Indications, contraindications and subject preparations for exercise stress testing (exercise ECG)
In this article we will discuss indications, contraindications and subject preparations. We will also discuss the relevance of withholding specific cardioactive medications during exercise testing (exercise ECG).
Indications for exercise ECG
Indications have been discussed in Introduction to Exercise ECG. The most common indications are as follows:
- Assessment of cardiovascular risk in screening.
- Detection of coronary artery disease (ischemic heart disease).
- Evaluation of coronary artery disease.
- Assessment of therapeutic response. Exercise testing can be used to evaluate the effect of medications or interventions such as PCI, CABG, CRT etc.
- Assessment of perioperative risk for noncardiac surgery.
- Exercise prescription.
- Determine degree of disability.
Contraindications for exercise ECG
Although exercise stress testing is a safe procedure, the risk of complications calls for careful consideration of contraindications. Contraindications may be absolute or relative. Briefly, exercise stress testing must not be performed in the presence of absolute contraindication. Relative contraindications call for an individualized assessment of the risks; if the benefit outweighs the risk, then relative contraindications may be disregarded.
Absolute contraindications for exercise ECG
- Aortic dissection – due to risk of progression and rupture.
- Acute myocardial infarction (AMI) within 48 hours – due to risk of aggravating the infarction, as well as inducing ventricular arrhythmias.
- Unstable angina pectoris in acute phase (before stabilization of symptoms) – due to risk of developing acute myocardial infarction and inducing ventricular arrhythmias.
- Presence of potentially serious arrhythmias – due to risk of circulatory collapse.
- Decompensated heart failure – due to risk of circulatory collapse and arrhythmias
- Pulmonary embolism in acute phase – due to risk of aggravation the condition.
- Pulmonary infarction in acute phase – due to risk of aggravating the condition.
- Perimyocarditis (myocarditis) in acute phase – due to risk of arrhythmias
- Severe aortic stenosis – due to risk of syncope, ischemia and arrhythmias
- Endocarditis – due to risk of embolization
- Deep venous thrombosis – due to risk of embolization
Relative contraindications for exercise ECG
- Severe hypertension (systolic blood pressure >200 mmHg or diastolic blood pressure >110 mmHg).
- Left main coronary artery stenosis
- Severe electrolyte imbalance
- Severe hyperthyroidism
- Moderate to severe aortic stenosis
- Insufficiently controlled arrhythmias which may cause hemodynamic compromise
- Obstructive hypertrophic cardiomyopathy
- Second- or third-degree AV block (which is not caused by medications)
- Stroke within 1 month
Preparations for exercise stress testing
The laboratory and personnel
Exercise stress testing may be conducted by physicians, nurses, biomedical analysts or other professionals. A physician is always formally responsible for conducting the test. All personnel must be appropriately trained and the laboratory must be equipped with defibrillators and other emergency instruments. Personnel conducting the test must be formally trained to assess cardiovascular response, symptoms and ECG changes. Although the risk of cardiac arrest is very small, personnel must be well-trained in resuscitation.
The procedure must be explained carefully to the patient, who must also be informed that his/her performance will affect the validity of the test. Hence, the patient must understand how the test is conducted in order to maximize its usefulness. The patient must be able to communicate, and an interpreter may be necessary if there is a significant lingual barrier.
Two hours fasting before the test is recommended. Shoes and clothing should be suitable for exercise. Motivation is of utmost importance, because the patient must perform a maximal workload. The meaningfulness of the test depends on the achievement of a high workload, preferably the patient’s peak exercise capacity.
The most recently recorded 12-lead (resting) ECG should be at hand before start of exercise. Another resting 12-lead ECG is recorded just before start of exercise. These two recordings are compared in order to determine whether the patient has developed arrhythmias or morphological changes (particularly myocardial infarction, which is typically assessed using criteria for pathological Q-waves).
The 12-lead resting ECG recorded before exercise is recorded using Mason-Likar’s limb lead placement (Figure 1), which implies that the limb leads are placed on the torso, instead of distally on the limbs (ECG limb lead placement has been discussed). Removal of chest hear will improve quality of the recording.
Physical examination and anamnesis must be obtained before start of exercise. Cardiopulmonary auscultation is mandatory. Symptoms, medications, medical history, allergies and contraindications must be scritinized carefully. Blood pressure is measured at rest before start of exercise.
Beta blockers, calcium channel blockers, nitrates
In some circumstances it is necessary to withhold cardioactive medications during the exercise test. Beta blockers have a negative inotropic effect (i.e reduces contractility) and negative chronotropic effect (i.e reduces heart rate). These two effects will reduce myocardial oxygen consumption and thereby alleviate myocardial ischemia, which will reduce both ischemic symptoms and ECG changes. Hence, beta blockers have anti-ischemic effects which may mask myocardial ischemia and thus cause a false negative test result. Beta blockers should therefore be withheld 24 hours before the test. The same is true for calcium channel blockers and nitrates, due to their anti-ischemic effect. Withholding these drugs for one day does not confer any significant risk to the patient.
Note that beta-blockers should not be withheld in patients conducting the test in order to assess functional capacity and cardiovascular response. The purpose of the test in that scenario is namely to assess capacity during optimal circumstances.
Digitalis (digoxin) may cause generalized ST segment depressions in all individuals. Such ST depressions may be accentuated during exercise. Digitalis should either be withheld 24 hours before exercise testing. Cardiac imaging can be recommended to improve the specificity in patients taking digitalis. Note that exercise induced ST depressions may persist for two weeks in some patients after discontinuation of digitalis.