Heart Rhythm and Arrhythmias The heart beats through a series of coordinated electrical impulses. Specialized cells in the right atrium (one of two chambers in the top half of the heart) initiate the electrical signal. The signal spreads throughout the atria to an area called the atrioventricular (A-V) node. The A-V node is a connection point between the atrium and the ventricles (the two lower chambers of the heart). From the A-V node, the electrical impulse travels throughout the ventricles.

A normal heart at rest beats about 60 to 80 times a minute. An arrhythmia is an abnormal heart rhythm. Bradycardia is a slow heart beat (less than 60 times a minute). If the condition persists, the heart can't pump enough blood to the body. Patients may experience fatigue, dizziness, lightheadedness or fainting.

A rapid heart beat is called a tachycardia. The fast rhythm interferes with the ability of the ventricles to fill with blood. The heart may not be able to pump out enough blood to meet the body's needs. A sustained tachycardia can cause heart palpitations, shortness of breath, chest pain, dizziness or fainting.

If the tachycardia originates in the atria, it can lead to a rhythm problem called atrial fibrillation. The top chambers of the heart are unable to pump and quiver instead. Blood can't completely empty from the top chambers, leading to the development of blood clots. A clot can break loose, travel through the circulatory system and lodge in a narrower artery feeding the brain. The clogged artery prevents blood from reaching a part of the brain, causing a stroke (death to a part of the brain). The American Heart Association estimates 2.2 million Americans have atrial fibrillation. The condition causes about 15 percent of strokes in the U.S.

Arrhythmias that originate in the ventricles are called ventricular tachycardias. This can lead to a more serious heart rhythm problem, called a ventricular fibrillation. The ventricles quiver and are unable to pump blood to the body. Without prompt treatment, the symptoms quickly lead to sudden cardiac death.

Treating Arrhythmias There are several different treatments for arrhythmias. Some arrhythmias can be controlled with medication. Other patients may require implantation of a cardioverter defibrillator (a device which monitors heart rhythm and provides an electric shock when an arrhythmia is detected to pace the heart back into a normal rhythm).

Another treatment for some patients is a technique called cardiac ablation. The goal of ablation is to eliminate the extra impulses that cause the heart to beat abnormally. First, doctors perform electrical conduction studies to map the pathway(s) of the abnormal heart rhythm. Then, the physician places an electrode-tipped catheter to the area. A small part of heart muscle in the target site is destroyed with radiofrequency energy, eliminating the ability of the area to cause an arrhythmia.

Some physicians are using a less invasive approach to stop arrhythmias, called transcatheter ablation. In this procedure, an electrode-tipped catheter is fed through the circulatory system. Once the catheter reaches the target area of the heart, the tissue is ablated. Once doctors have confirmed the arrhythmia has been successfully eliminated, the catheter is withdrawn.

Magnetic Guidance in the Heart While transcatheter ablation is very effective, it can be difficult. Sometimes the blood vessels in the heart are very twisted, making it hard for doctors to safely navigate the catheter through the winding vessels.

Borrowing from technology used to image the brain, researchers have come up with a way to guide heart catheters with a system of magnets. The Stereotaxis Niobe® Magnetic Navigation System uses two superconductive magnets, a magnetic-tipped guide wire and advanced computer imaging techniques.

The two large magnets create a magnetic field over the heart. The magnetic-tipped catheter is fed into the heart. Then, using special X-ray techniques, doctors monitor the placement of the catheter. Movement of the catheter inside the heart is controlled with a joystick, point and click of the computer mouse or through a touch screen. The technique can be used to map the heart and find the location of the arrhythmia. Once the catheter is in the location of the abnormal arrhythmia, doctors can release energy to destroy the affected area.

The magnetic navigation system provides quick, precise control of the catheter in areas of the heart that may otherwise be inaccessible. Researchers say the technology may have applications in surgery of the brain and lungs. Doctors say the Stereotaxis Niobe® Magnetic Navigation System is expected to become available for routine use in the U.S. sometime next year.

For information about the magnetic navigation system, http://www.stereotaxis.com/content/1_1_overview.php

For information on heart rhythm problems: American Heart Association, http://www.americanheart.org, or contact your local chapter