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(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.

Subjects: Medicine and Health.

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