Defibrillation and Cardioversion 

Defibrillation was first demonstrated by Prevost and Batelli, from the University of Geneva, Switzerland, in 1899. They discovered that small electrical shocks could induce ventricular fibrillation in dogs and that larger charges would reverse the condition. Transthoracic defibrillation was first used in humans using alternating current (AC) in 1956. Lown and his coworkers introduced direct current (DC) defibrillators into clinical practice.^[1] Electrical cardioversion has now become a routine procedure and is used electively or emergently to terminate cardiac arrhythmias.

Defibrillation is a nonsynchronized delivery of energy during any phase of the cardiac cycle, whereas cardioversion is the delivery of energy that is synchronized to the large R waves or QRS complex. The delivered shock in both defibrillation and cardioversion causes electric current to go from the negative to the positive electrode of the defibrillator, passing the heart on its way. It causes all the heart cells to contract simultaneously, thereby interrupting and terminating the abnormal electrical rhythm without damaging the heart, and thus allowing the sinus node to resume normal pacemaker activity. This article illustrates the basic principles and techniques of these procedures and clinical indications for their use.

• Synchronized electrical cardioversion

  • Supraventricular tachycardia
  • Atrial fibrillation
  • Atrial flutter
  • Ventricular tachycardia
  • Any patient with reentrant tachycardia with narrow or wide QRS complex (ventricular rate >150) who is unstable (eg, chest pain, pulmonary edema, hypotension)
• Defibrillation

  • Pulseless ventricular tachycardia (VT)
  • Ventricular fibrillation (VF)
  • Cardiac arrest due to or resulting in VF

• Dysrhythmias due to enhanced automaticity such as in digitalis toxicity and catecholamine-induced arrhythmia (In these conditions, a homogeneous depolarization state already exists. Therefore, cardioversion is not only ineffective but is also associated with a higher incidence of postshock ventricular tachycardia/ventricular fibrillation [VT/VF].)
• Multifocal atrial tachycardia

• Cardioversion is almost always performed under induction or sedation (short-acting agent such as midazolam). The only exceptions are if the patient is hemodynamically unstable or if cardiovascular collapse is imminent. For more information, see Procedural Sedation.
• Defibrillation is an emergent maneuver and when necessary should be promptly performed in conjunction with or prior to administration of induction or sedative agents.

• Defibrillators

  • Automated external defibrillators (AEDs)
  • Semi-automated AED
  • Standard defibrillators with monitors
• Paddle vs adhesive patch

  • The use of hand-held paddle electrodes may be more effective than self-adhesive patch electrodes.
  • The success rates are slightly higher for patients assigned to paddled electrodes because these hand-held electrodes improve electrode-to-skin contact and reduce the transthoracic impedance.^[2]
• Conductive gel or paste
• ECG monitor with recorder
• Oxygen equipment
• Intubation kit
• Emergency pacing equipment

• Paddle placement on the chest wall has 2 conventional positions: anterolateral and anteroposterior.

  • Anterolateral position: A single paddle is placed on the left fourth or fifth intercostal space on the midaxillary line. The second paddle is placed just to the right of the sternal edge on the second or third intercostal space.
  • Anteroposterior position: A single paddle is placed to the right of the sternum, as above, and the other paddle is placed between the tip of the left scapula and the spine. An anteroposterior electrode position is more effective than the anterolateral position for external cardioversion of persistent atrial fibrillation.^{[3, 4, 5]} The anteroposterior approach is also preferred in patients with implantable devices, to avoid shunting current to the implantable device and damaging its system.

• Emergent application, which may be lifesaving, and elective cardioversion should be used cautiously, with attention to patient selection and proper techniques. Repetitive, futile attempts at direct current cardioversion should be avoided.
• Advanced cardiac life support (ACLS) measures should be instituted in preparing the patient, such as obtaining intravenous access and preparing airway management equipment, sedative drugs, and a monitoring device.

Monophasic vs biphasic waveforms

• Defibrillators can deliver energy in various waveforms that are broadly characterized as monophasic or biphasic.
• Monophasic defibrillation delivers a charge in only one direction, while biphasic defibrillation delivers a charge in one direction for half of the shock and in the electrically opposite direction for the second half.
• Biphasic waveforms defibrillate more effectively and at lower energies than monophasic waveforms.^{[6, 7]}

Energy selection for defibrillation or cardioversion

• Synchronized electrical cardioversion begins with 25-50 J (or the biphasic equivalent, which is generally one half of that required with monophasic waveforms) to treat atrial flutter and 50-100 J (or the biphasic equivalent) to treat atrial fibrillation for patients in stable condition, as shown below. ECG strip shows a atrial fibrillation terminated by a synchronized shock (synchronization marks [arrows] in the apex of the QRS complex) to normal sinus rhythm.
• Rapid polymorphic ventricular tachycardia (rate >150 bpm) associated with hemodynamic instability should be treated with immediate, direct-current, nonsynchronized defibrillation with energies of 200-360 J (or biphasic equivalent [100-200 J]).
• Monomorphic ventricular tachycardia should be treated with a synchronized discharge of 100-200 J (or biphasic equivalent [50-100 J]).
• Ventricular fibrillation should be treated with unsynchronized electrical countershock with at least 200-360 J (or biphasic equivalent [100-200 J]) administered as rapidly as possible, as shown below. Ventricular fibrillation terminated by an unsynchronized shock (arrows) to normal sinus rhythm.

• The most common complications are harmless arrhythmias, such as atrial, ventricular, and junctional premature beats.
• Serious complications include ventricular fibrillation (VF) resulting from high amounts of electrical energy, digitalis toxicity, severe heart disease, or improper synchronization of the shock with the R wave.^[8]
• Thromboembolization is associated with cardioversion in 1-3% of patients, especially in patients with atrial fibrillation who have not been anticoagulated prior to cardioversion.
• Myocardial necrosis can result from high-energy shocks. ST segment elevation can be seen immediately and usually lasts for 1-2 minutes. ST segment elevation that lasts longer than 2 minutes usually indicates myocardial injury unrelated to the shock.
• Pulmonary edema is a rare complication of cardioversion and is probably due to left ventricular dysfunction or transient left atrial standstill.
• Painful skin burns can occur after cardioversion or defibrillation; they are moderate to severe in 20-25% of patients. They most likely are due to improper technique and electrode placement.^[9]