Cardioversion is a procedure used to treat cardiac arrhythmias. There are chemical and electrical means of cardioversion. However, we will focus here on electrical methods of cardioversion - specifically, synchronized and unsynchronized cardioversion used when providing emergent care.
During synchronized and unsynchronized cardioversion, electrical current is delivered through the patient’s chest to the heart in an effort to convert an unstable or potentially life-threatening arrhythmia to a stable cardiac rhythm. Ineffective cardiac output occurs during a cardiac arrhythmia and cardiac arrest. Interventions such as synchronized and unsynchronized cardioversion aim to restore the heart’s intrinsic rhythm. Cardioversion may be completed in various settings, ranging from pre-hospital to inpatient environments. Synchronized cardioversion may be scheduled as an elective procedure or utilized when guided by Advanced Cardiovascular Life Support (ACLS) or Pediatric Advanced Life Support (PALS) algorithms when providing emergent medical care for adult and pediatric populations. Unsynchronized cardioversion, also known as defibrillation, may be performed when providing emergent care using Basic Life Support (BLS), ACLS, or PALS algorithms. For now, we will focus here on emergent methods of electrical cardioversion. Synchronized cardioversion and unsynchronized cardioversion vary in that each method delivers a shock during a different time within the cardiac cycle. In addition, the energy required to convert a cardiac rhythm using synchronized cardioversion is typically less than what is necessary for unsynchronized cardioversion.
Synchronized cardioversion is utilized on hemodynamically unstable patients with a pulse. Hemodynamic instability may be demonstrated through signs and symptoms, such as an altered mental status, hypotension, chest pain, dyspnea, diaphoresis, acute congestive heart failure, or myocardial ischemia. Synchronized cardioversion is an intervention used to treat unstable supraventricular and ventricular cardiac rhythms.
Indications for synchronized cardioversion:
Unsynchronized cardioversion is utilized when there is either no QRS complex to track (ventricular fibrillation), or the patient’s condition would become worse if action was not taken immediately.
Indications for unsynchronized cardioversion:
There are no contraindications to synchronized or unsynchronized cardioversion. An implantable cardioverter-defibrillator (ICD) or a pacemaker do not preclude the patient from either form of cardioversion.
During cardioversion, energy is transferred from a device called a defibrillator to the patient through electrodes applied strategically to the patient’s body. The electrodes make contact with the body via adhesive pads applied to the patient’s skin or via hand-held paddles. Configuration of the electrodes on the patient’s body varies in location based on whether the individual is a pediatric or adult patient, and the manufacturer’s recommendations for the device. The goal of cardioversion is to restore the patient’s intrinsic cardiac rhythm by terminating unstable or lethal cardiac rhythms. Defibrillators typically have a “synchronize” mode that allows the same device to conduct both synchronized and unsynchronized cardioversion.
When conducting synchronized cardioversion, the defibrillator monitors the cardiac rhythm to coordinate a low energy shock delivery with the R wave within the QRS complex of the cardiac cycle. This coordination of the shock delivery with the R wave aims to avoid shock delivery with the T wave of the cardiac cycle (where the T wave occurs during the refractory period, known as repolarization). Shock delivery with the T wave can induce ventricular fibrillation (also known as the R-on-T phenomenon) and cardiac arrest. There is typically a delay before the shock is delivered, as the defibrillator evaluates the cardiac rhythm to ensure delivery is synchronous with the R wave.
Before initiating cardioversion, the patient’s cardiac rhythm should be identified, intravenous access should be established, and the following equipment should be prepared: a suction device, an oxygen saturation monitor, intubation equipment, and manual or supplemental oxygenation equipment. When possible, the patient should be sedated prior to this procedure. Recommendations for the energy levels utilized during this procedure are made by the device manufacturer. Follow the respective ACLS or PALS algorithm to guide the patient’s care during synchronized cardioversion.
Unsynchronized cardioversion, or defibrillation (in cases of ventricular fibrillation), results in the administration of the shock to the patient as soon as the defibrillation button is pushed on a manual defibrillator or an automated external defibrillator (AED). The shock delivery may occur at any point within the cardiac cycle. If the shock were to fall during the T wave, ventricular fibrillation and cardiac arrest may develop.
Before defibrillating the patient, it is imperative to continue resuscitation of the patient until the defibrillator is available and prepared. Energy administered during unsynchronized cardioversion is a high energy shock. Dosing of the shock for defibrillation should adhere to the device manufacturer’s recommendations. Dosing differs between adult and pediatric patients; for pediatric patients, dosing is contingent on the patient's weight or age. Follow the respective BLS, ACLS, or PALS algorithm to guide care of the patient.
There are potential risks to the patient associated with synchronized cardioversion, which may include dysrhythmia (such as ventricular fibrillation or asystole) or hypotension. Inadequate ventilation by the patient may occur during the procedure, necessitating manual ventilation by the healthcare professional. Due to sedation, the patient may aspirate stomach contents, which may result in obstructed ventilation or lead to pneumonia. Cardioversion may contribute to the development of a stroke, as the electrical shock may dislodge an existing thrombus within the body or contribute to the development of a new thrombus following cardioversion. Burns to the skin or pain to the chest area may occur due to the delivery of electrical shocks.
Risks associated with unsynchronized cardioversion include the potential development of ventricular fibrillation and cardiac arrest, as shock delivery could occur during repolarization or the refractory period (during the T wave). In addition, burns to the skin or pain to the chest area may occur following the delivery of electrical shocks.
Monophasic waveform defibrillators use electrical current that travels in one direction, whereas biphasic waveform defibrillators use electrical current that travels in two directions. The latest defibrillators tend to use a biphasic waveform, which permits a lower energy level to be utilized to successfully convert a cardiac rhythm through cardioversion. Defibrillators with biphasic waveforms are known to have an increased ability to halt ventricular dysrhythmias compared to defibrillators that use a monophasic waveform, which is why they are preferred by many healthcare professionals. In addition, biphasic waveform defibrillators are just as effective as monophasic waveform defibrillators but require much less energy to be effective. They also tend to have fewer complications following cardioversion, including burns to the skin, cardiac dysfunction, and dysrhythmias.
Multiple resources are available on the American Medical Resource Institute (AMRI) website to reinforce and evaluate your knowledge in preparation of your certification course. If you seek additional opportunities to support and enhance your BLS, ACLS, or PALS knowledge and skills, practice questions are available. If you prefer scenario-based learning, a library of case studies is available to you to practice applying ACLS and PALS principles and protocols using clinical scenarios. The healthcare professional carrying ACLS or PALS certifications must be proficient in identifying cardiac rhythms to perform cardioversion safely. An index of cardiac rhythms that the healthcare professional must be knowledgeable of is available as a reference on the AMRI website. Detailed information is presented regarding each cardiac rhythm to assist in the identification and treatment of cardiac rhythms found in ACLS and PALS algorithms.
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