Version May 2024
INTRODUCTION — This topic will review the technique of electrical countershock, including automated external defibrillator (AED) use, in children. The basic principles that underlie countershock treatment; the clinical indications for these procedures and the side effects that may be seen; and the development, use, allocation, and efficacy of AEDs are discussed separately.
●(See "Basic principles and technique of external electrical cardioversion and defibrillation".)
●(See "Cardioversion for specific arrhythmias".)
●(See "Automated external defibrillators".)
DEFINITIONS — Defibrillation and cardioversion are methods of delivering electrical energy to the heart through the chest wall in an attempt to restore the heart's normal rhythm. There is an important distinction between defibrillation and cardioversion:
Defibrillation — Defibrillation is the asynchronous delivery of energy, such as the shock is delivered randomly during the cardiac cycle. It is indicated for patients with ventricular fibrillation (VF) or pulseless ventricular tachycardia (VT).
Cardioversion — Cardioversion is the delivery of energy that is synchronized to the QRS complex. It is indicated for patients who are hemodynamically unstable with either ventricular or supraventricular tachycardia, including atrial fibrillation or flutter.
Defibrillation and cardioversion may be accomplished using a manual defibrillator, which requires users to recognize the dysrhythmia and preselect the energy to be delivered. Alternatively, automated external defibrillators (AEDs) may be used. AEDs are computerized machines that automatically diagnose VF and use voice prompts to instruct rescuers to defibrillate, if appropriate. In addition, based on preset values for heart rate and R-wave morphology, AEDs may advise defibrillation for VT.
ANATOMY AND PHYSIOLOGY — Located in the upper pole of the right atrium, the sinoatrial node serves as the site of initial electrical impulse (depolarization) during normal cardiac contraction. This wave of depolarization spreads through the atria, resulting in atrial contraction. It is then conducted in succession through the atrioventricular node, bundle of His, bundle branches, and Purkinje fibers to produce a timed and coordinated ventricular contraction (figure 1). Deflections on the electrocardiogram reflect the measurable portions of this wave of depolarization (figure 2) and correlate with cardiac activity (figure 3).
In patients with tachyarrhythmias or fibrillation, this normal conduction is disrupted. Electrical countershock attempts to reinstate normal cardiac depolarization and contraction. (See 'Mechanism of action' below.)
Anatomically, pads or electrodes are placed on the chest so that an adequate portion of the delivered shock passes through the myocardium. The anterior/apex position requires less patient movement (figure 4). However, anterior/posterior pad or paddle placement is acceptable and may maximize current delivery (figure 5). (See 'Electrode placement' below.)
Mechanism of action
Defibrillation — Despite its wide use, there is still controversy concerning the electrophysiologic mechanisms by which electrical current terminates atrial or ventricular fibrillation, arrhythmias which involve multiple microreentrant circuits. Fibrillation involves the entire atrial or ventricular myocardium and is considered to be a very recalcitrant unstable rhythm. (See "The electrocardiogram in atrial fibrillation" and "Pathophysiology and etiology of sudden cardiac arrest", section on 'Mechanism of ventricular fibrillation'.)
Dosing for ventricular fibrillation or pulseless ventricular tachycardia in children is provided in the algorithm (algorithm 1) and discussed separately [1,2]. (See 'Defibrillation dose' below.)
Evidence suggests that a certain amount of myocardium must be available to sustain atrial or VF, and the entire myocardium must be uniformly depolarized in order to terminate the arrhythmia (critical mass hypothesis). However, the shock strength must also be greater than the largest shock that reinitiates fibrillation in vulnerable regions of the myocardium (the upper limit of vulnerability). (See "Basic principles and technique of external electrical cardioversion and defibrillation", section on 'Electrophysiology of defibrillation and cardioversion'.)
Cardioversion — Cardioversion terminates arrhythmia by the delivery of a synchronized shock that depolarizes the tissue involved in a reentrant circuit. By depolarizing all excitable tissue of the circuit and making the tissue refractory, the circuit is no longer able to propagate or sustain reentry. As a result, cardioversion terminates those arrhythmias resulting from a single reentrant circuit, such as supraventricular tachycardia, atrial flutter, or monomorphic ventricular tachycardia. (See "Basic principles and technique of external electrical cardioversion and defibrillation", section on 'Electrophysiology of defibrillation and cardioversion' and "Reentry and the development of cardiac arrhythmias".)
Cardioversion dosing in children is provided in the algorithm (algorithm 2) and discussed separately. (See 'Cardioversion dose' below.)
Shock delivery — First-generation defibrillators were monophasic, delivering waveforms with one direction of current. Biphasic defibrillators invert the current direction in the last phase of the shock (waveform 1). Compared with monophasic devices, biphasic units have a greater first shock efficacy and expose the heart to less peak current. Decreasing the energy level necessary for successful defibrillation decreases the risk of burns or myocardial damage. Most manufacturers have stopped making monophasic devices although there may be some still in use. (See "Basic principles and technique of external electrical cardioversion and defibrillation", section on 'Monophasic versus biphasic waveforms'.)
Regarding the frequency of electrical shocks, three stacked shocks in rapid succession are no longer recommended. Older monophasic defibrillators had a low first-shock efficacy. Three stacked shocks were recommended to decrease impedance in an attempt to increase efficacy. Newer generation biphasic defibrillators have a first-shock efficacy approaching 90 percent. (See "Basic principles and technique of external electrical cardioversion and defibrillation", section on 'Monophasic versus biphasic waveforms'.)
Failure of defibrillation after a first shock suggests that subsequent shocks in rapid succession are also likely to fail. In this setting, cardiopulmonary resuscitation (CPR) is likely to be more beneficial so a single shock should be immediately followed by resumption of CPR for two minutes, not a second shock. This approach will minimize interruptions of CPR associated with pulse checks and shock delivery.
Coordination of shock delivery and chest compressions — According to the American Heart Association (AHA) guidelines, patients who experience unwitnessed arrest should undergo 2 minutes of CPR prior to attempted defibrillation. (See "Pediatric basic life support (BLS) for health care providers".)
Since 2010, there has been a greater emphasis placed on the importance of adequate chest compressions while performing CPR. (See "Pediatric basic life support (BLS) for health care providers", section on 'Chest compressions'.)
Chest compressions should be interrupted only to deliver ventilation (assuming no advanced airway), to perform rhythm checks, or to deliver shocks. During two-person CPR, 15 chest compressions should be performed followed by a brief pause to deliver 2 breaths. Further, compressions should continue while a defibrillator is charging.
There are insufficient data to know whether or not CPR prior to defibrillation improves survival for in-hospital cardiac arrest [3,4]. Guidelines from the AHA state that, "healthcare providers who treat cardiac arrest in hospitals and other facilities with automated external defibrillators (AEDs) on-site should provide CPR and should use the AED/defibrillator as soon as it is available" [5]. The logistics involved with mobilizing a defibrillator are such that typically CPR does precede defibrillation; however, a shock should be delivered as soon as possible after an in-hospital cardiac arrest and CPR should be resumed immediately after attempted defibrillation [1,2,6].
The AHA guidelines for pediatric basic and advanced life support also emphasize that chest compressions should be hard (eg, at least one-third of the anterior-posterior diameter of the chest) and fast (eg, 100 per minute). The rescuer should allow for complete chest recoil after a compression and minimize interruptions between compressions. (See "Pediatric basic life support (BLS) for health care providers".)
INDICATIONS — The application of electrical current is an essential component of advanced CPR guidelines for the treatment of VF, pulseless VT (algorithm 1), and unstable and/or drug resistant organized cardiac rhythms, such as supraventricular tachycardia (algorithm 2):
●Defibrillation is indicated in the treatment of the following: ventricular fibrillation and pulseless ventricular tachycardia.
●Cardioversion should be used in unstable patients with organized cardiac rhythms, such as supraventricular tachycardia, atrial fibrillation, atrial flutter, or ventricular tachycardia with a palpable pulse.
The procedure for defibrillation and cardioversion are identical except that synchronized mode with a reduced dose of initial electricity is selected for cardioversion. (See 'Machine operation' below.)
Defibrillation can be performed with an automated external defibrillator (AED) in children greater than one year old with VF or pulseless VT. AEDs do not deliver synchronized shocks and thus, cannot be used for cardioversion.
CONTRAINDICATIONS AND PRECAUTIONS — Cardiac rhythms that should not be treated with electrical current include sinus rhythm, stable supraventricular tachycardia, asystole, pulseless electrical activity, and bradycardia.
Rescuer and bystander safety — Risk of electrical shock to a bystander or rescuer and fire are the two main safety issues related to the use of electrical countershock [7]. Prior to electrical discharge, all bystanders and the rescuer should ensure that they are not in contact with the patient or the stretcher. In prehospital settings, the patient should be moved from wet, soaked ground or standing water before receiving electric countershock. Of note, reports of inadvertent shocks to bystanders have demonstrated only minor adverse outcomes, such as tingling in the involved extremity, transient lethargy, or minor burns [7]. In addition, there are no reports of serious injury to lay responders who have used automated external defibrillators. Inappropriate electric countershock in a healthy person has been associated with serious morbidity and mortality.
Sparks from hand-held defibrillator paddles have caused fires involving adjacent flammable materials [7]. This hazard can be reduced by using electrode pads instead of hand-held paddles for shock delivery and by ensuring that oxygen delivery devices are at least 1 m away from the patient during electric countershock. In addition, flammable alcohol pads should never be used as contact materials for defibrillation or cardioversion.
PREPARATION
Evaluation — As time allows, clinicians obtain patient history regarding conditions that may have led to the dysrhythmia or may influence the likelihood of success of defibrillation, such as known cardiac disease, current medications, or evidence of poisoning. The acquisition of additional medical history may have to be deferred until after defibrillation is performed.
Anticipation — In anticipation of the need for defibrillation or cardioversion, any patient who has severe cardiopulmonary distress warrants placement of defibrillation pads on the chest. Examples include children with known history of unstable arrhythmias in the past, patients presenting with cardiac arrhythmias (eg, ventricular tachycardia with pulses or supraventricular tachycardia), or a child with significant exposure to poisons that may induce an arrhythmia (table 1).
Patient counseling/informed consent — The conditions under which defibrillation and emergency cardioversion is performed generally preclude the discussion of risks, benefits, and complications with the patient or parents/primary caregivers.
However, the specific risks and benefits of cardioversion of stable rhythms should be provided to the child's caretaker prior to the procedure.
PROCEDURE — The tables summarize the procedure for defibrillation (table 2) and cardioversion (table 3) and provide clinical tips for the use of a manual (table 4) or automated (table 5) defibrillator. The algorithms indicate recommended rhythms, dosing, and adjunct treatments for the use of cardioversion (algorithm 2) and defibrillation in children (algorithm 1).
Analgesia and sedation — Patients with VF or pulseless VT are unconscious and do not require sedation or analgesia. In contrast, patients requiring synchronized cardioversion may be awake and responsive to pain. Unless they are too unstable to delay the cardioversion, they should receive medications that will provide an appropriate level of sedation and analgesia prior to cardioversion. (See "Procedural sedation in children: Approach".)
Monitoring — Prior to defibrillation, clinical assessment of the adequacy of CPR may be determined by noting breath sounds and chest wall rise and palpating distal pulses during compressions.
If appropriate, confirmation of proper endotracheal tube position is made by noting the depth of insertion at the lips and listening for equal breath sounds bilaterally. Of note, end-tidal CO2 may not be detected in a child in cardiac arrest, even in the setting of effective assisted ventilation. (See "Carbon dioxide monitoring (capnography)", section on 'Verification of ETT placement'.)
The pulse and blood pressure of conscious patients needing cardioversion should be assessed frequently.
Methods: Manual defibrillator use — Successful delivery of an electric countershock relies on the selection of the proper electrodes, conductors, and energy.
Electrode choice — Clinicians may use either handheld paddles or self-adhesive electrode pads to defibrillate or cardiovert. Electrode pads offer several advantages:
●They can be used to monitor the heart rhythm without the need for additional electrocardiogram electrodes that may interfere with pad placement (although paddles often have monitoring capabilities, as well).
●Creams or gels are not needed, making arcing of electrical current across the chest unlikely.
●Unlike paddles, they are not associated with sparks that may ignite fires.
●A rescuer is less likely to contact the patient's stretcher during shock delivery, as might occur with paddle use.
●Improper application of paddle pressure is eliminated as a possible reason for failure of defibrillation.
Electrode size — In general, one should use the largest paddles or electrode pads that will fit on the child’s chest without touching. Paddles and electrode pads designed for adults are recommended for children who weigh more than 10 kg. Of these, those 12 cm in diameter seem to be superior to those that are 8 cm in diameter [5]. Infant paddles or pads are to be used for smaller infants weighing <10 kg (picture 1) [8].
Electrode placement — The anterior/apex position for pad or paddle placement may be used. The paddle or electrode pad held in the rescuer's left hand is placed to the right of the sternum below the clavicle [3]. The paddle or electrode pad held in the rescuer's right hand is placed in the left midaxillary line, lateral to breast tissue, at the level of the nipple. If paddles are used, they must be applied with considerable, firm and steady pressure (figure 4).
Alternatively, an anterior/posterior pad or paddle placement may be used with the anterior pad or paddle applied with the center of the paddle slightly to the left of the sternum and the posterior pad or paddle applied to the middle of the upper back (figure 5). This position may be preferred if adult electrodes must be used to deliver a countershock to an infant <10 kg should infant paddles be unavailable. In this situation, the anterior/posterior placement avoids the possibility of the large paddles contacting each other during shock delivery.
Electrode-chest interface — A flow of electrical current is needed for successful defibrillation. A high, transthoracic impedance will decrease the likelihood of success. When using paddles, concurrent use of conductive materials, such as electrode cream or paste will decrease transthoracic impedance.
Paddles and electrode pads must not contact each other, and care must be taken to avoid interface materials on one side of the chest contacting the material placed on the opposite side. Either of these conditions can result in arcing of the electrical current across the chest wall rather than conduction toward the heart.
Interface materials to be avoided include saline, isopropyl alcohol, and ultrasound gel as well as the use of bare paddles. In addition to lower efficacy, isopropyl alcohol poses a risk of fire. (See 'Rescuer and bystander safety' above.)
Machine operation — The clinician should gain familiarity with the specific functions of the defibrillator in use in their health care setting. The following provides the typical steps involved in using a manual defibrillator:
●Apply electrode pads of the proper size or if paddles are used, a conductive material to the paddles.
●Turn on the manual defibrillator.
●If paddles are employed, use them to monitor the heart rhythm; this will avoid the need for separate EKG electrodes.
●Next, select asynchronous mode to defibrillate (eg, ventricular fibrillation, ventricular tachycardia without a pulse) or synchronous mode to cardiovert (eg, unstable supraventricular tachycardia, ventricular tachycardia with a pulse).
●Choose the energy dose for defibrillation or cardioversion. (See 'Defibrillation dose' below and 'Cardioversion dose' below.)
●Deliver the current as follows:
•The electrode pads or paddles are placed in the anterior/apex or anterior/posterior positions and the machine is charged. At the same time, oxygen sources and any flammable material should be at least 1 m away from the patient.
•Ensure all personnel are clear from the patient and the patient's stretcher by loudly stating "All Clear!" prior to shock delivery.
•Discharge the electrode pads or paddles. Both charging and energy release may be initiated by using buttons on the paddle, or if electrical pads are used, by utilizing a button on the machine itself or by using an attached foot pad.
Defibrillation dose — The American Heart Association and the International Liaison Committee on Resuscitation recommend the following defibrillation doses for children with VF or VT without a pulse (pVT) (algorithm 1) [1,2]:
●First attempt: 2 J/kg
●Second attempt: 4 J/kg
●Subsequent attempts: 4 J/kg or higher (maximum dose 10 J/kg, or adult maximum [200 J, biphasic; 360 J monophasic])
The currently recommended doses are based on limited evidence. Although rates of termination for VF or pVT at these doses were as high as 91 percent of 57 delivered shocks in one small case series [9], subsequent studies suggest that currently recommended doses for children may not be as effective as previously thought [10-13]. As an example, an observational study of 266 children with 285 in-hospital events warranting defibrillation found that an initial shock dose of 2 J/kg resulted in termination of VF/pVT in only 55 percent of children but that increasing the initial dose was not associated with a greater likelihood of termination of VF/pVT [11]. Furthermore, the 52 patients who received initial shock doses of 4 J/kg were less likely to have termination of VF/pVT or to survive the event when compared to the 186 children who received 2 J/kg (adjusted odds ratio [OR] 0.42 [95% CI 0.18-0.98] for termination of VF/pVT and adjusted OR 0.41 [95% CI 0.21-0.81] for event survival). More recently, in a systematic review of 10 small observational studies in children that assessed defibrillation energy dosing, sustained return of spontaneous circulation or survival was not associated with initial defibrillation doses [13]. Thus, further study is necessary to identify optimal defibrillation doses in children.
Cardioversion dose — The dose for the first shock should be 0.5 to 1 J/kg; subsequent shocks are 2 J/kg (algorithm 2). Cardioversion is appropriate for unstable patients noted to have SVT, atrial fibrillation, atrial flutter, or VT with palpable pulses.
Automated external defibrillator use in infants and children — The US Food and Drug Administration (FDA) has approved automated external defibrillators (AEDs) for use in children [9]. The most recent AHA and international guidelines state that AEDs may be used for shock delivery in infants and children for treatment of out-of-hospital VF or pulseless VT [14,15]. The order of preference for the appropriate device to be used is as follows [16-18]:
●(1) Manual defibrillator for infants
●(2) AED with a dose attenuator device for children under eight years of age
●(3) AED without a dose attenuator for children nine years of age or older
Several recent advances in AED technology have allowed for their pediatric use. Studies show that AEDs are highly accurate in detecting abnormal rhythms in children [9]. They have demonstrated both high sensitivity in detecting VF and high specificity in identifying non-shockable rhythms [19]. A second advance is the development of attenuation devices, such as pads and cables which decrease the energy delivered to children.
For in-hospital defibrillation, there are no data comparing manual defibrillators with AEDs in children [3-5], nor are there clear guidelines specifying the use of one over the other. The AHA does state that "AEDs may be considered for the hospital setting as a way to facilitate early defibrillation (a goal of ≤3 minutes from collapse), especially in areas where staff have no rhythm recognition skills or defibrillators are used infrequently" [5]. Thus, for defibrillation of infants and children, institution-specific practices will prevail, and a clinician may use either a manual defibrillator or an AED with a pediatric dose attenuation device.
A large cohort study that evaluated the use of AEDs for hospitalized adults who suffered a sudden cardiac arrest found no survival benefit in adults with shockable rhythms and worse outcomes for adults without a shockable rhythm who were treated with an AED. Use of the AED in adults is discussed separately. (See "Automated external defibrillators", section on 'In-hospital AED allocation'.)
Automated external defibrillator operation — A principal reason for the growing prevalence of AEDs in society is their ease of use. The typical AED provides voice prompts for each step in its use after the machine is turned on:
●Apply adhesive electrode pads supplied with the machine. As noted earlier, pediatric attenuated electrodes should be used in patients under eight years of age, and the anterior/posterior placement is preferred in this age group. The anterior/apex position is recommended for pad placement for older children.
●Plug pads into the AED.
●Stay clear of the patient while the machine is analyzing the cardiac rhythm.
●If a shock is indicated, perform cardiac compressions while the machine is charging.
●Stop compressions and deliver the shock by pressing the button when prompted.
●Resume CPR immediately after shock delivery.
Dose — Most AEDs in use today deliver between 150 to 360 J of energy, depending on the model. A standard AED without a dose attenuator is recommended for children older than eight years [20]. For those under eight years of age, an initial pediatric attenuated dose should be given. These attenuation devices will decrease the delivered dose to 35 to 50 J depending on the specific AED; some will allow higher doses for subsequent shocks [21]. Note that dosing is not weight-based. However, there appears to be a wide therapeutic range of energy doses [22]. The energy dose needed to produce histologic damage to myocardium is many times greater than that needed to defibrillate [19]. Thus, a standard AED without a dose attenuator is acceptable for infants and younger children, if it is the only device available [20].
COMPLICATIONS — Inappropriate defibrillation of a patient with a perfusing, organized rhythm may cause ventricular fibrillation.
Oxygen use represents an important fire hazard when electrical current is being delivered. Most patients in arrest receive 100 percent oxygen via bag-valve-mask (BVM) ventilation. At the moment of shock delivery, the BVM apparatus may be inadvertently placed such that oxygen is blowing across the patient's chest. This represents a significant fire hazard if a spark from a poorly placed paddle contacts the oxygen. All oxygen sources must be removed at least 1 m from the patient before defibrillation.
Although uncommon, other potential dose-related complications include arrhythmias, myocardial injury, or skin burns [3]. Risk of these problems is decreased by using lower energy doses and decreasing transthoracic impedance.
FOLLOW-UP CARE — Following successful defibrillation or cardioversion, a child will need to be hospitalized for continuous cardiac monitoring in an intensive care setting. Depending on the etiology of the arrhythmia, consultation with a pediatric cardiologist and/or medical toxicologist may also be appropriate.
SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Basic and advanced cardiac life support in children".)
SUMMARY AND RECOMMENDATIONS
●Definitions – Defibrillation and cardioversion are methods of delivering electrical energy to the heart through the chest wall in an attempt to restore the heart's normal rhythm (see 'Definitions' above):
•Defibrillation – Defibrillation is the asynchronous delivery of energy, such as, the shock is delivered randomly during the cardiac cycle.
•Cardioversion – Cardioversion is the delivery of energy that is synchronized to the QRS complex.
●Indications – Defibrillation is indicated in the treatment of ventricular fibrillation and pulseless ventricular tachycardia. (See 'Indications' above.)
Cardioversion should be used in unstable patients with organized cardiac rhythms, such as supraventricular tachycardia (SVT), atrial fibrillation, atrial flutter, or ventricular tachycardia with a palpable pulse. (See 'Indications' above.)
●Contraindications and precautions – Cardiac rhythms that should not be treated with electrical current include sinus rhythm, stable SVT, asystole, pulseless electrical activity, and bradycardia. (See 'Contraindications and precautions' above.)
Risk of electrical shock to a bystander or rescuer and fire are the two main safety issues related to the use of electrical countershock.
●Procedure – The tables summarize the procedure for defibrillation (table 2) and cardioversion (table 3) and provide clinical tips for the use of a manual (table 4) or automated (table 5) defibrillator.
The algorithms indicate recommended rhythms, dosing, and adjunct treatments for the use of defibrillation (algorithm 1) and cardioversion (algorithm 2) in children. (See 'Procedure' above.)
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