Diagnosing Heart Disease - Thallium Stress Test

Have you ever struggled with a recurrent medical problem at home but when each time you visit the physician, the symptoms were gone? Ischemic heart disease is usually like this. People with ischemic heart disease have problems with getting enough blood and oxygen to the heart. Often ischemic heart disease causes angina, which is chest pain with exertion. This makes sense when you consider that the heart is a muscle and every muscle needs increasing amounts of oxygen and blood flow with increasing amounts of exertion. Each time we exert ourselves we increase the activity of the heart because we put increased demands on the body. In this time of increased oxygen demand (exercise) people with ischemic heart disease experience chest pain because the heart is starved of oxygen and nutrients. However when the patient is sitting comfortably in the doctor’s office, there might not be any pain.

 

 

For this reason, the cardiac stress test was developed. During an exercise stress test a patient runs on a treadmill at ever increasing levels of difficulty while the heart is being monitored. In this way doctors hope to elicit the same chest pain but in a controlled manner. Also the heart will go through characteristic changes on an electrocardiogram (EKG) when it lacks proper oxygen which can provide doctors with important information about heart function.

 

However an enhanced test is available to study the way that exercise affects the heart: the thallium stress test. A thallium stress test is a nuclear medicine study that combines a typical cardiac stress test with a small amount of radioactive tracer called thallium. This thallium is the detected with a special sensor. As the heart is “stressed” by exercise, its oxygen demands increase. Normally this also causes blood flow to the heart to increase the coronary arteries as well. In a person with a healthy heart, the thallium will be distributed evenly throughout the heart. In a patient who has had a previous heart attack which has destroyed part of the heart, a portion of the heart will be “cold” i.e. no thallium signal. Further, when a patient has ischemic heart disease, the exercised heart will be cold in some areas but then “light up” when the heart comes back to rest. Obviously the thallium stress test is a very powerful tool for diagnosing heart disease.

 

Some patients express concern when they learn that a thallium stress test requires the infusion of a radioactive substance into the blood. Thallium stress test side effects themselves are infrequent and mild. In fact there is more risk from the other medications administered during a stress test and from the exertion itself in some people, than from thallium stress test side effects. The amount of radiation in the dose of thallium that is used is extremely small and considered safe. In fact, both the National Institutes of Health and the Environmental Protection Agency do not consider thallium to be cancer causing. In most people, the risks of not having a thallium stress test far outweigh the risk of the thallium itself.