1. How can a patient exercise during stress testing?
Exercise stress testing (EST) is routinely performed to diagnose myocardial ischemia and to assess cardiopulmonary reserve. 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 Bruce Protocol, which is performed on a treadmill and has become the most commonly protocol used in clinical practice. Exercise stress tests may involve only electrocardiographic (ECG) monitoring or may employ in addition echocardiography or nuclear myocardial perfusion imaging, improving the sensitivity and specificity of the test.
2. What is the difference between a maximal and submaximal exercise stress test?
Maximal EST or symptoms-limited EST is the preferred way to perform an exercise stress test and attempts to achieve the maximal tolerated exercise capacity of the patient. It is terminated based on patient symptoms (e.g., fatigue, angina, shortness of breath); an abnormal ECG (e.g., significant ST depression or elevation, arrhythmias); or an abnormal hemodynamic response (e.g., abnormal blood pressure response).A goalofmaximal ESTisto achieveaheart rate responseofatleast 85% the maximal predicted heart rate (see Question 9).
Submaximal EST is performed when the goal is lower than the individual maximal exercise capacity. Reasonable targets are: 70% of the maximal predicted heart rate, 120 beats per minute, or 5 to 6 metabolic equivalents (METs) of exercise capacity (see Question 12). Submaximal EST is used early after myocardial infarction (see Question 8).
3. How helpful is an exercise stress test in the diagnosis of coronary artery disease? Multiple studies have been reported comparing the accuracy of exercise stress testing with coronary angiography. However, different criteria have been used to define a significant coronary stenosis, and this lack of standardization has complicated the issue. 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 adding imaging techniques, including echochardiography or myocardial perfusion imaging.
4. What are the risks associated with exercise stress testing?
When supervised by an adequately trained physician the risks are very low. In the general population, the mortality is less than 0.01%, and the morbidity is less than 0.05%. 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 exercise stress testing facilities, myocardial infarction and death can be expected in 1 per 2,500 tests.
5. What are the indications for exercise stress testing?
The most common indications for EST, according to the current American College of Cardiology (ACC) and American Heart Association (AHA) guidelines.
INDICATIONS FOR EXERCISE STRESS TESTING
When diagnosing suspected obstructive coronary artery disease (CAD) based on age, gender, and clinical presentation, including those with right bundle branch block and less than 1 mm of resting ST depression
For risk stratification, functional class assessment, and prognosis in patients with suspected or known CAD based on age, gender, and clinical presentation
When evaluating patients with known CAD who witnessed a significant change in their clinical status To evaluate patients with vasoespastic angina
To evaluate patients with low- or intermediate-risk unstable angina after they had been stabilized and who had been free of active ischemic symptoms or heart failure
After myocardial infarction for prognosis assessment, physical activity prescription, or evaluation of current medical treatment before discharge with a submaximal stress test 4 to 6 days after myocardial infarction or after discharge with a symptoms-limited EST at least 14 to 21 days after myocardial infarction
To detect myocardial ischemia in patients considered for revascularization
After discharge for physical activity prescription and counseling after revascularization as part of a cardiac rehabilitation program
patients with chronic aortic regurgitation to assess the functional capacity and symptomatic responses in those with a history of equivocal symptoms
When evaluating the proper settings in patients who received rate-responsive pacemakers
When investigating patients with known or suspected exercise-induced arrhythmias
6. Should asymptomatic patients undergo exercise stress tests?
In general, asymptomatic patients should not undergo EST because the pretest probability of coronary artery disease in this population is low, leading to a significant amount of false-positive results, requiring unnecessary follow-up tests and expenses without well-documented benefit. Individually, some asymptomatic patients may be selectively considered for EST (e.g., diabetic patients planning to enroll in a vigorous exercise program, certain high-risk occupations).
7. What are contraindications for exercise stress testing?
The contraindications for EST according to the current ACC/AHA guidelines are summarized in Box 7-2.
8. What parameters are monitored during an exercise stress test?
During EST three principal 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, etc.), and the ECG changes that occur during exercise and the recovery phase of EST.
9. What is an adequate heart rate to ellicit an ischemic response?
When a significant coronary artery stenosis exists, it is accepted that a heart rate of 85% of the maximal predicted heart rate for the age of the patient is sufficient to elicit an ischemic response and is considered an adequate heart rate for a diagnostic exercise EST.
CONTRAINDICATIONS FOR EXERCISE STRESS TESTING
Absolute Contraindications Acute myocardial infarction within 2 days Unstable angina
Uncontrolled cardiac arrhythmias causing symptoms or hemodynamic compromise Symptomatic, severe aortic stenosis Acute aortic dissection Uncontrolled, symptomatic heart failure Acute pulmonary embolism or infarction Acute myocarditis or pericarditis
Relative Contraindications Left main coronary stenosis Moderate aortic stenosis Electrolyte abnormalities Uncontrolled hypertension Arrhythmias
Hypertrophic cardiomyopathy and other forms of left ventricular outflow obstruction Mental or physical impairment leading to inability to exercise adequately High-degree atrioventricular block
10. How do I calculate the predicted maximal heart rate?
The maximal predicted heart rate can be estimated with the following formula:
Maximal predicted heart rate = 220 - Age
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?
Metabolic equivalents are defined as the caloric consumption of an active individual compared with the resting basal metabolic rate at rest. 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.
13. What is considered a hypertensive response to exercise?
The current ACC/AHA guidelines for exercise stress testing 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.
14. Can I order an exercise stress test in a patient taking beta-blockers?
Exercise stress test 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 exercise stress test?
Patients with left bundle branch block (LBBB), ventricular pacing, more than 1 mm baseline ST depression, 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 of image stress testing.
16. When can an exercise stress test 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 (3–6 weeks) symptom-limited EST. Exercise stress testing 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 exercise stress testing after myocardial infarction, although one small study demonstrated that physicians were more apt to allow patients to return earlier to various activities after a negative stress test.
17. Are the patient’s sex and age considerations for exercise stress testing? Women appear to have more false-positive ST-segment depression during EST than men, which may limit the sensitivity of EST for the detection of coronary artery disease in this population. This problem reflects differences in exercise physiology, body habitus, coronary physiology, prevalence of coronary artery disease, and ECG response to exercise. Based on this, the use of imaging EST (i.e., nuclear or echocardiography EST) traditionally have been favored for women. Age is not an important consideration for EST if the patient is fit to complete an exercise protocol adequately.
18. When is an exercise stress test interpreted as positive?
It is important for the physician supervising the test to consider the 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 and hemodynamic and clinical response to exercise. Electrocardiographic changes consistingofgreater thanorequalto1mmofhorizontalordown-sloping ST-segment depression or elevation at least 60 to 80 msec after the end of the QRS complex during EST are considered positive for myocardial ischemia (Fig. 7-1). 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 report.
19. What are the indications to terminate an exercise stress test?
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, 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 (e.g., ataxia, dizziness, near syncope), signs of poor perfusion (cyanosis or pallor), difficulties monitoring the ECG or blood pressure, patient request 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.-1.jpg)
Figure 7-1. Abnormal electrocardiographic response to exercise in a patient found to have a severe stenosis of the right coronary artery. A, Normal baseline ECG. B, Abnormal ECG response at peak exercise with marked downsloping ST depression and T-wave inversion.-1.jpg)
20. What is a cardiopulmonary exercise stress 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.
21. What are the indications for a cardiopulmonary exercise stress test? 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.
22. Can one obtain a stress test if a patient cannot exercise?
If the patient is unable to exercise, pharmacologic methods can detect ischemia with the use of echocardiography and myocardial nuclear perfusion imaging. Both stress imaging methods increase the accuracy for detection of coronary artery disease compared with EST alone but cannot predict functional capacity.
