People that are having certain heart problems such as chest pain with exertion may be referred by their physician for a cardiac stress test. In a traditional stress test, a person is connected to various heart monitors and asked to walk or run on a treadmill. The intensity of the treadmill workout is increased until the patient experiences chest tightness, they cannot tolerate the level of exertion or some other factor that limits their performance. This exercise cardiac stress test is a fairly sensible way to diagnose ischemic heart disease or diseases in which the heart is not getting the blood that it needs.
While an exercise cardiac stress test is a useful and reproducible diagnostic exam, what if a person is wheelchair-bound, has had an amputation, or cannot exercise sufficiently? In cases where jogging on a treadmill for several minutes is not possible, a chemical stress test may be performed instead. Instead of using exercise to stress the heart, a chemical stress test involves the infusion of a drug that “stresses” the heart artificially.
There are several drugs that can stimulate the heart, but the most common agents used in a pharmacological or chemical stress test are adenosine, dobutamine, and dipyridamole (Persantine). In 2008, an agent called regadenoson (Lexiscan) was approved by the FDA for use in chemical stress tests. Adenosine and regadenoson directly stimulate adenosine receptors. When stimulated, adenosine receptors dilate the coronary arteries and blood flow to the heart increases. Persantine works in a similar manner except that it causes the body’s own adenosine to be released into the bloodstream, which affects the coronary arteries in much the same way as a direct infusion of adenosine.
Dobutamine stimulates the same receptors on the heart that would be stimulated by adrenaline. Instead of directly and only causing the blood vessels around the heart (coronaries) to dilate, dobutamine increases heart rate, blood pressure, and heart muscle contraction.
With adenosine chemical stress test protocols, the medication opens all coronary arteries around the heart but diseased arteries do not open as much as healthy arteries. Therefore blood flow greatly increases to the regions of the heart that have healthy coronary arteries but only to a small degree in regions fed by diseased coronaries. This imperfect chemical stress test can be made more sensitive and specific for ischemic heart disease by combining the adenosine chemical stress test with mild to moderate treadmill walking. Thus the chemical stress test is enhanced by adding an exercise stress test component.
Many scientists and physicians believe that dobutamine provides better results as a chemical stress test than the adenosine related compounds; however, adverse reactions occur in fully 75 percent of dobutamine chemical stress test procedures, which severely limits its use. In addition to the several chemical stress test side effects with dobutamine, there are several contraindications to using dobutamine. Even in ideal conditions many people are simply not permitted to receive dobutamine for safety reasons.
While chemical stress tests can provide positive results in some people, especially those with significant coronary artery disease, physicians agree that exercise stress tests are much more sensitive. If your physician refers you for cardiac stress, you should discuss the advantages and disadvantages of exercise and chemical stress test protocols and discuss whether you are physically able to perform a full exercise stress test.