Thallium and sestamibi stress tests Health Article

What abnormal results mean

In your heart pictures, an area may lack the radiotracer and thus show a spot of a different color, called a “defect”. Defects represent poor uptake of the radiotracer by the heart because of reduced blood flow.

When a defect occurs at peak exercise and not at rest, the most likely cause is a significant blockage of a coronary artery. When a defect is observed both at rest and with exertion, that indicates that previous damage from a heart attack has occurred and that the heart muscle has a scar.

What the risks are

Nuclear imaging stress tests are very safe. The estimated risk of complications are only about 1 in 1,000 to 1 in 2,000 cases. These complications involve rare skin rashes, large fluctuations in blood pressure, arrhythmias, and difficulty breathing or asthma-like reactions. These, and any additional risks that may apply specifically to you, will be explained to you in advance by your doctor and by the health care provider performing the test.

Radiation exposure to radiotracers can be a concern for the nuclear lab staff, but not for patients undergoing an occasional nuclear imaging test.

Special considerations

Sometimes a thallium or sestamibi test produces heart image that looks like a defect, but it’s a pseudo-defect that gives a “false positive” test result (i.e., a falsely abnormal test). This is due to interference with the heart image from non-heart tissues such as the diaphragm (diaphragm attenuation), and, in women, the breast tissue ("breast attenuation").

When non-heart tissue attenuation is clearly the cause of an abnormal image, nothing additional needs to be done. If an attenuated image instead is thought to coincide with a true defect or area of ischemia (reduced blood flow), then your doctor may recommend additional testing such as a stress echocardiogram or a cardiac catheterization.