What is Cardioversion?
Cardioversion refers to the treatment used to restore normal heart rhythm in patients with heart rhythm disturbance. It is often recommended to patients with atrial fibrillation, a common heart rhythm disorder originating from the upper chambers of the heart (atria).
Why do I need Cardioversion?
Normally, each heartbeat originates from a region within the right atrium where specialised "pacemaker" cells are located. Electrical impulses generated by these cells (usually 1 to 2 times per second) are transmitted throughout the heart's electrical network in an organised fashion resulting in coordinated and rhythmic heartbeats. In patients with atrial fibrillation, the atria quiver because of chaotic electrical activities circulating within these chambers. As a result, the heart rhythm becomes irregular and rapid, and the heart is unable to effectively pump blood to the body. Most patients experience rapid heart beating, shortness of breath, or fatigue but some may be unaware of this rhythm disturbance. If you have atrial fibrillation, your Cardiologist will evaluate your symptoms and medical profile to determine whether cardioversion is warranted to restore normal heart rhythm.
What are the Different Types of Cardioversion?
Cardioversion can be achieved pharmacologically or electrically. Pharmacological cardioversion refers to the use of medications to resume normal heart rhythm. These medications are often taken orally and they work by altering the heart's electrical properties. Electrical cardioversion is a procedure during which a synchronised electrical current (shock) is delivered to the heart through the chest wall. This activates all the heart cells simultaneously, thereby interrupting and terminating abnormal electrical circuit(s) in the heart so normal rhythm can resume. The current delivered is limited and can be repeated a few times if necessary without damaging the heart.
What happens during your Admission for Electrical Cardioversion?
You will be admitted to hospital and electrical cardioversion is performed in the cardiac angiography suite, coronary care unit or recovery room. It is necessary for you to fast for at least 6 hours prior to the procedure but you can take your morning medications with a small amount of water. Patients on Warfarin should have a blood test within a day or two of admission to check the level of blood thinning (INR).
During the procedure deep sedation or light anaesthesia will be administered intravenously by an anaesthetist and oxygen will be delivered to you via a mask. If your Cardiologist wants to make sure there are no residual blood clots within the atria, an ultrasound probe will be inserted into your oesophagus to image your heart (transoesophageal echocardiogram) prior to cardioversion. Paddles applied over gel pads or large self-adhesive electrodes will be placed on the front of your chest, and sometimes the back to deliver the electrical current.
Your heart rhythm will be monitored by connecting to an external defibrillator, which also generates the electrical current for cardioversion. If the first shock fails to restore normal heart rhythm, repeated shocks at progressively higher energy levels will be delivered until normal rhythm resumes or the Cardiologist decides to abort. If the abnormal heart rhythm relapses after initial successful reversion, repeated shocks will be delivered. The overall success rate depends on various factors and you should discuss this with your Cardiologist prior to consenting to the procedure. Most patients wake up from anaesthesia promptly with little recollection of events during the procedure. You will be discharged after a few hours, and informed regarding follow-up and medications. You cannot drive home and will need to have someone staying with you overnight. You should avoid driving or making important decisions for 24 hours after discharge in case there are residual effects from the sedation and anaesthesia. Even after successful cardioversion, Warfarin will be continued for a period of time specified by your Cardiologist.
What are the Risks of Electrical Cardioversion?
When properly executed in appropriately selected patients, electrical cardioversion is a very safe and effective treatment. Some patients experience minor skin irritation on the chest which responds to application of moisturiser. The only significant risk is that of embolisation when a blood clot formed within the atrium as a result of the abnormal heart rhythm is dislodged and enters the blood stream. If the clot travels to a vital organ, it can potentially cause problems such as a stroke. For this reason, if atrial fibrillation has been present for more than 48 hours, or of unknown duration, blood-thinning medication such as Warfarin needs to be taken for a period of time prior to cardioversion. In this case, the risk of embolisation will be less than 1 in 1000. There is also a very small risk (less than 1 in 1000) associated with the use of sedatives and anaesthetic agents