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Nuclear Cardiology
The main clinical examination performed in Nuclear Cardiology is
myocardial perfusion imaging. This technique involves small doses of
radioisotopes injected intravenously, either during exercise or after
stimulation of the blood flow to the heart, using intravenous medications.
This results in uptake of the radioisotope in part of the heart receiving
normal blood flow. Areas which are supplied only by blocked blood vessels
will show less uptake of the radioisotope, and are seen as “holes” in the
subsequent pictures of the heart, which are displayed in complete
3-dimensional format, such as in a computerized tomographic scan using
x-rays. This technique also has the advantage of giving an assessment of the
volume of the total heart, which is not obtaining adequate blood supply. The
larger the volume of the heart not receiving adequate blood, the more
dangerous the situation is for the patient if this decreased blood flow is
not corrected. By closely tracking the position of the heart muscle during
different phases of the cardiac cycle, one is able to display in real time
the squeezing action of the heart and calculate the percentage of blood
being ejected from the heart with each beat. This number, called the
ejection fraction, is an important descriptor of overall heart function in
an individual patient.
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Myocardial Perfusion Imaging -- computer-generated pictures -- is a procedure that shows the flow of blood to the heart muscle. The blood vessels are first dilated through exercise or pharmacologic stress agents. Then a small amount of radioactive imaging agent is injected. This agent emits signals that are detected by a special camera. The images taken by this camera show if any part of the heart is not getting enough blood.
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If the myocardial perfusion scan is normal, generally speaking, it is
safe for the patient to be treated only with medicines with no further
invasive cardiac workup for blockages required. At the Cardiovascular Center
of Excellence, a new reclining chair is in place for patient comfort. This
new development also decreases the interference of soft tissue underlying
the patient’s diaphragm, from interfering with test interpretation.
A gated radionuclide ventriculargram [MUGA] is used to assess the patient’s
ejection fraction when information on blood flow to the heart muscle is not
required. In this test, the patient’s red blood cells are labeled with the
radioisotope, and the motion of the blood pool as the heart moves is
recorded. This test is used to check for changes in the ejection fraction
over time, and for close assessment of the rapidity of cardiac filling.
