glossary Arrhythmia (Heart Rhythm Disorders) Heart rhythm disorders (arrhythmias) are problems that affect the electrical system, or "wiring," of the heart muscle. Heart arrhythmias are very common and millions of people will experience an abnormal heart rhythm some time during their lives. Most are not serious. Atrial Fibrillation (AF or A Fib) More than 2 million people in the United States have atrial fibrillation, making it a very common heart rhythm disorder. In A Fib, the heartbeat is irregular and rapid, sometimes beating as often as 300 time a minute in the upper chambers (atria) and 100-150 times a minute in the lower chambers (ventricles). Although it isn't life threatening, A Fib can lead to other rhythm problems, chronic fatigue and congestive heart failure. Chances of having a stroke are five times higher for those with A Fib. There are a number of effective treatments to control AF and/or reduce the risk that it will cause serious health problems. Atrial Flutter (AFL) Atrial flutter is similar to A Fib because it too is characterized by a rapid heartbeat. Instead of many disorganized signals, however, AFL is caused by a single electrical wave that circulates very rapidly in the atrium, about 300 times a minute, leading to a very fast, steady heartbeat. Atherosclerosis Atherosclerosis is a form of arteriosclerosis in which the inner layers of artery walls become thick and irregular due to deposits of fat, cholesterol and other substances. This buildup is sometimes called plaque. As the interior walls of arteries become lined with layers of these deposits, the arteries become narrowed, and the flow of blood through them is reduced. Automatic External Defibrillator (AED) External defibrillators deliver brief, high-energy shocks through paddles or electrode patches applied to the patient's chest. The display on an AED gives simple instructions to rescuers - and has a built-in safeguard. The defibrillator will override attempts to deliver a shock until sensors in the machine confirm the victim is in cardiac arrest. Bradycardia Bradycardia is characterized by an abnormally slow heart rhythm (less than 60 beats a minute). A normal heart contracts about 100,000 times each day, at a rate of 60 to 100 times a minute. The weak pace may mean the heart doesn't beat often enough to ensure blood flow. Heart block (or AV Block) and Sick Sinus Syndrome are forms of bradycardia. Cardiac Resynchronization Therapy Cardiac resynchronization relies on electrical leads to correct difficulty of the normal electrical impulse in conducting through the heart, which is commonly diagnosed in patients experiencing heart failure. The leads electrically stimulate heart muscle to synchronize the contractions of the heart's two lower chambers, or ventricles. Only when the lower chambers beat in harmony can they contract with enough force to push blood carrying oxygen through the body. Catheter Ablation In this procedure, one or more flexible, thin tubes (catheters) are guided via x-ray into the blood vessels and directed to the heart muscle. A burst of radiofrequency (or other) energy destroys very small areas of tissue that give rise to abnormal electrical signals. Coronary Artery Disease CAD occurs when the blood vessels become clogged. Devices for Heart Failure The U.S. Food and Drug Administration (FDA) recently approved a special type of pacemaker for certain patients with heart failure. In Cardiac Resynchronization Therapy, an implanted device paces both the left and right ventricles (lower chambers) of the heart simultaneously. This resynchronizes muscle contractions and improves the efficiency of the weakened heart. Ejection Fraction (EF) The ejection fraction (EF) is a measure of the proportion (or fraction) of blood that is expelled by the ventricle with each contraction, or heart beat. The healthy heart pumps out 55 percent or more of the blood in the left ventricle with each beat. If the ejection fraction falls below 55 percent, it is an indication that the heart muscle is weakened. Heart Attack (Myocardial Infarction) When arteries are clogged to the point of decreasing or stopping the flow of blood to the heart muscle, a lack of oxygen damages or kills heart muscle causing a heart attack. Recognizing symptoms and getting prompt emergency treatment can eliminate, prevent or limit the amount of heart muscle damage. Heart Block Heart Block occurs when electrical impulses generated in the upper chambers of the heart are not properly transmitted to the lower chambers. The heart then beats too slowly, reducing the oxygen that gets to the body and brain. Heart Failure Heart failure, or cardiomyopathy, occurs when the heart muscle is too weak to effectively pump blood through the body. Early diagnosis and treatment can stop or slow progression of heart failure. Heart Valve Problems Heart valve problems can be inherited or can develop and can wreak havoc on the heart's ability to push blood from chamber to chamber. Medication and surgery are treatment options. Implanted Cardioverter Defibrillators (ICDs) ICDs are 99 percent effective in stopping life-threatening arrhythmias and are the most successful therapy to treat ventricular fibrillation, the major cause of sudden cardiac arrest. ICDs continuously monitor the heart rhythm, automatically function as pacemakers for heart rates that are too slow, and deliver life-saving shocks if a dangerously fast heart rhythm is detected. Left Ventricular Hypertrophy Left Ventricular Hypertrophy is a thickening of the muscle wall of the left ventricle. Long QT Syndrome (LQTS) Long QT Syndrome is a disorder of the electrical system. It can be inherited, acquired after taking certain medications, or caused by a combination of heredity and medications. People with LQTS are susceptible to ventricular fibrillation. Pacemakers Devices that "pace" the heart rate when it is too slow (bradycardia) can take over for the heart's natural pacemaker, the sinoatrial node, when it is functioning improperly. Pacemakers monitor and regulate the rhythm of the heart and transmit electrical impulses to stimulate the heart if it is beating too slowly. Palpitations The sensations of feeling the heart beat are called "palpitations." Peripheral Artery Disease Peripheral Artery Disease is a clogging of the arteries in the legs or, less often, in the arms. Premature Contractions Extra, early or "skipped" beats are the most frequent cause of irregular heart rhythms. These can start in the upper or lower chambers of the heart. Sick Sinus Syndrome (SSS) SSS is not a specific disease, but a group of signs or symptoms that indicate the heart's natural electrical pacemaker, the sinoatrial node, is not functioning properly. In SSS, the heart rate can switch back and forth between a slow rate (bradycardia) and a fast rate (tachycardia). A permanent pacemaker, sometimes in combination with medication, is the primary treatment. SSS affects about 3 out of every 10,000 people. It becomes more common as we age. Sinus Tachycardia A harmless rhythm, sinus tachycardia is a normal increase in heart rate that happens with fever, excitement, and exercise. It does not require treatment except in rare cases when an underlying problem, such as anemia or hyperthyroidism, should be treated. Stroke Although not true "heart" disorders, strokes are a related condition. While some strokes occur when a blood vessel bursts, most strokes happen for the same reasons as a heart attack, clogged or blocked vessels. All strokes pose serious health threats. Sudden Cardiac Arrest (SCA) In SCA, the heart abruptly and unexpectedly ceases to function (cardiac arrest). The most common cause of SCA is a heart rhythm disorder (arrhythmia) called ventricular fibrillation (VF). VF is an "electrical problem" in the heart. Suddenly, the electrical signals that regulate the pumping action of the lower chambers of the heart (ventricles) become rapid and chaotic. The normal rhythmic contractions of the ventricles stop, and the heart can't pump blood to the rest of the body. The brain is starved of oxygen, and the individual loses consciousness in seconds. Without immediate emergency help, death follows within minutes of an episode of ventricular fibrillation. Supraventricular tachycardia (SVT) The most common type of SVT is atrial fibrillation, an irregular and rapid heartbeat in the upper chambers of the heart (or atria). Syncope (Fainting) Fainting, or feeling as if one might faint, can be caused by serious heart rhythm disorders and needs to be evaluated carefully. Sometimes the cause is not heart related, for instance when low blood sugar is to blame, but still can be dangerous. No matter what the cause, fainting can be dangerous simply because of the potential for injuries from falling. Tachycardia An abnormally fast heart rhythm, or tachycardia can prove dangerous because the racing interferes with the heart's ability to contract properly. As a result, a victim may suffer a range of symptoms, from lightheadedness to sudden cardiac arrest. Ventricular Fibrillation (VF) Sudden cardiac arrest, caused by ventricular fibrillation, poses the greatest threat and accounts for half of all cardiac arrests. Also known as cardiac arrest, sudden cardiac arrest is due to an electrical circuitry problem. It is not a the same as a heart attack, or myocardial infarction, which is a circulatory problem caused by clogged blood vessels that cut off the supply of blood to the heart. In VF, the heartbeat is rapid and chaotic, which causes the lower heart chambers, or ventricles, to go into a spasm. Sometimes, however, a heart attack can lead to VF. VF is abrupt and happens without any warning and it halts all heart functioning. The lack of oxygen throughout the body, and especially to the brain, is deadly. Ventricular Tachycardia (VT) Characterized by a very fast heart rate, VT usually is seen in the setting of other serious heart disease. Occasionally, it occurs in people with normal hearts. It usually requires prompt treatment, sometimes with medication. Sometimes it is treated with radiofrequency ablation or surgery. Often people with VT are protected by implantation of a defibrillator. Because VT can lead to ventricular fibrillation (see above) it is considered a serious condition that warrants aggressive monitoring and treatment.