The heart is composed of four chambers enclosed within a wall of muscle. The upper two chambers (atria) will help fill the lower two chambers (ventricles) with blood. The ventricles are larger and more heavily muscled than the atria. They pump blood to the lungs and throughout the rest of the body.
The heart's natural pacemaker, located in the upper part of the heart, normally regulates your heart rate. This natural pacemaker, called the sino-atrial node (S-A node), is a small cluster of specialized cells that produce electrical signals at regular intervals. The S-A node automatically increases your heart rate in response to your body's needs - for example, during exercise, when a faster blood flow is required.
The electrical impulses sent out by the S-A node travel to the atrioventricular node (A-V node), a second cluster of cells located near the center of the heart. The A-V node then transmits the electrical signals out to the walls of the ventricles.
This natural electrical pathway is very important because when the signals reach the lower heart, both ventricles contract, pumping blood throughout the body. Any problem with this natural electrical pathway may cause a change in heart rate and/or rhythm and effect circulation of blood from the heart to the rest of the body. An abnormal rhythm (arrhythmia) is a change in either the speed or pattern of the heartbeat. An arrhythmia becomes serious when the heart beats too slowly or too rapidly to pump blood effectively, or when there is a threat to the person's life.
When basic diagnostic tests do not provide all of the necessary information to properly diagnose or locate an arrhythmia, an electrophysiology (EP) study may be recommended by your cardiologist.
An EP study is performed in an EP lab in the Cardiac Cath Lab in the hospital. During an EP study, your electrophysiologist inserts a long, thin tube into a blood vessel in the upper leg (groin) or arm. The tube is gently directed to the heart. The special electrode catheters used for the procedure are long and flexible wires that can conduct electrical impulses to and from the heart. One or more catheters are inserted into the body and advanced toward the heart, while the staff follows their progress on a television screen. The catheters are then positioned inside the heart.
The EP study is done to diagnose or locate your heart rhythm problem. Basically, the EP study is performed by doing two things:
- Recording Electrical Signals: Electrode catheters sense electrical activity in various areas of the heart and measure how fast electrical impulses travel.
- Pacing the Heart: Electrode catheters can also be used to deliver tiny electrical impulses to pace the heart. By doing so, doctors try to induce (bring on) certain abnormal heart rhythms, so that they can be observed under controlled conditions.
If an arrhythmia is induced, medications may be given through the IV line to test their effect on the heart rhythm.
An EP study helps determine the location of the heart's abnormal electrical activity causing arrhythmia. The location and type of heart rhythm problem will determine whether catheter ablation is a treatment option.
During catheter ablation, your electrophysiologist inserts an ablation electrode catheter into the heart. He positions the catheter so that it lies close to the abnormal electrical pathway that is causing the arrhythmia, then he passes radio-frequency energy through the electrode catheter.
The tip of the catheter heats up and destroys the small area of heart tissue that contains the abnormal pathway. This produces scar tissue which is unable to transmit electrical impulses. As a result, the abnormal electrical pathway is no longer capable of producing arrhythmias.