Cardioversion

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What is it?

Cardioversion is the process of restoring the normal heart rhythm from an abnormal rhythm. Most elective cardioversions are performed to treat atrial fibrillation, a benign heart rhythm disturbance originating in the upper chambers (atria) of the heart. It involves applying an electric shock to the heart whilst you are under anaesthetic or effects of a drug.

Why do I need a cardioversion?

Normally, each heartbeat starts in the upper right chamber (right atrium) of the heart in a region containing specialised “pacemaker” cells. Each time these cells fire (usually 1 to 2 times per second) this electrical impulse is transmitted in an organised way throughout the heart, resulting in a coordinated rhythmic heartbeat.

In patients with atrial fibrillation, instead of the normal organised electrical activity, the atria fibrillate (or quiver) because of chaotic electrical activity that circulates throughout both atria, resulting in less efficient blood pumping and an irregular or fast heartbeat. Some patients have no symptoms, whereas others may feel rapid heart beating, shortness of breath, or fatigue. Depending on your specific medical history and symptoms, you may be advised to have a cardioversion to return your heart to normal rhythm.

What are the different types of cardioversion?

Cardioversion can be chemical or electrical. Chemical cardioversion refers to taking anti-arrhythmia medication to restore the heart’s rhythm to normal. Such medications work by altering the heart’s electrical properties to suppress the abnormal heart rhythms and restore a normal rhythm. These medications are usually given as an outpatient, but sometimes you may be admitted to hospital for this therapy.

Electrical cardioversion (also known as direct-current or DC cardioversion) involves a synchronised electrical current (shock) being delivered through the chest wall to the heart. The shock is delivered through special electrodes or paddles on the chest and sometimes the back. The purpose of the cardioversion is to interrupt the abnormal electrical circuit(s) in the heart and to restore a normal heartbeat, like rebooting a computer.

The delivered shock causes all the heart cells to contract simultaneously, thereby interrupting and terminating the abnormal electrical rhythm (typically fibrillation of the atria) without damaging the heart. The heart’s electrical system then restarts a normal heartbeat in its place.

The procedure

You will usually be admitted to the hospital on the morning of your cardioversion procedure. The electrical cardioversion is performed in the angiography suite, coronary care unit or recovery room. It is necessary for you to fast for at least 6 hours prior to the cardioversion. You can take your usual medications on the morning of the procedure with a small amount of water. In many cases you will have been on warfarin prior to the cardioversion. It is important that the level of the blood thinning (the INR) is checked prior to the cardioversion, usually the day prior or the morning of the procedure.

Special cardioversion pads are used to minimise any skin burning or irritation from the electrical shock. You will be connected to an external defibrillator to allow monitoring of your heart rhythm and to allow the application of the necessary energy to restore your heart’s rhythm back to normal. Because the shock may be uncomfortable, some form of sedation or anesthesia is administered intravenously. Once you are sedated, the shock is delivered. Additional shocks at higher energy levels can be delivered if the first shock does not restore the rhythm back to normal.

The success rate depends upon a number of factors, but there is an approximately 90% chance that the normal rhythm (sinus rhythm) will be restored. In some patients the arrhythmia subsequently recurs, and repeated cardioversion may be required. Patients generally wake quickly and without any recollection of the shocks because of the effects of the sedatives. Even if the cardioversion is successful, warfarin is usually continued for at least a month after the procedure.

You will not be able to drive yourself home from the procedure and will need someone to stay with you overnight after the procedure. You should not drive or make any important decisions for 24 hours after the procedure.

You should be aware that this form of treatment is only undertaken by specially trained cardiologists, who will obviously make every effort to minimise your risk. However, emergency equipment is readily available to help deal with any complications that may occur.

Risks

Cardioversion is a very safe and effective treatment for atrial fibrillation. The only significant risk is that of embolization, where a blood clot is dislodged from the heart into the blood stream. If the clot travels to a major organ, it can cause problems such as a stroke or heart attack. For this reason if the atrial fibrillation has been present for more than 48 hours, or its duration is unknown, the blood must be thinned prior to the cardioversion. If adequate blood thinning is undertaken, the risk of an embolus is less than 1 in 100. There is a very small risk associated with the administration of the sedation required for the cardioversion, but the likelihood of a significant anaesthetic complication is also less than 1 in 100.

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Disclaimer: This page has been prepared by HeartCare Partners for informational purposes only and is not medical advice. All care has been taken to ensure the accuracy of information, however, this information may be changed, improved, or updated without notice.