Fernando Boccalandro, MD, FACC, FSCAI

1. What is the purpose of exercise stress testing (EST) and how can a patient exercise during stress testing?

    EST using electrocardiography (ECG) is routinely performed to diagnose myocardial ischemia, estimate prognosis, evaluate the outcome of therapy, and assess cardiopulmonary reserve. Exercise is used as a physiological stress to detect cardiac abnormalities that are not present at rest. They are accomplished with a treadmill, bicycle ergometer, or, rarely, with an arm ergometer, and may involve ventilatory gas analysis (the latter is called a cardiopulmonary stress test). Different protocols of progressive cardiovascular workload have been developed specifically for EST (e.g., Bruce, Cornell, Balke-Ware, ACIP, mAICP, Naughton, Weber). Bicycle ergometers are less expensive and smaller than treadmills and produce less motion of the upper body, but early fatigue of the lower extremities is a common problem that limits reaching maximal exercise capacity. As a result, treadmills are more commonly used in the United States for EST. Much of the reported data are based on the multistage Bruce Protocol, which is performed on a treadmill and has become the most commonly used protocol in clinical practice. ESTs may involve only ECG monitoring or may be combined with other imaging modalities (i.e., nuclear imaging, echocardiography).

2. What is the difference between a maximal and submaximal EST?

3. How helpful is an EST in the diagnosis of coronary artery disease?

    Multiple studies have been reported comparing the accuracy of EST with coronary angiography. However, different criteria have been used to define a significant coronary stenosis, and this lack of standardization, in addition to a variable prevalence of coronary artery disease in different populations, complicates the interpretation of the available data. A meta-analysis of 24,074 patients reported a mean sensitivity of 68% and a mean specificity of 77%. The sensitivity increases to 81% and the specificity decreases to 66% for multivessel disease, and to 86% and 53%, respectively, for left main disease or three-vessel coronary artery disease. The diagnostic accuracy of EST can be improved by combining other imaging techniques with EST such as echocardiography or myocardial perfusion imaging.

4. What are the risks associated with EST?

    When supervised by an adequately trained physician, the risks are very low. In the general population, the morbidity is less than 0.05% and the mortality is less than 0.01%. A survey of 151,944 patients 4 weeks after a myocardial infarction showed slight increased mortality and morbidity of 0.03% and 0.09%, respectively. According to the national survey of EST facilities, myocardial infarction and death can be expected in 1 per 2,500 tests.

5. What are the indications for EST?

    The most common indications for EST, according to the current American College of Cardiology (ACC) and American Heart Association (AHA) guidelines, are summarized in Box 6-1. When considering ordering an EST, three fundamental factors need to be considered to have an optimal diagnostic test: a normal baseline ECG, a patient who is able to exercise to complete the exercise protocol planned, and an appropriate indication for EST.

6. Should asymptomatic patients undergo ESTs?

    In general, asymptomatic patients should be discouraged from undergoing EST because the pretest probability of coronary artery disease in this population is low, leading to a significant number of false-positive results, requiring unnecessary follow-up tests and expenses without a well-documented benefit. There are no data from randomized studies that support the use of routine screening EST in asymptomatic patients to reduce the risk of cardiovascular events. Nevertheless, selected asymptomatic patients may be considered for EST under specific clinical circumstances if clinically appropriate (e.g., diabetic patients planning to enroll in a vigorous exercise program, certain high-risk occupations, positive calcium score, family history).

7. What are contraindications for EST?

    The contraindications for EST according to the current ACC/AHA guidelines are summarized in Box 6-2.

8. What parameters are monitored during an EST?

    During EST, three parameters are monitored and reported: the clinical response of the patient to exercise (e.g., shortness of breath, dizziness, chest pain, angina pectoris, Borg Scale score), the hemodynamic response (e.g., heart rate, blood pressure response), and the ECG changes that occur during exercise and the recovery phase of EST.

9. What is an adequate heart rate to elicit an ischemic response?

    It is accepted that a heart rate of 85% of the maximal predicted heart rate for the age of the patient is usually sufficient to elicit an ischemic response in the presence of a hemodynamic significant coronary stenosis, and is considered an adequate heart rate for a diagnostic EST.

10. How do I calculate the predicted maximal heart rate?

    The maximal predicted heart rate can be estimated with the following formula:

11. What is the Borg scale?

    The Borg Scale is a numeric scale of perceived patient exertion commonly used during EST. Values of 7 to 9 reflect light work and 13 to 17 hard work; a value above 18 is close to the maximal exercise capacity. Readings of 14 to 16 reach the anaerobic threshold. The Borg Scale is particularly useful when evaluating the patient functional capacity during EST.

12. What is a metabolic equivalent (MET)?

    METs are defined as the caloric consumption of an active individual compared with their resting basal metabolic rate. They are used during EST as an estimate of functional capacity. One MET is defined as 1 kilocalorie per kilogram per hour and is the caloric consumption of a person while at complete rest (i.e., 2 METs will correspond to an activity that is twice the resting metabolic rate). Activities of 2 to 4 METs (light walking, doing household chores, etc.) are considered light, whereas running or climbing can yield 10 or more METs. A functional capacity below 5 METs during treadmill EST is associated with a worse prognosis, whereas higher METs during exercise are associated with better outcomes. Patients who can perform more than 10 METs during EST usually have a good prognosis regardless of their coronary anatomy.

13. What is considered a hypertensive response to exercise?

    The current ACC/AHA guidelines for EST suggest a hypertensive response to exercise is one in which systolic blood pressure rises to more than 250 mm Hg or diastolic blood pressure rises to more than 115 mm Hg. This is considered a relative indication to terminate an EST.

14. Can I order an EST in a patient taking beta-blockers?

    An EST in patients taking beta-blockers may have reduced diagnostic and prognostic value because of inadequate heart rate response. Nonetheless, according to the current ACC/AHA guidelines for exercise testing, stopping beta-blockers before EST is discouraged to avoid “rebound” hypertension or anginal symptoms.

15. What baseline ECG findings interfere with the interpretation of an EST?

    Patients with left bundle branch block (LBBB), ventricular pacing, baseline ST depressions (such as with “LVH with strain”), and those with preexcitation syndromes (Wolf-Parkinson-White syndrome) should be considered for imaging stress testing because their baseline ECG abnormalities prevent an adequate ECG interpretation during exercise. Right bundle branch block does not reduce significantly the accuracy of the EST for the diagnosis of ischemia. Digoxin may also cause false-positive ST depressions during exercise and is also an indication for imaging during stress testing.

16. When can an EST be performed after an acute myocardial infarction?

    Submaximal EST is occasionally recommended after myocardial infarction as early as 4 days after the acute event. This can be followed by later (3 to 6 weeks) symptom-limited EST. EST in this circumstance assists in formulating a prognosis, determining activity levels, assessing medical therapy, and planning cardiac rehabilitation. It is unclear if asymptomatic patients who had an acute myocardial infarction (MI) with a consequent revascularization procedure benefit from follow-up EST after myocardial infarction, although it is not generally recommended if the patient is clinically stable.

17. Are the patient’s sex and age considerations for EST?

    Women have more false-positive ST-segment depression during EST than do men, which may limit the sensitivity of EST for the detection of coronary artery disease in this population. This problem reflects differences in exercise and coronary physiology with a higher sympathetic activation, which could lead to coronary vasospasm, a cyclic hormonal milieu, different body habitus, different ECG response to exercise, and a lower prevalence of coronary artery disease compared with men. Despite these limitations, EST should be considered as the initial diagnostic test in the evaluation of women with a normal baseline ECG when ischemic heart disease is suspected, because functional capacity and hemodynamic response are robust predictors of cardiovascular events independent of the ECG findings. The use of imaging EST (i.e., nuclear or echocardiography EST) needs to be considered for women with abnormal baseline ECG or poor exercise tolerance. Age is not an important consideration for EST if the patient is fit to complete an exercise protocol adequately.

18. When is an EST interpreted as positive?

    It is important for the physician supervising the test to consider the individual pretest probability of the patient undergoing EST to have underlying coronary artery disease while interpreting the results, and to consider not only the ECG response but all the information provided by the test, including functional capacity, hemodynamic response, and symptoms during exercise. ECG changes consisting of greater than or equal to 1 mm of horizontal or down-sloping ST-segment depression or elevation at least 60 to 80 msec after the end of the QRS complex during EST in three consecutive beats are considered a positive ECG response for myocardial ischemia (Fig. 6-1). Also, the occurrence of angina is important, particularly if it forces early termination of the test. Abnormalities in exercise capacity, blood pressure, and heart rate response to exercise are also important to be considered when reporting the results of EST.

19. What are the indications to terminate an EST?

    The absolute indications to stop EST according to the current ACC/AHA guidelines include a drop of more than 10 mm Hg in the systolic blood pressure despite an increased workload in addition to other signs of ischemia (i.e., angina, ventricular arrhythmias), ST elevation of more than 1 mm in leads without diagnostic Q waves (other than V1 and aVR), moderate to severe angina, increased autonomic nervous system symptoms (i.e., ataxia, dizziness, near syncope), signs of poor perfusion (i.e., cyanosis or pallor), difficulties monitoring the ECG or blood pressure, the patient requests to stop the test, and sustained ventricular tachycardia.

    Relative indications include a drop of more than 10 mm Hg in the systolic blood pressure despite an increased workload in the absence of other evidence of ischemia; excessive ST depression (more than 2 mm of horizontal or downsloping ST depression) or marked QRS axis shift; arrhythmias other than sustained ventricular tachycardia; fatigue, shortness of breath, wheezing, leg cramps, or claudication; development of bundle branch block or intraventricular conduction delay that cannot be distinguished from ventricular tachycardia; hypertensive response to exercise; and increasing nonanginal chest pain.

20. What is a cardiopulmonary EST and what are the indications of this diagnostic test?

    During a cardiopulmonary EST, the patient’s ventilatory gas exchange is monitored in a closed circuit and measurements of gas exchange are obtained during exercise (i.e., oxygen uptake, carbon dioxide output, anaerobic threshold), in addition to the information provided during routine EST. Cardiopulmonary EST is indicated to differentiate cardiac versus pulmonary causes of exercise-induced dyspnea or impaired exercise capacity. It is also used in the follow-up of patients with heart failure or who are being considered for heart transplantation.

21. Can I localize which coronary artery is affected using the ECG during EST?

    The ability of an ECG to localize an ischemic coronary territory during EST depends on the type of ST segment change noted during exercise. Exercise-induced ST depression is a nonspecific ischemic change, and cannot be used to localize any given coronary territory. Conversely, ST elevation in a lead with no prior Q waves in a patient with no history of prior myocardial infarction is consistent with transmural ischemia, and can be used to localize the coronary territory affected.

22. Can one obtain a stress test if a patient cannot exercise?

    If the patient is unable to exercise, pharmacologic methods can detect ischemia employing imaging modalities such as echocardiography, myocardial nuclear perfusion imaging, computed tomography, or magnetic resonance imaging. Imaging methods can increase the accuracy for detection of coronary artery disease at a higher cost compared with EST alone, but cannot predict functional capacity.

23. How often should an EST be repeated?

    Repeating an EST without a specific clinical indication at any interval has not been shown to improve risk stratification or prognosis in patients with or without known coronary artery disease, and is discouraged. An EST can be repeated when a significant change in the patient’s cardiovascular status is suspected, or according to the appropriate indications as noted in Box 6-1. In patients who had prior revascularization, stress imaging studies are preferred because they provide better information regarding the coronary distribution and severity of myocardial ischemia when compared with EST.

24. Can I use the ECG tracings from the stress test to interpret my patient’s 12-lead ECG?

    To avoid motion during exercise, the conventional 12-lead ECG positions require that the extremity electrodes move close to the torso. This alternate lead positioning is called the Mason-Likar modification and requires placing the arm electrodes in the lateral aspect of the infraclavicular fossa, and the leg electrodes between the iliac crest and below the rib cage. This lead change causes a right axis deviation and increased voltage in the inferior leads, which can obscure inferior Q waves and create new Q waves in aVL. Thus the ECG tracing obtained during an EST should not be used to interpret a diagnostic 12-lead ECG.

25. What is the Duke treadmill score?

    This is a validated ECG treadmill score that was created at Duke University based on data from 2,758 patients who had chest pain and underwent EST and coronary angiography. The goal of the Duke treadmill score was to more effectively estimate the prognosis after EST. This treadmill score used three exercise-derived parameters:

    Patients can be stratified: a low risk score is +5 or greater, moderate risk scores range from +4 to −10, and a high risk score is −11 or less.

    The treadmill score adds independent prognostic information to that provided by clinical information, left ventricular function, or coronary anatomy, and it can be used to identify patients in the moderate to high-risk group that may benefit from further risk stratification.

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