A sudden electric shock to the heart can sound alarming, especially when people associate it with what they have seen in emergencies.
But electrical cardioversion and defibrillation are not simply two names for the same procedure. Although both use an electrical impulse, they are used in different circumstances and in different ways.
Key takeaways
- Cardioversion and defibrillation both deliver an electrical shock, but their timing and clinical purposes differ.
- Electrical cardioversion is usually a planned procedure for certain abnormal heart rhythms.
- Defibrillation is an emergency treatment for specific life-threatening rhythms, particularly when there is no effective pulse.
- Cardioversion may be considered when restoring a normal heart rhythm is appropriate after assessing the underlying arrhythmia and the patient’s circumstances.
- The choice between treatment options depends on the type of rhythm disturbance, symptoms, medical history and other clinical factors.
Why does the timing of the shock matter?
The key difference is whether the electrical shock is synchronised with the heart’s rhythm.
During electrical cardioversion, the shock is synchronised with a particular part of the heart’s electrical cycle. This is intended to help restore a more regular rhythm while reducing the risk of delivering the shock at a vulnerable point in the cardiac cycle.
Defibrillation, by contrast, is an emergency intervention used when certain dangerous heart rhythms prevent the heart from pumping blood effectively. The shock is not delivered in the same synchronised manner because immediate restoration of an effective rhythm takes priority.
So, while both procedures involve electrical energy, they are not interchangeable.
When might electrical cardioversion be considered?
Electrical cardioversion may be used for selected abnormal heart rhythms, such as certain cases of atrial fibrillation or atrial flutter, when restoring a normal rhythm is considered appropriate.
The decision is not based simply on whether the heartbeat is irregular. Doctors may consider factors such as,
- The specific type of arrhythmia
- How long the abnormal rhythm has been present or is believed to have been present
- Symptoms and their severity
- Other heart or medical conditions
- Previous treatment and response
- The risk of blood clots and stroke
For some arrhythmias, medication or other approaches may be considered instead. This is why an assessment is needed before deciding whether cardioversion is suitable.
Does cardioversion always mean an emergency?
No. This is one of the most useful distinctions to understand.
Electrical cardioversion is often performed as a planned procedure, rather than during a cardiac arrest. Medication may be given beforehand to help the patient remain comfortable during the brief electrical treatment.
In contrast, defibrillation is associated with cardiac emergencies where an immediately dangerous rhythm requires urgent treatment.
The visual similarity can therefore be misleading: the equipment and electrical principle may look familiar, but the clinical situation is quite different.
What happens before electrical cardioversion?
Before cardioversion, the doctor needs to establish whether restoring the rhythm is appropriate and whether there are factors that could affect the procedure.
For certain arrhythmias, particularly atrial fibrillation, the risk of a blood clot needs careful consideration. Depending on the duration of the arrhythmia and the individual’s circumstances, anticoagulation or other assessment may be required before cardioversion.
This is one reason cardioversion should not be viewed as simply “resetting” the heart.
What happens after the shock?
The heart rhythm is monitored to determine whether a normal rhythm has been restored. Further management may also be needed because cardioversion does not necessarily prevent an arrhythmia from returning.
The next step can vary. Some patients may require medication, monitoring or discussion of other rhythm-management options depending on the underlying condition.
Frequently asked questions
Is cardioversion painful?
The electrical shock itself is brief. For planned cardioversion, medication is commonly used so that the patient is comfortable and does not experience the procedure in the same way as an awake emergency defibrillation.
Can cardioversion be used for every irregular heartbeat?
No. Different rhythm disturbances require different approaches. A cardiologist first needs to identify the rhythm and consider the patient’s overall medical circumstances.
Is cardioversion the same as restarting a stopped heart?
No. Cardioversion is generally used to correct certain abnormal rhythms when the heart is still beating. Defibrillation is an emergency treatment for particular life-threatening rhythms.
Can an abnormal rhythm return after cardioversion?
Yes. Restoring a normal rhythm does not necessarily mean the underlying tendency towards an arrhythmia has been eliminated. Further treatment or monitoring may therefore be discussed.
Do I need to prepare before planned cardioversion?
Preparation depends on the type and duration of the arrhythmia and your medical history. Your cardiologist will advise you about medication, fasting and any assessments required beforehand.
Schedule a consultation to discuss abnormal heart rhythm with a cardiologist
An irregular or unusually fast heartbeat can have several possible causes, and treatment decisions should be based on the rhythm identified and the individual’s circumstances rather than the symptom alone.
If you have been advised to consider cardioversion or want to understand your options for managing an abnormal heart rhythm, TT Lim Cardiology Clinic provides cardiology assessment with Dr. Lim Tai Tian and Dr. Peter Chang. A consultation can help clarify what the rhythm means and whether electrical cardioversion or another approach may be appropriate for your situation.
