Reported June 2008

WHAT IS ARRHYTHMIA? An arrhythmia occurs when the heart beats too fast, too slow, or irregularly. This keeps the heart from pumping blood properly. Normally, the heartbeat starts in the right atrium, when a special group of cells (the "pacemaker" of the heart) sends an electrical signal causing the muscles to contract. These signals travel through connecting fibers to all parts of the ventricles and must follow the exact route in order for the heart to pump properly. There are many types of arrhythmias, which are identified by where they occur in the heart (in the atria or ventricles), and by what happens to the heart's rhythm when they occur. One example is atrial fibrillation, an irregular heartbeat that interferes with the heart's ability to pump blood. Abnormal electrical signals cause the atria, or upper chambers of the heart, to contract erratically. Blood then pools in the atria and forms clots. These can travel to the brain and cause a stroke. The most serious arrhythmia is ventricular fibrillation, where the lower chambers quiver and the heart can't pump any blood. This can result in collapse and sudden death if there isn't immediate medical attention.

HOW CT SCANS WORK: CT scans use X-rays to image the body. X-rays can pass through most materials. It all depends on the size of the atoms that make up the material; larger atoms absorb X-ray photons, while smaller atoms do not and the X-rays pass right through. For instance, the soft tissue in the body is composed of smaller atoms, so it doesn't absorb X-rays very well, but calcium atoms in the bones are much larger and do absorb X-rays. A camera on the other side of the patient records the patterns of X-ray light passing through the patient's body. In a CT scan, a series of X-ray beams is directed through the body from different angles. This creates cross-sections so scientists can get a better view of the body. The images are put together by computer into a stack of pictures that can be viewed rapidly, like flipping through a deck of cards.

The American Association of Physicists contributed to the information contained in the TV portion of this report.

If you would like more information, please contact:

David March, Senior Media Relations Representative
Johns Hopkins Medicine
Baltimore, MD 21231
(410) 955-1534
dmarch1@jhmi.edu

Jason Bardi
American Institute of Physics
for the American Association of Physicists in Medicine
(301) 209-3091
jbardi@aip.org

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