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.

The Mason-Likar limb lead placement¹⁸ (Fig. 19-1) 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, ²⁰, ²¹ 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).

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, ²³, ²⁴, ²⁵, ²⁶ 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.²⁵,²⁶ 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.⁴,⁸,²⁷,²⁸ 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.³,⁴,⁸,²²,²⁵,²⁷ 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.⁴,⁸,²⁹ 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

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.¹⁷,⁴⁹,⁵⁰ 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, ⁵⁰, ⁵¹ 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.⁴,⁸,¹⁷,⁵⁰

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.⁵³,⁵⁴ 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.⁴,⁸ 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.