Norm of Pharmacologic Stress Test
Usage of Pharmacologic Stress Test
Coronary artery disease; detection of ischemia and assessment of myocardial viability; evaluation of left ventricular function; preoperative cardiac risk stratification; and valvular competence.
Description of Pharmacologic Stress Test
Pharmacologic stress testing is used to evaluate individuals with suspected or proven coronary artery disease who are unable to perform satisfactory levels of exercise to reach 85% of their maximal heart rate. A pharmacologic agent is used to elevate heart rate and blood pressure, and cardiac response is examined through an imaging technique. The dobutamine echocardiographic stress test induces pharmacologic stress by the infusion of dobutamine, a synthetic amine that increases myocardial contractility. Dobutamine directly stimulates cardiac alpha1- and beta1-adrenergic receptors, thereby increasing oxygen demand. When this occurs in the presence of an impaired oxygen supply, echocardiography can directly visualize myocardial wall motion abnormalities in individuals with fixed coronary artery stenosis. The adenosine pharmacologic stress test is a potent vasodilator that mimics the effect of exercise on the heart. Use of adenosine is preferred over dobutamine because adenosine's short duration of action and the fact that reversal agents are not needed.
Professional Considerations of Pharmacologic Stress Test
Consent form IS required.
Risks of Dobutamine Infusion
Cardiac ischemia, including myocardial infarction and dysrhythmias, dizziness, flushing, hypotension, hypertension, and palpitations.
Contraindications for Adenosine
Active bronchospasm, asthma history, atrioventricular block (high-degree). Drugs include methylxanthines such as theophylline, aminophylline, caffeine or cafergot, and oral dipyridamole.
Contraindications for Dobutamine
Tachyarrhythmias (atrial, ventricular). Drugs include beta blockers.
- Have emergency equipment readily available.
- Establish intravenous access.
- See Client and Family Teaching.
- Just before beginning the procedure, take a “time out” to verify the correct client, procedure, and site.
- The stress test is performed by specially trained (that is, ACLS-certified) nurses and echocardiographers. The American Association of Cardiovascular and Pulmonary Rehabilitation has recommended direct physician supervision of all initial stress tests and tests for individuals considered at high risk for complications.
- Attach electrocardiogram leads and a blood pressure cuff.
- Obtain a baseline 12-lead ECG and blood pressure cuff.
- The individual is placed in the best position to obtain echocardiographic images (usually left lateral decubitus), and baseline images are obtained.
- Dobutamine is diluted according to institutional policy and procedure and administered by means of an infusion pump at an initial rate of 5 mg/kg/minute.
- The infusion rate is increased every 3 minutes to 10, 20, and a maximum of 40 mg/kg/ minute unless end points develop.
- Heart rate and ECG rhythm strip are monitored continuously, and blood pressure and 12-lead ECG are recorded at each stage of drug infusion.
- Continuous echocardiography is also performed. Direct recordings of images are made at rest, at mid infusion, at peak infusion, and at 1–2 minutes after infusion.
- The test is terminated when any of the following occurs:
- a. Signs of ischemia are present (ST-segment depression of <1–2 mm for a duration >0.06 second, or ST-segment elevation).
- b. Heart rate is >75%–85% of predicted maximum for age.
- c. There is development of new wall motion abnormality.
- d. Hypertension >210–260 mm Hg systolic blood pressure or diastolic blood pressure >100 mm Hg occurs.
- e. New dysrhythmias occur.
- f. Chest pain with or without ECG changes occurs.
- g. Symptomatic hypotension or blood pressure decrease more than 20 mm Hg occurs.
- h. Heart rate decreases more than 20 beats per minute.
- Prespecified dosage of dobutamine has been reached or target heart rate has been reached.
- j. The client requests to terminate test.
- The client should be monitored until the heart rate, blood pressure, and electrocardiogram are at baseline values.
- Remove the electrodes and the blood pressure cuff.
Client and Family Teaching
- The entire procedure lasts approximately 60 minutes.
- According to physician preference and instructions, gradually discontinue beta-blocker drugs before the test. Antianginal agents may also be discontinued 24–48 hours before testing to maximize test sensitivity.
- Fast from food and fluids and refrain from smoking and caffeine usage for 4 hours before the test.
- Clients may take all their medications as usual.
- The administration of dobutamine is associated with mild side effects such as chest tightness, dyspnea, flushing, nausea, headache, paresthesias, chills, anxiety, or palpitations. Individuals are instructed to immediately report any side effects they experience to the technician. Side effects generally subside quickly after the dobutamine is discontinued.
- Do not take caffeine-containing foods, herbs, or drinks for 24 hours before the test. These include coffee, colas and chocolate.
Factors That Affect Results
- Chest wall deformities, emphysema, and severe obesity limit visualization of the heart with transthoracic probes.
- The half-life of dobutamine is 2 minutes.
- Side effects may be treated with intravenous beta-adrenergic blockers.
- Abnormalities of ventricular contraction detected by echocardiography precede ECG signs or symptoms of ischemia.
- The adenosine or dipyridamole stress tests also induce pharmacologic cardiac stress that is examined through radionuclide (thallium, sestamibi) imaging. See also Heart scan.
- See also Stress/exercise test.