n. any deviation from the normal rhythm (sinus rhythm) of the heart. Arrhythmias result from a disturbance of the generation or the conduction of electrical impulses from the *sinoatrial node and may be intermittent or continuous. They are subdivided into tachyarrhythmias (fast rate) and bradyarrhythmias (slow rate). They include *ectopic beats (extrasystoles), *re-entry tachycardia, ectopic tachycardias (see supraventricular tachycardia; ventricular tachycardia), atrial and ventricular *fibrillation, and *heart block (which is often associated with slow heart rates). Symptoms include palpitations, breathlessness, and chest pain. In more serious arrhythmias the *Stokes-Adams syndrome or *cardiac arrest may occur. Arrhythmias may result from most heart diseases but they also occur without apparent cause.... arrhythmia
(countershock) n. restoration of normal heart rhythm in patients with tachyarrhythmia (see arrhythmia). Electrical (synchronized) cardioversion involves the application of a controlled shock, synchronized with the R wave of the *electrocardiogram, through electrodes placed on the chest wall of the anaesthetized patient. The apparatus is called a cardiovertor and is a modified *defibrillator. It is synchronized (usually by pressing a specific button on the control panel) because inadvertent delivery of the shock at the peak of the T wave can trigger ventricular fibrillation. Pharmacological cardioversion is achieved through oral, or more commonly intravenous, drug administration.... cardioversion
a familial condition affecting the heart, characterized by unexplained thickening (hypertrophy) of the wall of the left ventricle. In many cases this is an incidental finding and patients have a good outcome. However, more severely affected patients may suffer chest pain, tachyarrhythmia (see arrhythmia), heart failure, and sudden death. In some cases there is focal thickening of muscle around the left ventricular outflow tract (asymmetric septal hypertrophy, ASH), and this can result in restriction of blood flow to the body (hypertrophic obstructive cardiomyopathy, HOCM). The diagnosis is made by electrocardiography, echocardiography, and cardiac *magnetic resonance imaging. Usually drug treatment is sufficient to control symptoms, but some patients require cardiac *catheterization or surgical treatment. Those deemed at highest risk of sudden death may require an *implantable cardiovertor defibrillator.... hypertrophic cardiomyopathy
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