The Heart's Electrical System

The heart is divided by muscle and fibrous tissue into a right and left side. Each side has an upper chamber or atrium that collects blood returning to the heart and a muscular lower chamber or ventricle that pumps that blood away from the heart. The right atrium (RA) receives blood from the body and pumps it into the right ventricle (RV). The right ventricle then pumps the blood to the lungs. From the lungs, blood returns to the left atrium (LA) and then the left ventricle (LV). From the left ventricle it is pumped out of the heart, to the body.%u2028%u2028To make sure that the different parts of the heart work together, and pump the blood with the right timing and sequence, the heart has an "electrical system" which coordinates all the heart’s actions. In the right atrium is the SA node – the "pacemaker" of the heart. It begins the electrical impulses just like a spark plug in a car, and therefore sets the heart rate. This impulse spreads throughout the atria like ripples in a pond, and then travels down to a region called the AV node. The AV node is a connection between the atria and the ventricles and is responsible for passing along the electrical impulses. Past the AV node, the electrical system divides to 2 branches called the right and left bundle branch, allowing the even spread of the electrical signal to both ventricles simultaneously.

The Diagnostic Electrophysiology Study

Introduction:
As described above, the heart produces electrical signals that spread through the heart muscle to make the muscle contract in a coordinated manner. These signals are small but can be picked up on an electrocardiograph machine. The electrocardiogram (EKG) is helpful but often the signals doctors need to see are so small that they cannot be seen unless a wire is placed inside the heart via a vein in the leg. An electrophysiology study (EPS) is a diagnostic test that allows your cardiologist to look at these heart signals in more detail and determine if you have an abnormality of your heart beat (otherwise called a cardiac arrhythmia), and where the problem lies. For a more detailed description of various arrhythmias, see sections below. An EP study is done to diagnose the source of a problem and determine whether a curative catheter ablation (see below) is performed, usually during the same procedure. From a patient’s point of view, an EP study is very similar to an angiogram with the important exception that a low-pressure leg vein is used instead of a high-pressure artery.

The EP laboratory room looks a lot like a cardiac catheterization room with a large X-ray machine along with many computer screens and other medical equipment (see figure below). During the procedure, there will be 1 or 2 nurses along with one technologist and 1-3 doctors in the room. The nurse or technician will escort you into the room and help you onto the X-ray table. They will then connect you up to an automatic blood pressure cuff and a machine that continuously monitors your oxygen level. You will already be wearing a hospital gown which allows the nurses to attach electrodes to the skin on your chest and shoulders. They will then apply 3 large sticky pads to your body - one on the front chest and another on the back and a third on your upper leg. Once these are all connected, the nurses may give you some sedating medication through your intravenous line to help you relax. In many cases, the drugs will make you fall asleep for much of the procedure and forget most of it. In other cases where an anesthesiologist is present, he or she will give you the drugs you need to keep you relaxed. The nurse will cover you with a warm blanket and expose the upper portion of your right leg and your left shoulder. If necessary, they will shave these areas.%u2028
The physician will clean the right groin and left shoulder areas and then place a large drape over your chest, abdomen and legs to keep the cleaned areas and equipment sterile. The doctor will then inject some local anesthetic so that these areas will become numb. You should not feel any discomfort after the local freezing takes effect so please let the nurse or doctor know if you feel pain. The physician will use a needle to enter the veins that run past the groin and left shoulder and thread small wires (see figure below, left) up to the heart using a small amount of X-ray to guide their placement in the proper locations in the heart(figure below, right). These soft wires are used to pace your heart at different speeds and record electrical signals from inside your heart.
   
Recordings and measurements will help the doctors determine the cause and location of your heart rhythm problem. If necessary, the doctors may give you one or more drugs through the intravenous line to speed up your heart rate in order to help determine the electrical problem, if one exists. Once the measurements are complete, the doctors will decide whether an ablation is possible during the same procedure, applying energy to a troublesome spot or ‘short circuit’ to eliminate the source of heart racing.  If an ablation is not an option based on the results of the EP study, then the staff will remove the wires and put pressure on the areas where the veins were punctured to seal the puncture holes. Small bandages will be put on these areas. The little cuts in the skin where the veins are punctured are very small and do not leave any significant scarring.

You will then be transferred to a stretcher and taken to a room to recover. We ask you not to raise your head off the bed and not coughing too vigorously for the next two hours because this can lead to bleeding from the vein puncture sites. Your doctor will likely talk to your family about the test results first. When the sedation has worn off, the physician will talk to you and your family to make sure you are aware of the findings from the EP study and answer any questions.

Risks of the test procedure: No procedure, especially one that involves the heart, is 100% safe but an EP study is associated with a low rate of complications of approximately 1% or less. You should expect some bruising at the site where the veins are punctured. Mild pain at these sites is normal for several days after the procedure. Because the leg (femoral) artery is located next to the vein, puncture of the artery can occur. Rarely, serious injury to the artery can occur with resulting blockage of blood flow in the leg. This rare complication would require a surgical procedure to repair. In puncturing the vein in the left shoulder, the needle passes by the lung and can make contact with it. This may cause a leak of air and the lung to collapse. A partial collapse may be sufficiently small that nothing more than close observation for a day or two in hospital is required. If the lung collapse is large, a chest physician specialist may be called in to insert a small needle into the chest to drain the air and re-expand the lung and your stay in hospital may be extended by several days until the problem is resolved. Although the thin wires used to record signals from your heart are soft, it is possible for one of these wires to poke through the wall of heart muscle (perforation). This can cause some chest or right shoulder pain at the time but usually resolves when the wire is pulled back. Rarely, muscle perforation can cause bleeding around the heart wall that impairs the heart's ability to pump effectively and requires a surgical procedure to drain the blood and close the small hole in the heart wall.

An explanation of the risks of the electrophysiology study will be provided during your visit prior to the procedure. Feel free to ask any questions you may have concerning the procedure or risks at that time.

Acknowledgements: Contributors to this information were: Arrhythmia service physicians and staff members.