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Direct cardioversion-defibrillation
Last reviewed: 23.04.2024
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Transthoracic direct cardioversion-defibrillation of sufficient intensity depolarizes the entire myocardium as a whole, leading to instantaneous refractoriness of the entire heart and repetition of depolarization. After this, the fastest internal pacemaker, usually a sinus node, resumes control of the heart rhythm. Direct cardioversion-defibrillation very effectively stops tachyarrhythmias arising from re-entry. At the same time, the procedure is less effective for stopping arrhythmias due to automatism, since the restored rhythm is often automatic tachyarrhythmia. For the treatment of arrhythmias other than VF, direct cardioversion-defibrillation should be synchronized with the complex (called direct cardioversion), since a discharge that appears in a sensitive period (near the peak of the T wave) can lead to VF development. With VF, synchronization with the complex does not matter, in addition, it can not be performed. Direct cardioversion-defibrillation, performed without synchronization with the complex, is called direct defibrillation.
If a cardioversion is selected by the treatment method, the patient should not take food for 6-8 hours before the procedure to prevent aspiration. Because the procedure can cause anxiety in the patient and is painful, a short anesthetic or intravenous analgesia and sedation (for example, fentanyl at 1 μg / kg, then midazolam 1-2 mg every 2 minutes to a maximum dose of 5 mg) is applied as needed. There should be personnel trained in the organization of artificial ventilation.
Electrodes (plates or pads) used for cardioversion may be located at the front and back (along the left edge of the sternum in the third to fourth intercostal space and in the left subscapular area) or in front and side (between the clavicle and the second intercostal space along the right edge of the sternum and fifth-sixth intercostal space at the apex of the heart). After synchronization with the complex, confirmed on the monitor, discharge is performed. The most effective level of discharge depends on the type of tachyarrhythmia. The effect of cardioversion increases with the use of two-phase discharges, in which the current polarity partially changes the character of the discharge wave. Complications usually happens a little, basically in the form of an atrial and ventricular extrasystole, and also pains in muscles. Less often, mainly in patients with altered LV functions or after using several discharges, cardioversion-induced myocyte death and electromechanical dissociation develop.
Direct cardioversion-defibrillation can be used directly on the heart during thoracotomy or with the installation of an intracardiac catheter, in these cases much smaller discharges are needed.
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