Cardioversion
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217067639
2008-06-04T13:44:36Z
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Date the maintenance tags or general fixes
'''Synchronized electrical cardioversion''' is the process by which an abnormally fast [[heart rate]] or [[cardiac arrhythmia]] is terminated by the delivery of a therapeutic dose of [[electrical current]] to the [[heart]] at a specific moment in the [[cardiac cycle]].
'''Pharmacologic cardioversion''' uses medication instead of an electrical shock to convert the [[cardiac arrhythmia]].
==Synchronized electrical cardioversion==
To perform synchronized electrical cardioversion two [[electrode]] pads are used, each comprising a metallic plate which is faced with a saline based conductive gel. The pads are placed on the chest of the patient, or one is placed on the chest and one on the back. These are connected by cables to a machine which has the combined functions of an [[electrocardiogram|ECG]] display screen and the electrical function of a [[defibrillator]]. A synchronizing function (either manually operated or automatic) allows the cardioverter to deliver a reversion shock, by way of the pads, of a selected amount of [[electrical current]] over a predefined number of [[millisecond]]s at the optimal moment in the [[cardiac cycle]] which corresponds to the R wave of the [[QRS complex]] on the [[electrocardiogram|ECG]]. Timing the shock to the R wave prevents the delivery of the shock during the 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 haemodynamically unstable or unconscious, the shock is given immediately upon confirmation of the [[arrhythmia]]. 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 may cause burns of the [[epidermis (skin)|epidermis]] at the pad sites. 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) [[tachycardia]]s, 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]].
==Pharmacologic cardioversion==
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Various [[antiarrhythmic agent]]s can be used to return the heart to normal [[sinus rhythm]]. Pharmacological cardioversion is an especially good option in patients with fibrillation of recent onset. Drugs that are effective at maintaining normal rhythm after electric cardioversion, can also be used for pharmacological cardioversion. 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.There are two classes of agents that are most effective for pharmacological cardioversion.
Class I agents: Procainamine, quinidine and disopyramide are Class Ia agents, while flecainide and propafenon are Class Ic agents.
Class III agents: Amiodarone and sotalol are effective Class III agents.
If the patient is stable, [[Adenosine]] may be administered first, as the medicine performs a sort of "chemical cardioversion" and may stabilize the heart and let it resume normal function on its own without using electricity.
==See also==
* [[Implantable cardioverter-defibrillator]] (ICD)
* [[Transcutaneous pacing]]
==External links==
* [http://www.nlm.nih.gov/medlineplus/ency/article/007110.htm ''Cardioversion'' from the National Institutes of Health]
* [http://www.aafp.org/afp/980800ap/dello.html ''Pharmacological Cardioversion'' from the American Academy of Family Physicians]
* [http://www.emedicine.com/med/topic2968.htm ''Synchronized Electrical Cardioversion'' from eMedicine Online]
* [http://hrspatients.org/patients/treatments/cardioversion.asp ''Cardioversion'' from the Heart Rhythm Society]
[[Category:Cardiology]]
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[[es:Desfibrilación y Cardioversión eléctrica]]
[[nl:Cardioversie]]