Exercise testing is a form of cardiovascular stress testing that uses exercise with electrocardiography (ECG) and blood pressure monitoring. This form of stress testing is usually performed with exercise protocols using either a treadmill or bicycle. Patients who are unable to exercise may benefit from the administration of a pharmacologic agent that simulates the activity of the heart during exercise. This article will specifically focus on treadmill exercise stress testing.
With exercise stress testing, we can determine a patient’s functional capacity, assess the probability and extent of coronary artery disease (CAD) as well as assess risks, prognosis and effects of therapy.
Exercise is associated with sympathetic stimulation and changes in coronary vasomotor tone which affects coronary blood flow. Several studies have reported that the coronaries dilate during exercise. Some reported mechanisms that may contribute to this dilatation include the release of vasoactive substances from the endothelium due to increased myocardial oxygen consumption, passive relaxation due to the increase in coronary arterial pressure and endothelium-mediated limitation of constrictor effects of catecholamine.
During exercise, the increase in myocardial oxygen demand and coronary vasodilation allows for increased oxygen delivery which is crucial to myocardial perfusion thereby preventing ischemia. It is through this hyperemic effect that we can identify ischemia, as stenotic vessels do not vasodilate as well as normal vessels.
Due to sympathetic stimulation and vagal inhibition, stroke volume, heart rate, and cardiac output increase. Alveolar ventilation and venous return also increase as a consequence of selective vasoconstriction. The hemodynamic response depends on the amount of muscle mass involved, exercise intensity, and overall conditioning. As exercise progresses, skeletal muscle blood flow increase and peripheral resistance decrease leading to an increase in systolic blood pressure (SBP), mean arterial pressure (MAP), and pulse pressure. Diastolic blood pressure (DBP) may remain unchanged, slightly increase or slightly decrease.
The age-predicted maximum heart rate is a useful measurement for estimating the adequacy of stress on the heart to induce ischemia. The goal is usually 85% of the age-predicted maximum heart rate, which is calculated by subtracting the patient’s age from 220.
Indications for treadmill testing include:
Contraindications for treadmill testing include:
Exercise stress testing is generally safe. Complications are rare, and the frequency of serious adverse cardiac events (i.e., myocardial infarction, sustained ventricular arrhythmia, and death) has been estimated to be approximately 1 in 10,000 patients.
All persons conducting exercise stress test should be trained on how to diagnosis and manage complications, should they arise. Emergency resuscitation equipment and drugs should also be readily available.
Exercise stress testing is performed in a designated lab, supervised by a trained healthcare personnel. Electrodes are placed on the chest, which is attached to an ECG machine that is recording the electrical activity of the heart. Your resting ECG, heart rate, and blood pressure are obtained prior to starting the exercise regimen.
The baseline ECG should be evaluated closely prior to starting the exercise portion of the test. There are several baseline ECG changes that can obscure the test results and make it difficult to interpret for ischemia. Such baseline changes include ST-segment changes that are greater than or equal to 1 mm, left bundle branch block, ventricular paced rhythm, left ventricular or right ventricular hypertrophy, ventricular pre-excitation (i.e., WPW syndrome), T wave inversions due to strain pattern or previous injury, conduction abnormalities and medication-induced ST-T wave changes. If any of these ECG abnormalities are noted, the test should be performed with the addition of an imaging modality. The resting ECG is usually obtained both supine and standing, since patient position can influence the QRS and T wave axes.
Once it is determined that there are no limiting factors based on baseline ECG, the patient is placed on a treadmill with a designed protocol that increases in intervals as you exercise. Blood pressure and heart rate are monitored throughout exercise, and the patient is monitored for any developing symptoms such as chest pain, shortness of breath, dizziness or extreme fatigue. The most common protocol used during treadmill exercise stress testing is the Bruce protocol. This protocol is divided into successive 3-minute stages, each of which requires the patient to walk faster and at a steeper grade. The testing protocol could be adjusted to a patient’s tolerance, aiming for 6 to 12 minutes of exercise duration. There is a modified Bruce protocol for those who cannot exercise vigorously, which adds two lower workload stages to the beginning of the standard Bruce protocol, both of which require less effort than Stage 1. There are a number of other protocols for patients who have a limited exercise tolerance; however, other methods that do not include exercise are also available for such patients.
During the exercise test, data about heart rate, blood pressure and ECG changes should be obtained at the end of each stage and at any time an abnormality is detected with cardiac monitoring. In general, heart rate and systolic blood pressure should rise with each stage of exercise until a peak is achieved. Patients should be questioned about any symptoms they experience during exercise. All patients should be monitored closely during the recovery period until heart rate, and ECG are back to baseline, as arrhythmias and ECG changes can still develop.
It is not necessary to stop exercise at the onset of mild symptoms if there are no abnormalities noted on ECG and patient is hemodynamically stable. Indications for terminating the test include if the patient request to stop due to severe symptoms (i.e., chest pain, shortness of breath or fatigue), severe exercise-induced hypotension or hypertension, horizontal or downsloping ST depression of greater than or equal to 1 mm or ST-segment elevation, new bundle branch block, AV block, ventricular arrhythmia, if patients achieve their maximal heart rate or all stages have been completed.
At the conclusion of testing, a report should be included. This report should outline the baseline ECG interpretation, baseline heart rate, and blood pressure, ECG changes during exercise including the presence of arrhythmia/ectopy and the onset of such changes, maximal heart rate, and blood pressure during exercise, estimated exercise capacity in METs, exercise duration and Stage completed, symptoms experienced during exercise and the reason for terminating the test.
A normal test is when patient’s blood pressure and heart rate increase appropriately to graded exercise. There should be no ECG changes suggestive of ischemia and no arrhythmias during testing. Failure of the blood pressure to increase or a decrease with signs of ischemia has a significant prognostic indication. Angina or significant ST depression (greater than 2 mm) before completing Stage 2 of the Bruce protocol and/or ST depressions that persist for more than 5 minutes into recovery suggest severe ischemia and high risk for coronary events. Exercise testing will either be positive, negative, equivocal or uninterpretable if there is a limiting factor such as heart rate.
A Duke Treadmill Score (DTS) is a validated scoring system that can assist with the risk assessment of a patient who has undergone an exercise stress test. The DTS was developed to provide accurate diagnostic and prognostic information for the evaluation of patients with suspected coronary artery disease. The DTS uses three exercise parameters: exercise time, ST segment deviation (depression or elevation) and exertional angina to determine if patients are at a low, intermediate or high risk for ischemic heart disease. The typical range is from +15 to -25. If patient’s score greater than or equal to 5, they are considered low risk while those who score less than or equal to -11 are considered high risk. This scoring system predicts 5-year mortality, where low-risk scores have a 5-year survival of 97%, intermediate risk scores have a 5-year survival of 90%, and high-risk scores indicate a 5-year survival of about 65%. Patients with an intermediate risk assessment should generally be referred for additional risk stratification with imaging modality.
Patients should be instructed not to eat, drink, or smoke for at least three hours before the examination, as this allows for maximal exercise capacity. The patient should bring comfortable exercise clothing and walking shoes to the testing facility. The healthcare professional perming the test should explain benefits the risks, benefits and possible complications to the patient before testing and patient is given an informed consent form to review and sign.
Medications should be discussed with the patient beforehand, as some medications such as beta blockers, calcium-channel blockers, digoxin, and anti-arrhythmic medications can affect maximal heart rate achieved. An ischemic response can also be affected if patients are taking nitrates. A thorough history and physical examination should be performed in all patients before referral for exercise stress testing.
Treadmill exercise testing is helpful as part of the diagnostic evaluation of patients with known or suspected coronary disease, and it provides significant prognostic information for patients with known disease. Exercise stress testing without an imaging modality has a sensitivity and specificity of about 70% and 75%, respectively. Patients with abnormal stress testing may or may not have coronary artery disease depending upon the diagnostic accuracy of the test performed and the pretest likelihood of each patient. The ACC/AHA guidelines suggest that exercise radionuclide myocardial perfusion imaging or exercise echocardiography has potential use as a follow-up test in patients with intermediate or high risk. If follow-up testing is positive, patients may benefit from guideline-directed medical therapy versus cardiac catheterization with revascularization. The choice of revascularization and the type of procedure is dependent upon coronary anatomy, left the ventricular systolic function, and the presence or absence of comorbidities such as diabetes. Patients should have an in-depth discussion with their physician as to the next steps involved when an exercise stress test is reported to be positive or uninterpretable. 
When patients with atypical chest pain or new onset heart failure present to the primary care provider, internist and nurse practitioner, one option to assess the heart is with a treadmill test. The test is usually performed by a cardiologist and is helpful as part of the diagnostic evaluation of patients with known or suspected coronary disease, and it provides significant prognostic information for patients with known disease. Exercise stress testing without an imaging modality has a sensitivity and specificity of about 70% and 75%, respectively.
Current guidelines suggest that exercise radionuclide myocardial perfusion imaging or exercise echocardiography can be used as follow-up test in patients with intermediate or high risk. If follow-up testing is positive, patients may benefit from guideline-directed medical therapy versus cardiac catheterization with revascularization.
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