The Electrophysiology (EP) Laboratory and EP Procedures

Cardiac electrophysiology is a medical specialty devoted to the diagnosis and treatment of abnormal heart rhythms. Electrophysiologists are fully trained cardiologists who have undertaken additional fellowship training in clinical cardiac electrophysiology. Cardiac electrophysiologists have expertise in the invasive diagnosis and treatment of cardiac arrhythmias. They perform invasive procedures including diagnostic electrophysiology testing, radiofrequency catheter ablation, and implantation of antiarrhythmic devices such as pacemakers and cardioverter-defibrillators.

Which Patients May Benefit From an Electrophysiology Procedure?

In general, electrophysiology studies are performed for specific reasons including:

1. Determine the precise mechanism of a problematic or potentially curable tachyarrhythmia documented by and ECG test or 24-hour ambulatory ECG recording.
2. Perform curative catheter ablation of problematic, medically refractory tachyarrhythmias.
3. Evaluate the need for implantation of a cardioverter-defibrillator in patients with who have a documented, potentially life-threatening, ventricular tachyarrhythmia.
4. Define the risk of having a dangerous arrhythmia in patients with severe underlying heart disease who have ECG documentation of non-sustained ventricular tachycardia or have had syncope.

Because there are some small risks of invasive electrophysiology procedures, they are generally only performed in the case of potentially life-threatening ventricular tachyarrhythmias, or in patients with problematic and medically refractory supraventricular tachyarrhythmias that are significantly affecting the their quality of life.

Performance of Electrophysiology Procedures

Electrophysiology studies are performed in a specialized procedure room called an electrophysiology (EP) laboratory (Figure 1). As seen in this figure, the EP laboratory houses a moveable procedure table and a fluoroscopy (x-ray) machine that is suspended over the table. In addition, there is a large number of special electronic and computer equipment in the laboratory that is used during the electrophysiology (or EP) study. While modern electrophysiology laboratories may look imposing with all the computers and machinery, in reality the primary goal of any EP laboratory is efficient and successful performance of the EP procedure under the safest and most comfortable conditions possible. Patient safety is the first and most important job in the EP laboratory.

Figure 1.  Schematic diagram summarizing components of the electrophysiology (EP) laboratory.

After positioning the patient on the table, specially trained electrophysiology nurses put ECG electrode pads on the patient's chest, shoulders and legs. As a safety precaution, a pair of large defibrillation pads will be placed the patient's back and chest and are connected to an external cardiac defibrillator. The defibrillator is only used to control a "run-away" or dangerous heart rhythm that cannot be controlled by medication or the temporary electrical pacing wires positioned in the patient's heart. It is rare that the defibrillator has to be used during EP studies. If a shock has to be administered it is only delivered after the patient has been put completely to sleep. If the patient has not already had an intravenous line placed in an arm by a nurse before entry into the EP laboratory, the electrophysiology nurses will do so upon the patient's arrival. After insertion of the intravenous line, the nurses will start to administer short-acting sedative drugs that will initially help the patient relax and ultimately let them drift off to sleep from which you can be easily aroused. At all times during your time in the EP laboratory the patient's heart rate, blood pressure, respiration, blood oxygen level, and electrocardiogram are continuously monitored by the nurses and doctors in the room.

The nurses will thoroughly cleanse the patient's right groin region and right neck region with special soap. Sometimes the right neck region must also be used, and it may also be cleansed. The patient is covered with a blue sterile drape to create a sterile field that provides a work area for insertion of the electrode catheter wires and allow performance of the entire study in a sterile fashion. During an electrophysiology procedure, 2-4 temporary electrode catheters (Figure 2) are inserted into multiple heart chambers. The catheters, or wires, are usually inserted into a large vein in the right groin area while the patient lies on the procedure table. For some types of electrophysiology procedures, a catheter may also be inserted in a vein in the right neck region. The electrode catheters are positioned in characteristic locations in the heart (Figure 2). The wires permit electrical stimulation (electrical pacing) of the heart tissue and recording of electrical conduction properties throughout the heart. The patterns of the electrical conduction through the heart are displayed on a computer monitor and recorded on an optical disk (Figure 1).

Figure 2. Example of distal end of an electrode catheter (left panel). Catheters are about 50" long and the electrodes are located near the tip (shown here). These electrodes come in contact with the patient's heart tissue. Some catheters have a fixed curve; others have a capability for producing a variable curve using a hand-held controlling device (not shown). During an EP study, electrode catheters may be positioned in multiple locations in the heart (right panel). However, usually they are positioned in 1) the right atrium, 2) the AV node and His bundle region at the junction between the right atrium and right ventricle, 3) the right ventricular apex and, 4) the coronary sinus and great cardiac vein. The coronary sinus catheter is generally only used in patients with certain types of supraventricular tachycardia. After the completion of the procedure all the catheters are removed.

In order to do this with a minimum of discomfort, the skin overlying these veins must be anesthetized using a local anesthetic injected into the skin using a very tiny needle. The small needle stick and injection of the anesthetic will cause a stinging and burning pain that should resolve within a few moments. After the anesthetic takes effect, the patient may still feel a pressure and pushing sensation as the physician proceeds with the insertion of the catheters, but there should be little or no pain. Once the wires are inserted into the veins through small vein punctures produced using a larger needle, the wires are positioned into the patient's heart in characteristic locations (Figure 3) by advancing them through the veins that are in direct connection with the heart. The x-ray (fluoroscopy) machine overlying the patient is used to guide the positioning of the wires.

After insertion of the wires, the diagnostic portion of the electrophysiology study will begin. This involves electrical pacing of the heart and recording of electrical signals. This may cause the patient to feel their heart beating fast, often mimicking the patient's tachycardia or palpitations. The electrophysiology physicians performing the study analyze these electrical signals to determine the type of supraventricular tachycardia the patient has and the location of the abnormal circuit. A crucial part of the study is to provoke, or induce, the tachycardia, particularly if curative catheter ablation is contemplated. Only by inducing the patient's tachycardia can the physicians locate the abnormal circuit causing the arrhythmia. During the study, the electrophysiologists can generally turn the tachycardia "on and off" easily and painlessly using the wires in the heart. The patient should not feel alarmed if they feel their heart beating fast or irregularly during the procedure because this is a normal part of the study.

Some EP studies are only performed for diagnostic purposes, for example to determine if the patient has ventricular tachycardia. In other patients, an EP study may be performed for both diagnostic and therapeutic purposes. For example, if catheter ablation of supraventricular tachycardia is anticipated, the first part of the test will be the diagnostic portion to localize the ablation target (the arrhythmia circuit or focus), while during the therapeutic portion of the procedure the ablation is performed to eliminate the arrhythmia. Not all arrhythmias can be ablated. While the majority most types of supraventricular can be ablated using radiofrequency energy, only a small minority of patients with ventricular tachycardia can be treated with ablation. In these cases, the EP study is terminated after the diagnostic portion.

The entire procedure (diagnostic and therapeutic portions) generally takes 1-3 hours; however, in very rare cases when the abnormal circuit/focus is difficult to find or reach with the ablation catheter, therapeutic studies may take longer, sometimes many hours. During the procedure the patient remains sedated and critical vital signs are continuously monitored. At the end of the procedure all the catheters and monitoring equipment are removed and the patient is taken to a regular hospital room where monitoring of vital signs and heart rhythm is continued. After an ablation procedure the patient must lay in bed for 4-6 hours with the right leg remaining straight to avoid any bleeding from the puncture sites in the groin. After that time, the patient can begin moving about, and generally is ready to go home that same day assuming no complications. When an ablation procedure is completed late in the day, the patient is kept overnight and discharged home the following morning. If only a diagnostic study was performed, some patients may have to stay in the hospital for further treatment before going home.

What are the Benefits and Risks of Electrophysiology Procedures?

With the guidance of their electrophysiologist or cardiologist, patients should evaluate the benefits and risks of undergoing an electrophysiology procedure given their particular clinical situation. Patients need to weigh the small risks of the procedure against the potential benefits, including the possibility of the catheter ablation cure or diagnosing the risk or presence of a potentially life-threatening tachyarrhythmia. The risks of the radiofrequency catheter ablation procedure are very small, although as with any invasive procedure it is not a risk-free procedure. The most serious reported complications in the medical literature include death, stroke, heart attack, cardiac perforation requiring emergency surgery, heart valve damage, artery damage, lung damage, blood clots, bleeding, or infection are rare. Some patients with supraventricular tachycardia undergoing catheter ablation have a risk of complete heart block requiring implantation of a permanent pacemaker, although in our experience the risk is still low. Complete heart block is generally only a potential risk in the case of ablation performed for AV nodal reentrant tachycardia or AV reciprocating tachycardia with an abnormal electrical circuit located close to the AV node. Patients with the potential for a life-threatening ventricular tachyarrhythmia also must balance the risk of not undergoing the study and not confirming the diagnosis. In these cases, failure to detect the arrhythmia and provide definitive treatment exposes the patient to a much higher risk than undergoing the EP procedure. Therefore, in all cases the cardiac electrophysiologist should discuss the specific risks with each patient given their unique clinical situation.