Cardioversion is a medical procedure used to restore a normal heart rhythm in patients experiencing certain types of abnormal heartbeats, known as arrhythmias. These arrhythmias, such as atrial fibrillation, atrial flutter, or supraventricular tachycardia, can compromise blood flow and oxygen delivery throughout the body.
Because the heart and lungs are closely linked in maintaining effective oxygenation and perfusion, understanding cardioversion is important not only for physicians and nurses but also for respiratory therapists.
What is Cardioversion?
Cardioversion is a medical procedure designed to restore a normal heart rhythm in patients with certain arrhythmias. Unlike defibrillation, which delivers unsynchronized shocks during cardiac arrest, cardioversion uses carefully timed electrical energy or medication to reset the heart’s rhythm.
The electrical shock is synchronized with the R wave of the ECG to avoid the vulnerable phase of the T wave, where an untimely shock could trigger dangerous rhythms such as ventricular fibrillation.
Cardioversion typically uses lower energy levels than defibrillation and is considered for tachyarrhythmias such as supraventricular tachycardia, atrial flutter, atrial fibrillation, or stable ventricular tachycardia with a pulse. It is indicated when arrhythmias cause symptoms like hypotension, chest pain, pulmonary congestion, or reduced consciousness.
Why is Cardioversion Relevant to Respiratory Care?
1. Impact on Oxygen Delivery
Abnormal heart rhythms can reduce cardiac output, which directly impacts how well oxygenated blood is circulated to the tissues. Even if a patient’s lungs are functioning properly, an ineffective heartbeat may result in poor oxygen delivery.
Note: Restoring a normal rhythm improves both circulation and oxygen transport, which are critical concepts in respiratory care.
2. Respiratory Therapist’s Role During the Procedure
Respiratory therapists may be called upon to assist in cardioversion, especially in critical care or emergency settings. Their responsibilities can include:
- Administering and monitoring oxygen therapy before, during, and after the procedure.
- Assisting with airway management, particularly if sedation or anesthesia is required.
- Monitoring ventilator settings in intubated patients to ensure optimal oxygenation and ventilation.
- Recognizing changes in patient status, such as hypoxemia or respiratory depression, which may occur with sedatives.
3. Connection to Critical Care
Many patients who require cardioversion are admitted to intensive care units, where respiratory therapists play a central role in managing complex cases. Knowledge of cardioversion helps respiratory therapists anticipate complications and collaborate effectively with the healthcare team.
Clinical Considerations for Respiratory Therapists
- Pre-Procedure: Ensure supplemental oxygen is available, and assist with patient preparation.
- During Procedure: Monitor respiratory function closely, particularly if the patient is sedated.
- Post-Procedure: Observe for complications such as arrhythmia recurrence, hypoxemia, or airway compromise.
Cardioversion vs. Defibrillation
Cardioversion and defibrillation are both procedures that use electrical energy to correct abnormal heart rhythms, but they differ in purpose and technique. Cardioversion is used for patients who are stable yet experiencing organized arrhythmias such as atrial fibrillation, atrial flutter, supraventricular tachycardia, or ventricular tachycardia with a pulse. It delivers a synchronized shock, timed with the R wave on the ECG, to avoid shocking during the vulnerable T wave period.
In contrast, defibrillation is an emergency intervention for life-threatening, pulseless rhythms like ventricular fibrillation or pulseless ventricular tachycardia. Defibrillation uses higher, unsynchronized energy because precision timing is not possible in cardiac arrest.
Note: Both procedures aim to restore a normal rhythm but are applied in very different clinical scenarios.
Cardioversion Practice Questions
1. What is cardioversion?
A medical procedure used to restore a normal heart rhythm in patients with certain arrhythmias.
2. How does cardioversion differ from defibrillation?
Cardioversion delivers synchronized shocks during organized arrhythmias, while defibrillation delivers unsynchronized shocks during cardiac arrest.
3. Why is the electrical shock synchronized with the R wave during cardioversion?
To avoid shocking during the T wave, which could trigger dangerous rhythms such as ventricular fibrillation.
4. What types of arrhythmias are typically treated with cardioversion?
Atrial fibrillation, atrial flutter, supraventricular tachycardia, and stable ventricular tachycardia with a pulse.
5. What symptoms may indicate the need for cardioversion?
Hypotension, chest pain, pulmonary congestion, or decreased consciousness.
6. How does an abnormal heart rhythm affect oxygen delivery?
It reduces cardiac output, which decreases the circulation of oxygenated blood to tissues.
7. Why is restoring a normal rhythm important for respiratory care?
It improves both circulation and oxygen transport, supporting adequate tissue oxygenation.
8. What is the respiratory therapist’s role before cardioversion?
Ensure supplemental oxygen is available and assist with patient preparation.
9. What is the respiratory therapist’s role during cardioversion?
Monitor respiratory function, assist with oxygen therapy, and manage the airway if sedation is used.
10. What should respiratory therapists monitor after cardioversion?
Signs of arrhythmia recurrence, hypoxemia, or airway compromise.
11. Why might airway management be necessary during cardioversion?
Because sedatives or anesthesia can cause respiratory depression.
12. In which hospital setting is cardioversion commonly performed?
In intensive care units or emergency departments.
13. What type of electrical energy is used in cardioversion compared to defibrillation?
Cardioversion uses lower, synchronized energy; defibrillation uses higher, unsynchronized energy.
14. When is defibrillation indicated instead of cardioversion?
For pulseless, life-threatening rhythms such as ventricular fibrillation or pulseless ventricular tachycardia.
15. True or False: Cardioversion is performed only in patients who have a pulse.
True
16. True or False: Defibrillation can be used in stable atrial fibrillation.
False
17. What patient condition makes synchronized cardioversion unsafe?
If the rhythm is pulseless, requiring defibrillation instead.
18. What is the main goal of cardioversion?
To reset the heart’s electrical activity and restore a normal sinus rhythm.
19. Which wave on the ECG must cardioversion shocks be timed with?
The R wave.
20. Why is knowledge of cardioversion important for respiratory therapists?
It allows them to anticipate complications, support oxygenation, and collaborate effectively in critical care.
21. Which heart rhythms can be treated with synchronized cardioversion?
Conscious ventricular tachycardia with a pulse, rapid atrial fibrillation, supraventricular tachycardia, and atrial flutter.
22. What are the main indications for cardioversion?
The patient must be in a cardiovertible rhythm, symptomatic, unstable, or resistant to drug therapy.
23. What energy level is typically used for cardioversion in adults?
50–150 joules
24. What is the recommended starting energy for atrial flutter during cardioversion?
50 joules, which is often effective.
25. What energy dose is recommended for pediatric cardioversion?
0.5–1 joule per kilogram of body weight.
26. How should a patient be prepared for cardioversion?
Obtain consent, consider fasting status, ensure IV access, provide oxygen, apply monitoring, place defibrillator pads, turn on manual mode, and activate the sync button.
27. What is the minimum required team for performing cardioversion?
Two doctors (one airway-trained), an ALS-trained nurse, and a scribe.
28. What medications are commonly used to sedate patients during cardioversion?
Propofol, fentanyl, or midazolam.
29. What safety command must be voiced before delivering a shock?
“Stand clear, shocking.”
30. What should be done if the initial shock is unsuccessful?
Repeat the shock and consider increasing the joule setting.
31. How many shocks are typically attempted during synchronized cardioversion?
A maximum of three shocks.
32. What is defibrillation?
The delivery of an unsynchronized shock to restart the heart into a sinus rhythm during cardiac arrest.
33. When is defibrillation indicated?
In an unconscious patient with a shockable rhythm such as pulseless ventricular tachycardia or ventricular fibrillation.
34. Which rhythms cannot be treated with shocks?
Asystole, pulseless electrical activity (PEA), and ventricular tachycardia with a pulse.
35. What energy dose is recommended when defibrillating an adult?
150–200 joules, depending on the monitor/defibrillator used.
36. What is the defibrillation dose for pediatric patients?
4 joules per kilogram of body weight.
37. For which patient should synchronized cardioversion be considered to terminate ventricular tachyarrhythmias?
A patient with a ventricular rate greater than 150 beats per minute and a pulse.
38. What is the safest approach for performing cardioversion on a patient with an implanted ICD?
Keep the defibrillator pads or paddles away from the ICD site.
39. What symptom indicates instability in a patient with supraventricular tachycardia requiring cardioversion?
Chest pain
40. When performing cardioversion on a responsive adult with SVT, what is the correct action?
Activate the sync mode before delivering the shock.
41. Which patient has an increased risk for complications during synchronized cardioversion?
A patient with low potassium levels.
42. After synchronized cardioversion, which patient complaint is most concerning?
Shortness of breath
43. For a pediatric patient weighing 30 kg, which electrodes should be used for cardioversion?
Adult electrodes
44. When preparing a patient for synchronized cardioversion, what should the nurse instruct the patient to do beforehand?
Empty the bladder
45. Why might a patient report pain after successful cardioversion?
Because sedation may be inadequate during emergency shocks.
46. How should a nurse explain post-procedure discomfort to a patient who required immediate cardioversion for unstable VT?
“Your condition was so serious we had to shock you immediately.”
47. During synchronized cardioversion, the patient’s rhythm deteriorates into ventricular fibrillation. What should be done next?
Administer an unsynchronized defibrillation shock immediately.
48. Why must sync mode always be used during cardioversion?
To ensure the shock is delivered on the R wave and not during the T wave.
49. How does the energy level used in cardioversion compare with defibrillation?
Cardioversion uses lower energy, while defibrillation requires higher energy.
50. What is the ultimate goal of both cardioversion and defibrillation?
To restore a normal sinus rhythm and stabilize the patient’s condition.
51. What is synchronized cardioversion?
A controlled form of defibrillation used for patients with organized cardiac activity and a pulse.
52. What are the main emergency indications for synchronized cardioversion in unstable patients?
Perfusing ventricular tachycardia, paroxysmal supraventricular tachycardia, rapid atrial fibrillation, and atrial flutter.
53. What are the three common electrode placement options for cardioversion?
Transthoracic, anterior/posterior, and lateral/lateral.
54. Why should hair be removed before placing electrodes?
To ensure good skin contact and effective delivery of the electrical shock.
55. What electrode placement is recommended in most adult and pediatric emergencies?
Transthoracic placement.
56. In transthoracic placement, where are the pads positioned?
One pad is placed to the right of the upper sternum below the clavicle, and the other over the apex of the heart in the left anterior axillary line.
57. In anterior/posterior placement, where are the pads positioned?
One pad is placed over the precordium on the chest, and the other is placed posteriorly behind the heart.
58. Which electrode placement may be used in infants when only adult-sized paddles are available?
Anterior/posterior placement
59. Which electrode placement may be useful in patients with an implanted cardioverter-defibrillator (AICD)?
Anterior/posterior placement
60. What are the three types of paddle-to-skin interfaces used in cardioversion or defibrillation?
Conductive cream/paste, saline-soaked pads, and pre-packaged gel pads.
61. Why is cardioversion synchronized with the R wave of the ECG?
To avoid shocking during the relative refractory period of the T wave.
62. During cardioversion, at what point in the QRS complex is the countershock delivered?
At the peak of the R wave.
63. What medications are commonly used for premedication during synchronized cardioversion?
Midazolam, diazepam, or morphine.
64. When activating the sync mode, what is the monitor detecting?
The R wave of the QRS complex.
65. What is the recommended energy dose for unstable atrial fibrillation during cardioversion?
Monophasic: 200 joules; Biphasic: 120–200 joules.
66. What is the recommended shock dose for unstable atrial flutter or paroxysmal supraventricular tachycardia (PSVT)?
50–100 joules, monophasic or biphasic.
67. What is the recommended shock dose for monomorphic ventricular tachycardia with a pulse?
100 joules, monophasic or biphasic.
68. What must be done when delivering the cardioversion shock?
Press and hold both discharge buttons simultaneously until the countershock is delivered.
69. If there is a delay in delivering the countershock due to sensing, what must be done?
Turn the sync mode back on and repeat the procedure.
70. If a patient develops ventricular fibrillation or pulseless VT during cardioversion, what is the next step?
Start CPR, turn off the sync switch, charge, and immediately defibrillate at the correct dose.
71. What is the common purpose of both cardioversion and defibrillation?
To treat tachydysrhythmias by depolarizing a critical mass of myocardial cells.
72. How does electrical current restore normal rhythm during cardioversion or defibrillation?
By depolarizing myocardial cells, allowing the SA node to resume control as the pacemaker.
73. What is the key difference between cardioversion and defibrillation?
Cardioversion is synchronized with the patient’s cardiac cycle, while defibrillation is unsynchronized.
74. Which device is used for both cardioversion and defibrillation?
A defibrillator
75. Why does defibrillation require higher energy than cardioversion?
Because it must immediately depolarize chaotic rhythms without synchronization, which may cause more myocardial damage.
76. What type of defibrillator is most commonly manufactured today?
Biphasic defibrillators
77. How do biphasic defibrillators deliver current?
They send an electrical charge from one paddle and then automatically redirect it back to the originating paddle.
78. Why must the manufacturer’s recommended energy setting be followed for defibrillation?
Because energy requirements vary by device.
79. What are the two common pad placements for delivering defibrillation or cardioversion?
Anterior/lateral (standard) or anterior/posterior.
80. What advantage do multifunction conductor pads provide over paddles?
They allow hands-off shocks, improving electrical safety and reducing risk to staff.
81. Why is sedation often used during synchronized cardioversion?
Because the procedure can be painful and anxiety-provoking for conscious patients.
82. What is the primary risk if a shock is delivered during the T wave instead of the R wave?
It can induce ventricular fibrillation.
83. Why is it important to confirm the “sync” function is activated before delivering a shock?
To ensure the shock is delivered at the correct point of the cardiac cycle.
84. What should always be monitored continuously during cardioversion?
The patient’s ECG and oxygen saturation.
85. Why is it necessary to provide supplemental oxygen during cardioversion?
To prevent hypoxemia caused by arrhythmias or sedation.
86. What immediate post-procedure test should be performed after cardioversion?
A 12-lead ECG to confirm rhythm restoration.
87. What complication may occur if cardioversion is attempted without anticoagulation in atrial fibrillation?
An embolic stroke due to dislodged clots.
88. In atrial fibrillation lasting longer than 48 hours, what must be done before elective cardioversion?
Anticoagulation therapy for at least three weeks.
89. What is the success rate of cardioversion in restoring sinus rhythm in atrial flutter compared to atrial fibrillation?
It is generally higher in atrial flutter.
90. Why might multiple shocks be needed during cardioversion?
Because some arrhythmias may not convert with the first attempt.
91. What can cause cardioversion to fail despite correct technique?
Electrolyte imbalances, inadequate energy delivery, or underlying structural heart disease.
92. Which electrolyte imbalance increases the risk of complications during cardioversion?
Hypokalemia
93. Why is synchronized cardioversion not performed in patients with pulseless rhythms?
Because immediate unsynchronized defibrillation is required instead.
94. What monitoring device ensures the patient’s airway and breathing are safe during sedation for cardioversion?
Capnography.
95. What is the difference between monophasic and biphasic cardioversion?
Monophasic delivers current in one direction, while biphasic delivers current in two phases for greater efficiency.
96. Why are biphasic shocks preferred over monophasic shocks?
They require less energy and cause less myocardial injury.
97. In which clinical scenario is cardioversion contraindicated?
In patients with digoxin toxicity or untreated atrial thrombus.
98. Why must staff stand clear during cardioversion?
To avoid accidental electrical shock to personnel.
99. What should be checked on the defibrillator before delivering cardioversion?
The sync mode, selected energy level, and pad placement.
100. What is the ultimate therapeutic goal of synchronized cardioversion?
To restore a stable sinus rhythm and improve cardiac output.
Final Thoughts
Cardioversion is an essential procedure that restores normal heart rhythm in patients experiencing arrhythmias, ultimately improving circulation and oxygen delivery. For respiratory therapists, a solid understanding of this intervention is vital since it directly impacts a patient’s ability to receive and utilize oxygen effectively.
Whether assisting with oxygen therapy, airway management, or monitoring ventilation during sedation, RTs play a crucial role in supporting safe and successful outcomes.
By recognizing the connection between cardiac function and respiratory care, respiratory therapists can better anticipate patient needs and contribute meaningfully to the interdisciplinary healthcare team.
Written by:
John Landry is a registered respiratory therapist from Memphis, TN, and has a bachelor's degree in kinesiology. He enjoys using evidence-based research to help others breathe easier and live a healthier life.
References
- Goyal A, Singh B, Chhabra L, et al. Synchronized Electrical Cardioversion. [Updated 2023 Mar 27]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025.