Adenosine or Lexiscan Nuclear Stress Test
What is a ‘stress test’ and why is it called a stress test?
The resting heart muscle’s blood supply needs are usually well met even in the presence of blocked arteries. When the heart is stressed either by exercise or chemicals, the demand for blood increases. The blood flow through the blocked arteries- while adequate at rest- may not be able to keep up with the demands of a stressed heart. This can show up on the pictures of the heart taken after stress. This is the principle behind all the stress tests. The term ‘stress test’ is used for any means used to increase heart muscle’s demand for blood. This can be done by exercise or by chemical means.
What is an Adenosine or Lexiscan nuclear scan?
It is similar to the exercise nuclear stress test except for the fact that Adenosine or Lexiscan is used to stress the heart. Adenosine is infused over 4-6 minutes, while Lexiscan is given over a few seconds.
Why is a chemical instead of exercise used to stress the heart?
The Adenosine or Lexiscan is used instead of exercise to stress the heart in the following situations:
- If you cannot walk on treadmill for some reasons.
- Your EKG shows an abnormality called left bundle branch block (LBBB).
- An adenosine stress test may be a preferable test for certain people with pacemakers.
How do you prepare for this test?
The preparation is mostly the same as for exercise stress test. In addition, you should not consume caffeine containing beverage for several hours before the test. Ask your provider how long you need to be without caffeine before the test. Caffeine intake before this test affects quality of the test.
What are the shortcomings of this test?
Adenosine can cause several side effects including slow pulse, chest pressure, facial flushing, ‘weird’ feeling etc. Most of the side effects should dissipate soon after stopping Adenosine. In some cases, you may continue to feel bad for a day or so. If you feel any unusual symptoms, you should let your provider know. Adenosine should not be used in patients with asthma.
Lexiscan is expected to cause fewer side effects. It has the potential of causing headache apart from other side effects.
Which one is better- Adenosine/Lexiscan stress test or exercise stress test?
As a general rule, if possible, exercise should be used to stress the heart. This is the natural, physiological way to increase heart muscle’s demand for blood. Adenosine/Lexiscan are preferred in certain situations described above.