Tachycardia(redirected from CMT)
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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.
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.