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Cardioversion and Defibrillation

What is cardioversion & defibrillation?
Both cardioversion and defibrillation deliver an electrical shock to the heart. The shock can restore a normal heartbeat. Both types of treatment are used in people who have abnormal heartbeats or heart rhythms, called arrhythmias.

Cardioversion is a lower-energy shock delivered to your heart. Cardioversion can stop a very fast arrhythmia.

Defibrillation is a high-energy shock delivered to your heart. You need this treatment if you have a very fast and chaotic arrhythmia in your heart's lower chambers (ventricles). For instance, defibrillation is needed for arrhythmias like ventricular tachycardia (VT) or ventricular fibrillation (VF). Defibrillation is the only effective treatment for VF. If VF is not treated, it can quickly lead to sudden cardiac death (SCD).

The concept behind cardioversion and defibrillation is the same. Both types of treatment stop all electrical activity in the heart for a second. When the heart resumes beating, its electrical system often works correctly once again. If you want to learn more about your heart's electrical system, go to the Heart & Blood Vessel Basics section.

How is cardioversion or defibrillation done?
Internal cardioversion is delivered by an implanted device. If you have an implantable cardioverter defibrillator (ICD), it can sense a fast arrhythmia. The ICD then delivers a low-energy shock. The shock can stop the arrhythmias and restore a normal heartbeat.
External cardioversion is delivered by an external device. This is a scheduled treatment often used to treat fast arrhythmias in the heart's upper chambers (atria).

Internal defibrillation is delivered by an ICD device. When the device senses an arrhythmia like ventricular fibrillation (VF), the ICD delivers a lifesaving shock.
External defibrillation is delivered by an external defibrillator. You've probably seen external defibrillators on TV medical dramas. The machine is connected to two paddles that deliver a shock to the outside of the chest. Because brain damage starts to occur within 4-6 minutes after VF begins, defibrillation should be done as soon as possible. Because fast arrhythmias can be so dangerous, some public buildings and airplanes now have external defibrillators.

What can I expect?
Internal cardioversion or defibrillation from an implanted device can come as a surprise if you aren't having symptoms. You will feel cardioversion but it may not be painful. On the other hand, a high-energy shock from defibrillation can be painful. But an arrhythmia like VF will rarely stop on its own—it must be treated for the person to survive. So defibrillation is typically a lifesaving therapy.

External cardioversion is usually a scheduled treatment in your doctor's office. Your doctor may recommend it if your atrial arrhythmias do not respond to medications. You undress and put on a hospital gown or sheet. You lie on an exam table and an intravenous (IV) line is put into your arm. The IV delivers fluids and medications during the short procedure. The medication makes you groggy, but not unconscious. Your doctor puts patches called electrodes on your chest. The electrodes connect to wires on the device. The device delivers the shock. Most people say they have little or no pain afterwards.

External defibrillation is done in an emergency situation. Someone who receives this treatment is typically unconscious. After the shock is delivered, there may be some pain and skin irritation on the chest (from the paddles).

Important Safety Information
Medications, procedures and tests can have some risks and possible side effects. Results may vary
from patient to patient. This information is not meant to replace advice from your doctor. Be sure to talk
to your doctor about these risks and possible side effects.

An implantable cardioverter defibrillator can protect you from the effects of sudden cardiac arrest by
reviving your heart rhythm. But it is not for everyone, including people with certain steroid allergies.
Procedure risks include infection and tissue damage. In some cases, the device may not respond to
irregular heartbeats or may deliver inappropriate shocks. In rare cases severe complications or device
failures can occur. Electrical or magnetic fields can affect the device. Only your cardiologist knows what
is right for you.

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