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.
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:
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.
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.
The following preparations are made for an EPS:
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.
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:
Normal EPS results show that the heart initiates and conducts electrical impulses within normal limits.
Abnormal results include confirmation of arrhythmias, such as:
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Maggie Boleyn, R.N., B.S.N. Monique Laberge, Ph. D.
The relatively simple EPS is performed in a special laboratory under controlled clinical circumstances by cardiologists, nurses, and technicians with special training in electrophysiology.