Electrophysiology study of the heart

Definition

An electrophysiology study (EPS) of the heart is a test performed to analyze the electrical activity of the heart. The test uses cardiac catheters and sophisticated computers to generate electrocardiogram (EKG) tracings and electrical measurements with exquisite precision from within the heart chambers.

Purpose

Heart disease is the leading killer in the United States, accounting for more than 50% of all annual deaths. The normal function of the heart depends on its electrical activity, and the effect of this activity on each of its cells. When a heart is diseased, impaired electical activity is often the factor that leads to sudden death, thus the need for EPS tests.

An EPS can be performed solely for diagnostic purposes or to pinpoint the exact location of electrical signals (cardiac mapping) in conjunction with a therapeutic procedure called catheter ablation (tissue removal). A cardiologist may recommend an EPS when the standard EKG, Holter monitor, event recorder, stress test , echocardiogram, or angiogram cannot provide enough information to evaluate an abnormal heart rhythm (arrhythmia).

An EPS offers more detailed information about the heart's electrical activity than many other noninvasive tests because electrodes are placed directly on heart tissue. This placement allows the electrophysiologist to determine the specific location of an arrhythmia and, often, to correct it during the same procedure. This corrective treatment is considered a permanent cure; in many cases, the patient may not need to take heart medications.

EPS may be helpful in assessing:

• certain tachycardias (fast hearbeats) or bradycardias (slow heartbeats) of unknown cause
• patients who have been resuscitated after experiencing sudden cardiac arrest
• various symptoms of unknown cause, such as chest pain, shortness of breath, fatigue, or syncope (dizziness/fainting)
• response to anti-arrhythmic therapy

Precautions

Pregnant patients should not undergo EPS because the study requires exposure to radiation, which may harm the growing baby. Patients who have coronary artery disease may need to be treated prior to EPS. EPS is contraindicated in patients with an acute myocardial infarction, as the infarct may be extended with rapid pacing. The test is also contraindicated for patients who are uncooperative.

Description

The rhythmic pumping action of the heart, which is essentially a muscle, is the result of electrical impulses traveling throughout the walls of the four heart chambers. These impulses originate in the sinoatrial (SA) node (specialized cells situated in the right atrium, or top right chamber of the heart). Normally, the SA node, acting like a spark plug, spontaneously generates the impulses, which travel through specific pathways throughout the atria to the atrioventricular (AV) node. The AV node is a relay station sending the impulses to more specialized muscle fibers throughout the ventricles (the lower chambers of the heart). If these pathways become damaged or blocked or if extra (abnormal) pathways exist, the heart's rhythm may be altered (too slow, too fast, or irregular), which can seriously affect the heart's pumping ability.

To undergo EPS, the patient is placed on a table in the EPS lab and connected to various monitors. Sterile technique is maintained. A minimum of two catheters are inserted into the right femoral (thigh) vein in the groin area. Depending on the type of arrhythmia, the number of catheters used and their route to the heart may vary. For certain tachycardias, two additional catheters may be inserted in the left groin and one in the internal jugular (neck) vein or in the subclavian (below the clavicle) vein. The catheters are about 0.08 in (2 mm) in diameter, about the size of a spaghetti noodle. The catheters used in catheter ablation are slightly larger.

With the help of fluoroscopy (x rays on a television screen), all catheters are guided to several specific locations in the heart. Typically, four to 10 electrodes are located on the end of the catheters, which have the ability to send electrical signals to stimulate the heart (called pacing) and to receive electrical signals from the heart, but not at the same time (just as a walkie-talkie cannot send and receive messages at the same time).

First, the electrodes are positioned to receive signals from inside the heart chambers, which allows the doctor to measure how fast the electrical impulses travel in the patient's heart at that time. These measurements are called the patient's baseline measurements. Next, the electrodes are positioned to pace. That is, the EPS team tries to induce (sometimes in combination with various heart drugs) the arrhythmia that the patient has previously experienced so the team can observe it in a controlled environment, compare it to the patient's clinical or spontaneous arrhythmia, and decide how to treat it.

Once the arrhythmia is induced and the team determines that it can be treated with catheter ablation, cardiac mapping is performed to locate the precise origin and route of the abnormal pathway. When this is accomplished, the ablating electrode catheter is positioned directly against the abnormal pathway, and high radio-frequency energy is delivered through the electrode to destroy (burn) the tissue in this area.

Pediatric patients present challenges for EPS. In 2001, an analysis of 45 children who underwent EPS was conducted. The researchers concluded that success rates and the prevention of complications in children may be increased by using ultrasound guidance for access to the internal jugular vein for coronary sinus cannulation (insertion of a tube for the transport of fluid) during EPS. Access was successfully obtained in all 45 of the patients without major complications using this technique.

Diagnosis/Preparation

The following preparations are made for an EPS:

• Blood tests usually are ordered one week prior to the test.
• The patient may be advised to stop taking certain medications, especially cardiac medications, that may interfere with the test results.
• The patient fasts for six to eight hours prior to the procedure. Fluids may be permitted until three hours before the test.
• The patient undergoes conscious sedation (awake but relaxed) during the test.
• A local anesthetic is injected at the site of catheter insertion.
• Peripheral pulses are marked with a pen prior to catheterization. This permits rapid assessment of pulses after the procedure.

Aftercare

The patient needs to rest flat in bed for several hours after the procedure to allow healing at the catheter insertion sites. The patient often returns home either the same day or the next day. Someone should drive the patient home. To minimize bleeding and pain, the patient is advised to keep the extremity in which the catheter was placed immobilized and straight for several hours after the test.

Risks

EPS and catheter ablation are considered low-risk procedures. There is a risk of bleeding and/or infection at the site of catheter insertion. Blood clot formation may occur and is minimized with anticoagulant medications administered during the procedure. Vascular injuries causing hemorrhage or thrombophlebitis are possible. Cardiac perforations are also possible. If the right internal jugular vein is accessed, the potential for puncturing the lung with the catheter exists and could lead to a collapsed lung.

Because ventricular tachycardia or fibrillation (lethal arrhythmias) may be induced in the patient, the EPS lab personnel must be prepared to defibrillate the patient as necessary.

Patients should notify their health care provider if they develop any of these symptoms:

• numbness or tingling in the extremities
• heavy bleeding
• change in color and/or temperature of extremities
• loss of function in extremities

Normal results

Normal EPS results show that the heart initiates and conducts electrical impulses within normal limits.

Abnormal results include confirmation of arrhythmias, such as:

• supraventricular tachycardias
• ventricular arrhythmias
• accessory pathways
• bradycardias

Resources

books

grubb, blair p., and brian olshansky. syncope: mechanisms and management. armonk, ny: futura publishing, 1997.

hummel, j. d., s. j. kalbfleisch, and j. m. dillon. pocket guide for cardiac electrophysiology. philadelphia: w. b. saunders co., 1999.

josephson, m. e. clinical cardiac electrophysiology: techniques and interpretations. philadelphia: lippincott williams & wilkins publishers, 2001.

pagana, kathleen d., and timothy j. pagana. diagnostic testing and nursing implications. 5th ed. st. louis: mosby, 1999.

singer, igor. interventional electrophysiology. baltimore: williams & wilkins, 1997.

periodicals

asirvatham, s. j., c. j. bruce, and p. a. friedman. "advances in imaging for cardiac electrophysiology." coronary artery disease 14 (february 2003): 3–13.

binah, o. "cytotoxic lymphocytes and cardiac electrophysiology." journal of molecular and cellular cardiology 34 (september 2002): 1147–1161.

kocic, i. "sudden cardiac death: from molecular biology and cellular electrophysiology to therapy." current opinions in investigative drugs 3 (july 2002): 1045–1050.

liberman, l., a. j. hordof, d. t. hsu, and r. h. pass. "ultrasound-assisted cannulation of the right internal jugular vein during electrophysiologic studies in children." journal of interventional cardiology and electrophysiology 5, no. 2 (june 2001): 177–179.

organizations

american association of critical-care nurses. 101 columbia, aliso viejo, ca 92656-4109. (800) 899–2226. <www.aacn.org/>.

the american college of cardiology heart house, 9111 old georgetown road, bethesda, md 20814-1699. (800) 253–4636 <www.acc.org>.

american heart association. 7272 greenville ave., dallas tx 75231-4596. (800) 242–1793. <www.amhrt.org>.

cardiac arrhythmia research and education foundation (c.a.r.e.). 2082 michelson dr. #301, irvine, ca 92612. (800) 404–9500. <www.longqt.com/>.

cardiac electrophysiology society. <www.cardiaceps.org>.

Maggie Boleyn, R.N., B.S.N. Monique Laberge, Ph. D.

WHO PERFORMS THE PROCEDURE AND WHERE IS IT PERFORMED?

The relatively simple EPS is performed in a special laboratory under controlled clinical circumstances by cardiologists, nurses, and technicians with special training in electrophysiology.

QUESTIONS TO ASK THE DOCTOR

• What is the purpose of the EPS test?
• How do I prepare for cardiac electrophysiology?
• Will it hurt?
• How is the test performed?
• How long will it take?
• Are there any risks involved?

Electrophysiology Study of the Heart

Definition

An electrophysiology (EP) study of the heart is a nonsurgical analysis of the electrical conduction system (normal or abnormal) of the heart. The test employs cardiac catheters and sophisticated computers to generate electrocardiogram (EKG) tracings and electrical measurements with exquisite precision from within the heart chambers.

The EP study can be performed solely for diagnostic purposes. It also is performed to pinpoint the exact location of electrical signals (cardiac mapping) in conjunction with a therapeutic procedure called catheter ablation.

The test is simple, not painful, and performed in a special laboratory under controlled clinical circumstances by cardiologists and nurses who subspecialize in electrophysiology.

Purpose

A cardiologist may recommend an EP study when the standard EKG, Holter monitor, event recorder, stress test, echocardiogram, or angiogram cannot provide enough information to evaluate an abnormal heart rhythm, called an arrhythmia.

An EP study also may be beneficial in diagnosing a suspected arrhythmia in a patient who shows symptoms of an arrhythmia but in whom it could not be detected from other tests.

The purpose and great value of an EP study is that it offers more detailed information to the doctor about the electrical activity in the heart than the aforementioned noninvasive tests because electrodes are placed directly on heart tissue. This allows the electrophysiologist to determine the specific location of an arrhythmia and, oftentimes, correct it during the same procedure. This corrective treatment is permanent and considered a cure, and, in many cases, the patient may not need to take heart medications.

EP studies may be helpful in assessing:

• certain tachycardias or bradycardias of unknown cause
• patients who have been resuscitated after experiencing sudden cardiac death
• various symptoms of unknown cause, such as chest pain, shortness of breath, fatigue, or syncope (dizziness/fainting)
• response to anti-arrhythmic therapy

Precautions

Pregnant patients should not undergo an EP study because of exposure to radiation during the study, which may be harmful to the growing baby.

Patients who have coronary artery disease may need to have that treated before having an EP study.

Description

The rhythmic pumping action of the heart, which is essentially a muscle, is the result of electrical impulses traveling throughout the walls of the four heart chambers. These impulses originate in the sinoatrial (SA) node, which are specialized cells situated in the top right chamber of the heart: the right atrium. Normally, the SA node, acting like a spark plug, spontaneously generates the impulses, which travel through specific pathways throughout the atria to the atrioventricular (AV) node. The AV node is a relay station, sending the impulses to more specialized muscle fibers throughout the bottom chambers of the heart: the ventricles. If these pathways become damaged or blocked or if extra (abnormal) pathways exist, the heart's rhythm may be altered (perhaps too slow, too fast, or irregular), which can seriously affect the heart's pumping ability.

The patient is transported to the x-ray table in the EP lab and connected to various monitors. Sterile sheets are placed over him or her. A minimum of two catheters are inserted into the right femoral (thigh) vein in the groin area. Depending on the type of arrhythmia, the number of catheters used in an EP test and their route to the heart may vary. For certain tachycardias, two more catheters may be inserted in the left groin and one in the internal jugular (neck) vein or in the subclavian (below the clavicle) vein. The catheters are about 0.08 in (2 mm) in diameter, about the size of a spaghetti noodle. The catheters used in catheter ablation are slightly larger.

With the help of fluoroscopy (x rays on a television screen), all the catheters are guided to several specific locations in the heart. Typically, four to 10 electrodes are located on the end of the catheters, which have the ability to send electrical signals to stimulate the heart (called pacing) and to receive electrical signals from the heart-but not at the same time (just as a walkie-talkie cannot send and receive messages at the same time).

First, the electrodes are positioned to receive signals from inside the heart chambers. This allows the doctor to measure how fast the electrical impulses travel currently in the patient's heart. These measurements are called the patient's baseline measurements. Next, the electrodes are positioned to pace: The EP team actually tries to induce (sometimes in combination with various heart drugs) the arrhythmia that the patient has previously experienced so the team can observe it in a controlled environment, compare it to the patient's clinical or spontaneous arrhythmia, and decide how to treat it.

Once the arrhythmia is induced and the team determines it can be treated with catheter ablation, cardiac mapping is performed to locate precisely the origin and route of the abnormal pathway. When this is accomplished, the ablating electrode catheter is positioned directly against the abnormal pathway, and high radio-frequency energy is delivered through the electrode to destroy (burn) the tissue in this area.

Preparation

The following preparations are made for an EP study:

• the patient may be advised to stop taking certain medications, especially heart drugs, that may interfere with the test results.
• blood tests usually are ordered the week before the test.
• the patient undergoes conscious sedation (awake but relaxed) during the test. This is accomplished quite often with the anesthetic drugs VersedR (Roche laboratories) and fentanyl.
• a local anesthetic is injected at the site of catheter insertion.

Aftercare

The patient needs to rest flat in bed for several hours after the procedure to allow healing at the catheter insertion sites.

The patient often returns home either the same day of the test or the next day. Someone should drive him or her home.

The doctor may prescribe drugs and/or insert an AFCD to treat the arrhythmia and may do a possible follow-up EP study.

Risks

The EP diagnostic study and catheter ablation are low-risk procedures. There is a small risk of bleeding and/or infection at the site of catheter insertion, but this occurs less than 1% of the time. Blood clot formation occurs only two in 1,000 instances and is minimized with blood thinner medications administered during the procedure. Vascular injuries causing hemorrhage or thrombophlebitis are possible but occur less than 0.7% of the time. Cardiac perforations occur only in one or two per 1,000 instances. If the right internal jugular vein is accessed, the small possibility of puncturing the lung with the catheter exists, which, at worst, could cause a collapsed lung.

Because ventricular tachycardia or fibrillation (lethal arrhythmias) may be induced in the patient, the EP lab personnel must be prepared to defibrillate the patient as necessary.

Normal results

The heart initiates and conducts electrical impulses normally.

Abnormal results

Confirmation of arrhythmias, such as:

• supraventricular tachycardias
• ventricular arrhythmias
• accessory (extra) pathways
• bradycardias

Resources

ORGANIZATIONS

Cardiac Arrhythmia Research and Education Foundation (C.A.R.E.). 2082 Michelson Dr. #301 Irvine, CA 92612 1-800-404-9500. 〈http://www.longqt.com〉.

Medtronics Manufacturer of Therapeutic Devices. 710 Medtronic Parkway NE, Minneapolis, MN 55432-5604. (800) 328-2518. 〈http://www.medtronic.com〉.

Midwest Heart Specialists. Physician Office Building, 3825 Highland Ave., Tower 2, Ste. 400, Downers Grove, Illinois 60515. (630) 719-4799. 〈http://www.midwestheart.com〉.

United States Catheter Instruments (USCI). 129 Concord Road Billerica, MA 01821. (800) 826-2273.

KEY TERMS

Ablation— Remove or destroy, such as by burning or cutting.

Angiogram— X ray of a blood vessel after special x-ray dye has been injected into it.

Bradycardia— Slow heartbeat.

Cardiac catheter— Long, thin, flexible tube that is threaded into the heart through a blood vessel.

Cardiologist— Doctor who specializes in diagnosing and treating heart diseases.

Echocardiogram— Ultrasound image of the heart.

Electrocardiogram— Tracing of the electrical activity of the heart.

Electrode— Medium for conducting an electrical current-in this case, platinum wires.

Electrophysiology— Study of how electrical signals in the body relate to physiologic function.

Event recorder— A small machine, worn by a patient usually for several days or weeks, that is activated by the patient to record his or her EKG when a symptom is detected.

Fibrillation— Rapid, random contraction (quivering).

Holter monitor— A small machine, worn by a patient usually for 24 hours, that continuously records the patient's EKG during usual daily activity.

Stress test— Recording a patient's EKG during exercise.

Supraventricular tachycardia— A fast heart beat that originates above the ventricles.

Tachycardia— Fast heartbeat.

Vascular— Pertaining to blood vessels.