What is a nuclear stress test?

What is a nuclear stress test?

Usual stress test for the heart is a treadmill exercise ECG. It is commonly part of general health check up and is widely available. But there are certain situations when the exercise ECG is not interpretable as in a person with an electrical conduction system abnormality of the heart known as left bundle branch block. Then a nuclear stress test will be useful.

While exercise ECG tells you that there is a probability of blocks in blood vessels of the heart, it most often does not identify the region of heart muscle which has the blocked blood vessel. Nuclear stress test will tell you which is the region of heart muscle that is affected. If there is already significant damage to the heart muscle due to a block, nuclear stress test will also give an indication on whether the damage is reversible if the blood vessels are opened up with a procedure. The procedure could be either a coronary angioplasty or coronary artery bypass graft surgery.

A radioactive tracer like technetium sestamibi is injected into a vein and a nuclear scan using a gamma camera is obtained after about 20 minutes. This will show the amount of radioactive tracer in each part of the heart at rest.

After that those who can walk on a treadmill will be connected with electrodes for monitoring ECG during the test. Treadmill slope and speed are typically increased every three minutes and maximal exercise without chest pain or ECG changes is achieved. The test is terminated earlier in case of significant chest pain, other major symptoms or ECG changes. The ECG printouts are analysed by the supervising physician.

At maximal exercise, one more injection of radioactive tracer is given. One more nuclear scanning is done after waiting about 20 minutes with the gamma camera. The rest images are compared with the exercise images by the nuclear medicine specialist.

Those who are unable to exercise on the treadmill may be given medications to stress the heart as injection or infusion instead and nuclear stress images of the heart obtained as described above.

Caffeinated drinks are avoided for 24 hours prior to the procedure. Any medications containing caffeine has also to be avoided. Asthmatics on a medication known as theophylline will have to hold it for 48 hours. Heart patients will be asked not to take medications which dilate the blood vessels of the heart on the day of the test. All these are followed strictly as per the advice of the individual’s treating physician as the exact medical condition may mandate some modifications.