28: Defibrillation and Cardioversion

Defibrillation and cardioversion are used for rapid termination of a tachyarrhythmia (a fast abnormal rhythm originating either in the atrium or ventricle) that is unresponsive to baseline treatment or is causing the patient to have cardiovascular compromise (inadequate systemic perfusion). Baseline treatment consists of correcting metabolic problems, use of vagal maneuvers (bag of ice water over the eyes and face of the infant without obstructing the airway, pressure on closed eyelids), use of medications (adenosine, digoxin, propranolol, verapamil, amiodarone, procainamide, lidocaine, or magnesium sulfate), or transesophageal pacing. It is best to try these maneuvers or medical therapy if intravenous access is available. Neonatal arrhythmias are rare, and the majority of them can be treated with these initial measures.

Current defibrillators are capable of delivering 2 modes of shock: synchronized and unsynchronized. Synchronized shocks are lower dose and used for cardioversion. Unsynchronized shocks are higher dose and used for defibrillation. Pediatric cardiology consultation is recommended for all infants with a tachyarrhythmia.

1. Cardioversion (synchronized cardioversion)

   1. Unstable patients with tachyarrhythmias who have a perfusing rhythm but evidence of poor perfusion, heart failure, or hypotension (signs of cardiovascular compromise). Examples of tachyarrhythmias are:

      1. Tachycardia (supraventricular tachycardia [SVT] or ventricular tachycardia [VT]) with a pulse and poor perfusion

      2. Supraventricular tachycardia with shock and no vascular access

      3. Atrial flutter with shock

      4. Atrial fibrillation with shock (very rare in infants)

   2. Elective cardioversion in infants with stable SVT, VT, or atrial flutter (good tissue perfusion and pulses) unresponsive to other treatments. This is always done under the close supervision of a pediatric cardiologist. Sedation and a 12-lead electrocardiogram are recommended before cardioversion.

2. Defibrillation (asynchronized). Used in pulseless arrest with a shockable rhythm (VT and ventricular fibrillation). It is used in between cardiopulmonary resuscitation (CPR) and not used in asystole or pulseless electrical activity (PEA). The most common cause of a ventricular arrhythmia in a neonate is electrolyte imbalance. Defibrillation will not stop the arrhythmia in these patients. Defibrillation is the most effective treatment for ventricular fibrillation and pulseless ventricular tachycardia.

1. External standard defibrillator (manual or semiautomated) and 2 paddles of the correct sizes with conductive pads. For infants, use the smallest size (usually measuring 4.5 cm). It is important to be familiar with your institution's equipment because there are many different types and models of machines. Pediatric-capable automatic external defibrillators (adult-automated external defibrillators with energy reducer pads) can be used for infants.

2. Other equipment. Heart rate monitor, airway equipment, resuscitation medications, antiarrhythmic medications, and equipment used in basic and advanced life support.

1. Adequate sedation (may not be possible in emergency situations), preoxygenation, and continuous heart monitoring are essential. Emergency airway equipment should be readily available.

2. Pain management. During a code, pain relief is not focused on. Depending on the type of procedure, sedation may be considered.

   1. Planned cardioversion. Use propofol (short-acting, side effects are rare). Induction dosing: 2.5–3.5 mg/kg over 20–30 seconds, then 200–300 mcg/kg/min.

   2. Emergent cardioversion. These patients are usually too unstable to wait for appropriate sedation. It is best to proceed with cardioversion without sedation.

   3. Defibrillation. These patients are unconscious, so do not require sedation.

3. Wipe any cream or soap off the chest.

4. Place the pads firmly on the chest wall. To prevent skin burns, be sure the conductive pad totally covers the paddle and that the skin is not in contact with any noninsulated part of the paddle. If the pads are in contact with each other, this can cause the electric current to arch across the chest instead of toward the heart. There are 2 different positions for pad placement (see Figures 28–1 and 28–2).

   1. Anterolateral positioning. (Figure 28–1)The anterior pad is placed to the right of the upper sternum, and the posterior pad is placed below the left nipple toward the axilla.

   2. Anteroposterior positioning. (Figure 28–2) This may be preferred in atrial tachycardia. The anterior pad is placed on the midsternal border, and the posterior pad is placed between the scapulae. The paddles or pads should not be in contact with one another. With dextrocardia, the pads need to be placed across the right chest.

5. Charge the defibrillator

   1. Cardioversion uses lower energy. Charge the defibrillator to 0.5 J/kg and synchronize. The SYNC button must be activated each time because the default setting on a defibrillator is on the asynchronized setting.

   2. Defibrillation uses higher energy. Charge the defibrillator to 2 J/kg.

   3. Once charged, make sure everybody is clear of the patient, including the person holding the oxygen. Ask if everyone is clear, and visually check while they answer. Use the accepted phrase “I'm clear, you're clear, oxygen clear.” Verify that oxygen is not flowing across the area. It is best to disconnect the bag and verify that no one is touching the endotracheal tube or any part of the ventilation circuit. The machine will indicate that it is charged and ready for discharge with an audible signal and/or a flashing red light either on the machine or the end of the paddle based on the model.

6. Deliver the shock by pressing both buttons together

   1. Cardioversion. If the first attempt does not work, additional attempts should be made. Repeat steps C–E using 1 J/kg, then up to a max of 2 J/kg.

   2. Defibrillation. In pulseless infants, continue CPR with appropriate compressions, ventilation, and medications between attempts. Additional attempts should be made by repeating steps C–E. The second and any subsequent shock should have a dose of 4 J/kg. Acidosis and hypoxia decrease the success of defibrillation, and correction increases the likelihood of success.

Risk of complications are increased when there is an increased energy dose, multiple shocks, increased impedance, or decreased interval between shocks.

1. Altered skin integrity. Soft tissue injury, chest wall lesions, skin burns, bruising, and pain can occur. Burns can be moderate to severe in 20–25% of patients. They are usually due to improper pad placement.

2. Pulmonary edema. A rare complication. It is most likely due to left ventricular dysfunction, but true mechanism is unknown.

3. Neurologic impairment. This can occur from a stroke from a thromboembolic event after cardioversion and most often occurs when cardioverting atrial flutter or atrial fibrillation. A preelective cardioversion echocardiogram to evaluate for atrial clots could aid in determining whether the patient is at risk for an embolic event.

4. Cardiac arrhythmias. Dysrhythmias due to enhanced automaticity such as digitalis toxicity or catecholamine-induced arrhythmias have increased risk of VT/VFib with shock. Premature beats can also occur. Vfib can also occur with poor synchronization of the shock administration.

5. Myocardial necrosis. When excessive energy is delivered, heart tissue can be damaged. This can cause necrosis with elevated ST segments seen on electrocardiogram. If myocardial damage is severe enough, this can cause shock.

6. Cardiogenic shock. Patients can develop transient decreased cardiac output with left ventricular diastolic dysfunction and damage of the myocardium after cardioversion or defibrillation.

7. Fire (rare). Fire has resulted from sparks in the presence of oxygen and cotton. The infant's stocking cap and part of the sheet caught on fire. Use of oxygen can increase the risk of fire. To avoid this, place the oxygen at least 1 meter away from the patient before defibrillation.

8. Electrical shock to health care providers. This can result in tingling, minor burns, or transient lethargy.