When people hear the term nuclear they tend to get a bit nervous; however, a nuclear adenosine stress test is simply a way to detect abnormalities in the heart and heart function. A nuclear adenosine stress test is comprised of at least two components, a nuclear medicine scan, and an adenosine chemical stress test. When combined they offer a powerful tool for examining the current health of the heart, past insults that may have occurred to the heart, and how the heart performed when confronted with a stressor, in this case, chemical stress.
Adenosine is a compound that is found naturally in our bodies. When it is injected into a vein, one of the things that adenosine does is to cause some blood vessels to dilate. Adenosine can cause the coronary arteries to dilate, that is, the arteries that supply blood to the heart. If the coronary arteries are normal, adenosine will cause a large dilation. If the coronaries are diseased, however, such as by atherosclerosis, the degree of dilation is diminished. This is apparently because diseased arteries around the heart are already nearly maximally dilated in response to long term disease. Occasionally adenosine stress tests are combined with treadmill exercise, if the patient is able, which further strains the heart and provides important information about heart function.
Dilating the coronary arteries may lead to changes in the electrocardiogram (EKG, ECG), especially when combined with exercise; however, the addition of a small amount of a nuclear tracer into the blood can provide some very important information about the vessels around the heart. The “nuclear” component of the nuclear adenosine stress test describes the special radioactive tracer is infused into the blood and collects in regions of increased blood flow. The patient lies very still on an examination counter as a gamma camera senses the amount of nuclear tracer present around the heart. The nuclear medicine physician and cardiologist can then take those images and determine relative amounts of blood flow to various regions of the heart.
In people that have had a heart attack in the past, the heart will not have much signal, since some of the heart muscle has died. This “cold” area will remain cold (without tracer) even after the adenosine component of the nuclear adenosine stress test is administered. In patients with heart disease but without a history of a full heart attack, the diseased areas will appear less intense than healthier areas through the gamma camera. Not only does a nuclear adenosine stress test provide information to the physician that the vessels around the heart are diseases, but it can also show which specific coronary arteries are diseased. This is critically important if corrective procedures are going to be performed such as angioplasty, stent placement, or coronary artery bypass graft (CABG) surgery.
A nuclear adenosine stress test is not something to worry about because a physician is supervising the process at all times. Moreover, the amount of radiation that is injected into the body is very low and is cleared from the body relatively quickly. However, for diagnostic purposes, few non-invasive procedures can provide the degree of clinical information that is gained from a nuclear adenosine stress test.