Cardioversion
PREREQUISITE NURSING KNOWLEDGE
• Understanding of the anatomy and physiology of the cardiovascular system, principles of cardiac conduction, basic dysrhythmia interpretation, and electrical safety is needed.
• Basic and advanced cardiac life support knowledge and skills are essential.
• Clinical and technical competence in the use of the defibrillator is important.
• Synchronized cardioversion is recommended for termination of those dysrhythmias that result from a reentrant circuit, which include unstable supraventricular tachycardia, atrial fibrillation, atrial flutter, and unstable monomorphic ventricular tachycardia with a pulse.3,6 Because ventricular tachycardia is often a precursor to ventricular fibrillation, cardioversion has the potential to prevent this life-threatening dysrhythmia.
• The electrical current delivered with cardioversion depolarizes the myocardial tissue involved in the reentrant circuit. This depolarization renders the tissue refractory; thus, it is no longer able to initiate or sustain reentry.3,6 A countershock synchronized to the QRS complex allows for the electrical current to be delivered outside the heart’s vulnerable period in which a shock can precipitate ventricular fibrillation.2,3,5–7 This synchronization occurs a few milliseconds after the highest part of the R wave but before the vulnerable period associated with the T wave.3,5,6
• Cardioversion may be implemented in the patient with an emergent condition. The aforementioned dysrhythmias are converted with synchronized cardioversion when the patient develops symptoms from the rapid ventricular response. Symptoms may include hypotension, chest pressure, shortness of breath, dyspnea on exertion, decreased level of consciousness, pulmonary edema, crackles, rhonchi, jugular vein distention, peripheral edema, and ischemic electrocardiogram (ECG) changes.5
• Elective cardioversion may be used to convert hemodynamically stable atrial fibrillation or atrial flutter into normal sinus rhythm.1,2,7 With use to convert atrial fibrillation or atrial flutter, anticoagulation therapy is considered for 3 weeks before cardioversion to decrease the risk of thromboembolism.2,7,9 Anticoagulation therapy may not be necessary if atrial fibrillation or atrial flutter has been present for less than 48 hours.2,7 A physician or advanced practice nurse may choose to perform a transesophageal echocardiogram to exclude the possibility of an atrial thrombus before cardioversion for patients at high risk for thromboembolism. The patient is started on intravenous heparin, and the cardioversion is performed within 24 to 48 hours.1,2,7,9 Anticoagulation therapy should be continued for 4 weeks after cardioversion because of the possibility of delayed embolism.1,2,7,9
• Elective cardioversion also may be used in patients with hemodynamically stable ventricular or supraventricular tachydysrhythmias unresponsive to medication therapy.1
• If time and clinical condition permit, the patient should be given a combination of analgesia and sedation to minimize discomfort.2,3,5–7
• Defibrillators deliver energy or current in waveform patterns. Delivered energy levels may differ among the various defibrillators and waveforms. Various types of monophasic waveforms are used in older defibrillators. Biphasic waveforms have been designed more recently and are used in implantable defibrillators, automatic external defibrillators, and most manual defibrillators.
Monophasic waveforms deliver energy in one direction. The energy travels through the heart from one paddle or pad to the other.3,6,10
Biphasic waveforms deliver energy in two directions. The energy travels through the heart in a positive direction then reverses itself and flows back through the heart in a negative direction.3,6,10 Biphasic waveform technology is able to decrease the amount of current needed to terminate the dysrhythmia, decreasing the amount of potential damage to the myocardium.3 In more recent studies, atrial fibrillation was successfully cardioverted with biphasic waveform shocks that ranged from 100 to 120 J.3,11,12,14 More research is needed to determine a specific recommendation for biphasic waveform cardioversion.3 For that reason, the American Heart Association states that biphasic waveform shocks are acceptable if documented as clinically equivalent to reports of monophasic shocks.3,5
• Biphasic defibrillators measure and compensate for transthoracic impedance before the delivery of the shock, which allows the defibrillator to deliver the actual amount of energy selected by the rescuer.3,6
EQUIPMENT
• Defibrillator/monitor with ECG oscilloscope/recorder capable of delivering a synchronized shock
• Conductive gel or paste, prepackaged gelled conduction pads or self-adhesive defibrillation pads connected directly to the defibrillator
• Intravenous sedative or analgesic pharmacologic agents as prescribed
• Bag-valve device with mask and oxygen delivery
• Flow meter for oxygen administration, oxygen source
• Emergency suction and intubation equipment
Additional equipment to have available as needed includes the following:
PATIENT AND FAMILY EDUCATION
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