The need for treatment of arrhythmias Overview of Arrhythmias The normal heart beats in a regular, coordinated way because electrical impulses generated and spread by myocytes with unique electrical properties trigger a sequence of organized myocardial... read more 
depends on the symptoms and the seriousness of the arrhythmia. Treatment is directed at causes. If necessary, direct antiarrhythmic therapy, including antiarrhythmic drugs Medications for Arrhythmias The need for treatment of arrhythmias depends on the symptoms and the seriousness of the arrhythmia. Treatment is directed at causes. If necessary, direct antiarrhythmic therapy, including antiarrhythmic... read more , direct current (DC) cardioversion-defibrillation, implantable cardioverter-defibrillators Implantable Cardioverter-Defibrillators (ICD) The need for treatment of arrhythmias depends on the symptoms and the seriousness of the arrhythmia. Treatment is directed at causes. If necessary, direct antiarrhythmic therapy, including antiarrhythmic... read more 
(ICDs), pacemakers Cardiac Pacemakers The need for treatment of arrhythmias depends on the symptoms and the seriousness of the arrhythmia. Treatment is directed at causes. If necessary, direct antiarrhythmic therapy, including antiarrhythmic... read more 
(and a special form of pacing, cardiac resynchronization therapy Cardiac Resynchronization Therapy (CRT) The need for treatment of arrhythmias depends on the symptoms and the seriousness of the arrhythmia. Treatment is directed at causes. If necessary, direct antiarrhythmic therapy, including antiarrhythmic... read more ), catheter ablation Ablation for Cardiac Arrhythmia The need for treatment of arrhythmias depends on the symptoms and the seriousness of the arrhythmia. Treatment is directed at causes. If necessary, direct antiarrhythmic therapy, including antiarrhythmic... read more , surgery Surgery for cardiac arrhythmias The normal heart beats in a regular, coordinated way because electrical impulses generated and spread by myocytes with unique electrical properties trigger a sequence of organized myocardial... read more , or a combination, is used.
A transthoracic DC shock of sufficient magnitude depolarizes the entire myocardium Electrophysiology The normal heart beats in a regular, coordinated way because electrical impulses generated and spread by myocytes with unique electrical properties trigger a sequence of organized myocardial... read more , rendering the entire heart momentarily refractory to repeat depolarization. Thereafter, the most rapid intrinsic pacemaker, usually the sinoatrial (SA) node, reassumes control of heart rhythm. Thus, DC cardioversion-defibrillation very effectively terminates tachyarrhythmias that result from reentry. However, it is less effective for terminating tachyarrhythmias that result from automaticity because the return rhythm is likely to be the automatic tachyarrhythmia. For tachyarrhythmias other than ventricular fibrillation (VF) and pulseless ventricular tachycardia (VT), the DC shock must be synchronized to the QRS complex (called DC cardioversion) because a shock that falls during the vulnerable period (near the peak of the T wave) can induce VF. In VF, synchronization of a shock to the QRS complex is neither necessary nor possible. A DC shock applied without synchronization to a QRS complex is DC defibrillation.
Direct current (DC) cardioversion or defibrillation can be delivered as
Monophasic current
Biphasic current
Monophasic current travels in one direction between the two electrodes. In biphasic devices, the current reverses direction part way through the shock waveform. The biphasic device requires lower energy and has been shown to lead to higher rates of return of spontaneous circulation (ROSC). However, survival outcomes are similar in both devices (1 General reference The need for treatment of arrhythmias depends on the symptoms and the seriousness of the arrhythmia. Treatment is directed at causes. If necessary, direct antiarrhythmic therapy, including antiarrhythmic... read more ). Most manual and automated external defibrillators (AEDs) are now biphasic because of increased efficiency at restoring sinus rhythm. Biphasic devices are also smaller in size (making the devices more portable).
Procedure for DC cardioversion
When DC cardioversion is elective, patients should fast for 6 to 8 hours to avoid the possibility of aspiration. Because the procedure is frightening and painful, brief general anesthesia or IV analgesia and sedation (eg, fentanyl 1 mcg/kg, then midazolam 1 to 2 mg every 2 minutes to a maximum of 5 mg) is necessary. Equipment and personnel to maintain the airways Airway and Respiratory Devices If no spontaneous respiration occurs after airway opening and no respiratory devices are available, rescue breathing (mouth-to-mask or mouth-to-barrier device) is started; mouth-to-mouth ventilation... read more must be present.
The electrodes (pads or paddles) used for cardioversion may be placed anteroposteriorly (along the left sternal border over the 3rd and 4th intercostal spaces and in the left infrascapular region) or anterolaterally (between the clavicle and the 2nd intercostal space along the right sternal border and over the 5th and 6th intercostal spaces at the apex of the heart). After synchronization to the QRS complex is confirmed on the monitor, a shock is given.
The most appropriate energy level varies with the tachyarrhythmia being treated. Cardioversion and defibrillation efficacy increases with use of biphasic shocks, in which the current polarity is reversed part way through the shock waveform.
For defibrillation of ventricular fibrillation Ventricular Fibrillation (VF) Ventricular fibrillation causes uncoordinated quivering of the ventricle with no useful contractions. It causes immediate syncope and death within minutes. Treatment is with cardiopulmonary... read more 
or pulseless ventricular tachycardia, the energy level for the first shock is
120 to 200 joules for biphasic devices (or according to manufacturer specification) although many practitioners use the maximum device output in this setting
360 joules for monophasic devices (or according to manufacturer specification)
Subsequent shocks are at the same or higher energy level for biphasic devices and are at the same level for monophasic devices.
For synchronized cardioversion of atrial fibrillation Atrial Fibrillation Atrial fibrillation is a rapid, irregularly irregular atrial rhythm. Symptoms include palpitations and sometimes weakness, effort intolerance, dyspnea, and presyncope. Atrial thrombi may form... read more , the energy level for the first shock is
100 to 200 joules for biphasic devices (or depending on manufacturer specification)
200 joules for monophasic devices (or according to manufacturer specification)
Subsequent shocks are at the same or higher energy level for both biphasic and monophasic devices.
DC cardioversion-defibrillation can also be applied directly to the heart during a thoracotomy or through use of an intracardiac electrode catheter; then, much lower energy levels are required.
Complications of DC cardioversion
Complications are usually minor and include atrial and ventricular premature beats and muscle soreness. Less commonly, but more likely if patients have marginal left ventricular function or multiple shocks are used, cardioversion precipitates myocyte damage and electromechanical dissociation.
General reference
1. Schneider T, Martens PR, Paschen H, et al: Multicenter, randomized, controlled trial of 150-J biphasic shocks compared with 200-J to 360-J monophasic shocks in the resuscitation of out-of-hospital cardiac arrest victims. Circulation 102:1780–1787, 2000.
Drugs Mentioned In This Article
| Drug Name | Select Trade |
|---|---|
fentanyl |
ABSTRAL, Actiq, Duragesic, Fentora, IONSYS, Lazanda, Onsolis, Sublimaze, SUBSYS |
midazolam |
Nayzilam, Versed, Versed Syrup |
