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arrhythmia(ārĭth`mēə), disturbance in the rate or rhythm of the heartbeat. Various arrhythmias can be symptoms of serious heartheart,
muscular organ that pumps blood to all parts of the body. The rhythmic beating of the heart is a ceaseless activity, lasting from before birth to the end of life. Anatomy and Function
The human heart is a pear-shaped structure about the size of a fist.
..... Click the link for more information. disorders; however, they are usually of no medical significance except in the presence of additional symptoms. The heart's rhythm is controlled by an electrical impulse that is generated from a clump of tissue on the right atrium called the sinoatrial node, often referred to as the heart's natural pacemaker. It travels to a second clump of tissue called the atrioventricular node and then to the ventricles.
Bradycardia, or slow heartbeat, is often present in athletes. It may, however, indicate conduction problems, especially in older people. In one type of bradycardia, called sinoatrial or atrioventricular block, or heart block, rhythm can be maintained by implanted electrodes that act as artificial pacemakerspacemaker, artificial,
device used to stimulate a rhythmic heartbeat by means of electrical impulses. Implanted in the body when the heart's own electrical conduction system (natural pacemaker) does not function normally, the battery-powered device emits impulses that trigger
..... Click the link for more information. .
Tachycardia, or heartbeat faster than 100 beats per minute in the adult, can be precipitated by drugs, caffeine, anemia, shock, and emotional upset. It may also be a sign of overactivity of the thyroid glandthyroid gland,
endocrine gland, situated in the neck, that secretes hormones necessary for growth and proper metabolism. It consists of two lobes connected by a narrow segment called the isthmus. The lobes lie on either side of the trachea, the isthmus in front of it.
..... Click the link for more information. or underlying disease. Flutters, and the even faster fibrillations, are rapid, uncoordinated contractions of the atrial or ventricular muscles that usually accompany heart disorders. Atrial fibrillation may be idiopathic, the result of rheumatic mitral valve disease (see rheumatic feverrheumatic fever
, systemic inflammatory disease, extremely variable in its manifestation, severity, duration, and aftereffects. It is frequently followed by serious heart disease, especially when there are repeated attacks. Rheumatic fever usually affects children.
..... Click the link for more information. ) in young people or hypertensive heart disease (see hypertensionhypertension
or high blood pressure,
elevated blood pressure resulting from an increase in the amount of blood pumped by the heart or from increased resistance to the flow of blood through the small arterial blood vessels (arterioles).
..... Click the link for more information. ) and arteriosclerotic heart diseases (see arteriosclerosisarteriosclerosis
, general term for a condition characterized by thickening, hardening, and loss of elasticity of the walls of the blood vessels. These changes are frequently accompanied by accumulations inside the vessel walls of lipids, e.g.
..... Click the link for more information. ) in older people. It may result in a rapid pulse rate and may be associated with thrombus formation in the atria and a risk of embolization to the brain (strokestroke,
destruction of brain tissue as a result of intracerebral hemorrhage or infarction caused by thrombosis (clotting) or embolus (obstruction in a blood vessel caused by clotted blood or other foreign matter circulating in the bloodstream); formerly called apoplexy.
..... Click the link for more information. ) or other organs. Atrial fibrillation is often treated with digitalisdigitalis
, any of several chemically similar drugs used primarily to increase the force and rate of heart contractions, especially in damaged heart muscle. The effects of the drug were known as early as 1500 B.C.
..... Click the link for more information. and other drugs that regulate heart rhythm or heart rate. It may also be treated by catheter ablation, in which an electrode produces heat to destroy cells causing the arrhythmia. Ventricular fibrillation is a sign of the terminal stage of heart failure and is usually fatal unless defibrillation is achieved by immediate direct-current defibrillation. Some tachycardias can be managed by the implantation in the upper chest of small defibrillatorsdefibrillator,
device that delivers an electrical shock to the heart in order to stop certain forms of rapid heart rhythm disturbances (arrhythmias). The shock changes a fibrillation to an organized rhythm or changes a very rapid and ineffective cardiac rhythm to a slower, more
..... Click the link for more information. that sense dangerous fibrillations and administer an electric shock to the heart to restore normal rhythm.
disruption of the normal rhythm of the heart. Arrhythmia is manifested as an increase in frequency (tachycardia) or a slowing (bradycardia) of the heart contractions, in the appearance of premature or additional contractions (extrasystole), in heart palpitations (paroxysmal tachycardia), and in complete irregularity of the intervals between individual contractions (fibrillation). Arrhythmia may appear, among other causes, as a result of heart disease (myocarditis, cardiosclerosis); it may be functional or be caused by disturbance of the nervous regulation of the heart—for example, when the interconnection between the auricles and ventricles is interrupted (heart block). So-called respiratory or juvenile arrhythmia (acceleration of heartbeat upon inspiration) is a physiological phenomenon in children and adolescents. Some arrhythmias cause disturbance of blood circulation, unpleasant feelings of “irregularity of heart action,” dizziness, and the like. Other arrhythmias are not felt by patients. Treatment is directed toward removing the basic disease and restoring the normal heart rhythm.