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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 It might be outdated or ideologically biased.



decrease in frequency of heart contractions to less than 60 beats per minute.

Bradycardia may be found as a normal, constitutionally conditioned phenomenon in perfectly healthy persons, in well-trained athletes, and as one of the symptoms in many diseases. More often, bradycardia is observed as a result of organic disturbances of auriculoventricular conductivity—heart blockage, myocardial infarction, and inflammatory (infectious or toxic) diseases of the heart muscle. Complete blockage of the heart with a pulse frequency of 30–40 beats per minute or less threatens brain complications: loss of consciousness, convulsions, and cessation of heart activity. Prophylaxis and treatment are directed toward removal of the cause.

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


Slow heart rate.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
PE infusion (dark gray box) resulted in an increase in AP that drove a baroreflex-mediated reduction in heart rate (bradycardic phase).
The patient became bradycardic and lost consciousness.
Although the age-dependent decrease in SBP and HR we observed may not be characterized as a hypotensive and bradycardic state, as seen in cases of Kwashiokor and marasmus, it showed a trend in the same direction, i.e., reduction in SBP and HR.
Sympatholytic or bradycardic actions of [alpha]2-adrenoceptor agonists may be deleterious in hypovolemic patients or patients with fixed stroke volume.
At presentation to the emergency department, she was hypotensive and bradycardic. Eight hours later, a blood sample (Fig.
Second, the formula used for the calculation of MAP with the auscultatory method may have been less accurate in either bradycardic or tachycardic patients, due to the length of the systole changing with the heart rate [35].
In order to further prove the effects of SSYX and cumulate the clinical data, a randomized, double-blind, placebo-controlled clinical study was designed to fully evaluate the efficacy and safety of SSYX in patients experiencing bradycardic arrhythmias.
The ventricular rate in untreated patients with normal atrioventricular conduction is typically between 100 and 160 bpm, but normo-and bradycardic ventricular response rates are possible.
As regards the sinus rhythm, 18 participants had a normal rhythm, 5 had a bradycardic rhythm, and 2 had a tachycardic rhythm.
She is given a saline bolus, and her blood pressure normalizes, but she remains markedly bradycardic and complains of feeling weak.
"He's bradycardic [experiencing slow heart rate] without any good reason to be bradycardic," Topol said to his colleague, Hashim Khan, watching as a graph of blips roller-coastered across his phone's screen.
In addition, the human dive reflex, a physiological phenomenon similar to the bradycardic reflex (Smith et al., 2012), might explain the lower heart rate response in the aquatic environment.