None — The Heart's Electrical System
The heart beat is controlled by a system of electrical signals spreading from the top of the heart to the bottom. The electrical signal is initiated in an area of the upper right chamber, called the sinoatrial (SA) node (also referred to as the sinus node). From here, the signal spreads throughout both upper chambers. Next, the signal travels through the atrioventricular node (AV node), the pathway connecting the upper and lower chambers, through a bundle of tissue and fibers (called the His-Purkinje system), then through the ventricles.
The SA node emits an electrical signal about 60 to 100 times a minute. When the signal spreads through the atria, it causes the upper chambers to contract (beat), causing blood in the upper chambers to be pumped into the lower chambers. A split second later, when the electrical signal reaches the lower chambers, it causes the ventricles to contract and pump blood through the aorta to the rest of the body.
Arrhythmias – Atrial Fibrillation
An arrhythmia is an abnormal heart beat. The heart may beat too fast (tachycardia), too slow (bradycardia) or erratically. The most common type of heart arrhythmia is atrial fibrillation (A-fib), which occurs when the upper chambers of the heart beat very fast and irregularly. The disorganized signals prevent the muscles in the atria from effectively pumping blood into the ventricles, limiting the amount of blood to the body. Patients may have heart palpitations, a racing heart, dizziness, fainting, sweating, shortness of breath or chest pain.
According to the American Heart Association, about 2.2 million Americans have atrial fibrillation. Risk increases with age. It's more common in men, smokers and patients with medical problems, like coronary artery disease, high blood pressure, diabetes, heart valve disease, emphysema, asthma and hyperthyroidism. Certain medications, excessive consumption of alcohol and strong emotional stress can also trigger an arrhythmia in susceptible people.
Atrial fibrillation can lead to significant problems. Clots can form in the stagnating blood in the upper chambers. The clot can break free, travel through the circulatory system and become trapped in a narrower artery elsewhere in the body, leading to organ damage. In the brain, such a clot can block the flow of blood and cause a stroke. A-fib can cause the ventricles to beat too fast as they attempt to get blood to the body, eventually leading to heart failure.
Treating Atrial Fibrillation and Other Arrhythmias
Atrial fibrillation and other arrhythmias can often be treated with lifestyle changes, medications, and sometimes, a pacemaker or implantable cardioverter defibrillator (ICD). Another treatment for abnormal heart rhythms is cardiac catheter ablation. Using X-rays for guidance, a catheter is snaked through the circulatory system to the heart. Doctors use images and electrical measurements to locate the area of the heart where the abnormal signal originates. Then, the tip of the catheter releases energy waves or intense cold to the target area. This procedure destroys a small amount of tissue, blocking the path of the abnormal signal, and, hopefully, stopping the arrhythmia.
During cardiac ablation, doctors must be very careful not to damage healthy areas of the heart. X-rays, CT scans and electrophysiology studies are done to ensure the catheter is at the precise location before the tissue is ablated. The process takes time, and, in some cases, can expose the patient to a significant amount of X-ray radiation.
The CARTO® 3 System
Last year, the FDA approved a new system for heart mapping, called CARTO® 3. CARTO 3 uses advanced GPS-like magnetic technology and rapid, high resolution mapping of the heart.
Himanshu Shukla, M.D., Cardiologist with Mountain Vista Medical Center in Mesa, AZ, says the system enables doctors to precisely locate the origin of the arrhythmia and follow the positioning of the tips of the catheters in real-time, creating a 3D map of the heart. The planning and treatment can be done quickly and with less radiation exposure to the patient.
Shukla says cardiac ablation is generally used when patients fail currently recommended therapies. Unlike a pacemaker or ICD, ablation typically provides a permanent cure because it eliminates the source of the arrhythmia.
For information about CARTO® 3, click here.
For general information about heart arrhythmias or atrial fibrillation:
American Heart Association Heart Rhythm Society National Heart, Lung and Blood Institute
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