Patients Guide to Electrophysiology 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:
Determine the precise mechanism of a problematic or potentially curable tachyarrhythmia documented by and ECG test or 24-hour ambulatory ECG recording.
Perform curative catheter ablation of problematic, medically refractory tachyarrhythmias.
Evaluate the need for implantation of a cardioverter-defibrillator in patients with who have a documented, potentially life-threatening, ventricular tachyarrhythmia.
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 patients quality of life.
Performance of Electrophysiology Procedures
Electrophysiology studies are performed in a specialized procedure room called an electrophysiology (EP) laboratory. 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.
After positioning the patient on the table, specially trained electrophysiology nurses put ECG electrode pads on the patients chest, shoulders and legs. As a safety precaution, a pair of large defibrillation pads will be placed the patients 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 patients 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 patients arrival. After insertion of the intravenous line, the anaesthesiologist 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 patients 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 patients 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 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. 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. (http://www.emedicine.com/med/topic3578.htm)
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. Sometime the small needle stick and injection of the anesthetic will cause a stinging and burning pain that should resolve within a few moments. Once the wires are inserted into the veins through small vein punctures produced using a larger needle, the wires are positioned into the patients heart in characteristic locations in the heart. 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.
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. 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 patients 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.
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.
Web Resources
HeartCenter Online website. Available at: http://www.heartcenteronline.com
Accessed November 22, 2004
North American Society of Pacing and Electrophysiology
http://www.hrspatients.org/patients/heart_tests/electrophysiology_study.asp
Accessed on November 22, 2004
Radiofrequency Catheter Ablation
Until the late 1980s or early 1990s, the only practical treatment option for most abnormal tachycardias was medication. While it is true that rare patients with severe and medically refractory forms of tachycardia were treated with open-heart surgery or high energy direct current internal ablations, for the vast majority of patients with cardiac arrhyhtmias medication was the only realistic choice. Radiofrequency (RF) catheter ablation is an invasive procedure developed in 1990 that, unlike trteatment using medication, offers the opportunity to cure many types of cardiac arrhythmias. The following tachyarrhythmias may be amenable to cure using RF catheter ablation:
- AV nodal reentrant tachycardia
- AV reciprocating tachycardia (WPW syndrome)
- Many, but not all, forms of atrial tachycardia and atrial flutter
- Selected patients with paroxysmal atrial fibrillation
- Some varieties of atypical ventricular tachycardia
The success rate for cure varies. In general, AV nodal reentrant tachycardia and AV reciprocating tachycardia have the highest success rates, although some forms of atrial flutter, atrial tachycardia, and atypical ventricular tachycardia may also have high cure rates.
The principle behind catheter ablation is simple. Elimination of an arrhythmia can be achieved by destroying a small, but critical, patch of heart tissue responsible for causing the arrhythmia. Controlled destruction of the target cardiac tissue is accomplished using radiofrequency energy. RF energy is similar to microwave energy or electrocautery used during surgery. Just as microwave energy can heat food in a microwave oven, precisely directed RF energy delivered through the small tip of a temporary intracardiac electrode catheter can “heat-up” and destroy a tiny patch of cardiac tissue critical to the initiation or maintenance of a tachyarrhythmia. The three factors that tend to limit the success of the RF catheter ablation technique are 1) inability to localize (or “map”) the arrhythmia, 2) inability to position the tip of the catheter at the critical target site of the arrhythmia and, 3) inability to deliver adequate RF energy and heating at the critical target site.
To perform a catheter ablation procedure temporary electrode catheters must be placed inside the heart through veins and arteries, 2) a diagnostic analysis (electrophysiology study also known as EP study is then performed to define the mechanism of the arrhythmia and localize the critical target tissue that must be destroyed and, 3) perform the actual ablation procedure during which the tip of the ablation catheter is positioned at the critical target tissue and adequate RF energy is delivered to destroy the critical patch of tissue. For details this website provides good patient education booklets.