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EP Fundamentals - Arrhythmia Analysis

Arrythmia Analysis

Arrhythmia Analysis


          Arrhythmia analysis is a key skill for working in the EP lab. Even if you knew nothing about electrophysiology, understanding the process of analysis applied to recording of electrograms will provide a strong set of skills for anyone who works in the lab.

          The ability to apply arrhythmia analysis is nothing more than understanding a set of tools that use a logical approach of systematic review of the information specific to the rhythm being analyzed. This approach uses a combination of pattern recognition intermixed with a basic knowledge of how the heart functions under normal conditions. With these simple tools, it is possible to develop a strong argument regarding the nature and origin of most arrhythmias.

          One of the best methods of learning to use a new set of tools is to apply them to something you are more familiar with. For electrophysiology, which is devoted to understanding abnormal cardiac rhythms, the best method of practice is to start using our analysis techniques on what we already know, and that is normal sinus rhythm.


        Let us start the analysis process by reviewing the combination of intracardiac and surface electrograms that we encountered in the previous pages. If we think back to those sections, we can recall the information on the Surface ECG's and Intracardiac EGM pages. When looking at sets of combined information, we should always start with the surface first.

Surface ECG

          The process of interpreting surface electrocardiograms was discussed previously. For purposes of arrhythmia analysis, the proper lead selection is important. In the image above, recorded during on of my earlier cases, leads II, AVF and V1 are shown. This selection is not ideal and does not provide the level of information that could be obtained from a more appropriate setup.

          In the lab, the standard set up should be Lead I, AVF and V1. Lead I is used to assess right to left activation. AVF is used to analyze the vertical axis and shows high to low activation. V1 will show how the bundles activate. This combination provides the user with a substantial amount of information from the surface leads alone.

          The first of the two beats shown in the example above is a sinus beat. The P wave shows high to low activation of the atria in leads II and AVF. Lead I would show right to left activation as the sinus node is located on the lateral wall of the right atrium. Normal depolarization in the atria travels from the lateral wall of the right atrium across to the lateral wall of the left atrium.

          The ventricular activation shows activation exiting the bundles in the papillary muscles near the base (initial positive deflection) followed by the depolarization moving from the apex to the base (negative deflection). V1 shows normal bundle activation. If a right bundle were present, the QRS morphology would be predominately upright and wider. A left bundle would be fully negative and wider.

          Now let us examine the PVC that occurs just after the sinus beat. The morphology of this beat suggests a strong low to high activation pattern as indicated by the completely negative deflection in the inferior leads II and AVF. This indicates that the signal is moving away from the positive electrode which is located below the heart. V1 is showing a right bundle configuration indicating that this PVC originates in the right ventricle. Lead I would also show a primarily positive deflection.

Intracardiac EGM's

Activation Sequence

The electrodes used to record intracardiac electrograms are closer to the onset of depolarization. This tells us that the intracardiac electrogram should precede the surface electrocardiogram, usually by around 30ms. This knowledge provides us with a valuable tool that we will use to determine if we are close to the origin of the rhythm being analyzed. It also involves the basic tool that is used with bipolar intracardiac electrograms to determine the nature of abnormal rhythms. This tool is known as activation sequence.

Activation sequence is nothing more than looking at what happens first and what sequence follows the initial event. The process of placing catheters in known locations throughout the heart and evaluating the sequence in which events recorded off the electrodes from these catheters occur has been the basis of conventional EP for over 40 years.

Catheter Placement

The key to activation sequence is catheter placement. Knowing where each catheter is located allows the EP practitioner to accurately determine which regions of the heart depolarize in what order. It was this function of recording electrograms that lead to the standard catheter positions used today. Most diagnostic electrophysiology studies use a four catheter set up. The types of catheters and the location where they are placed are listed below;

High Right Atrium (near the sinus node): Quadrapolar (4 electrode) catheter
HIS Bundle: Quadrapolar catheter
Coronary Sinus: Decapolar catheter
RV Apex: Quadrapolar catheter

The image below shows representations of these catheter positions.

Activation Sequence - Complex Case

The next example we are going to look at is a complex case involving an atrial flutter.


        In this case, we see three catheters, a 20 pole duo-deca catheter in the right atrium, a quadrapolar HIS catheter positioned through the tricuspid valve and a decapolar coronary sinus catheter.

        Each of the recording pairs has been labeled to make the process of mapping the activation sequence easier. Keep in mind the the CS catheter is used to look at left atrial activation. The duo-deca will show us right atrial activation and the HIS catheter should represent the area between the chambers.

        In some instances, the coronary sinus catheter may be positioned in a manner so that the proximal recording pair (CS9-10) is located in the right atrium. The fluoro image here demonstrates that this is not the case. The CS catheter is advanced well out in the coronary sinus.




         Intracardiac is closer to the onset of depolarization. This tells us that the intracardiac electrogram should precede the surface electrocardiogram. If we think about normal sinus rhythm, we know that the sinus node is located in the right atrium near the RA / SVC junction on the posterior aspect of the lateral wall. The high right atrial (HRA) catheter is placed in this region, so we should expect to see activation occur on one of the HRA electrodes first. Analysis of the recording above demonstrates this to be true.  We should also look to see that the electrgram from the intracardiac recording occurs before the onset of the corresponding surface electrocardiogram.  The IC A wave precedes the surface P wave on this waveform, but not by a great amount. If we mapped the earliest activation of the sinus node it should precede onset of surface activation by around 20-30ms.
           Note that there are two electrograms that are being recorded from the HRA catheter. There is the proximal pair and the distal pair. The recording that comes first will be determined by the orientation of the high right atrial catheter. Because the position of these catheters is determined by how the physician places them as well as their orientation to the specific patient's sinus node, either electrogram could be the earliest signal.  Note that in this recording, it is the electrogram from the proximal pair of electrodes that comes first. By examining the location of this catheter, you could determine the approximate location of the sinus node by visualizing where the proximal recoding electrodes were located. The physician may even try to "bracket" the node by moving the HRA catheter around until the distal electrogram becomes earlier than the proximal recording.  At the moment when this happens, the physician knows that the sinus node is now closer to the distal pair.  The location where that happens is noted or labeled for future reference.

          His catheter

           Coronary Sinus

          First V in RV apex catheter at apex and last V at His as contraction occurs from the apex back towards the base to maximize blood flow out of the chamber.

(Add in later example of epicardial activation where surface onset occurs before intracardiac)

          Now let's examine the electrograms from the second beat in this recording.  As we discussed in the introduction to intracardiac section, the RVA distal electrogram is first indicating that this catheter is closest to the onset.  Again, we could move this catheter around and try to find an earlier signal, but for now we know that this beat originates somewhere near the right ventricular apex.  If we know nothing more than that, we can be certain that this beat is a PVC (premature ventricual contraction).

          Note that many electrophysiologists use the phrase premature ventricual depolarization to denote the electrical activity.  This differentiation points out the fact that observation of the electrical activity does not always proove the corresponding mechanical activity has occurred. (Electrical mechanical dissociation)




Let’s start by looking at SR. On the surface (what we originally saw – Einthoven)
1. P wave – atrial activation
2. QRS – ventricular depolarization
3. T Wave – ventricular repolarization

A comes before V so on surface the order we see is p, qrs, t.

1. P becomes A = atrial activation
2. QRS becomes V = ventricular activation
3. In between A & V we find the HIS which has A h and V
4. The CS has A and V which shows LA & LV activation septal to lateral.

Intracardiac is closer to the origin, so we will see these signals first

Show standard surface + IC recording
Activation sequence in normal sinus. Activation sequence is the key to bipolar arrhythmia analysis.
We know what should come first normally.
Now look at abnormal – IC recordings of PVC without surface: where is the origin of the beat, which comes first?
Now add surface to confirm.
Now do atrial tach ic then with surface
Now do left APW ic and surface
Now do VT ic and then surface or with surface

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? See EGM Interpretation

Correlate with intracardiac A

Intracardiac activation sequence

Table showing arrhythmia analysis steps

Start with normal, you must always be able to recognize sinus




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.

Catheter placement to RA, His,
Coronary Sinus and RVA

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.


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.

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