Cardioversion
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Synchronized electrical cardioversion is the process by which an abnormally fast heart rate or cardiac arrhythmia is terminated by the delivery of therapeutic dose of electrical current to the heart at a specific moment in the cardiac cycle as determined by a computer.
Pharmacologic cardioversion uses medication instead of an electrical shock to convert the cardiac arrhythmia.
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[edit] Synchronized electrical cardioversion
To perform synchronized electrical cardioversion, two electrical pads are used. They are placed on the chest of the patient, or one is placed on the chest and one on the back. These pads are connected to an ECG machine which can deliver a specified amount of electrical current over a designated number of milliseconds at the optimal moment in the cardiac cycle which corresponds to the R wave or QRS complex on the ECG. Timing the shock to the R wave helps prevent the delivery of the shock during the so-called vulnerable period (or relative refractory period) of the cardiac cycle, which could induce ventricular fibrillation. If the patient is conscious, various drugs are often used to help sedate the patient and make the procedure more tolerable. However, if the patient is hemodynamically unstable or unconscious, the shock is given immediately upon confirmation of the rhythm. When synchronized electrical cardioversion is performed as an elective procedure, the shocks can be performed in conjunction with drug therapy until sinus rhythm is attained. Multiple electrical shocks can cause burning of the epidermis. After the procedure, the patient is monitored to ensure stability of the sinus rhythm.
Synchronized electrical cardioversion is used to treat hemodynamically significant supraventricular (or narrow complex) tachycardias, including atrial fibrillation and atrial flutter. It is also used in the emergent treatment of wide complex tachycardias, including ventricular tachycardia, when a pulse is present. Pulseless ventricular tachycardia and ventricular fibrillation are treated with unsynchronized shocks referred to as defibrillation. Electrical therapy is inappropriate for sinus tachycardia, which should always be a part of the differential diagnosis.
[edit] Pharmacologic cardioversion
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Various antiarrhythmic agents can be used to return the heart to normal sinus rhythm. Drugs like amiodarone, cardizem, and metoprolol are frequently given before cardioversion to decrease the heart rate, stabilize the patient and increase the chance that cardioversion is successful.
If the patient is stable Adenosine may be administered first, as the medicine preforms a sort of "chemical cardioversion" and may stop the heart and let it resume normal function on its own without using electricity.
