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Diagnostic EP
Record Information
Start with Surface
QRS - regular or irregular
Can you identify clear P waves
P to R Ratio - 1:1 or not?
Location of P wave to QRS - before, after???
P wave morphology - where is it coming from?
Correlate with intracardiac A
Intracardiac activation sequence
Table showing arrhythmia analysis steps
Start with normal, you must always be able to recognize sinus
So now you know that an EP study is an examination that focusses on the electrical conduction system of the heart. One of the first questions that may come to mind is "Why would we do an EP study?".
The patient's you see in the EP lab will present with a wide variety of indications. They may have had a history of palpitations in the chest, dizziness or light headed moments. Some have even passed out completely. This is called syncope. Still other patients have had documented episodes of a very fast heart rate. All these things may be caused by problems with the hearts electrical system.
Sometimes the heart rate goes to slow. This may occur when there is a block in the system that conducts the electrical signal through the heart. It may also be due to the fact that the heart is not generating enough signals each minute to circulate the amount of blood the body needs. Either way, the heart rate is to slow and the body does not get the amount of oxygen it needs. The result is that you feel tired, light headed or dizzy, and you may even pass out. During an EP study, we look for blocks in the conduction system and test how well the heart generates its own electrical signals.
The most common reason we see patients in the EP lab is due to the heart rate going to fast. The medical term for this is "tachycardia" and it can be caused by a number of different reasons. Sometimes the heart produces way more signals than it needs. This build up of extra signals is called an "automatic" tachycardia. Another type of tachycardia occurs when an electrical signal in the heart gets caught in a loop. This is known as a "reentry" tachycardia and is one of the major reasons patients are sent to the lab.
When a tachycardia occurs in the top part of the heart it is called "supraventricular tachycardia", or SVT. This type of heart rhtyhm is uncomfortable and may require medications given in the Emergency Department to resolve it. A tachycardia that occurs in the lower part of the heart, is labeled "ventricular tachycardia", or V-tach. This is much more dangerous than SVT. V-tach can cause a patient's blood pressure to drop quickly and can lead to a situation where the heart rate is sending out so many signals the heart muscle can not respond. In effect, it stops pumping blood. This rhythm is called ventricular fibrillation, or V-fib, and often is the cause of a sudden death episode.
During an EP study, we will try to locate areas where electrical problems may develop. We may find an area where the signal does get caught in a loop, or find a group of cells that is sending out a lot of extra signals. When we locate a source that may be causing problems, we evaluate the best way to take care of it. This information helps your doctor decided what is the best treatment for the patient.
Performing an EP Study >
To perform an electrophysiology study, there are two things we must be able to do. First, we need to be able to record the electrical signal as it passes through the heart muscle. Second, we must be able to stimulate the heart to see how it performs under specific conditions. Both these tasks are accomplished using catheters designed specifically for these purposes.
For the average EP study, a catheter is placed in one of the upper chambers of the heart. This chamber is called the right atrium. A second catheter is placed in the center of the heart just under the atrial ventricular node. The AV node is where the electrical signal of the heart usually passes from the top of the heart, (the atria), to the bottom of the heart, (the ventricles). A third catheter is also placed in the right ventricle. The ventricles are usually larger than the atria and are responsible for pumping most of the blood that is circulated through the body. Each of the catheters that we place in the heart have a number of metal electrodes that can be setup to record an electrical signal as it passes by them, or to deliver a signal on command from a device we call the stimulator.
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Catheter placement to RA, His,
Coronary Sinus and RVA |
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Fluoro Image showing catheters placed in Rt Atrium, His, RVA |
Images courtesy of St Jude Medical |
Once the catheters are in place, we record the normal signal and measure the time it takes for the signals to pass through the various areas of the heart. This gives us baseline intervals that we can compare to the signals we will record when we stimulate the heart. After this, we perform a number of tests using the stimulator to force the heart to beat at certain speeds. The specific tests performed will often be determined by the type of problem a patient has.
One of the first tests we do allows us to check the response of the sinus node. This is the heart's natural control center. Most of the time, the sinus node determines how fast the heart will beat. There are times, however, when the sinus node does not produce enough signals. This can cause the heart rate to be to slow, even when the person is physically active and need a faster heart rate.
After we have tested the sinus node, we try to determine how well the AV node carries the signal from the top of the heart to the bottom. In some patients, the sinus node produces enough signals only to have some of them blocked before they reach the ventricles. These blocks can often occur just below the AV node. Testing how well the AV node functions under stress can also indicate if there is a problem with the tissue inside the node itself. Diseased tissue will often prevent a signal from passing through the node when the heart rate elevates even a little above normal. We also check to see if there is more than one pathway for the electrical signal to pass through the center of the heart. If the AV node contains two pathways, the electrical signal could get caught in a loop. This causes one of the most frequent forms of tachycardia that we see in the lab.
When we have finished testing how the AV node responds, we then try to determine if there is an alternate route that the normal electrical signal may be taking that bypasses the AV node entirely. Some people are born with extra sets of cells that allow the signal to quickly pass from the atria to the ventricles without passing through the AV node. These extra sets of cells are called accessory pathways. There presence indicates another situation where a "loop" may develop causing the heart rate to accelerate to very rapid levels.
After we have finished testing the upper areas of the heart, we will then move on to test the right ventricle. During the tests in the lower portion of the heart, we are looking to see if the signal passes backwards, or retrograde, through the AV node or an accessory pathway, back up to the top of the heart. More importantly, we are looking to see if the patient may have some form of ventricular tachycardia. V-Tach can be caused by an automatic focus in the ventricle or by a reentry mechanism that involves only the lower portions of the heart.
Many times, when we are looking for tachycardias, normal stimulation will not be sufficient to trigger the rapid heart rate. If we complete a full range of testing and have not found the cause of a patient's problem, we will often administer a drug called Isuprel. Isuprel is an overall cardiac stimulant that increases the speed at which the electrical signal travels through the heart. Often, testing the various areas of the heart after giving the patient Isuprel, will be enough to trigger the patient's tachycardia and help us pinpoint where it is coming from.
After
Once the EP study is finished, the physician will decide what is the best course of treatment for the patient. Some of the possible choices are listed below.
Nothing: There are times when we do extensive testing and find there is no evidence of any problems with the electrical system of the heart. This may indicate that the patient experienced an isolated incident that should not reoccur. The original event may have been due to chemical imbalances in the blood chemistry that have since been corrected. It is also possible that there is an alternate cause that can not be identified, but is not due to abnormalities in the conduction system of the heart. Many patients feel frustrated when they are told that there is nothing wrong. They know that something happened, and it may be difficult not knowing the cause.
Medications: In some cases, the physician may recommend medications to control a patients heart rate. Usually, medications are not given alone, but in combination with some of the other therapies. An example of this would be the physician prescribing amiodarone to a patient that also receives and ICD. (See below)
Permanent Pacemaker Implant: If a block is found in the conduction system, or if the heart is not generating enough signals to provide an adequate blood supply, the doctor may recommend a permanent pacemaker implant. The pacemaker is a small electronic device that monitors the electrical activity in the patient's heart. If the heart does not produce enough signals, the pacemaker will provide a signal to stimulate the heart muscle.
ICD Implant: The ICD, or implantable cardiac defibrillator, is another electronic device that is designed to help keep the electrical signals in the heart under control. Most ICD's act in the same way as a pacemaker does, but they go one step farther. When the heart rate goes too fast, the ICD will provide therapy to slow the heart rate down. It does this using one of two methods. It may try to block the fast rhythm by sending electrical signals faster than the heart is generating them, and then suddenly stopping. This is called overdrive pacing and is often effective in stopping a rapid heart rate. The other therapy the ICD may deliver is an electrical shock. This shock "resets" the electrical signals in the heart and gives the normal signals a chance to take over again.
Ablation: One of the most common therapies a patient may receive after an EP study is radio frequency ablation. RF ablation is a very effective therapy for many types of tachycardias. As described previously, a reentry tachycardia occurs when the heart's electrical signal gets caught in a loop. Ablation can be used to create a "permanent break" in the loop that will prevent the problem from occurring again. Automatic tachycardias are fast heart rates that occur when an irritable portion of the heart sends out repeated signals at an accelerated rate. Ablation may also be successful in eliminating the irritable area and thus eliminate the rapid heart rate. Overall, ablation is the primary therapy used in electrophysiology labs.
Procedure Steps>
Hopefully, by now, you have some idea of what you might find when you bring your patient into the lab. If not, you will want to go with your basic setup. You don't have a basic setup you say??? Well, now is a good time to come up with one.
Every electrophysiologist has a standard setup that he will start with if there is little or no information to guide him. The equipment he uses will be the basis for your basic setup. In our lab, the basic setup utilizes two catheters, one 5 french CRD2 catheter for this HIS and a 6F josephson quadrapolar catheter for the RA. The RA catheter will be repositioned into the RV apex and RV outflow track as needed. We use a sterile cath lab pack that contains all the basic equipment like towels, 4x4's, basins, patient drape, gowns, and equipment covers. To this, we add gloves, a cook needle, a 5F and 6F introducer, the two catheters and corresponding cables.
The patient is brought into the lab and a patient interview is conducted while we set up if this has not already occurred. Once the patient is on the table, they will be hooked up to the twelve lead connection from the monitoring system. A single defibrillator is used with pads placed in the #1 position. (See Equipment/Defibrillators). The leads we use for both the defib pads and electrocardiograms are radio opaque so they do not show under fluoro.
The patient's right and left groin are prepped and the patient is draped. In standard Cath Lab procedures, there may be standing orders from specific physicians for patient sedation. We will usually hold sedation until the physician requests that it be given. Sedation may make it difficult to reproduce the patient's arrhythmia, so it is given only when the physician specifically requests it. Note that there will be patients that come into the lab in an extreme state of anxiety. They may be afraid almost to the point of panicking. If this happens, notify the physician immediately. Often times these patients are so keyed up that nothing you say will register with them and sedation may be the only way to get them through the procedure.
Once the patient is draped, the scrub person will hand off the end of the EP cables that connect to the junction box to the monitor tech. Now the real fun begins. Just exactly how do you hook this thing up so that it makes sense on the monitor? This is the most highly guarded secret in electrophysiology!! Actually, no one is really sure how to do this, so we just tell everyone it's a secret. OK, that's not it either! We obviously do know or we couldn't do EP. It's just a little complicated, so we try not to think about it too much. However, since this is an educational web page about electrophysiology, it would be a good idea to include this information. There is a fair amount of detail involved with this, so I have included it under the "Connecting the Cables". (Clever name for that section, don't you think!!)
Once you are hooked up and ready to go, all you have to do is wait for the physician. Maybe I have been lucky, but I have found that the EP docs I have worked with seem to be on time far more frequently that the interventional docs. How is it in your lab? Anyway, the sections above describe the basic setup we use in our lab. This setup works for a large percentage of the cases we do. We will, however, modify this setup depending on the patients diagnosis as follows;
Indications that the patient may have VT: We add a second defibrillator. Catheters are unchanged.
Indications of AVRT: We prep the neck and add a 6F coronary sinus catheter. The CS catheter is most easily placed by accessing the internal jugular vein, usually on the right side, and advancing the catheter down the SVC. Some physicians will use the subclavian vein for a CS catheter.
Indications of atrial flutter: We add a 7F 20 pole catheter for mapping the flutter.
Known left sided pathway: We will have ready, but don't open all the transseptal equipment. This includes pressure lines, brockenbrough sheath and needle, specialty sheath(s), ICE catheter and ultrasound unit and pericardiocentesis tray. We may not use all of this, but if we know that we will be ablating a left sided pathway, we like to have this equipment available.
Note that having a prepackaged tray for pericardial taps is a very good idea. These kits have everything you need to do an emergency tap, and it saves time having it all packaged together. When you need to use one of these kits, it is usually a very urgent situation and every second counts. In accordance with this, you should familiarize yourself with everything you may need if this situation arises. If your physician uses current of injury, make sure you know how to hook the tap needle wire to your monitoring system. In the middle of a lab emergency is not the time to learn how to do this.
If you have any questions about the EP Lab, Let us know. 