Cardioversion and Defibrillation

Published on 22/03/2015 by admin

Filed under Critical Care Medicine

Last modified 22/04/2025

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W6 Cardioversion and Defibrillation

Raúl J. Gazmuri

image Before Procedure

Indications

• Emergency reestablishment of an organized electrical rhythm (defibrillation):

• Ventricular fibrillation
• Pulseless ventricular tachycardia
• Narrow or wide QRS complex tachycardia (ventricular rate >150) associated with hemodynamic instability, chest pain, or pulmonary edema
• Hemodynamically unstable polymorphic ventricular tachy-cardia

• Elective reestablishment of sinus rhythm:

• Atrial fibrillation
• Atrial flutter
• Hemodynamically stable ventricular tachycardia unresponsive to medical treatment
• Others

Contraindications

• Specific advance directives (e.g., do not attempt resuscitation for cases of ventricular fibrillation)
• Digitalis toxicity–associated tachycardia
• Sinus tachycardia caused by various clinical conditions
• Rhythms not responsive to electric shocks (e.g., multifocal atrial tachycardia)
• Atrial fibrillation or atrial flutter without proper anticoagulation or exclusion of atrial thrombi

Equipment

• Automated external defibrillator or manual defibrillator
• Proper age-adjusted pads or paddles

image Anatomy

The heart is located behind the sternum. Its base is at the level of the third intercostal space immediately to the right of the sternum, and its apex is at the level of the fifth intercostal space inferior and usually just medial to the nipple. External cardioversion or defibrillation is attempted by delivering one or more electric shocks through the chest cavity for the purpose of passing an electric current of sufficient energy through the heart muscle to fully depolarize the atria (e.g., atrial fibrillation or atrial flutter) or the ventricles (e.g., ventricular fibrillation or ventricular tachycardia). Cardioversion should enable the natural or artificial cardiac pacemaker to resume control of the cardiac rhythm. Electrodes (paddles or pads) can be positioned on the anterior chest wall with one electrode below the right clavicle lateral to the sternum and the other electrode below the breast tissue along the midaxillary line. Electrodes (pads; paddles more difficult) can also be positioned in an anteroposterior position, with the anterior electrode placed over the precordium and the posterior electrode at the right infrascapular location. For internal cardioversion or defibrillation, specially designed paddles are applied directly to the epicardial surface of the ventricles.

image Procedure

• For external elective cardioversion, many of the following steps may have to be shortened or circumvented in hemodynamically unstable patients—especially if unconscious—requiring rapid termination of life-threatening arrhythmia (e.g., ventricular fibrillation or pulse ventricular tachycardia as part of cardiopulmonary resuscitation).
• Admit the patient to an appropriately equipped hospital area with capability for monitoring cardiac rhythm, oxygenation, and vital signs, along with airway management and cardiopulmonary resuscitation.
• Fast the patient overnight or for at least 6 to 8 hours.
• Establish vascular access.
• Obtain an electrocardiogram.
• For sedation, consider using a short-acting anesthetic agent (e.g., midazolam, propofol, or etomidate) under the supervision of an anesthesiologist and adequate supportive personnel. An alternative to anesthesia is conscious sedation, in which the patient maintains consciousness but in a somnolent state. This has the advantage that it can be given by trained physicians without supervision by an anesthesiologist.
• Attach monitor leads to the patient, and ensure proper display of the patient’s rhythm.
• Place electrodes properly separated (as described under Anatomy). Apply coupling gel if using paddles, and to prevent current traversing superficially through the chest, avoid smearing the gel over the chest wall. In patients with permanent pacemakers or implantable cardioverter-defibrillators, place electrodes away from the device generator to avoid device malfunction. Consider reevaluating pacing thresholds in patients with permanent pacemakers and interrogation of implantable cardioverter-defibrillator function.
• Engage the synchronization mode, and identify markers on the R waves indicating adequate synchronization. If necessary, adjust the gain of the monitor until markers appear with each R wave.
• Select the energy level that will deliver the necessary current based on the patient’s waveform, age, and arrhythmia. Organized rhythms with a simple reentry circuit, such as atrial flutter and monomorphic ventricular tachycardia, usually require less current than more complex rhythms such as atrial and ventricular fibrillation.
• Press the charge button on the unit or paddles.
• If using paddles, apply approximately 12 kg pressure to each paddle.
• Press the discharge button on the unit or paddles simultaneously.
• Check the monitor. If the arrhythmia persists, increase the energy level according to protocol for the specific rhythm.
• Reset the synchronization. Most units default to the unsynchronized mode (allowing immediate defibrillation if ventricular fibrillation ensues).
• Repeat the shock until conversion of the arrhythmia or completion of the protocol is obtained.
• Deliver unsynchronized shocks only for ventricular fibrillation or pulseless ventricular tachycardia.

image After Procedure

Postprocedure Care

• Obtain an electrocardiogram.
• Assess hemodynamic and respiratory status.
• Observe the patient until recovery from anesthesia or sedation is complete.
• Consider hospital discharge if the procedure was elective.

Complications

• Cardioversion and defibrillation are relatively safe procedures with infrequent complications that may include:

• Induction of ventricular fibrillation if the electric shock is improperly synchronized
• Transient conduction abnormalities
• Myocardial dysfunction (after high-energy and repetitive delivery of electric shocks)
• Release of cardiac enzymes
• Pulmonary edema
• Embolization of thrombi formed within the cardiac chambers (e.g., atrial fibrillation, atrial flutter)
• Respiratory depression associated with anesthesia or sedation

image Outcomes and Evidence

• Sinus rhythm will be restored in a high percentage of patients.
• Underlying conditions may predispose to recurrence of arrhythmias.
• Early defibrillation of ventricular fibrillation is associated with improved survival.

Suggested Reading

Nolan JP, Soar J. Defibrillation in clinical practice. Curr Opin Crit Care. 2009;15:209-215.

Dosdall DJ, Fast VG, Ideker RE. Mechanisms of defibrillation. Annu Rev Biomed Eng. 2010;12:233-258.

Link MS, Atkins DL, Passman RS, Halperin HR, Samson RA, White RD, et al. Part 6: electrical therapies: automated external defibrillators, defibrillation, cardioversion, and pacing: 2010 American Heart Association guidelines for cardiopulmonary resuscitation and emergency cardiovascular care. Circulation. 2010;122:S706-19.

Nusair M, Flaker GC, Chockalingam A. Electric cardioversion of atrial fibrillation. Mo Med. 2010;107:59-64.

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