Electrophysiology Study

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Electrophysiology Study

Test Overview

An electrophysiology study, or EP study, is a test to see if there is a problem with your heartbeat (heart rhythm) and to find out how to fix it.

In this test, the doctor inserts one or more flexible tubes, called catheters, into veins in your groin, arm, or neck. Then he or she threads these catheters into the heart. At the tip of these catheters are electrodes, which are small pieces of metal that conduct electricity. The electrodes collect information about your heart's electrical activity. Your doctor can tell what kind of heart rhythm problems you have and where those problems are.

Sometimes the problem can be fixed at the same time. A procedure called catheter ablation uses the catheters to destroy (ablate) small areas of your heart that are causing the problem.

Why It Is Done

An electrophysiology study is used to:

  • Identify heart rhythm problems.
  • See how well heart rhythm medicines work for you.
  • Check your heart before you have a pacemaker or an ICD (implantable cardioverter-defibrillator) implanted.
  • Treat certain problems with catheter ablation.

How To Prepare

Tell your doctor if you:

  • Are allergic to any medicines, including iodine, or to latex.
  • Have any bleeding problems or take blood-thinning medicine (anticoagulants), including any non-steroidal anti-inflammatory drugs (NSAIDs) like ASA or ibuprofen.
  • Are or might be pregnant.
  • Have diabetes.
  • Have ever had clots in your legs, groin, or pelvis.
  • Have a filter in a large vein to prevent clots from travelling to the heart.

Talk to your doctor about any concerns you have about the need for the test, its risks, how it will be done, or what the results will show. To help you understand the importance of this test, fill out the medical test information form (What is a PDF document?).

If you are taking blood-thinning medicine, your doctor will likely have you stop taking it a few days before the test.

Arrange for someone to take you home after the test. You may not have to stay in the hospital overnight.

Do not eat or drink (except for a small amount of water) for 6 to 12 hours before the test. If you are taking any medicines, ask your doctor if you should take them on the day of the test.

Take off any nail polish. That will make it easier for doctors and nurses to check the circulation in your fingers and toes.

Be sure to empty your bladder completely just before the test.

How It Is Done

Before the test

  • You will be taken to a special room, sometimes called a "cath lab" or "EP lab." You will lie on a flat table under a large X-ray machine.
  • Several small electrodes will be attached to your legs and arms with a special paste or gel. These are connected to an EKG machine that keeps track of the electrical activity of your heart during the test.
  • A device called a pulse oximeter may be clipped to your finger. It measures oxygen levels in your blood and monitors your pulse.
  • An intravenous (IV) needle will be inserted into a vein in one of your arms to give you fluids or medicine during the test. You will receive a medicine to help you relax (sedative) through the IV line. You may be awake during the test. But even if you are awake, the sedative may make you so sleepy that you may not remember much afterward.
  • The area where the doctor plans to insert a catheter will be shaved and cleaned. Sterile towels will be draped over your arm or leg, except for the area over the insertion site.

During the test

  • A local anesthetic is injected into your skin at the insertion site. This is usually in your groin. But sometimes it's in the crease of the elbow or in the side of the neck. When the area is numb, a doctor called a cardiologist inserts the catheter through your skin and into the vein.
  • The doctor slowly pushes the catheter through the vein toward your heart. Usually several catheters are used. The doctor moves the catheters into various places in the heart. An X-ray screen shows the doctor where to move the catheters.
  • The catheters have small electrical conductors, called electrodes, on their ends. The doctor can use the electrodes to do what is called "pacing." This means sending electrical currents through the catheters to try to recreate your heart rhythm problem. This can tell the doctor what kind of problem you have and the best way to treat it. The doctor may also use pacing to see how well medicines work to control your problem.
  • The electrodes also send information to a computer. The computer uses the information to draw pictures of your heart and its rhythm problems. This is called "mapping," because the pictures serve as maps that show the doctor exactly where the problem areas are.
  • A nurse or other assistant will help you stay comfortable and resist the urge to move around. Be careful not to touch the sheets or reach for your groin area, because you could contaminate the sterile areas and increase the risk of infection.
  • Your doctor may let you watch the video monitor so you can see the pictures of your heart.
  • The test takes 1 to 3 hours. Catheter ablation usually takes 2 to 6 hours. In rare cases, it can take longer.

After the test

  • It's important to prevent bleeding after the catheter is pulled out. For example, if the catheter was in your groin, firm pressure will be applied there for about 10 minutes to stop the bleeding. Then a pressure dressing will be placed over the area.
  • You will be taken to an observation room where nurses and others can watch your heart rate, blood pressure, and temperature for a while and check for signs of bleeding. They also watch the pulse, colour, and temperature of the arm or leg in which the catheter was placed.
  • If the catheter was in your leg, you may have to lie in bed with your leg extended for as long as 4 to 12 hours. This allows your blood vessels to heal.
  • If you have an EP study only and you do not need more treatment, you may be able to go home after about 6 hours.
  • If you also have ablation or other treatment, you may stay overnight in the hospital. How long you stay in the hospital depends on the type of ablation you have. Most people can go back to work and their normal routine in 1 or 2 days.

How It Feels

You will feel a sharp sting when the local anesthetic is injected to numb your skin at the catheter insertion site.

When the catheter is inserted, you may feel a brief, sharp pain. The movement of the catheter through your blood vessel may cause a feeling of pressure, but it is not usually considered painful. You may feel your heart skip when the catheter touches the walls of your heart. This is normal.

The temperature in the catheterization lab is kept cool so that the equipment does not overheat. For many people, the hardest part of the test is having to lie still for an hour or longer on the hard table. You may feel some stiffness or cramping.

Don't be afraid to speak up if you're worried about anything during the test. The doctors, nurses, and technicians want to know exactly how you're feeling.

It's especially important to tell the doctor if you have any of these symptoms during or after the test:

  • Chest pain
  • Extreme shortness of breath
  • Dizziness
  • Trouble speaking or swallowing
  • Paralysis in any part of your body

You may have some soreness and bruising at the insertion site. This should disappear in 2 weeks. It is normal for the site to feel tender for about a week. But call your doctor if:

  • Your arm or leg becomes pale, cold, painful, or numb.
  • You have redness, swelling, or discharge from the catheter insertion site.
  • You have a fever.


The risk involved in having an EP study is small. But problems can occur, including:1

  • Puncture of the heart or one of its blood vessels.
  • An abnormal collection of fluid in the space between the heart and the sac that surrounds it (cardiac tamponade).
  • Irregular heartbeats (arrhythmias). In rare cases, an EP study causes an abnormal heart rhythm that won't go away. The abnormal rhythm usually corrects itself or becomes normal after treatment with medicine. In some cases, an electrical shock (electrical cardioversion) may be needed to restore a normal rhythm.
  • Bruising where the catheters are put in.
  • Bleeding around the groin vessels where the catheters are put in (very rare).
  • Blood clots.
  • Infection.
  • Damage to the electrical system of the heart, requiring placement of a pacemaker.
  • Stroke (very rare).
  • Heart attack (very rare).
  • Death (very rare).

The chance of having problems increases if you also have treatment, such as ablation, during this test.

Anytime you are exposed to radiation, including the low levels of X-ray used for this test, there is a chance of damage to cells or tissue. But the risk of this damage is usually very low compared to the possible benefits of the test.


An electrophysiology study will show whether you have an abnormal heartbeat that needs treatment. (Sometimes the treatment is done during the test.)

What Affects the Test

Reasons you may not be able to have the test or why the results may not be helpful include:

  • Extreme anxiety that causes high blood pressure and irregular heartbeats.
  • Kidney or liver failure.
  • Not being able to follow directions during the procedure.
  • Not being able to lie flat.
  • Ongoing bleeding problems or infection.

What To Think About

  • An electrophysiology study can be scary. But it is considered safe and is mostly just uncomfortable. You may find it helpful to talk to your doctor ahead of time about your fears. If you are awake during the test, you can ask questions and let your doctor and others know how you're feeling.
  • This test is not usually done during pregnancy, because it involves X-rays. Radiation could damage the developing fetus.



  1. Miller JM, Zipes DP (2008). Diagnosis of cardiac arrhythmias. In P Libby et al., eds., Braunwald’s Heart Disease: A Textbook of Cardiovascular Medicine, 8th ed., vol. 1, pp. 763–778. Philadelphia: Saunders Elsevier.

Other Works Consulted

  • Akhtar M (2008). Techniques of electrophysiologic evaluation. In V Fuster et al., eds., Hurst's the Heart, 12th ed., pp. 1064–1076. New York: McGraw-Hill Medical.


By Healthwise Staff
Primary Medical Reviewer Martin Gabica, MD - Family Medicine
Primary Medical Reviewer Anne C. Poinier, MD - Internal Medicine
Specialist Medical Reviewer John M. Miller, MD - Electrophysiology
Specialist Medical Reviewer Stephen Fort, MD, MRCP, FRCPC - Interventional Cardiology
Last Revised June 3, 2010

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