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arrhythmia (ārĭᵺˈmēə), disturbance in the rate or rhythm of the heartbeat. Various arrhythmias can be symptoms of serious heart 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 pacemakers.

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 gland 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 fever) in young people or hypertensive heart disease (see hypertension) and arteriosclerotic heart diseases (see arteriosclerosis) 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 (stroke) or other organs. Atrial fibrillation is often treated with digitalis 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 defibrillators that sense dangerous fibrillations and administer an electric shock to the heart to restore normal rhythm.

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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



an increase in the frequency of cardiac contractions. In some cases it is not perceived subjectively; in others, it is accompanied by palpitations.

A distinction is made between sinus tachycardia, or the accelerated generation of impulses in the sinus node of the heart, and paroxysmal tachycardia. Sinus tachycardia, manifested by contractions generally ranging between 90 and 120 per minute, may be caused by such physiological factors as increased environmental temperature, physical and mental tension, or the ingestion of food. Sinus tachycardia may also be caused by such pathological states as fever, anemia, diffuse toxic goiter, heart failure, and neurasthenia. Nervous and humoral influences on the heart, such as adrenalin and thyroxine, are important contributing factors in the genesis of sinus tachycardia. The accelerated rhythm of cardiac contractions may have an unfavorable effect on metabolism in the myocardium and on blood circulation. When tachycardia is a symptom of disease, the underlying disease is treated.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.


Excessive rapidity of the heart's action.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
Her nonstress tests were all reactive with no evidence of fetal tachycardia or abnormal decelerations.
Furthermore, the incidence of fetal tachycardia with Ephedrine was more significant in another study.
Fetal tachycardia is the most common side effect of beta-adrenergic receptor agonists.
Clinical signs of chorioamnionitis generally include fever, maternal and/or fetal tachycardia, foul smelling or purulent amniotic fluid, uterine tenderness, and maternal leukocytosis.
An early warning sign of this is fetal tachycardia in the second stage of labor.
Fetal tachycardia was present so emergency caesarean section was performed (1).
Fetal tachycardia was strongly associated with fetal acidemia and adverse neonatal outcomes in both groups.
Under the 1982 criteria, a woman is diagnosed with chorioamnionitis if she has a fever (greater than 37.80 C) plus at least two of the following conditions: maternal or fetal tachycardia, uterine tenderness, foul odor of amniotic fluid, and maternal leukocytosis.
Fetal heart abnormalities were seen in 11 cases (23%) of which fetal tachycardia was seen more often than bradycardia.
* Identify indicators of infection, such as maternal fever and tachycardia, fundal tenderness, fetal tachycardia, and an elevated white blood cell count
Indicators of uterine infection included clinical chorioamnionitis; a maternal temperature above 37[degrees]C; acute placental inflammation; placental-fetal inflammation; maternal fever and at least two of the following clinical findings: fetal tachycardia, white blood count below 15,000, or a foul vaginal discharge.