Chapter 30. Cardioversion and Defibrillation

The application of electricity to the heart induces depolarization of the myocardial cells in a uniform fashion. This may interrupt reentry circuits that are inducing an arrhythmia. Once depolarization of the myocardium has been achieved, the sinus node may then resume its normal pacing function. This is accomplished with the transthoracic application of a direct-current electrical shock.

The techniques of cardioversion and defibrillation are relatively straightforward and practically identical. The main differences are the indications and use of synchronization with cardioversion. The purpose of cardioversion is to deliver a precisely timed electrical current to the heart to convert an organized rhythm to a more hemodynamically stable rhythm. The purpose of defibrillation is to deliver a randomly timed high-energy electrical current to the heart to restore a normal sinus rhythm. These techniques are currently performed by emergency medical technicians, nurses, paramedics, physicians, and a variety of other healthcare workers on a daily basis. This chapter discusses the techniques of manual cardioversion and defibrillation. A discussion of Advanced Cardiac Life Support (ACLS), cardiac rhythms, chemical cardioversion, and Pediatric Advanced Life Support is beyond the scope of this work. The technique of automatic external defibrillation is not discussed.

Cardioversion

In general, electrical cardioversion is performed either electively or emergently. In the Emergency Department, the role of electrical cardioversion is usually limited to urgent or emergent situations or when medical therapy has failed.1,2 This includes symptomatic reentry tachycardias (e.g., supraventricular tachycardia, atrial fibrillation, atrial flutter, and Wolff–Parkinson–White syndrome) and hemodynamically stable ventricular tachycardia associated with acute myocardial infarctions, altered levels of consciousness, chest pain, congestive heart failure, dizziness, dyspnea, hypotension, presyncope, pulmonary edema, shock, or syncope.

In the Emergency Department, electrical cardioversion is often preferred to chemical cardioversion for many reasons. Electrical cardioversion is simple and quick to perform. It is effective—in most cases almost immediately. It may be more successful than chemical cardioversion. The complications are usually minimal. Potential allergic reactions and toxic effects are nonexistent with electrical cardioversion.

Defibrillation

Defibrillation is indicated when ventricular fibrillation or ventricular tachycardia has not spontaneously converted to an organized rhythm. Ventricular fibrillation and ventricular tachycardia are rarely spontaneously reversible and are not compatible with life. Defibrillation must be performed immediately if the patient is found pulseless, unconscious and apneic, or during the ACLS protocol. “Fine” ventricular fibrillation can be present and may be confused with asystole. It may be secondary to low gain amplitude or improper lead positioning. If “quick-look” paddles are being used, they may be rotated 90°. If a monitor is being used, select a different lead and/or increase the gain to determine if the cardiac rhythm is fine ventricular fibrillation or asystole. Ventricular fibrillation or ventricular tachycardia secondary to myocardial ischemia or infarct, electrolyte abnormalities, long-QT syndromes, hypothermia, or drug toxicity (e.g., digoxin, tricyclic antidepressants, antiarrhythmics, antihistamine, and macrolide antibiotic combinations) may convert to a more stable rhythm with defibrillation.

Cardioversion

Cardioversion is contraindicated for several cardiac rhythms or conditions. Do not cardiovert a patient with a rhythm of ectopic atrial tachycardia, junctional tachycardia, multifocal atrial tachycardia, sick sinus syndrome, or sinus tachycardia. Cardioversion is not effective for these rhythms and may result in a worse (i.e., ventricular fibrillation or ventricular tachycardia) postshock rhythm. Cardioversion of atrial fibrillation should not be attempted unless it is known with certainty that the rhythm initiated within the last 48 hours. Cardioversion of chronic atrial fibrillation, or atrial fibrillation having lasted longer than 48 hours, may dislodge atrial thrombi, resulting in thrombus embolization and end organ injury (e.g., stroke). There is some controversy in the literature regarding the cardioversion of atrial flutter greater than 48 hours old without anticoagulation.3,4 In general, elective cardioversion of atrial flutter should not be performed if the rhythm has lasted for longer than 48 hours. Often times, atrial fibrillation and flutter can coexist. Do not cardiovert a patient with a known thrombus in the atria, atrial appendage, or ventricle without first consulting a Cardiologist. Cardioversion in patients with digoxin toxicity should be avoided. Cardioversion in digoxin toxicity is usually ineffective and has been associated with postshock ventricular tachycardia and ventricular fibrillation.5 Cardioversion is also contraindicated when the patient is without a pulse or has an underlying cardiac rhythm of asystole.

Alterations in the chemical or metabolic milieu of the myocardium may cause subsidiary pacemakers to become more dominant and overtake the sinus mode. This is referred to as enhanced automaticity and can be due to drugs (e.g., digoxin), hypoxia, or electrolyte abnormalities (e.g., hypokalemia or hypomagnesemia). Uniform depolarization with electricity does not terminate this abnormality, as uniform depolarization already exists. The rhythms that may occur are sinus tachycardia, ectopic atrial tachycardia, multifocal atrial tachycardia, and the digoxin toxic rhythms. Treatment of the underlying etiology is the treatment of choice.

Defibrillation

There are few contraindications to defibrillation. The main contraindication is in a patient who has made it clear that they does not wish to be resuscitated. Defibrillation should not be used for arrhythmias other than ventricular tachycardia or ventricular fibrillation.

• Cardioverter-defibrillator unit
• Conductive jelly or pads
• Suction source, tubing, and catheter
• Airway management supplies
• Advanced Cardiac Life Support (ACLS) medications
• Intravenous sedative agents
• Cardiac monitor
• Noninvasive blood pressure monitor
• Pulse oximeter
• Oxygen source and tubing
• Nasal cannula or face mask to deliver oxygen

The Cardioverter-Defibrillator Unit

The typical cardioverter-defibrillator unit performs both cardioversion and defibrillation (Figure 30-1). A list of available features on a typical unit is listed in Table 30-1. Newer models feature lower power outputs to accommodate their use in children, pediatric and adult paddles, biphasic waveforms, and cardiac pacing capabilities. Each Emergency Physician should be familiar with the specific unit at their facility. The general features of the unit are discussed below.

The unit is self-contained. It plugs into a standard electrical outlet. The unit also contains rechargeable batteries, which allow it to be portable. An oscilloscope provides real-time monitoring of the patient's cardiac rhythm. A continuous electrocardiographic (ECG) rhythm strip providing documentation on paper is standard with each unit, producing a hard copy to attach to the patient's medical record. Numerous dials or electronic touchpads with digital displays allow the operator to set the working mode, energy level, pacemaker settings, and oscilloscope input (e.g., ECG leads or “quick-look” paddles). The depolarizer within the machine provides direct electric current for cardioversion and defibrillation.

The synchronizer permits the discharge of electric current based on the patient's ECG waveform. It searches for the R and S waves of the ECG tracing to determine the proper time to discharge the current. It avoids delivering the current during the repolarization phase of the myocardial action potential, when the heart may convert to ventricular fibrillation or ventricular tachycardia. When the operator pushes the button to discharge the unit, a brief delay is noted while the synchronizer searches for an appropriate time to discharge the current.

Monophasic Versus Biphasic Units

In the past, all cardioverter-defibrillator units generated monophasic waveform current to deliver the shock. Biphasic waveform current generating units were developed in the late 1990s. The biphasic units deliver more current at a lower energy level to cardiovert or defibrillate (Tables 30-2 & 30-3). They have also been shown to be more effective in cardioverting and defibrillating a patient. Unfortunately, biphasic units are significantly more expensive than monophasic units. Determine which type of unit is available at your facility to determine the proper energy levels to administer.

Types of Electrodes

The electrodes are referred to as either paddles or patches depending on their configuration. The paddles or patches must be firmly applied to the patient's torso. They allow a “quick look” and transmit the patient's cardiac rhythm to the oscilloscope, letting the operator make medical decisions before the ECG leads are attached to the patient. Each paddle has a button on which a thumb is to be placed. This serves as a safety mechanism. Both buttons must be depressed simultaneously to discharge the current. This prevents accidental and premature discharge of current, which may injure the patient, the operator, or bystanders. Most newer units use self-adhesive, single patient use, disposable patches as an alternative to paddles. The patches apply to the torso similar to ECG leads. They connect by cables to the cardioverter-defibrillator unit.

Paddles or patches come in various shapes and sizes. Adult paddles or patches are round, oval, or rectangular in shape. They measure 8 to 10 cm in greatest diameter. They can be used on children weighing more than 10 kg or over 1 year of age, adolescents, and adults. Pediatric paddles or patches also come in a variety of shapes and measure 4 to 6 cm in greatest diameter. The pediatric paddles are to be used in children weighing less than 10 kg or less than 1 year of age. Some units contain both adult and pediatric paddles or the ability to use both adult and pediatric patches. In these units, the adult electrode slides off the paddle handle to reveal the pediatric-size electrode.

In choosing the proper paddle or patch for a small child, the cutoff of 10 kg and 1 year of age is relative. Choose the largest paddle or patch that will achieve complete and full contact with the child's chest wall. Larger paddles and patches will allow a greater amount of myocardium to be depolarized while decreasing the current density applied, so as to minimize myocardial injury. The paddles or patches must be at least 2 to 3 cm apart to prevent electrical bridging and burn injury to the child. Using paddles or patches that are too large will deliver the electric current over too great an area and decrease its effectiveness. The opposite is true in adults (using paddles or patches that are too small will deliver the electric current over a small area, which makes it too intense and increases the potential damage to the myocardium).

Electrode Positioning

The paddles or patches may be positioned in several different patterns.6,7,13 The most commonly used positions are anterolateral for paddles (Figure 30-2) and either anterolateral or anteroposterior (Figure 30-3) for patches. Anterolateral paddles or patches are positioned with the anterior paddle at the right upper sternal border over the second and third intercostal spaces. The lateral paddle or patch is placed in the left midaxillary line centered over the fourth and fifth intercostal spaces. Anteroposterior placement is often used with disposable patches rather than paddles (Figure 30-3). The anterior patch is centered over the sternum, and the posterior patch is placed between the scapulae. A randomized and prospective trial evaluated the anteroposterior versus anterolateral patch position in converting atrial fibrillation.13 The anteroposterior patch position was more effective in converting the rhythm. If pediatric paddles are required but not available, adult paddles can be substituted.6 Roll the child onto their right side and place the paddles in the anteroposterior position. Other paddle positions include the laterolateral (axilla-to-axilla) position and the parasternal-infraclavicular (oblique, left anterior chest to right posterior infrascapular) position.7

Conductive Contact Medium

Electrically conductive contact medium should always be applied between the electrode and the patient's chest wall. Conductive gel pads are commercially available and primarily used. The contact material helps to maximize current flow, minimize resistance, reduce transthoracic impedance, and prevent thermal or electrical burns to the chest wall. The self-adhesive disposable patches are prelubricated with contact medium and need no additional contact medium.

Contact medium is required with the older units that use paddles. Self-adhesive, disposable conductive gel pads can be used. An alternative is the gel or paste form of contact medium. The contact medium should be applied to the paddles generously. It should not connect the paddles, because then it would divert the electric current along the chest wall, away from the heart, and cause burns to the chest wall. If contact medium is not available, saline-soaked gauze squares can be used in an emergency. The saline must be squeezed out of the gauze squares to prevent the accumulation of liquid on the chest wall, which could bridge the two paddles.

Place the patient supine on a bed. Attach the cardiac monitor, noninvasive blood pressure monitor, pulse oximetry, and oxygen to the patient. Obtain intravenous access. Suction and resuscitation equipment should be readily available in case it is needed. Cardioversion is scary and extremely uncomfortable for patients. Briefly explain the procedure to the patient, including the risks, benefits, and complications. Premedicate the patient prior to cardioversion if no contraindications exist, the patient is hemodynamically stable, and they can tolerate a delay to cardioversion. The choice of the appropriate sedative agent is physician-dependent. Commonly used agents include etomidate, ketamine, midazolam, methohexital, propofol, and thiopental. Diazepam and lorazepam are not often used because of the long delay to onset of action.

Stand at the patient's left side. Turn on the cardioverter-defibrillator unit. Set the display to the “quick-look” paddles. Instruct the nurses to apply the ECG leads to the patient. Grasp the left paddle (sternum) with the left hand and the right paddle (apex) with the right hand. This is the anterolateral paddle position. Apply the paddles and observe the patient's cardiac rhythm. Set the mode as asynchronous (defibrillation) or synchronous (cardioversion) based on the patient's cardiac rhythm. Set the energy level (Tables 30-2 & 30-3). Older defibrillator units deliver monophasic waveform energy. Newer units deliver biphasic energy, which has been shown to be more effective, and deliver more current at lower energy settings.

Apply conductive pads to the patient's torso in the anterolateral position. Alternatively, apply conductive jelly to the paddles liberally and rub them together to coat the electrode surface completely. Apply the paddles firmly to the torso in the anterolateral position. The paddles should be separated from each other by at least 2 to 3 cm to prevent arcing of the current and injury to the patient.

Prepare to deliver the electric current to the patient. Charge the paddles. This must be done on the unit or the paddles before the initial and each subsequent discharge. It takes approximately 2 to 5 seconds to charge the paddles following activation of the charge button. Ensure that nurses and other assistants are not touching the patient or the stretcher by saying “clear.” The assistant ventilating through a bag-valve device attached to an endotracheal tube does not need to drop the bag, as plastic is nonconductive. Turn off any open oxygen sources during shock delivery. The person who will deliver the charge to the patient should ensure that their body is not in direct contact with the patient or the stretcher.

Reevaluate the patient's cardiac rhythm. If still required, deliver the charge by simultaneously pressing the discharge buttons on each paddle. Observe the monitor and reevaluate the patient's cardiac rhythm. The unit can be recharged to deliver another electric charge to the patient if indicated.

The technique using self-adhesive disposable patches on newer units is similar with a few exceptions. Apply the patches in the anteroposterior position. No supplemental contact medium is required. The desired energy level is selected (Tables 30-2 & 30-3). Charge the cardioverter-defibrillator unit by pressing the charge button on the unit. Press the discharge button on the cardioverter-defibrillator unit to deliver the charge to the patient. Again reevaluate the need for further therapies as above.

Occasionally, the cardioverter-defibrillator unit may not deliver a shock. Check that the unit is plugged in, no touching or bridging of the pads or gel has occurred on the patient's chest, and that the paddles are charged. The cardioverter-defibrillator unit may not be able to properly sense the R-wave in synchronization mode with a rapid supraventricular rhythm. Reattempt to deliver the shock by holding down the discharge button for 15 seconds. This will give the cardioverter-defibrillator unit more time to determine and find a proper time to deliver the shock. Switching to asynchronous mode will allow the delivery of the shock, but risks shocking at the inappropriate time and converting the rhythm to ventricular tachycardia or ventricular fibrillation. Consider intravenous medication to slow the heart rate or chemically convert the rhythm rather than applying an asynchronous shock.

No specific aftercare is required related to the procedure of cardioversion or defibrillation. If using a cardioverter-defibrillator unit with paddles and conductive gel or paste, it is possible to cause a thermal burn to the skin. This should be treated as any other skin burn. Continuously monitor the patient after they are cardioverted or defibrillated. Almost all patients receiving cardioversion or defibrillation will be admitted to the hospital. Occasionally, a successfully cardioverted patient may be discharged home. The decision to discharge the patient should be made in consultation with the patients' Primary Care Physician and a Cardiologist.

Complications of cardioversion and defibrillation can range from none to death. Thermal and electrical burns are potential injuries. Skin burns may result, the severity of which increases depending on the energy level utilized and the number of shocks delivered. Care must be taken to avoid contact between the ECG monitor leads and the paddles, or of the paddles with each other, as sparks or fire may result. Burns can be minimized by utilizing electrically conductive contact media and firmly applying the paddles to the patient. Remove any fluid materials on the chest wall (i.e., conductive jelly, saline, sweat, urine, and water), as they can form a bridge between the paddles or pads and result in arcing and thermal burns to the thorax. Also, remove any nitroglycerin patches or ointments from the patient's torso. Ensure that there are no open oxygen sources that could ignite when the unit is discharged. If performed properly, repeated shocks will produce only a mild erythema to the chest wall. Systemic emboli may occur from clots in the left atrium becoming dislodged if the underlying rhythm prior to the cardioversion or defibrillation is atrial fibrillation.

Occasionally hypertension, other arrhythmias, or heart block may develop. If a synchronized or nonsynchronized shock is delivered on the T wave, ventricular fibrillation may result.9–11 This usually occurs immediately and can be corrected with an nonsynchronized countershock. Ensure that the unit is in synchronous mode, not asynchronous mode, when cardioverting an organized cardiac rhythm. Always observe the monitor before delivering a countershock to ensure that it is required. If the T wave is large, change the monitor lead so that the T wave is smaller than the R wave and the unit will not cardiovert during a vulnerable period. Ventricular fibrillation that occurs within 30 to 60 seconds after the delivery of a synchronous shock is often due to digoxin toxicity and is difficult or impossible to correct. Transient ST-segment elevation may occur.12

Creatine kinase enzyme elevations may occur, most being skeletal muscle in origin.10 Cardiac enzymes can also become elevated. The higher the energy level used and the more countershocks given, the greater the muscle damage that may result. Usually, no significant permanent myocardial damage occurs.

Do not apply the paddles or patches directly over an implanted defibrillator or pacemaker. The electric discharge can permanently damage these devices. Adjust the paddle or patch position so they are not directly over these devices.

Avoid injury to yourself or others by ensuring that no one is in contact with the bed or the patient when the shock is administered. Such injuries can range from mild shocks and burns to cardiac dysrhythmias. An improperly functioning unit can cause injury despite being used properly. Periodic maintenance and calibration of the unit is necessary.

Cardioversion and defibrillation are the processes of applying elec-tric current to a patient's chest to terminate a dysrhythmia. Cardioversion is a safe and effective method of converting reentry arrhythmias. If the patient is stable, a trial of medical therapy is war-ranted. If the patient is “unstable,” cardioversion should be initiated as soon as possible. Consider administering parenteral sedation, as cardioversion is anxiety-provoking and painful for the patient. Cardioversion should be performed in the synchronized mode. Always be prepared for ventricular fibrillation or ventricular tachycardia as a result of cardioversion of an organized rhythm. ACLS medications and airway support must be readily available. Defibrillation is essentially cardioversion of unstable ventricular tachycardia or ventricular fibrillation. It is performed like cardioversion except that synchronization and sedation are not required.