WHAT IS ARRHYTHMIA? An arrhythmia occurs when the heart rhythm is disrupted and it 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.
WHAT IS ULTRASOUND? Sound is a pressure wave that causes the air around it to vibrate. The rate at which these fluctuations occur determines a sound wave's frequency. The human ear can interpret an impressively broad range of sound frequencies -- everything from a whisper to the roar of a jet engine -- but ultrasound uses such high frequencies (between 1 and 5 megahertz) that the fluctuations in the pressure wave are too fast for us to detect.