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 arrhythmia, 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 results in collapse and sudden death -- if there isn't immediate medical attention.
FREEZING THE HEART: One way to prevent arrhythmias is to locate the areas of the heart responsible for the problem and freeze them to kill the tissue. Doctors use a catheter loaded with a super-cold solution, and touch it to spots where the electrical signals are thought to be faulty. Doctors can test to see that it has worked, and thaw the tissue if they froze the incorrect spot. If it is working, they cool the probe even more, and kill the tissue.