Question:
Yesterday I had a chemical dual isotope stress test which was extreamly
uncomfortable. Previoulsy I have had the dual isotope test and run on the
treadmill but this year because of another disability neither the cardiologist
nor I were certain I could run well enough to give a meaningful test. Also
because of medication I am taking my pulse rate did not increase very much
during the run last year and he thought the chemical test might give a somewhat
higher rate.
I have not gotten the results yet but understand that my pulse rate did not go
up much this time either. Neverless the test was most stressful to me and I
assume also stressed the heart. How does the chemical test actually stress the
heart without increasing the heart rate a lot? Can someone explain this?
Answer:
The chemical used was probably adenosine or diypridamole. These drugs dilate
the arteries in the heart, increasing the amount of blood flow to the heart
without the heart having to speed up that much. Usually the heart rate
increases a bit, but nowhere near what it does during an exercise.
During a typical exercise stress test, we need the heart rate to get up to
the "target" or we cannot say that maximum stress was achieved. When using
adenosine or dipyridamole however, it's not necessary to have the heart rate
go up that fast in order to acheive the blood flow needed for the images.
If you are taking a beta-blocker (metoprolol, for example) or a
calcium-channel blocker (verapamil or diltiazem), your heart may not
speed up during the adenosine or dipyridamole infusions. These
medications decrease the heart rate by the mechanism of action. The
blood flow still increases due to adenosine or dipyridamole, to
measure if there is the deficit of blood flow or not, i.e. the test is
still useful, even though the heart rate may not go up.
