RE: RE Stress Test

[KJD@NUCMED.BIH.HARVARD.EDU]

For those of you interested in what a cardiac stress test is...

A patient can be stressed under a variety of protocols, from arm
ergometers to treadmill to pharmacologic stress with dobutamine,
persantine, or adenosine.  

The usual method is treadmill stress.  The speed and incline of
the treadmill is increased at intervals specified in the stress
protocol.  End point is usually patient fatigue, but can also
include things such as a drop in blood pressure or cardiac rhythm
irregularities.  This can all be done either with isotope
imaging, or without, depending on a lot of factors, such as prior
history and liklihood of disease.

If a study is done with isotopic imaging, either thallium-201 or
technetium-99m are used.  At a few centers, they also use
positron emitters such as rubidium and Flourine-18.

Technetium is labeled to MIBI (an isonitryl compound) which is a
lipophilic tracer that crosses the membrane of the heart muscle
cell.  Another recently available agent in Tetrofosmine.  In
either case with either of these agents, the Tc is just along for
the ride.  Doses range from 5 mCi to 25 mCi or more.

Thallium, on the other hand, is injected as a chloride salt. 
Thallium mimics potassium, at least until it enters the heart
muscle cell.  Typical doses are from 1 mCi to 4 mCi.

The positron emitters are not relevant in this case, because they
decay quickly.

If you have any specific questions, I would be glad to answer
them to the best of my ability (remember this is Friday).  Please
send a note to my e-mail address below, if you need more
information.

Kevin Donohoe, M.D.
kjd@nucmed.bih.harvard.edu