Exercise testing is a widely used, noninvasive procedure that provides diagnostic, prognostic, and functional information for a wide spectrum of patients with cardiovascular, pulmonary, and other disorders. Graded exercise tests are used to assess a patient’s ability to tolerate increased physical activity, while electrocardiographic, hemodynamic, and symptomatic responses are monitored in a controlled environment. Graded, progressive exercise can produce abnormalities that are not present at rest, the most important of which are manifestations of myocardial ischemia, including ST-segment changes on the electrocardiogram, symptoms, and electrical instability. The test is also commonly used to evaluate other system disorders, such as gas exchange abnormalities in patients with pulmonary disease or chronic heart failure, symptoms associated with peripheral vascular disease, and even neurologic disorders.
In cardiovascular medicine, the exercise test is commonly used for evaluating the efficacy of medical therapy, for the assessment of interventions, and as a first-choice diagnostic tool in patients with suspected coronary artery disease (CAD), a role in which it functions as a “gatekeeper” to more expensive and invasive procedures.1
In the latter role, the test has become even more important in the current era of health care cost containment. Although originally developed as a diagnostic tool, recent studies have established the role of the exercise test in the selection of patients for cardiac transplantation, risk stratification after a myocardial infarction (MI), and the assessment of disability.3
Because of the need to standardize the implementation and interpretation of the exercise test, professional organizations such as the American Heart Association (AHA), the American College of Cardiology (ACC),4
the American College of Sports Medicine (ACSM),8
the American Thoracic Society,3
and the European Society of Cardiology9
have developed guidelines designed to optimize the safety, methodology, and objectives of the test. The ACSM has developed certification programs for professional competency in exercise testing8
; ACSM certification has been strongly recommended for nurses, technicians, or physiologists who oversee exercise testing in clinical settings.10
This chapter describes the applications, methodology, and principles of exercise testing for the cardiovascular nurse and the professional standards for exercise testing described in the aforementioned guidelines.
INDICATIONS AND OBJECTIVES
The exercise test has numerous indications. Surveys have shown that the most common reason patients are referred for exercise testing is for the evaluation of chest pain13
or, more generally, to assess signs and symptoms of coronary disease. Other common clinical objectives include the following:
Physiologic response of post-MI and postrevascularization patients to exercise
Functional capacity for the purpose of exercise prescription
Exercise capacity for the purpose of work classification (disability evaluation) and risk stratification (prognosis)
The efficacy of medical, surgical, or pharmacologic treatment
The presence and severity of arrhythmias
Preoperative physiologic status
SAFETY AND PERSONNEL
Provided that contraindications to exercise testing are considered and patients who undergo exercise testing are appropriate, the test has been shown to be extremely safe. Widely cited data from the Cooper Clinic in Dallas15
suggest that an event serious enough to require hospitalization (e.g., sustained arrhythmia, heart attack, or death) occurs at a rate of 0.8 per 10,000 tests. More recent studies have confirmed the low event rate associated with exercise testing. In a survey of 71 medical centers within the Veterans Affairs Health Care System, an event rate of 1.2 per 10,000 tests was reported.14
Earlier surveys conducted in the 1970s suggested a somewhat higher event rate, ranging from 1 to 4 per 10,000.16
It has been suggested that the apparent improvement in the safety of the test reflected in the more recent surveys is due to a significantly better understanding of when to and when not to perform the test, when to terminate the test, and better preparation for any emergency that may arise.4
Clinical judgment is the most important consideration when deciding which patients should undergo exercise testing. Contraindications to testing usually describe conditions of cardiovascular instability, such as unstable angina, uncontrolled heart failure, and arrhythmias. A listing of the absolute and relative contraindications to testing is provided in Display 19-1
Historically, professional guidelines have suggested that physician supervision was necessary for all exercise testing in the clinical setting. Given the remarkable safety record of exercise testing, particularly in recent years,14
there is now some debate regarding the need for physician supervision for exercise testing.16
This has important implications for nursing because the nurse is frequently the person who prepares the patient and serves as the technician conducting the test, and in many centers the nurse may supervise the test as a surrogate for the physician. Although the most recent AHA/ACC guidelines4
continue to recommend physician supervision when testing patients with heart disease in a clinical setting, the guidelines also state that “…exercise testing in selected patients can be safely performed by properly trained nurses, exercise physiologists, physical therapists, or medical technicians working directly under the supervision of a physician, who should be in the immediate vicinity and available for emergencies.” The ACSM has outlined general guidelines regarding when physician supervision is recommended.8
The nurse, physiologist,
or technician conducting the test should have a comprehensive knowledge of the indications, contraindications, equipment, physiologic responses to exercise, and clinical condition of the patient to optimize the information yield and conduct the test safely.
A joint statement by the American College of Physicians, the ACC, and the AHA regarding clinical competence in exercise testing outlined the cognitive skills needed to perform exercise testing.11
These include knowledge of indications and contraindications to testing, basic exercise physiology, principles of interpretation, and emergency procedures. The committee suggested that at least 50 procedures were required during training to achieve these skills. ACSM certification8
is widely used to establish competency for technicians, nurses, or physiologists who oversee exercise testing and training.
Before an exercise test, all patients should undergo a complete medical evaluation and a physical examination to identify contraindications to exercise testing.4
If the reason the patient was referred for the test in unclear, it should be postponed until this is clarified. The medical history should include any remote or recent medical problems, symptoms, medication use, and findings from previous examinations and tests. Major CAD risk factors and signs and symptoms suggesting cardiopulmonary disease should be identified. Physical activity patterns, vocational requirements, and family history of cardiopulmonary and metabolic disorders should also be assessed. Identification of absolute contraindications (see Display 19-1
) should result in cancellation of the test and referral of the patient to the primary physician for further medical management. Patients with relative contraindications may be tested only after careful evaluation of the risk-to-benefit ratio.
Detailed verbal and written instructions, provided to the patient in advance, should include a request that the patient refrain from ingesting food, alcohol, and caffeine or using tobacco products within 3 hours of testing. Patients should be well rested and avoid vigorous activity the day of the test. Clothing should be comfortable and provide freedom of movement as well as allow access for electrode and blood pressure cuff placement. Properly fitting shoes with rubber soles should be worn to ensure good traction, particularly if a treadmill is the mode of testing. A thorough explanation of the potential risks and discomforts associated with exercise testing should be provided. Written informed consent has important ethical and legal implications and ensures the patient knows and understands the purposes and risks associated with the exercise test. There is sufficient case law to suggest that informed consent should always be obtained before beginning a test, although this issue has also been debated.12
A demonstration of how to get on and off the testing apparatus should be given, what is expected of the patient should be described (reporting of symptoms, level of exertion, testing endpoints), and any questions the patient has should be answered.
Whether patients should remain on all cardiovascular medicines for exercise testing has been the source of some debate. Many commonly used drugs can influence hemodynamic and electrocardiographic responses to exercise4
), but removing patients from their usual medicines can cause instability of symptoms, rhythm, blood pressure, and other problems. Recent versions of the aforementioned exercise testing guidelines4
suggest that most patients can remain on their medical regimen for testing without greatly compromising the diagnostic performance of the test. Tapering β-blockers over several days or discontinuing antianginal medications for a particular number of hours before testing should be reserved for particular patients in whom diagnostic sensitivity is paramount, and the tapering process should be carefully supervised by a physician.
Preparation for Electrocardiogram
Diagnostically, the electrocardiographic response is the cornerstone of the clinical exercise test. Thus, reliable test interpretation and patient safety mandate a high-quality exercise electrocardiogram. Proper skin preparation and precise electrode placement are critical to obtaining a high-quality electrocardiogram tracing. The goal of skin preparation is to decrease resistance at the skinelectrode interface and thus improve the signal-to-noise ratio. After removing hair from the general areas of placement, each site should be vigorously rubbed with an alcohol pad to remove skin oil. To further reduce resistance, the skin should be lightly
abraded using an abrasive pad or other product designed for this purpose. Finally, each electrode should be carefully placed in the proper location to ensure good skin contact with both the conducting gel and adhesive surfaces of the electrode.
Table 19-1 ▪ COMMON DRUGS AND THEIR IMPACT ON EXERCISE TESTING
Angina, hypertension, MI, arrhythmias, tremors, migraine headache
Rest: ↓, exercise: ↓
Rest: ↓, exercise: ↓
↓ Signs of ischemia
↑ In those with angina, ↓ in those without angina
Calcium channel blockers
Angina, coronary artery spasm, hypertension
Rest: ↓, exercise: ↓
Rest: ↓, exercise: ↓
↓ Signs of ischemia
↑ In those with angina, minimal effect in those without angina
Rest: ↓, Exercise: ↓
Will cause false-positive responses
↑ In those with CHF
Rest: ↓, Exercise: ↓
Delayed signs of ischemia
↑ In those with angina (and CHF)
The Mason-Likar limb lead placement18
) is the standard clinical configuration because it provides a 12-lead electrocardiogram with less artifact and less restriction to movement than does the standard limb placement. However, the Mason-Likar placement can result in differences in electrocardiographic amplitude and axis compared with the standard limb placement.19
Because these shifts may be misinterpreted as diagnostic changes, it is often recommended that a resting supine electrocardiogram be recorded using the standard limb lead placement. It is also important to note that position changes may alter the electrocardiogram. For this reason, diagnostic ST-segment changes should always be made relative to the resting baseline position (i.e., upright rather than supine position for treadmill and cycle ergometry).
▪ Figure 19-1 The Mason-Likar simulated 12-lead electrocardiogram electrode placement for exercise testing. (With permission from Froelicher, V. F., & Myers, J. . Exercise and the heart [5th ed.]. Philadelphia: W.B. Saunders.)
EXERCISE TEST SELECTION
The purpose of the test, the health and fitness of the patient, the exercise modality, and the exercise protocol are fundamental considerations when selecting the appropriate test for a given patient. In many exercise testing laboratories, these issues are determined by custom and the availability of equipment, but each can have a profound effect on the response to the exercise test. For example,
a treadmill test may be inappropriate for a patient who has difficulty with balance or gait, such as someone who has had a stroke or is otherwise neurologically impaired, or someone who has severe peripheral vascular disease, which causes difficulty in walking. A bicycle ergometer would be a more appropriate choice for such patients. Test specificity should also be considered. For example, it would be more appropriate to use a cycle ergometer to assess physiologic responses to a cycling program. Likewise, if a person is being assessed for readiness for return to work that requires arm strength, an arm ergometer test may provide more appropriate information than will a treadmill test.
An ideal exercise mode increases total body and myocardial oxygen demand to its highest level safely and in moderate, continuous, and equal increments. This requires a dynamic exercise device that uses major muscle groups, permitting large increases in cardiac output, oxygen delivery, and gas exchange. Many modalities have been used for diagnostic testing, including cycle ergometers, treadmills, arm ergometers, steps, and, more recently, pharmacologic agents. Isometric exercise, or static exercise, which involves muscle contraction without movement of the corresponding joint, causes a greater increase in systolic blood pressure and heart rate in relation to total body oxygen uptake and therefore a greater pressure load on the heart compared with dynamic exercise. Thus, it is not preferred for diagnostic exercise testing. However, isometric exercise has been used to provide occupation-specific information for patients whose job requires an extensive amount of isometric activity.
The bicycle ergometer and the treadmill are the most commonly used dynamic exercise devices. Bicycle ergometer testing is more commonly used in Europe, whereas the treadmill is more often used in the United States. The bicycle is usually less expensive, occupies less space, and is quieter. Upper body motion is decreased, making blood pressure and electrocardiographic recordings easier. The workload administered by simple, mechanically braked bicycle ergometers is not always accurate and depends on pedaling speed, causing variations in the work performed. These have largely been replaced by electronically braked bicycle ergometers, which maintain the workload at a specified level over a wide range of pedaling speeds, and are therefore more accurate. Bicycle ergometer work is commonly expressed in kilogrammeters per minute (kg · m/min) or watts. The treadmill is usually more expensive than the cycle ergometer, is relatively immobile, and makes more noise. Studies comparing treadmill and bicycle ergometer exercise tests have reported the maximal oxygen uptake to be approximately 10% to 20% higher and maximal heart rate 5% to 20% higher on the treadmill.22
Significant ST-segment changes have been reported to be more frequent and angina is elicited more frequently during treadmill testing compared with the cycle ergometer.25
In addition, exercise-induced myocardial ischemia by thallium scintigraphy was reported to be greater after treadmill testing than after cycle ergometry.23
Although most of these differences are minor, if assessing the functional limits of the patient and eliciting subjective or objective signs of ischemia are important goals of the test, the treadmill may be preferable.
The purpose of the test and the person tested are important considerations in selecting the protocol. Exercise testing may be performed for diagnostic purposes, for functional assessment, or for risk stratification. An often ignored but nevertheless consistent recommendation in the recent exercise testing guidelines is that the protocol be individualized for the patient being tested.4
For example, a maximal, symptom-limited test on a relatively demanding protocol would not be appropriate (or very informative) for a patient with severe limitations. Likewise, a very gradual protocol might not be useful for an apparently healthy, active person. Use of submaximal testing, gas exchange techniques, the presence of a physician, and the exercise mode and protocol should be determined by considering the person being tested and the goals of the test.
Commonly used exercise protocols, their stages, and the metabolic equivalent task (MET) level (metabolic equivalents; an estimated value representing a multiple of the resting metabolic rate) for each stage are outlined in Figure 19-2
. The most suitable protocols for clinical testing should include a low-intensity warm-up phase followed by progressive, continuous exercise in which the demand is elevated to a patient’s maximal level within a total duration of 8 to 12 minutes.3
In the absence of gas exchange techniques, it is important to report exercise capacity in METs rather than exercise time, so that exercise capacity can be compared uniformly between protocols. METs can be estimated from any protocol using standardized equations that have been put into tabular form.4
In general, 1 MET represents an increment on the treadmill of approximately 1.0 mph or 2.5% grade. On a cycle ergometer, 1 MET represents an increment of approximately 20 W (120 kg · m/min) for a person weighing 70 kg. The assumptions necessary for predicting MET levels from treadmill or cycle ergometer work rates (including not holding the handrails, that oxygen uptake is constant [i.e., steady-state exercise is performed], that the subject is healthy, and that all people are similar in their walking efficiency) raise uncertainties as to the accuracy of estimating the work performed for an individual patient. For example, the steady-state requirement is rarely met for most patients on most exercise protocols; most clinical testing is performed among patients with varying degrees of cardiovascular or pulmonary disease; and people vary widely in their walking efficiency.29
It has therefore been recommended that a patient be ascribed an MET level only for stages in which all or most of a given stage duration has been completed.30
Bruce Treadmill Protocol
Surveys have shown that the Bruce protocol is the most widely used in North America.14
An advantage of using this test is that a great deal of functional and prognostic data have been generated over several decades using the Bruce protocol, and many published normative values have been derived from it. For example, some of the most robust databases on the use of the exercise test for assessing prognosis, such as those from the Coronary Artery Surgery Study (CASS)32
and the Duke Treadmill Score,33
were generated from patients who underwent exercise testing using the Bruce test. Numerous studies have shown that patients who are unable to complete the first stage of this protocol (approximately 5 METs) have an extremely poor prognosis.32
However, the disadvantages of the Bruce protocol include its large and unequal increments in work, which have been shown to result in less accurate estimates of exercise capacity, particularly for patients with cardiac disease. Investigations have demonstrated that work rate increments that are too large or rapid result in a tendency to overestimate exercise capacity, less reliability for studying the effects of
therapy, and possibly even lowered sensitivity for detecting coronary disease.22
▪ Figure 19-2 Stages, workloads, and oxygen cost per stage of some commonly used protocols. USAFSAM, United States Air force School of Aerospace Medicine; ACIP, Asyptomatic Cardiac Ischemia Pilot; CHF, congestive heart failure (modified Naughton); kpm/min, kilopond meters/minute; %GR, percent grade; MPH, miles per hour.
Balke Treadmill Protocol
The Balke protocol, and modifications of it, has been widely used for clinical exercise testing. It uses constant walking speeds (2.0 or 3.0 mph) and modest increments in grade (2.5% or 5.0%), and it has been used particularly often in studies assessing angina responses. Modifications of the original Balke treadmill protocol have become widespread. One modification, developed by the United States School of Aerospace Medicine (Balke-Ware)38
consists of 5% grade increases every 2 minutes and a constant brisk walking speed of 3.3 mph (after an initial warm-up of 2.0 mph), which has been considered the most efficient speed for walking. The constant speed is advantageous in that it requires only an initial adaptation in stride.
Naughton Treadmill Protocol
The Naughton treadmill protocol39
is a low-level test that has become common for multicenter trials in patients with chronic heart failure. The test begins with 2-minute stages at 1 and 2 mph and 0% grade, then continually increases grade in approximately 1-MET increments at a constant speed of 2 mph for the next 8 minutes. Speed then increases to 3 mph with a slight decrease in grade, followed by increases in grade equivalent to approximately 1 MET. The Naughton protocol provides reasonable and gradual work rate increases for patients with more advanced heart disease. Because this protocol has been used extensively in patients with chronic heart failure, it provides a substantial amount of functional and prognostic comparative data. The Naughton test, however, can result in tests of excessive duration among more fit subjects.
Cycle Ergometer Protocols
Although there are specific bicycle protocols named after early researchers in Europe, such as Astrand and Rodahl,40
bicycle ergometer protocols tend to be more generalized than those for the treadmill. For example, 15- to 25-W increments per 2-minute stage are commonly used for patients with cardiovascular disease, whereas for apparently healthy adults or athletic individuals, appropriate work rate increments might typically be between 40 and 50 W per stage. Most modern, electronically braked cycle ergometers have controllers that permit ramp testing in which the work rate increments can be individualized in continuous fashion (see next section).
An approach to exercise testing that has gained interest in recent years is the ramp protocol, in which work increases constantly and continuously. In 1981, Whipp et al.41
first described cardiopulmonary responses to a ramp test on a cycle ergometer, and many of the gas exchange equipment manufacturers now include ramp software. Treadmills have also been adapted to conduct ramp tests.25
The ramp protocol uses a constant and continuous increase in metabolic demand that replaces the “staging” used in conventional exercise tests. The uniform increase in work allows for a steady increase in cardiopulmonary responses and permits a more accurate estimation of oxygen uptake.25
The recent call for “optimizing” exercise testing4
would appear to be facilitated by the ramp approach, because large work increments are avoided
and increases in work are individualized, permitting test duration to be targeted. Because there are no stages per se, the numbers of errors associated with predicting exercise capacity alluded to previously are lessened.4
In general, maximal, symptom-limited tests are not considered appropriate until 1 month after MI or surgery. Thus, submaximal exercise testing has an important role clinically for predischarge, post-MI, or postbypass surgery evaluations. Submaximal tests have been shown to be important in risk stratification44
for making appropriate activity recommendations, for recognizing the need for modification of the medical regimen, or for further interventions in patients who have sustained a cardiac event. A submaximal, predischarge test appears to be as predictive for future events as a symptom-limited test among patients less than 1 month after MI. Submaximal testing is also appropriate for patients with a high probability of serious arrhythmias. The testing endpoints for submaximal testing have traditionally been arbitrary but should always be based on clinical judgment. A heart rate limit of 140 beats/min and an MET level of 7 are often used for patients younger than 40 years, and limits of 130 beats/min and an MET level of 5 are often used for patients older than 40 years. For those using β-blockers, a Borg perceived exertion level in the range of 7 to 8 (1 to 10 scale) or 15 to 16 (6 to 20 scale) are conservative endpoints. The initial onset of symptoms, including fatigue, shortness of breath, or angina, is also indication to stop the test. A low-level protocol should be used, that is, one that uses no more than 1-MET increments per stage. The Naughton protocol39
is commonly used for submaximal testing. Ramp testing is also ideal for this purpose because the ramp rate (such as 5 METs achieved over a 10-minute duration) can be individualized depending on the patient tested.25
INTERPRETATION OF EXERCISE TEST RESPONSES
The important exercise test responses that should be monitored and recorded are heart rate, blood pressure, electrocardiographic changes, exercise capacity, and subjective responses, including chest discomfort, undue fatigue, shortness of breath, leg pain, and rating of perceived exertion. Each of these responses should be described in a comprehensive test report. Useful programs have been developed that automatically summarize the test responses and apply published regression equations that report pretest and posttest risks of coronary disease, and some provide mortality estimates.48
An example of one such report is presented in Display 19-2
Heart rate increases linearly with oxygen uptake during exercise. Of the two major components of cardiac output, heart rate and stroke volume, heart rate is responsible for most of the increase in cardiac output during exercise, particularly at higher levels. Thus, maximal heart rate achieved is a major determinant of exercise capacity.17
The inability to appropriately increase heart rate during exercise (chronotropic incompetence) has been associated with the presence of heart disease and a worse prognosis.49
Although maximal heart rate has been difficult to explain physiologically,52
it is affected by age, gender, health, type of exercise, body position, blood volume, and environment. Of these factors, age is the most important. There is an inverse relationship between maximal heart rate and age, with correlation coefficients typically in the order of −0.40. However, the scatter around the regression line is quite large, with standard deviations ranging from 10 to 15 beats/min (Fig. 19-3
). Thus, age-predicted “target” maximal heart rate is a limited measurement for clinical purposes and should not be used as an endpoint for exercise testing.4
Assessment of systolic and diastolic blood pressure at rest and during the exercise test is important for patient safety and can provide important diagnostic and prognostic information. Properly trained personnel can obtain accurate and reliable blood pressures using noninvasive auscultatory techniques, and guidelines have been developed for this purpose.53
Blood pressure should be measured at rest before the test in the supine and standing positions. Blood pressure at rest, when measured before an exercise test, may be elevated compared with normal resting conditions because of pretest anxiety. Uncontrolled hypertension is a relative contraindication to exercise testing.4
However, if blood pressure is elevated because of anxiety, it is not uncommon or of concern to observe a slight decrease in blood pressure during the initial stage of an exercise test when the workloads are light.
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