Chemical or pharmacologic stress testing is a common practice for assessing coronary perfusion; that is, for identifying any blockages in coronary arteries that would decrease blood flow to the heart. Chemical stress tests are used when patients are not physically able to perform an exercise stress test. Pharmacologic stress testing is used with nuclear medicine, such as thallium, and myocardial perfusion scans like positron emission tomography (PET scan).
Adenosine Stress Test
Adenosine is an anti-arrhythmic medication; it is used to control irregular heart rhythms. Adenosine can slow down heart rate (HR) and cause significant vasodilation or relaxation of blood vessels. These two properties make adenosine suitable to pharmacologic stress testing because they increase the flow of blood through the heart. Donna D. Ignatavicius, MS RN, and M. Linda Workman, Ph.D, authors of "Medical-Surgical Nursing: Critical Thinking for Collaborative Care", explain that adenosine does not assess heart muscle oxygen demand because it does not increase the HR like an actual exercise stress test would; but it does indicate the adequacy of blood flow through the coronary arteries.
Adenosine is given intravenously (IV). The patient reclines on a stretcher and has his blood pressure (BP) checked every one to two minutes throughout the procedure. Cardiac monitors measure HR and rhythm. Patients receiving adenosine often feel anxious, hot and flushed, short of breath and complain of pressure in the chest. The duration of an adenosine stress test is brief; however, the side effects are intense and some patients do not tolerate the test. Complications include the risk of very low BP, slow HR or even heart block, and bronchospasm. Patients with a history of lung disease cannot take adenosine.
Patients are scanned after receiving the drugs; the images show blood flow through the heart and physicians determine if any blockages are present.
Dobutamine Stress Test
Dobutamine can be used in place of an exercise stress test to simulate the effects of exercise on the heart. It can also be used with stress echocardiography rather than with nuclear imaging scans. Dobutamine increases the myocardial oxygen demand, or how much oxygen the heart requires, by increasing the rate and force of heart contractions. This chemical stress test is a good indicator of myocardial oxygen demand and perfusion.
Patients recline on a stretcher and receive dobutamine through an IV; BP and HR are monitored continuously. The increasing HR and force of heart contraction can make a patient feel anxious. He may experience palpitations, shortness of breath and chest discomfort. His BP will normally increase. A small portion of patients, approximately 8 percent, may experience a significant drop in BP. If this occurs, the test is stopped and another type of chemical stress test may be needed. After the dobutamine is injected, a physician views the nuclear imaging scans or the echocardiogram images and formulates a diagnosis from the results.
A2A-Specific Receptor Agonists
A 2009 article in the Journal of Nuclear Medicine Technology discusses the use of new medications, called A2A-specific receptor agonists, which work like adenosine but have fewer adverse side effects. Patients have shown better tolerance when receiving these drugs during stress testing.
References
- "Medical-Surgical Nursing--Critical Thinking for Collaborative Care;" Donna D. Ignatavicius MS RN, & M. Linda Workman Ph.D; 2006
- "Journal of Nuclear Medicine Technology;" Current Methods of Pharmacologic Stress Testing and the Potential Advantages of New Agents; Elias H. Botvinick; 2009
