. population will have some form of CVD (Go et al., 2013). A significant form of CVD, in terms of mortality and morbidity, is coronary heart disease (CHD). The diagnosis of CHD is dependent on the assessment of risk factors, symptoms, and noninvasive and invasive cardiac testing. NCST is commonly indicated in the evaluation of CHD in both the inpatient and outpatient settings. The purpose of this article is to inform the advanced practice nurse (APN) about NCST options to enhance appropriate test selection and to increase the understanding of the diagnostic value of each test.
For the majority of individuals, NCST is a component of the ischemia evaluation for obstructive CHD or it is used to assess prognosis in individuals with known CHD (Gajulapalli, Aneja, & Rovner, 2012). NCST elicits myocardial hyperperfusion, either physically or pharmacologically, to evaluate the adaptive ability of the coronary circulation to an increased workload or to assess for an appropriate vasodilatory response. Obstructive CHD may result in an observed imbalance between oxygen supply and demand manifesting as ischemic electrocardiographic (ECG) changes, arrhythmias, hemodynamic alterations, symptoms, and cardiac imaging abnormalities during stress testing.
CHD pretest risk assessment Before considering NCST, begin by completing a comprehensive evaluation of the individual to determine the pretest probability of CHD. The pretest probability of CHD
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Table 1 Pretest probability of coronary artery disease by age, gender, and symptomsa Typical/Definite Angina Pectoris Age (years) 30–39 40–49 50–59 60–69
Atypical/Probable Angina Pectoris
Nonanginal Chest Pain
Asymptomatic
Male
Female
Male
Female
Male
Female
Male
Female
Intermediate High High High
Intermediate Intermediate Intermediate High
Intermediate Intermediate Intermediate Intermediate
Very low Low Intermediate Intermediate
Low Intermediate Intermediate Intermediate
Very low Very low Low Intermediate
Very low Low Low Low
Very low Very low Very low Low
No data exist for patients 69 years, but it can be assumed that prevalence of coronary artery disease (CAD) increases with age. In a few cases, patients with ages at the extremes of the decades listed may have probabilities slightly outside the high or low range. High indicates >90%; intermediate, 10%–90%; low, 110, complex atrial or ventricular arrhythmias, or significant changes in HR (Rodgers et al., 2000). During dobutamine stress, echocardiogram images are continuously monitored during and after the infusion to detect new wall motion abnormalities. For dobutamine nuclear MPI studies, nuclear images are obtained preand post-dobutamine infusion, with the MPI tracer infused at the peak HR during the dobutamine infusion. Specific contraindications for dobutamine stress testing are uncontrolled hypertension (systolic >160 mmHg, diastolic >100 mmHg), unstable angina, uncompensated heart failure, severe valvular disease, hypertrophic cardiomyopathy, significant cardiac arrhythmias such as atrial tachycardia, and history of glaucoma (Pellikka et al., 2007). Side effects are common with rare adverse reactions of sustained ventricular arrhythmia, myocardial infarction, or death (Pellikka et al., 2007). For prolonged adverse symptoms, hypertension, arrhythmias, or ischemia, beta-adrenergic blockers may be administered.
Cardiac stress imaging Exercise and pharmacological NCST studies can be conducted with imaging techniques. Table 7 provides a comparison of NCST including exercise, echocardiogram and MPI.
Echocardiography Echocardiogram is an ultrasonic cardiac imaging modality that may be conducted in conjunction with exercise or dobutamine stress testing to increase the sensitivity and specificity of detecting and quantifying myocardial ischemia (Douglas et al., 2008). Prior to the stress component, baseline echocardiography is conducted to assess cardiac chamber size and thickness, wall motion, and left ventricular (LV) systolic function expressed as ejection fraction (EF), cardiac valves, and aortic root (Pellikka et al., 2007). Echocardiogram images are performed immediately post exercise with the goal of obtaining the stress images within the first minute post exercise at peak HR. Images are obtained continuously during dobutamine infusion to evaluate augmentation of cardiac contraction and to evaluate for the presence of ischemia by visualization of LV wall motion and function. During stress imaging, the LV regional and global wall motion, thickness, and timing are evaluated during contraction and relaxation (Pellikka et al., 2007). Global LV response to stress includes changes in shape, cavity size, and contractility and indicates the presence or absence of ischemia (Pellikka et al., 2007). LVEF is a fractional measurement of the volume of blood that the ventricle pumps with each contraction. The normal regional and global LV response to stress is an increase in LVEF compared with rest. LV regional decrease in LVEF function with stress compared to rest images is suggestive of ischemia (Pellikka et al., 2007) with global LVEF decrease indicative of multivessel or left main obstruction (Pellikka et al., 2007). Wall motion that is abnormal at rest and does not worsen with stress is considered a “fixed” defect and is suggestive of prior myocardial infarction (Pellikka et al., 2007). Right ventricular (RV) response to exercise is often omitted, however RV wall abnormalities that occur during dobutamine stress are an indication of obstructive right coronary artery or multivessel disease (Pellikka et al., 2007).
Myocardial perfusion imaging (MPI) MPI is an adjunct to either exercise or pharmacologic stress testing to visualize changes in coronary blood flow as an initial test choice or an alternative test when other modes are deemed difficult to interpret or inconclusive. 65
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Table 7 Comparison of noninvasive cardiac stress tests Type of test
Duration
Advantages
Limitations
Sensitivity/specificity
Exercise stress test (ETT)
15 min to prepare patient, then testing duration varies, Bruce protocol seven stages, 3 min = 21 min total
Low cost Readily available Rapid to complete Immediate results
For ST-segment depression in symptomatic, intermediate-risk: sensitivity women 61%, men 68%; specificity women 70%, men 77%
Echocardiogram Exercise stress echocardiogram (ESE) Dobutamine stress echocardiogram (DSE)
1 h–90 min
Myocardial perfusion imaging with exercise or pharmacological (MPI)
3–4 h
Moderate completion time Relatively low cost compared with nuclear imaging May identify cardiac structural abnormalities prior to exercise Can be used with abnormal ECG Immediate results possible More sensitive for detecting single-vessel disease Can be used in patients with an abnormal baseline ECG Best for LBBB and certain pacemakers
Requires normal ECG for accurate interpretation Lower diagnostic value, especially in women Results confounded in setting of digoxin therapy and LV hypertrophy Requires interpretable echocardiogram images (body habitus, breast implants, chronic lung disease) Requires reasonable BP Imaging difficult to acquire at peak exercise because of hypercapnea Exposure to radiation Longer test duration Requires intravenous line Higher cost Longer to obtain results Weight limit depending on camera May be difficult with claustrophobia Difficult interpretation of inferior wall segments in men because of diaphragmatic motion, and anterior wall segments in women because of breast tissue Radioactive for 3–4 days
For diagnosing obstructive CHD in symptomatic patients: sensitivity 76%–90%; specificity 79%–94%
For diagnosing obstructive CHD in symptomatic patients: sensitivity 76%–91%; specificity 64%–91%
Kohli & Gulati (2010).
The imaging improves diagnostic accuracy to detect significant obstructive lesions and offers the additional advantage of estimating LVEF and cavity size. MPI is indicated as the test of choice for individuals with LV conduction delay on ECG and for certain pacemaker settings that alter conduction through the LV or septum (Hendel et al., 2009). Imaging protocols are dependent on institutional guidelines and specific intravenous radioiodine agents that evaluate blood flow to the heart (Henzlova et al., 2009). Common isotopes in the U.S. are thallium (thallous chloride), technetium sestamibi (Cardiolite ), and technetium tetrofosim (Myoview ) (Henzlova et al., 2009). In general, MPI is a three-part test with an initial set of images completed at rest, followed by the stress component, completed with either exercise or a pharmacologic agent, and final imaging after the stress component (Henzlova et al., 2009). The images are obtained with a scanning R
R
66
camera rotating around the individual’s chest and the individual is required to be supine and still during each scanning period, a duration of approximately 20 min. The weight limit for most scanning cameras is 300 lbs because of technical limitations that occur when an individual is markedly overweight. Individuals with severe claustrophobia may be uncomfortable in the scanning device and may benefit by receiving a mild sedative to complete the test. The nuclear isotope achieves myocardial distribution that is in proportion to the flow of blood perfusion at the time of injection (Henzlova et al., 2009). A normal imaging study is determined when both the resting and stress images show uniform uptake throughout the heart (Table 8). Normal imaging during rest with reduced isotope uptake during stress is potentially due to ischemia or an indication of obstructive CHD. With previous myocardial infarction, there is a reduction of isotope uptake with no
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Table 8 Myocardial perfusion imaging (MPI) results Rest
Stress
Conclusion
Normal
Normal
Normal
Reversible perfusion defect Abnormal
Blood flow to coronary artery is likely normal Artery blockage may be present Heart has had prior injury or infarction
Abnormal
significant change between the rest and stress images indicating that a portion of the heart is not receiving appropriate blood perfusion at all times because of scar tissue. In individuals with diffuse ischemic disease, balanced ischemia in multiple vessels may lead to a normal appearing perfusion scan. This situation requires the evaluation of LV cavity size, as the LV will increase with stress in individuals with balanced ischemia when imaging does not indicate perfusion defects (Gajulapalli et al., 2012). After MPI, individuals will remain radioactive for several days following the injection of the isotope, which may be problematic for certain security systems, including airline travel. Individuals are provided with instructions and documentation after the test should they anticipate these situations. Stress modality risks associated with MPI are consistent with the risks for exercise testing and pharmacologic testing as described above. Although uncommon, allergic reaction to the radioactive isotope is a contraindication of MPI.
Considerations in women CVD is prevalent in women and the most common cause of death in U.S. women today. Studies indicate less sensitivity and specificity in ECG interpretation of ST segment depression with exercise in women than men (Table 7), with more false-positive tests occurring in women (Kohli & Gulati, 2010). However, ETT is recommended as the initial NCST in women with low or intermediate risk for CHD with a normal ECG by the 2002 AHA/ACC Guidelines for Exercise Testing (Gibbons et al., 2002) and the 2005 Guidelines for the Role of Noninvasive Testing in the Clinical Evaluation of Women with Suspected Coronary Artery Disease (Mieres et al. 2005). These recommendations are based upon studies that demonstrate that the gender difference does not negate the usefulness of ETT, because the evaluation of hemodynamic response, symptoms, exercise capacity, and the negative predictive value are useful in both genders (Kohli & Gulati, 2010); however an awareness of the inconsistency
is important when ordering or interpreting test results (Gibbons et al., 2002). The reasons for these differences are speculated and may be related to body habitus, exercise physiology, coronary anatomy, prevalence of CHD, and/or estrogen (Gibbons et al., 2002; Kohli & Gulati, 2010). There are no known significant gender differences with imaging NCST, echocardiography, or MPI (Kohli & Gulati, 2010). Women who are pregnant require special considerations, as many of the pharmacologic agents and the radiation associated with MPI have not been studies in this population. In general, exercise and echocardiogram are the safest alternatives if testing is indicated.
Interpretation and clinical implications NCST offers a plethora of valuable diagnostic cardiovascular information and a full discussion of NCST interpretation and clinical implications is outside the scope of this article. Generally, a comprehensive NCST interpretation provides a description of testing parameters, hemodynamic response, clinical findings, ECG interpretation, and if applicable cardiac imaging interpretation. The testing parameters include a description of the stress protocol, exercise time or dose of pharmacological agent, the MPHR achieved, and the reason for test termination. HR response is described and HR recovery is evaluated, with a rapid recovery associated with higher cardiovascular fitness or beta-blocker use. BP response to stress is interpreted to determine whether the BP responded appropriately or in a blunted or exaggerated manner. An individual with a symptomatic or hypertensive response to exercise may require more intensive pharmacologic and nonpharmacologic management of BP. Clinical findings include an evaluation of the individual’s symptoms to determine whether the symptoms are clinically indicative of ischemia. Chest pain, especially chest pain that limits the conduction of the test, is concerning for ischemia. Other symptoms that are monitored throughout testing are dyspnea, palpitations, lightheadedness, fatigue, leg discomfort, and dizziness. The ECG interpretation evaluates ST segment and T wave morphology to determine if the ECG is electrically positive, negative, or nondiagnostic for ischemia along with a description of any cardiac arrhythmias or symptoms. ECG changes that are diagnostically positive for ischemia are defined as an ST segment with horizontal or downsloping depression 60 to 80 milliseconds after the QRS complex >1 mm in two or more contiguous leads, or rarely, ST elevation. However, exerciseinduced ST segment depression does not localize to a
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specific site of myocardial ischemia or coronary artery (Chaitman, 2005). Nondiagnostic ECG interpretation indicates the ECG was either not interpretable at baseline or there were ST or T wave changes that occurred but did not meet the aforementioned diagnostic criteria for ischemia. If the baseline ECG is normal and ST and T wave remain normal throughout the test, the ECG is considered electrically negative for ischemia. ECG interpretation is less specific with LV hypertrophy and digoxin therapy (Gibbons et al., 2002). Vasodilator pharmacological stress test causes ECG changes suggestive of ischemia less frequently; however, if diagnostic ST depression does occur, these findings are highly specific for significant CHD. At times, there will be a discrepancy between the clinical, electrical, and cardiac imaging interpretation. When this occurs, the APN must critically evaluate the entirety of all portions of the NCST in the context of the individual patient history and presentation. In general, echocardiographic and MPI imaging supersedes ECG findings in the final interpretation of the studies. When interpreting any diagnostic results, the prognostic and diagnostic value of the test must be considered. Based upon the reported findings, the APN will need to determine whether further testing is indicated, management decisions changed or if the test met the desired result to answer a clinical question. If a test is deemed inconclusive or abnormal, a decision is often deliberated for the potential value of further testing. For example, an abnormal ETT may result in a consideration for NCST with accompanied imaging or an abnormal MPI may indicate a consideration for cardiac catheterization or referral to a cardiology specialist. Cardiovascular symptoms and disorders are commonly evaluated and managed by APNs. NCST is an integral component of the care and management of individuals at risk or with known histories of a variety of cardiovascular disorders. Primarily, NCST is an integral component of the evaluation, care, and management of CHD in both men and women. With an improved understanding of the various NCST options, the APN can ensure appropriate test selection and interpretation of the finding to ensure optimal care practices.
References Bourque, J. M., Charlton, G. T., Holland, B. H., Belyea, C. M., Watson, D. D., & Beller, G. A. (2009). Prognosis in patients achieving ≥10 METS on exercise stress testing: Was SPECT imaging useful? Journal of Nuclear Cardiology, 18, 230–223. Chaitman, B. R. (2005). Exercise stress testing. In D. Zipes, P. Libby, R. Bonow, & E. Braunwald (Eds.), Braunwald’s heart disease: A textbook of cardiovascular medicine (7th ed., pp. 153–185). Philadelphia, PA: Elsevier Saunders.
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Douglas, P. S., Khandheria, B., Stainback, R. F., Weissman, N. J., Petersen, E. D., Hendel, R. C. . . . Allen, J. M. (2008). ACCF/ASE/ACEP/AHA/ASNC/ SCAI/SCCT/SCMR 2008 appropriateness criteria for stress echocardiography. J Am Coll Cardiol, 51, 1127–1147. Fleisher, L. A., Beckman, J. A., Brown, K. A., Calkins, H., Chaikof, E., Fleischmann, K. E. . . . Robb, J. F. (2007). ACC/AHA 2007 guidelines on perioperative cardiovascular evaluation and care for noncardiac surgery: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Writing Committee to Revise the 2002 Guidelines on Perioperative Cardiovascular Evaluation for Noncardiac Surgery). Circulation, 116, e418–e499. Gajulapalli, R. D., Aneja, A., & Rovner, A. (2012). Cardiac stress testing for the diagnosis and management of coronary artery disease: A reference for the primary care physician. Southern Medical Journal, 105(2), 93–9. Gibbons, R. J., Balady, G. J., Beasley, J. W., Bricker, J. T., Duvernoy, W. F., Froelicher, V.F. . . . & Yanowitz, F. G. (1997). ACC/AHA guidelines for exercise testing: executive summary: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Committee on Exercise Testing). Circulation, 96(1), 345–354. Gibbons, R. J., Balady, G. J., Bricker, J. T., Chaitman, B. R., Fletcher, G. F., Froelicher, V. F. . . . Winters, W. L. Jr. (2002). ACC/AHA 2002 guideline update for exercise testing: summary article: a report of the ACC/AHA Task Force on Practice Guidelines (Committee to Update the 1997 Exercise Testing Guidelines). Circulation, 106, 1883–1892. Go, A. S., Mozaffarian, D., Roger, V. L., Benjamin, E. J., Berry, J. D., Borden, W. B . . . Turner, M. B. (2013). American Heart Association Statistics Committee and Stroke Statistics Subcommittee. Heart disease and stroke statistics–2013 update: a report from the American Heart Association. Circulation, 127, e6–e245. Goff, D. C. Jr, Lloyd-Jones, D. M., Bennett, G., Coady, S., D’Agostino, R. B. Sr, Gibbons, R., Greenland, P., Lackland, D. T., Levy, D., O’Donnell, C. J., Robinson, J., Schwartz, J. S., Smith, S. C. Jr, Sorlie, P., Shero, S. T., Stone, N. J., Wilson, P. W. (2013). ACC/AHA guideline on the assessment of cardiovascular risk: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines. Circulation. Published online 12 November 2013. Greenland, P., Alpert, J. S., Beller, G. A. Benjamin, E. J., Budoff, M. J., Fayad, Z. A., Foster, E., . . . Wenger, N. K. (2010). ACCF/AHA guideline for assessment of cardiovascular risk in asymptomatic adults: executive summary: a report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines. Circulation, 122, 2748–2764. Hendel, R. C., Berman, D. S., Di Carli, M. F., Heidenreich, P. A., Henkin, R. E., Pellikka, P. A., Pohost, G. M., Williams, K. A., Hendel, R. C., Berman, D. S., Di Carli, M. F., Heidenreich, P. A., Henkin, R. E., Pellikka, P. A., Pohost, G. M., Williams, K. A. (2009). ACCF/ASNC/ACR/AHA/ASE/SCCT/SCMR/ SNM 2009 appropriate use criteria for cardiac radionuclide imaging: a report of the American College of Cardiology Foundation Appropriate Use Criteria Task Force, the American Society of Nuclear Cardiology, the American College of Radiology, the American Heart Association, the American Society of Echocardiography, the Society of Cardiovascular Computed Tomography, the Society for Cardiovascular Magnetic Resonance, and the Society of Nuclear Medicine. Circulation, 119, e561–e587. Henzlova, M. J., Cerquiera, M. D., Hansen, C. L., Taillefer, R., & Yao, S. (2009). ASNC imaging guidelines for nuclear cardiology procedures: Stress protocols and tracers. Journal of Nuclear Cardiology, doi: 10.10007/s12350-009-9062-4. Kohli, P., & Gulati, M. (2010). Exercise stress testing in women: Going back to the basics. Circulation, 122, 2570–2580. doi: 10.1161/CIRCULATIONAHA.109.914754. Mieres, J. H., Shaw, L. J., Arai, A., Budoff, M. J., Flamm, S. D., Hundley, W. G . . . Wenger, N. K. (2005). Role of Noninvasive Testing in the Clinical Evaluation of Women With Suspected Coronary Artery Disease. Consensus Statement From the Cardiac Imaging Committee, Council on Clinical Cardiology, and the Cardiovascular Imaging and Intervention Committee,
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Council on Cardiovascular Radiology and Intervention, American Heart Association. Circulation, 111, 682–696. Pellikka, P. A, Nagueh, S. F., Elhendy, A. A., & Kuehl, C. A (2007). American Society of Echocardiography recommendations for performance, interpretation, and application stress echocardiography. Journal of the American Society of Echocardiography, 20(9), 1021–1041. doi:10.1016/j.echo.2007.07.003.
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Rodgers, G. P., Ayanian, J. Z., Balady, G., Beasley, J. W., Brown, K. A., Gervino, E. V., . . . Schlant R. C. (2000). American College of Cardiology/American Heart Association clinical competence statement on stress testing. Circulation, 102, 1726–1738. Ruffolo, R.R. (1987). The pharmacology of dobutamine. American Journal of Medical Science, 294, 244–248.
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Essentials of noninvasive cardiac stress testing Kelley M. Anderson, PhD, FNP (Assistant Professor, Nurse Practitioner)1,2 , Dorothy L. Murphy, MS, FNP (Nurse Practitioner, Clinical Instructor)1,2 , & Mimi Balaji, MS, FNP (Nurse Practitioner)3 1
School of Nursing and Health Studies, Georgetown University, Washington, DC Division of Cardiology, Medstar Georgetown University Hospital, Washington, DC 3 Student Health, American University, Washington, DC 2
Keywords Cardiovascular disease; cardiovascular risk; cardiac testing; advance practice nurse. Correspondence Kelley M. Anderson, PhD, FNP, School of Nursing and Health Studies, Georgetown University, Washington, DC 20057. Tel: 202-687-8135; Fax: 202-687-5553; E-mail: [email protected] Received: April 2013; accepted: September 2013 doi: 10.1002/2327-6924.12096 To obtain CE credit for this activity, go to www.aanp.org and click on the CE Center. Locate the listing for this article and complete the post-test. Follow the instructions to print your CE certificate. Disclosure
Abstract Purpose: To provide advanced practice nurses (APNs) with practice recommendations for noninvasive cardiac stress testing (NCST) to enhance diagnostic test selection and to improve the interpretation of the test results. Data sources: A review and synthesis of current scientific literature on noninvasive cardiac stress tests was conducted including a review of pertinent guidelines, indications, contraindications, procedures and findings of exercise, pharmacological, echocardiographic, and myocardial perfusion imaging studies. Conclusions: Noninvasive cardiac stress testing is an integral component in the care of men and women for the diagnosis, prognosis, and management of individuals at risk for cardiovascular conditions or with known histories of cardiovascular disorders. Implications for NPs: Cardiovascular disorders are common in our society. APNs care for a variety of individuals in the inpatient and outpatient settings that may require noninvasive cardiac stress tests for the evaluation of significant health histories and clinical presentations. An enhanced understanding of NCST improves test selection, preparation and education of patients, interpretation of test results, and implications for future patient care.
Dr. Anderson, Ms. Murphy, and Ms. Balaji have no conflicts of interest to report.
Noninvasive cardiac stress testing (NCST) is an integral component of the diagnosis, prognosis, and management of cardiovascular disease (CVD). According to the American Heart Association (Go et al., 2013) heart disease and stroke statistics, CVD is prevalent in the United States (U.S.), affecting nearly 83.6 million Americans or more than one in three adults (Go et al., 2013). Furthermore, it is estimated that by 2030, 40.8% of the U.S. population will have some form of CVD (Go et al., 2013). A significant form of CVD, in terms of mortality and morbidity, is coronary heart disease (CHD). The diagnosis of CHD is dependent on the assessment of risk factors, symptoms, and noninvasive and invasive cardiac testing. NCST is commonly indicated in the evaluation of CHD in both the inpatient and outpatient settings. The purpose of this article is to inform the advanced practice nurse (APN) about NCST options to enhance appropriate test selection and to increase the understanding of the diagnostic value of each test.
For the majority of individuals, NCST is a component of the ischemia evaluation for obstructive CHD or it is used to assess prognosis in individuals with known CHD (Gajulapalli, Aneja, & Rovner, 2012). NCST elicits myocardial hyperperfusion, either physically or pharmacologically, to evaluate the adaptive ability of the coronary circulation to an increased workload or to assess for an appropriate vasodilatory response. Obstructive CHD may result in an observed imbalance between oxygen supply and demand manifesting as ischemic electrocardiographic (ECG) changes, arrhythmias, hemodynamic alterations, symptoms, and cardiac imaging abnormalities during stress testing.
CHD pretest risk assessment Before considering NCST, begin by completing a comprehensive evaluation of the individual to determine the pretest probability of CHD. The pretest probability of CHD
C 2014 The Author(s) Journal of the American Association of Nurse Practitioners 26 (2014) 59–69
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Table 1 Pretest probability of coronary artery disease by age, gender, and symptomsa Typical/Definite Angina Pectoris Age (years) 30–39 40–49 50–59 60–69
Atypical/Probable Angina Pectoris
Nonanginal Chest Pain
Asymptomatic
Male
Female
Male
Female
Male
Female
Male
Female
Intermediate High High High
Intermediate Intermediate Intermediate High
Intermediate Intermediate Intermediate Intermediate
Very low Low Intermediate Intermediate
Low Intermediate Intermediate Intermediate
Very low Very low Low Intermediate
Very low Low Low Low
Very low Very low Very low Low
No data exist for patients 69 years, but it can be assumed that prevalence of coronary artery disease (CAD) increases with age. In a few cases, patients with ages at the extremes of the decades listed may have probabilities slightly outside the high or low range. High indicates >90%; intermediate, 10%–90%; low, 110, complex atrial or ventricular arrhythmias, or significant changes in HR (Rodgers et al., 2000). During dobutamine stress, echocardiogram images are continuously monitored during and after the infusion to detect new wall motion abnormalities. For dobutamine nuclear MPI studies, nuclear images are obtained preand post-dobutamine infusion, with the MPI tracer infused at the peak HR during the dobutamine infusion. Specific contraindications for dobutamine stress testing are uncontrolled hypertension (systolic >160 mmHg, diastolic >100 mmHg), unstable angina, uncompensated heart failure, severe valvular disease, hypertrophic cardiomyopathy, significant cardiac arrhythmias such as atrial tachycardia, and history of glaucoma (Pellikka et al., 2007). Side effects are common with rare adverse reactions of sustained ventricular arrhythmia, myocardial infarction, or death (Pellikka et al., 2007). For prolonged adverse symptoms, hypertension, arrhythmias, or ischemia, beta-adrenergic blockers may be administered.
Cardiac stress imaging Exercise and pharmacological NCST studies can be conducted with imaging techniques. Table 7 provides a comparison of NCST including exercise, echocardiogram and MPI.
Echocardiography Echocardiogram is an ultrasonic cardiac imaging modality that may be conducted in conjunction with exercise or dobutamine stress testing to increase the sensitivity and specificity of detecting and quantifying myocardial ischemia (Douglas et al., 2008). Prior to the stress component, baseline echocardiography is conducted to assess cardiac chamber size and thickness, wall motion, and left ventricular (LV) systolic function expressed as ejection fraction (EF), cardiac valves, and aortic root (Pellikka et al., 2007). Echocardiogram images are performed immediately post exercise with the goal of obtaining the stress images within the first minute post exercise at peak HR. Images are obtained continuously during dobutamine infusion to evaluate augmentation of cardiac contraction and to evaluate for the presence of ischemia by visualization of LV wall motion and function. During stress imaging, the LV regional and global wall motion, thickness, and timing are evaluated during contraction and relaxation (Pellikka et al., 2007). Global LV response to stress includes changes in shape, cavity size, and contractility and indicates the presence or absence of ischemia (Pellikka et al., 2007). LVEF is a fractional measurement of the volume of blood that the ventricle pumps with each contraction. The normal regional and global LV response to stress is an increase in LVEF compared with rest. LV regional decrease in LVEF function with stress compared to rest images is suggestive of ischemia (Pellikka et al., 2007) with global LVEF decrease indicative of multivessel or left main obstruction (Pellikka et al., 2007). Wall motion that is abnormal at rest and does not worsen with stress is considered a “fixed” defect and is suggestive of prior myocardial infarction (Pellikka et al., 2007). Right ventricular (RV) response to exercise is often omitted, however RV wall abnormalities that occur during dobutamine stress are an indication of obstructive right coronary artery or multivessel disease (Pellikka et al., 2007).
Myocardial perfusion imaging (MPI) MPI is an adjunct to either exercise or pharmacologic stress testing to visualize changes in coronary blood flow as an initial test choice or an alternative test when other modes are deemed difficult to interpret or inconclusive. 65
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Table 7 Comparison of noninvasive cardiac stress tests Type of test
Duration
Advantages
Limitations
Sensitivity/specificity
Exercise stress test (ETT)
15 min to prepare patient, then testing duration varies, Bruce protocol seven stages, 3 min = 21 min total
Low cost Readily available Rapid to complete Immediate results
For ST-segment depression in symptomatic, intermediate-risk: sensitivity women 61%, men 68%; specificity women 70%, men 77%
Echocardiogram Exercise stress echocardiogram (ESE) Dobutamine stress echocardiogram (DSE)
1 h–90 min
Myocardial perfusion imaging with exercise or pharmacological (MPI)
3–4 h
Moderate completion time Relatively low cost compared with nuclear imaging May identify cardiac structural abnormalities prior to exercise Can be used with abnormal ECG Immediate results possible More sensitive for detecting single-vessel disease Can be used in patients with an abnormal baseline ECG Best for LBBB and certain pacemakers
Requires normal ECG for accurate interpretation Lower diagnostic value, especially in women Results confounded in setting of digoxin therapy and LV hypertrophy Requires interpretable echocardiogram images (body habitus, breast implants, chronic lung disease) Requires reasonable BP Imaging difficult to acquire at peak exercise because of hypercapnea Exposure to radiation Longer test duration Requires intravenous line Higher cost Longer to obtain results Weight limit depending on camera May be difficult with claustrophobia Difficult interpretation of inferior wall segments in men because of diaphragmatic motion, and anterior wall segments in women because of breast tissue Radioactive for 3–4 days
For diagnosing obstructive CHD in symptomatic patients: sensitivity 76%–90%; specificity 79%–94%
For diagnosing obstructive CHD in symptomatic patients: sensitivity 76%–91%; specificity 64%–91%
Kohli & Gulati (2010).
The imaging improves diagnostic accuracy to detect significant obstructive lesions and offers the additional advantage of estimating LVEF and cavity size. MPI is indicated as the test of choice for individuals with LV conduction delay on ECG and for certain pacemaker settings that alter conduction through the LV or septum (Hendel et al., 2009). Imaging protocols are dependent on institutional guidelines and specific intravenous radioiodine agents that evaluate blood flow to the heart (Henzlova et al., 2009). Common isotopes in the U.S. are thallium (thallous chloride), technetium sestamibi (Cardiolite ), and technetium tetrofosim (Myoview ) (Henzlova et al., 2009). In general, MPI is a three-part test with an initial set of images completed at rest, followed by the stress component, completed with either exercise or a pharmacologic agent, and final imaging after the stress component (Henzlova et al., 2009). The images are obtained with a scanning R
R
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camera rotating around the individual’s chest and the individual is required to be supine and still during each scanning period, a duration of approximately 20 min. The weight limit for most scanning cameras is 300 lbs because of technical limitations that occur when an individual is markedly overweight. Individuals with severe claustrophobia may be uncomfortable in the scanning device and may benefit by receiving a mild sedative to complete the test. The nuclear isotope achieves myocardial distribution that is in proportion to the flow of blood perfusion at the time of injection (Henzlova et al., 2009). A normal imaging study is determined when both the resting and stress images show uniform uptake throughout the heart (Table 8). Normal imaging during rest with reduced isotope uptake during stress is potentially due to ischemia or an indication of obstructive CHD. With previous myocardial infarction, there is a reduction of isotope uptake with no
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Table 8 Myocardial perfusion imaging (MPI) results Rest
Stress
Conclusion
Normal
Normal
Normal
Reversible perfusion defect Abnormal
Blood flow to coronary artery is likely normal Artery blockage may be present Heart has had prior injury or infarction
Abnormal
significant change between the rest and stress images indicating that a portion of the heart is not receiving appropriate blood perfusion at all times because of scar tissue. In individuals with diffuse ischemic disease, balanced ischemia in multiple vessels may lead to a normal appearing perfusion scan. This situation requires the evaluation of LV cavity size, as the LV will increase with stress in individuals with balanced ischemia when imaging does not indicate perfusion defects (Gajulapalli et al., 2012). After MPI, individuals will remain radioactive for several days following the injection of the isotope, which may be problematic for certain security systems, including airline travel. Individuals are provided with instructions and documentation after the test should they anticipate these situations. Stress modality risks associated with MPI are consistent with the risks for exercise testing and pharmacologic testing as described above. Although uncommon, allergic reaction to the radioactive isotope is a contraindication of MPI.
Considerations in women CVD is prevalent in women and the most common cause of death in U.S. women today. Studies indicate less sensitivity and specificity in ECG interpretation of ST segment depression with exercise in women than men (Table 7), with more false-positive tests occurring in women (Kohli & Gulati, 2010). However, ETT is recommended as the initial NCST in women with low or intermediate risk for CHD with a normal ECG by the 2002 AHA/ACC Guidelines for Exercise Testing (Gibbons et al., 2002) and the 2005 Guidelines for the Role of Noninvasive Testing in the Clinical Evaluation of Women with Suspected Coronary Artery Disease (Mieres et al. 2005). These recommendations are based upon studies that demonstrate that the gender difference does not negate the usefulness of ETT, because the evaluation of hemodynamic response, symptoms, exercise capacity, and the negative predictive value are useful in both genders (Kohli & Gulati, 2010); however an awareness of the inconsistency
is important when ordering or interpreting test results (Gibbons et al., 2002). The reasons for these differences are speculated and may be related to body habitus, exercise physiology, coronary anatomy, prevalence of CHD, and/or estrogen (Gibbons et al., 2002; Kohli & Gulati, 2010). There are no known significant gender differences with imaging NCST, echocardiography, or MPI (Kohli & Gulati, 2010). Women who are pregnant require special considerations, as many of the pharmacologic agents and the radiation associated with MPI have not been studies in this population. In general, exercise and echocardiogram are the safest alternatives if testing is indicated.
Interpretation and clinical implications NCST offers a plethora of valuable diagnostic cardiovascular information and a full discussion of NCST interpretation and clinical implications is outside the scope of this article. Generally, a comprehensive NCST interpretation provides a description of testing parameters, hemodynamic response, clinical findings, ECG interpretation, and if applicable cardiac imaging interpretation. The testing parameters include a description of the stress protocol, exercise time or dose of pharmacological agent, the MPHR achieved, and the reason for test termination. HR response is described and HR recovery is evaluated, with a rapid recovery associated with higher cardiovascular fitness or beta-blocker use. BP response to stress is interpreted to determine whether the BP responded appropriately or in a blunted or exaggerated manner. An individual with a symptomatic or hypertensive response to exercise may require more intensive pharmacologic and nonpharmacologic management of BP. Clinical findings include an evaluation of the individual’s symptoms to determine whether the symptoms are clinically indicative of ischemia. Chest pain, especially chest pain that limits the conduction of the test, is concerning for ischemia. Other symptoms that are monitored throughout testing are dyspnea, palpitations, lightheadedness, fatigue, leg discomfort, and dizziness. The ECG interpretation evaluates ST segment and T wave morphology to determine if the ECG is electrically positive, negative, or nondiagnostic for ischemia along with a description of any cardiac arrhythmias or symptoms. ECG changes that are diagnostically positive for ischemia are defined as an ST segment with horizontal or downsloping depression 60 to 80 milliseconds after the QRS complex >1 mm in two or more contiguous leads, or rarely, ST elevation. However, exerciseinduced ST segment depression does not localize to a
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specific site of myocardial ischemia or coronary artery (Chaitman, 2005). Nondiagnostic ECG interpretation indicates the ECG was either not interpretable at baseline or there were ST or T wave changes that occurred but did not meet the aforementioned diagnostic criteria for ischemia. If the baseline ECG is normal and ST and T wave remain normal throughout the test, the ECG is considered electrically negative for ischemia. ECG interpretation is less specific with LV hypertrophy and digoxin therapy (Gibbons et al., 2002). Vasodilator pharmacological stress test causes ECG changes suggestive of ischemia less frequently; however, if diagnostic ST depression does occur, these findings are highly specific for significant CHD. At times, there will be a discrepancy between the clinical, electrical, and cardiac imaging interpretation. When this occurs, the APN must critically evaluate the entirety of all portions of the NCST in the context of the individual patient history and presentation. In general, echocardiographic and MPI imaging supersedes ECG findings in the final interpretation of the studies. When interpreting any diagnostic results, the prognostic and diagnostic value of the test must be considered. Based upon the reported findings, the APN will need to determine whether further testing is indicated, management decisions changed or if the test met the desired result to answer a clinical question. If a test is deemed inconclusive or abnormal, a decision is often deliberated for the potential value of further testing. For example, an abnormal ETT may result in a consideration for NCST with accompanied imaging or an abnormal MPI may indicate a consideration for cardiac catheterization or referral to a cardiology specialist. Cardiovascular symptoms and disorders are commonly evaluated and managed by APNs. NCST is an integral component of the care and management of individuals at risk or with known histories of a variety of cardiovascular disorders. Primarily, NCST is an integral component of the evaluation, care, and management of CHD in both men and women. With an improved understanding of the various NCST options, the APN can ensure appropriate test selection and interpretation of the finding to ensure optimal care practices.
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