Overview of Electrophysiologic Testing
In the past 25 years, doctors have been increasingly using a procedure called electrophysiological testing and ablation procedures worldwide. This test, also known as an EPS, is a method doctors use to study the heart’s electrical activity to detect and potentially treat certain heart diseases. Let’s look at what is involved in this procedure and what it can tell us about the condition of your heart.
EPS is a type of test that requires the placement of a small tube, called a catheter, into the right part of your heart. This is done through a vein in your leg, using a method called the Seldinger technique. The purpose of this test is to directly stimulate your heart using two techniques: ‘extra-stimulus pacing’ and ‘incremental pacing.’ Wondering what these weird terms mean? Let’s break it down.
– Extra-stimulus pacing – This involves giving your heart an extra electrical impulse. This test helps to reveal the response and recovery timing of your heart, which could help diagnose certain heart diseases.
– Incremental pacing – Similar to a stress test, this method involves gradually increasing the pace of the electrical impulses given to your heart. The aim is to observe how your heart behaves when put under stress conditions and how quickly it returns to normal function once the stimulation stops.
These techniques can provide valuable information about how your heart is working, potentially helping your doctor to diagnose any issues and decide on the best course of treatment. As with any medical procedure, there might be some risks or complications, but your doctor will discuss these with you in detail before the test.
Anatomy and Physiology of Electrophysiologic Testing
The heart’s structure and important markers that we need to keep in mind for an electrophysiology study (EP) are just as important to understand the signals inside the heart.
The right atrium, which is a critical part of the heart for an electrophysiologist, has several parts – the appendage, the terminal crest, the body, and the vestibule. This part of the heart contains significant parts of the heart’s electric system. The muscle bundle, known as Crista terminalis, positioned between the anteromedial wall of the right atrium in a vertical line to the cavotricuspid isthmus, plays a key role. Different orientations of muscles in the right atrium can cause unusual heart rhythms or arrhythmias.
The sinoatrial node (also known as SN) is a small, crescent-shaped structure at the junction of the right upper chamber (right atrium) with the inferior vena cava, a large vein. The SN, which controls the rate of heartbeats, receives blood flow from the sinus node artery, which can originate from the right (in 55% of people) or left coronary artery (in 45% of people). This node, which doesn’t contract, automatically produces electrical impulses, controlling the heart’s pace.
The electrical signal from the sinoatrial node then moves to the atrioventricular node (AVN). The AVN is a relay spot between the upper and lower regions of the heart and is located just at the apex of the Koch triangle, which is part of the heart muscle. The AVN, which can control the heart rate with 20-60 beats per minute, consists of two pathways – the fast pathway and the slow pathway. These pathways are responsible for regulating the most common form of rapid heart rhythm called atrioventricular nodal reentrant tachycardia (AVNRT), usually triggered by premature heartbeats.
The Koch triangle is a region in the right atrium that includes the atrioventricular node. This area’s size can vary greatly among different people, making it significant during mapping and procedures that destroy tissues causing irregular heart rhythms.
The cavotricuspid isthmus is another essential part of the heart: it lies between the inferior vena cava and the tricuspid valve, the main valve controlling blood flow from the upper right chamber to the lower right chamber of the heart. It is divided into three parts and plays a critical role in maintaining a regular heart rhythm. However, some people might have a U-shaped or recessed cavotricuspid isthmus, which can make treatments to correct irregular heart rhythms trickier. The Eustachian valve, a flap located at the junction between the inferior vena cava and the right atrium, sometimes can be large and may hinder the access of the catheters into the right atrium.
Why do People Need Electrophysiologic Testing
Electrophysiologic testing is a type of heart test that helps doctors understand different heart rhythm problems (also known as arrhythmias). These irregular heartbeats can originate from three main processes, known as “automaticity,” “triggering,” and “reentry “. Most arrhythmias operate on the principle of reentry, meaning it requires a specific route in the heart to continue.
The use of electrophysiologic testing is recommended in certain circumstances:
It helps in diagnosing a condition called Supraventricular tachycardia (SVT), resulting in a fast heart rate and a specific pattern on heart tracings (QRS complex shorter than 120ms). In heart rhythm disorders where the pattern of the heartbeat seen on tracing (QRS complex) is irregular, electrophysiologic testing is used to determine the exact nature of the heartbeat irregularity and to plan for a specific treatment called catheter ablation if needed.
Electrophysiologic testing is also used to identify patients at risk for a sudden cardiac arrest when a specific kind of irregular heartbeat, known as ventricular tachycardia, is spotted. Ventricular tachycardia is a rapid heart rhythm that starts in the lower chambers of the heart. Depending on whether these heart rhythm irregularities are continuous (sustained) or not (non-sustained), the test can be crucial in determining who should get a particular treatment called an implantable cardiover device (ICD).
These tests can also be of value for people with heartbeats that keep changing in shape and size (known as polymorphic VTs). It is usually seen in conditions like a recent heart attack, heart muscle diseases, or genetic conditions that make individuals susceptible to abnormal heart rhythms. While it is not commonly performed for heart attack patients, certain inherited diseases may be exceptions.
When patients experience what’s known as premature ventricular contractions (when additional, abnormal heartbeats begin in one of the lower heart chambers), electrophysiologic testing can help guide the decision for a treatment type called radiofrequency ablation. Lastly, problems with the natural pacemaker of the heart, the sinus node, or other conduction problems in the heart (like a block in the communication path between chambers) may also lead doctors to perform this test.
In all these cases, electrophysiologic testing helps doctors to decide on the most appropriate treatment plan basis the specific heart rhythm disorder present. The goal is to minimize symptoms, prevent complications, and improve the overall quality of life for these patients.
Equipment used for Electrophysiologic Testing
The C-arm is a special medical device that doctors use to get a clear picture of what’s happening inside your body. It’s named this way because it has a C-shaped arm that holds an X-ray source on one side and an X-ray detector on the other. This system is also known as a fluoroscopy system or imaging scanner intensifier. It provides high-quality X-ray images in real-time, which is extremely helpful for the doctor while they are placing and positioning the catheter (tube) during the procedure. It can also adjust to a variety of viewing angles.
The radiographic table is where you will lie during your procedure. It’s an adjustable table, able to move forward and backward, and left and right. These movements aid in the insertion and positioning of the catheter.
Other essential equipment in this type of procedure includes a data acquisition system, a cardiac stimulator, and a radiofrequency energy generator. The data acquisition system gathers and stores data, the cardiac stimulator helps to control heart rhythm, and the radiofrequency energy generator uses radio wave energy to treat certain conditions. Moreover, there are additional devices to monitor your health during the procedure, like an arterial pressure monitor and cuff to check your blood pressure and a pulse-oximeter to measure the oxygen levels in your blood. For emergency situations, an external defibrillator (to restart the heart), resuscitation equipment (a set that includes an intubation kit and emergency drugs), and a temporary external pacemaker are also at hand.
Who is needed to perform Electrophysiologic Testing?
An electrophysiological study (EPS, a test that measures the electrical activity of your heart) needs a skilled team which includes one or two heart electricians (electrophysiologists), a technician, and one or two nurses. The heart electricians handle the heart wires (catheters) while the technician manages the outside device that sends electrical signals (stimulator), the system that collects data, and the device that uses heat to destroy problematic heart tissue (ablation generator). The nurse is in charge of preparing the patient, checking the patient’s blood pressure and heart rate (hemodynamic status) and keeping an eye on their oxygen levels using a special device called a pulse oximeter. The nurse also gives medication and oxygen as needed.
Preparing for Electrophysiologic Testing
The Electrophysiology Study (EPS) is a procedure that doctors use to help diagnose heart rhythm problems. Before doing an EPS, it’s important for patients to stop taking certain medicines known as antiarrhythmic drugs for a while. This ensures that the procedure provides accurate results. Doctors usually instruct patients to stop taking these medications for at least five half-lives, a term that refers to the time it takes for half of the drug to be eliminated from the body.
Also, patients are typically asked to not eat or drink for at least six hours before the procedure. Patients who are on anticoagulation therapy, which is medication that prevents blood clots, may also need to stop this treatment before the procedure. Those taking medicine for low blood sugar should adjust their routine because of this fasting period.
Medical professionals will also need to establish one or two routes into your veins before you get to the Electrophysiology (EP) lab for the procedure. Once you are in the lab, they will prepare you for the procedure by attaching electrocardiogram (ECG) electrodes to you. An ECG is a simple test that checks for problems with the electrical activity of your heart. They will use a cuff on your arm to monitor your blood pressure and will attach a small device called a pulse-oximeter to check your oxygen levels throughout the procedure.
The ECG takes readings from 12 different angles, giving doctors a detailed understanding of how your heart is functioning. Similarly, during the procedure, special tools called catheters are used to gather information directly from inside the heart, including the location, timing, and voltage of the heart’s electrical signals. By doing this, doctors can get a better understanding of what might be causing your heart rhythm problems.
How is Electrophysiologic Testing performed
Electrophysiologic study, often simply referred to as EPS, is a test that doctors use to understand and map the electrical activity within your heart. Here’s a simplified explanation of how it works.
To perform the standard EPS, usually four catheters are needed, although some doctors might use only three. These catheters have electrodes attached to them, and it’s through these electrodes that the electrical activity of your heart gets recorded.
These electrodes pick up electrical signals from different parts of the heart. These include the upper right chamber of your heart (the right atrium), a spot in the heart called the His bundle, the tip of the right lower chamber of your heart (the right ventricle), and a vein in the heart called the coronary sinus. The last one is quite crucial because it allows the doctor to record signals from both the left upper and lower chambers of your heart (the left atrium and left ventricle).
The results of this recording are shown as electrograms, which are essentially graphs of the electrical activity of your heart. There are several things that the doctor can measure from these electrograms, including:
– PA: The time it takes for the electrical signals to travel from the area of the sinus node (the area that usually starts each heartbeat) to the atrioventricular node (the area that helps regulate heartbeats). Normally, this is around 25 to 55 milliseconds.
– AH: The time it takes for the signals to go through the atrioventricular node, usually between 55 and 125 milliseconds.
– H: This is the length of time that the His bundle signal should last, usually less than 30 milliseconds.
– HV: This measures the time it takes for signals to travel through the ventricular system, the lower part of your heart. Normally, this is around 35 to 55 milliseconds.
The doctor also measures something called the sinus node recovery time or SNRT. This is how long it takes for your regular heartbeat to return after the doctor artificially stimulates your atrium (upper chamber of your heart) for 30 seconds at varying speeds. This value should ideally be less than 1500 milliseconds.
There is also a technique called atrial extra-stimulus testing, which helps the doctor test how well the AV node conducts signals, helps measure the refractory period of the atrium, and helps to trigger specific irregular heart rhythms.
A similar technique is used for the lower chambers of your heart, known as ventricular extra-stimulus testing. This helps doctors understand how signals travel back through the AV node, helps identify any extra pathways (which could cause irregular heart rhythms), checks the refractory period of the ventricles, and helps to trigger certain specific irregular heart rhythms.
The doctor will also use a method called incremental atrial pacing, where the signals in the upper chamber of your heart are artificially stimulated at a progressively faster rate. One of the important observations during this procedure is something called the Wenkebach cycle length – this is the fastest cycle at which the 1:1 conduction over the AV node stops. This procedure is repeated in a similar way for the lower chambers of your heart, known as incremental ventricular pacing.
If a doctor suspects there may be extra, or accessory, pathways in the heart that could be causing irregular heartbeat, pacing may be performed from other sites as well. Sometimes, medications such as isoproterenol and atropine may be used during the EPS to help trigger an irregular heartbeat.
Overall, these tests give your doctor a detailed look at the electrical functioning of your heart and can help identify what may be causing any heart rhythm problems you’re experiencing.
