Defibrillation and Cardioversion
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Defibrillation is nonsynchronized random administration of shock during a cardiac cycle. In 1956, alternating current (AC) defibrillation was first introduced to treat ventricular fibrillation in humans. [1] Later in 1962, direct current (DC) defibrillation was introduced. [2] See the video below.
Cardioversion is a synchronized administration of shock during the R waves or QRS complex of a cardiac cycle. See the video below.
During defibrillation and cardioversion, electrical current travels from the negative to the positive electrode by traversing myocardium. It causes all of the heart cells to contract simultaneously. This interrupts and terminates abnormal electrical rhythm. This, in turn, allows the sinus node to resume normal pacemaker activity.
Indications for defibrillation include the following:
Pulseless ventricular tachycardia (VT)
Cardiac arrest due to or resulting in VF
Indications for electrical cardioversion include the following:
Supraventricular tachycardia (atrioventricular nodal reentrant tachycardia [AVNRT] and atrioventricular reentrant tachycardia [AVRT])
Atrial flutter (types I and II)
Ventricular tachycardia with pulse
Any patient with reentrant tachycardia with narrow or wide QRS complex (ventricular rate >150 bpm) who is unstable (eg, ischemic chest pain, acute pulmonary edema, hypotension, acute altered mental status, signs of shock)
Contraindications include the following:
Dysrhythmias due to enhanced automaticity, such as in digitalis toxicity and catecholamine-induced arrhythmia
Multifocal atrial tachycardia
For dysrhythmias due to enhanced automaticity such as in digitalis toxicity and catecholamine-induced arrhythmia, 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).
Defibrillation is an emergent maneuver and, when necessary, should be promptly performed in conjunction with or prior to administration of induction or sedative agents.
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.
Equipment includes the following:
Defibrillators (automated external defibrillators [AEDs], semiautomated AEDs, standard defibrillators with monitors)
Paddle or adhesive patch
Conductive gel or paste
ECG monitor with recorder
Oxygen equipment
Intubation kit
Emergency pacing equipment
Blood pressure cuff (automatic or manual)
Pulse recorder
Oxygen saturation monitor
Intravenous access
Suction device
Code Cart with ACLS (Advanced Cardiovascular Life Support) medications
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]
Paddle placement on the chest wall has 2 conventional positions: anterolateral and anteroposterior.
In the 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.
In the 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 life-saving, 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 cardiovascular 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.
For elective procedures, prepare as follows:
Nil per os (NPO) for 8 hours prior to the procedure
Stop digoxin 48 hours prior to the procedure
Continue medications on the morning of the procedure under the direction of the physician
After the procedure, do not drive, operate machinery, or sign important documents for 24 hours and/or until sedation has worn off
There is no patient preparation for emergency procedures.
Defibrillation and cardioversion are demonstrated in the videos below.
Defibrillators can deliver energy in various waveforms that are broadly characterized as monophasic or biphasic.
Monophasic defibrillation delivers a charge in only one direction. Biphasic defibrillation delivers a charge in one direction for half of the shock and in the electrically opposite direction for the second half.
Newer defibrillators deliver energy in biphasic waveforms. Biphasic waveform defibrillators deliver a more consistent magnitude of current. They tend to successfully terminate arrhythmias at lower energies than monophasic waveform defibrillators. [6, 7, 8]
In 2010, the American Heart Association issued guidelines for initial energy requirements for monophasic and biphasic waveforms. [9]
Atrial fibrillation energy requirements are as follows:
200 Joules for monophasic devices
120-200 Joules for biphasic devices
Atrial flutter energy requirements are as follows:
100 Joules for monophasic devices
50-100 Joules for biphasic devices
Ventricular tachycardia with pulse energy requirements are as follows:
200 Joules for monophasic devices
100 Joules for biphasic devices
Ventricular fibrillation or pulseless ventricular tachycardia energy requirements are as follows:
360 Joules for monomorphic devices
120-200 Joules for biphasic devices
See the images below.
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. [10, 11]
Thromboembolization is associated with cardioversion in 1-3% of patients, especially in patients with atrial fibrillation who have not been anticoagulated prior to cardioversion. Current American College of Cardiology (ACC)/American Heart Association (AHA) guidelines recommend to anticoagulate for 3-4 weeks before and after cardioversion. The presence of an intracardiac thrombus should be excluded using transesophageal echocardiography prior to cardioversion if therapeutic anticoagulation has not been achieved.
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.
Myocardial dysfunction is due to an absence of cardiac output and coronary blood flow during arrest, resulting in ischemia. Myocardial dysfunction due to stunning may reverse within first 24-48 hours. Left ventricle function evaluation should be delayed for 48 hours after arrest. [12]
Pulmonary edema is a rare complication of cardioversion. It is probably due to transient left atrial standstill and left ventricular systolic dysfunction. It is more common in atrial fibrillation due to valvular heart disease or left ventricular systolic dysfunction.
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. It occurs less with use of biphasic waveform defibrillators and use of gel-based pads. Prophylactic use of steroid cream or topical ibuprofen reduces pain and inflammation. [13, 14]
Allergic reaction to sedation medication is a potential complication.
Antiarrhythmic medications are used to alter flow of electrical activity through the heart. Based on the clinical situation, chemical cardioversion can be performed in the hospital in monitored setting or in an outpatient setting.
This is also known as direct current (DC) cardioversion. Electrical shock is synchronized (perfectly timed) to convert an abnormal rhythm to a normal sinus rhythm. DC cardioversion is performed in the hospital in a monitored setting.
Internal cardioversion is performed less frequently nowadays, owing to the presence of biphasic waveform defibrillators and intravenous ibutilide. It is performed if external cardioversion fails. It is performed using preexisting implantable cardioverter defibrillators (ICDs), epicardial wires during surgery, or internal paddles applied to the epicardium in the presence of sternotomy wires. Advantages of internal cardioversion are that this technique avoids the risk of a skin irritation from external shock. Disadvantages are that it may damage ICD systems, it consumes the battery of the ICD, and it does not always convert atrial arrhythmias.
Digoxin overdose or toxicity can present with any type of tachyarrhythmias or bradyarrhythmias. Cardioversion in the setting of digoxin toxicity is a relative contraindication. Digitalis sensitizes the heart to the electrical stimulus. Prior to cardioversion, electrolytes should be normalized. Cardioversion may cause additional arrhythmias, especially ventricular fibrillation.
Cardioversion in patients with permanent pacemaker/ICD should be performed with extra care. Improper technique may damage the device, lead system, or myocardial tissue, resulting in device malfunction. The electrode paddle or patch should be at least 12 cm from the pulse generator and anteroposterior paddle position. [15, 16] The lowest amount of energy should be used during cardioversion, based on the patient’s clinical condition. After cardioversion, the pacemaker/ICD should be interrogated to ensure normal function of the device.
Cardioversion can be performed safely in pregnant women. The fetal heart rate should be monitored during the procedure using fetal monitoring techniques.
Zoll PM, Linenthal AJ, Gibson W, Paul MH, Norman LR. Termination of ventricular fibrillation in man by externally applied electric countershock. N Engl J Med. 1956 Apr 19. 254(16):727-32. [Medline].
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Schneider T, Martens PR, Paschen H, Kuisma M, Wolcke B, Gliner BE, et al. Multicenter, randomized, controlled trial of 150-J biphasic shocks compared with 200- to 360-J monophasic shocks in the resuscitation of out-of-hospital cardiac arrest victims. Optimized Response to Cardiac Arrest (ORCA) Investigators. Circulation. 2000 Oct 10. 102(15):1780-7. [Medline].
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Kirchhof P, Eckardt L, Loh P, Weber K, Fischer RJ, Seidl KH, et al. Anterior-posterior versus anterior-lateral electrode positions for external cardioversion of atrial fibrillation: a randomised trial. Lancet. 2002 Oct 26. 360(9342):1275-9. [Medline].
Niebauer MJ, Brewer JE, Chung MK, Tchou PJ. Comparison of the rectilinear biphasic waveform with the monophasic damped sine waveform for external cardioversion of atrial fibrillation and flutter. Am J Cardiol. 2004 Jun 15. 93(12):1495-9. [Medline].
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[Guideline] Link MS, Atkins DL, Passman RS, Halperin HR, Samson RA, White RD, et al. Part 6: electrical therapies: automated external defibrillators, defibrillation, cardioversion, and pacing: 2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation. 2010 Nov 2. 122(18 Suppl 3):S706-19. [Medline].
Kirchhof P, Mönnig G, Wasmer K, et al. A trial of self-adhesive patch electrodes and hand-held paddle electrodes for external cardioversion of atrial fibrillation (MOBIPAPA). Eur Heart J. 2005 Jul. 26(13):1292-7. [Medline].
Nakagawa Y, Sato Y, Kojima T, Wakabayashi T, Morita S, Amino M, et al. Electrical defibrillation outcome prediction by waveform analysis of ventricular fibrillation in cardiac arrest out of hospital patients. Tokai J Exp Clin Med. 2012 Apr 20. 37(1):1-5. [Medline].
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Kirkland S, Stiell I, AlShawabkeh T, Campbell S, Dickinson G, Rowe BH. The efficacy of pad placement for electrical cardioversion of atrial fibrillation/flutter: a systematic review. Acad Emerg Med. 2014 Jul. 21(7):717-26. [Medline].
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Sandy N Shah, DO, MBA, FACC, FACP, FACOI Cardiologist
Sandy N Shah, DO, MBA, FACC, FACP, FACOI is a member of the following medical societies: American College of Cardiology, American College of Osteopathic Internists, American College of Physicians, American Medical Association, American Osteopathic Association, American Society of Nuclear Cardiology, Society for Cardiovascular Angiography and Interventions
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Mary L Windle, PharmD Adjunct Associate Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference
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Laurie Scudder, DNP, NP Nurse Planner, Medscape; Senior Clinical Professor of Nursing, George Washington University
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Mark A Clark, MD Medical Director, Block Island Medical Center; Assistant Clinical Professor, Department of Emergency Medicine, St Luke’s-Roosevelt Hospital Center
Mark A Clark, MD is a member of the following medical societies: American Academy of Emergency Medicine, American College of Emergency Physicians, Society for Academic Emergency Medicine, Council of Emergency Medicine Residency Directors
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Luis M Lovato, MD Associate Clinical Professor, University of California, Los Angeles, David Geffen School of Medicine; Director of Critical Care, Department of Emergency Medicine, Olive View-UCLA Medical Center
Luis M Lovato, MD is a member of the following medical societies: Alpha Omega Alpha, American College of Emergency Physicians, Society for Academic Emergency Medicine
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Luis C Afonso, MD Assistant Professor, Department of Internal Medicine-Cardiology, Program Director of Cardiology Fellowship Program, Wayne State University School of Medicine; Director of Echocardiography Laboratory, Harper University Hospital
Luis C Afonso, MD is a member of the following medical societies: American College of Cardiology, American College of Physicians, American Medical Association, and American Society of Echocardiography
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Masooma Athar, MBBS Research Assistant, Department of Internal Medicine, Detroit Medical Center, Wayne State University School of Medicine
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Sony Jacob, MD Assistant Professor, Department of Cardiology, Division of Electrophysiology, Wayne State University School of Medicine
Sony Jacob, MD is a member of the following medical societies: American College of Cardiology, American Medical Association, American Society for Artificial Internal Organs, International Society for Heart Research, Royal College of Physicians of Ireland, and Royal College of Surgeons of Ireland
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Suchitra Kamineni, MD Research Associate, Department of Internal Medicine, Detroit Medical Center
Suchitra Kamineni, MD is a member of the following medical societies: Indian Medical Association
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Ashok K Kondur, MD Clinical Assistant Professor, Department of Internal Medicine, Detroit Medical Center, Wayne State University School of Medicine
Ashok K Kondur, MD is a member of the following medical societies: American College of Physicians and Michigan State Medical Society
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Raju V T Penumetcha, MD Clinical Assistant Professor, Department of Internal Medicine, Wayne State University School of Medicine; Medical Director, Academic Hospitalist, Division of General Medicine, Department of Internal Medicine, Detroit Medical Center
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Defibrillation and Cardioversion
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