The purpose of the cardioversion is to interrupt the abnormal electrical circuit(s) in the heart and to restore a normal heartbeat. The delivered electrical 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 restores a normal heartbeat.
The heart is a pump responsible for maintaining blood supply to the body. It has four chambers. The two upper chambers (the right atrium and left atrium) are the chambers which receive blood as it returns from the body via the veins. The lower chambers (the right and left ventricle) are the chambers responsible for pumping the blood out to the body via the arteries. Like any pump, the heart has an electrical system that controls how it functions.
In order for the heart to do its work (pumping blood throughout the body), it needs a sort of spark plug or electrical impulse to generate a heartbeat. Normally this electrical impulse begins in the upper right chamber of the heart (in the right atrium) in a place called the sino-atrial (SA) node. The SA node is the natural pacemaker of the heart. The SA node gives off electrical impulses to generate a heartbeat in the range of 60 to 100 times per minute. If you are exercising, doing strenuous work or you are under a lot of stress, your heart rate may be faster. When you rest or sleep your heart rate will slow down. If you take certain medications, your heart rate may be slower.
From the SA node, the electrical impulse is relayed along the heart’s conduction system. It spreads throughout both the right and left atria causing them to contract evenly. When the impulse spreads over the right atrium it reaches the atrio-ventricular (AV) node. This is a very important structure in the heart because it is the only electrical connection between the top chambers and the bottom chambers. It is therefore the only way in which an electrical impulse can reach the pumping chambers (the ventricles). The impulse spreads through the AV node and down into the lower chambers or ventricles of the heart. This causes them to contract and pump blood to the lungs and body.
Patients are referred for EPS for many reasons.
Some of the more common reasons are:
In some hearts, an abnormal heart rhythm develops when an electrical impulse either starts from a different location, other than the SA node, or follows a route (or pathway) that is not normally present.
Your doctor will explain the exact nature of your abnormal heart rhythm and the following diagrams should help you understand the mechanism.
You will be transferred to the Electrophysiology Laboratory (EP lab) from your ward. Usually before leaving your ward you will be given a light sedative and your groin will be shaved.
The EP lab has a patient table, X-Ray tube, ECG monitors and various equipment. The staff in the lab will all be dressed in hospital theatre clothes and during the procedure will be wearing hats and masks.
Many ECG monitoring electrodes will be attached to your chest area and patches to your chest and back. These patches may momentarily feel cool on your skin.
A nurse or doctor will insert an intravenous line usually into the back of your hand. This is needed as a reliable way to give you medications during the study without further injections. You will also be given further sedation if and as required. You will also have a blood-pressure cuff attached to your arm, which will automatically inflate at various times throughout the procedure.
The oxygen level of your blood will also be measured during the EP study and a small plastic device will be fitted on your finger for this purpose. Your groin area and possibly your neck or arm will be washed with an antiseptic cleansing liquid and you will be covered with sterile sheets leaving these areas exposed.
The doctor will inject local anaesthetic to the area where the catheters are to be placed. After that, you may feel pressure as the doctor inserts the catheters but let the staff know if there is any discomfort so some more local can be given. Once the catheters are in place you may feel your heart being paced and possibly your abnormal heart rhythm will be induced.
Radiofrequency is a low power, high frequency energy that causes a tiny region of the heart near the tip of the catheter to increase in temperature, thus ablating a small area of tissue.
Radiofrequency energy has been used for decades by surgeons to cut tissue or to stop bleeding. For the treatment of palpitations, a much lower power of radio-frequency is used.
Depending on the findings at your EP study it may be possible to ablate the mechanism for your abnormal heart rhythm. This is usually done at the same time as your EP study as the necessary electrodes within the heart are already in place.
Before the advent of radio-frequency ablation patients had two options to control their palpitations.
One is life-long medication,which works well in some patients, but requires the patient to take daily medication. There is also the possibility of side-effects from these drugs.
The other way of controlling the problem was by open-heart surgery to cut the accessory pathway. This was a very successful technique and many patients were cured of their palpitations in this way. Besides the small risk of open heart surgery and operation leaves a permanent scar on the chest.
You will receive a letter outlining the date of your procedure and date and time of your admission to the hospital admission.
In some cases a letter asking you to cease taking your medication is enclosed. This generally refers only to the medication you are taking for your abnormal heart rhythm and this should be stopped 5 days prior to your procedure. If you are taking anti-coagulation (blood thinning) medication eg Warfarin then you will need to stop this for 5-7 days prior to your procedure. If this is not mentioned in your letter, or if you are unsure please phone us with a list of your medications and we will clarify which medications to stop.
If you are to be admitted to the Royal Melbourne Hospital, you will be required to attend a Pre-admission clinic on the day prior to your procedure. Some country patients may need to make arrangements to stay overnight with family or friends.
At the pre-admission clinic you will see a doctor who will record your medical history. You will also require an ECG and blood test. The doctor will also confirm the time you should be at the hospital for admission the following day.
You will be required to fast for at least six hours before the study. If your procedure is in the afternoon you may have a light breakfast. If your procedure is in the morning, DO NOT EAT OR DRINK AFTER MIDNIGHT, except for sips of water to help you swallow your pills.
After your procedure you will be transferred back to your ward where you will have to lie flat for 4-6 hours depending on which blood vessels have been punctured. During this time, it is important to keep your legs straight and your head relaxed on the pillow.
Most patients stay in hospital overnight and their heart rhythm may be monitored during this time.
The majority of patients have 2-3 days away from work.
If there is any chance you may be pregnant, please notify the doctor performing the procedure.
The EP study is a very low-risk procedure and should a complication arise, it will be dealt with at once. The world wide complication rate for EP/RF studies is less than 0.5%.
Although most people undergoing EP/ RF studies do not experience any complications, you should be aware of the following risks.
Major complications – stroke, heart attack, death are very rare. More than 1200 patients have been successfully treated at The Royal Melbourne Hospital during the last eight years by radio-frequency ablation, and no major complications have occurred.
Radio-frequency is an effective and safe way to cure patients suffering from palpitations.
Please do not hesitate to discuss any aspect of the procedure including potential complications with your doctor prior to your procedure.