Intracardiac electrophysiology study (EPS) is a test that allows doctors to determine the details of abnormal heartbeats, or arrhythmias.

The study involves placing wire electrodes within the heart to measure electrical activity along the heart's conduction system and within heart muscle cells themselves.

The procedure is done in a hospital laboratory by a trained staff that includes cardiologists, technicians, and nurses. The environment is safe and controlled to minimize any danger or risk to the patient.

A health care provider will clean your groin area and apply a numbing medication (anesthetic). The cardiologist makes a small surgical cut into the groin area and inserts a thin tube (catheter) into a vein. This catheter holds the electrodes, which are connected to special monitors.

The doctor uses moving x-ray images to carefully guide the catheter up into the heart and place the electrodes into the proper areas.

The electrodes detect the heart's electrical activity and map out any irregular heartbeats. This helps the doctor see the type of arrhythmia you have and where the problem starts in your heart. Abnormal electrical activity can occur anywhere along this heart's conduction system. Normally, the heart's electrical signals move through the the two chambers on the top of the heart (the atria), to the atrioventricular (AV) node, and then to the lower chambers of the heart (the ventricles).

Test preparations are similar to those for a cardiac catheterization. Food and fluid will be restricted for 6 - 8 hours before the test. The procedure will take place in a hospital, and you will wear hospital clothing. You must sign a consent form for the procedure.

Your health care provider will give you instructions regarding any changes to your normal medications. Do not stop taking or change any medications without consulting your health care provider.

A mild sedative is usually given 30 minutes before the procedure. You may not be able to drive home yourself if you are discharged the same day.

During the test, you will be awake and able to follow instructions.

A simple EPS generally lasts from 20 minutes to 1 hour. It may take longer if other procedures are involved.

Your doctor may order this test if you have signs of an abnormal heart rhythm (arrhythmia). Information from this study helps your doctor determine the severity of the arrhythmia as well as appropriate treatment. However, before this test is done, your cardiologist will order other, less invasive tests such as ambulatory cardiac monitoring.

An EPS may be done to:

• Pinpoint the location of a known arrhythmia and determine the best therapy
• Determine the severity of the arrhythmia and whether you are at risk for future heart events, especially sudden cardiac death
• See if medicine is controlling an abnormally heart rhythm
• Evaluate the need for a permanent pacemaker or an implantable cardioverter-defibrillator (ICD)

Abnormal results may be due to:

• Sick sinus syndrome
• Wolff-Parkinson-White syndrome
• Ventricular fibrillation and ventricular tachycardia

This list may not be all-inclusive.

The exact location and type of the arrhythmia must be determined so that specific therapy can be applied. The arrhythmia may start from any area of the heart's electrical conduction system.

The procedure is generally very safe. Possible risks include:

• Arrhythmias
• Bleeding
• Blood clots that lead toembolism
• Cardiac tamponade
• Heart attack
• Infection
• Injury to the vein
• Low blood pressure

A catheter ablation may be done during EPS to treat the arrhythmia.

Miller JM. Diagnosis of Cardiac Arrhythmias. In: Libby P, Bonow RO, Mann DL, Zipes DP, eds. Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine, 8th ed. St. Louis, Mo: WB Saunders; 2007: chap. 32.