Overview of Electrophysiologic Study Interpretation
In recent years, the study of heart electrical activity, known as electrophysiology, has become a vital part of heart health research. Through thorough studies called electrophysiologic studies (EPS), scientists have learned more about heart rhythm disorders, leading to the creation of effective treatment methods. An EPS is used to record signals within the heart that can’t be seen on a surface heart monitor (ECG). This involves measuring their timing and seeing how they relate to the ECG signals recorded at the same time. Still, many younger heart doctors find reading these recordings complicated and confusing.
In this summary, we’ll briefly explain the primary findings of an EPS. Additionally, we’ll discuss how understanding these EPS results aids in diagnosing and treating common heart rhythm disorders.
Anatomy and Physiology of Electrophysiologic Study Interpretation
The EPS, or electrophysiology study, begins with placing special types of catheters inside the heart to collect electrical signals from the heart. These signals are then amplified, cleaned up, changed into a digital format, and finally, displayed along with a regular ECG, or heart recording. The recording of the heart’s electrical activity (referred to as electrograms, or EGMs) is mainly divided into two types: “unipolar” and “bipolar.”
A unipolar signal measures the voltage difference between an intracardiac (inside the heart’s chambers) catheter tip and an extracardiac (outside the chambers of the heart) electrode. These are generally found in the inferior vena cava, the main vein that carries deoxygenated blood from the lower half of the body back to the heart. In contrary, bipolar signals are the electrical activities recorded from one pair of electrodes located in close proximity (2 to 3 mm apart) inside the heart.
Bipolar recordings are mainly used in an EPS because they are less likely to pick up signals coming from far away areas. But unipolar recordings are helpful when doctors need pinpoint the exact location of an abnormal rhythm or arrhythmogenic focus inside the heart. This is because a unipolar electrode records only one single electrical impulse that passes through the point of contact with the heart tissue. A bipolar electrode, on the other hand, displays the culmination of two recordings, each from the proximal (close) and the distal (far) pole of the pair of electrodes.
In a standard EPS, the EGMs usually come from catheters placed in the following parts of the heart: the high right atrium near the sinus node (the heart’s natural pacemaker), the area around the His-bundle (part of the heart’s electrical system), the coronary sinus (a collection of veins joined together to form a large vessel that collects blood from the heart muscle), and the apex of the right ventricle (the lower right chamber of the heart).
The most common way to display the readings usually follows the pattern of a normal heart rhythm. This sequence includes two or three ECG leads (usually I, III and V1), readings from the high right atrium, His distal, His proximal, coronary sinus and right ventricle.
Why do People Need Electrophysiologic Study Interpretation
Doctors carry out a heart test called an electrophysiological study (EPS) to assess different heart problems. This test is often done in conjunction with other non-invasive techniques, meaning those that don’t require a surgical procedure.
This study provides important information in figuring out or predicting heart disorders, including:
- Sinus node dysfunction: which is when the heart’s natural pacemaker isn’t working properly
- Atrioventricular (AV) conduction abnormalities: this is when the electrical signals between the upper and lower chambers of the heart aren’t transmitted properly
- Supraventricular tachyarrhythmias (SVTs): which are abnormally fast heart rhythms starting from the top chambers of the heart
- Ventricular tachyarrhythmias (VT): this is when heartbeats are too fast, starting from the lower chambers of the heart
- Outcome of an ablation procedure: Ablation is a procedure to scar or destroy tissue in your heart to block abnormal electrical signals, EPS is used to check its effectiveness
In simpler terms, doctors use EPS to understand better what’s causing your heart to behave irregularly and how to treat it.
When a Person Should Avoid Electrophysiologic Study Interpretation
There are some situations where it’s not safe for a person to have an EPS, or an electrophysiology study. This is a test that checks the electrical signals in your heart to find out what’s causing your heart rhythm problem:
1. If someone has an “acute coronary syndrome” (a sudden blockage of blood flow to the heart) or if their heart failure symptoms are getting rapidly worse, an EPS might make their symptoms even worse and cause instability in blood circulation.
2. During an EPS, the patient receives an anticoagulant (a blood-thinning drug) called heparin. So, if someone is already at a high risk for bleeding, the anticoagulant might increase their bleeding risk.
3. Arrhythmogenic conditions are conditions that can cause abnormal heart rhythms. If these conditions are present, they can decrease the accuracy of the EPS test. These conditions include imbalance in body’s salts and minerals (electrolyte abnormalities), side effects of certain drugs (drug toxicity), an overactive thyroid (hyperthyroidism), and others.
4. If a person is pregnant, they cannot have an EPS because it involves exposure to radiation. However, in certain cases, for patients whose abnormal heart rhythms can’t be controlled with medication, a different procedure called “ablation” can be performed with special precautions to protect the mother and baby.
Equipment used for Electrophysiologic Study Interpretation
An electrophysiologic laboratory, a place where doctors study the electrical activities of the heart, is fully prepared with all necessary tools and equipment, including:
Firstly, a C-arm fluoroscopy is present. This is a special type of X-ray machine that allows the doctors to see live images of your body. It comes with a table for the patient to lie on and an image intensifier to improve the image quality.
Next, there is the electrophysiologic data acquisition system and the cardiac stimulator. The data system collects information from your heart for the doctors to study, while the cardiac stimulator can send electrical impulses to your heart in a controlled manner to predict how your heart might react under certain conditions.
The doctor will also use hemodynamic monitoring equipment. This helps in understanding how well your heart is pumping blood to the rest of your body.
An external defibrillator and temporary pacing system are in place to keep your heart beating properly during the procedure. The defibrillator sends an electrical shock to your heart if it starts beating in an abnormal rhythm, while the pacing system helps maintain a steady heart rate.
Additionally, a fully equipped resuscitation cart and intravenous infusion systems are present. The resuscitation cart contains all the necessary tools and drugs needed to revive a patient if an emergency occurs, and the infusion systems are used to deliver drugs and fluids into your blood circulation during the procedure.
Lastly, there are some standby equipment not always in the room but can be quickly brought in if there are any unexpected complications. These include an echocardiographer (a device that uses sound waves to produce images of your heart), a pericardial aspiration set (a kit used to draw fluid from around your heart if needed), and a ventilator (a machine that can breathe for you if you are unable to breathe on your own).
Who is needed to perform Electrophysiologic Study Interpretation?
Performing an Electrophysiology Study (EPS) needs a team of heart rhythm specialists. This team may include:
* An electrophysiologist, a type of heart doctor who puts special wires, or catheters, into the heart to understand its electrical rhythm.
* Another electrophysiologist or a technician helps to collect and understand the data.
* A nurse who takes care of the patient’s overall well-being during the procedure. This may involve monitoring vital signs like heart rate and breathing, and giving required drugs through an IV (a tube that goes into your vein).
* Additional medical staff may be present, including an anesthetist (who helps with pain relief), an interventional cardiologist (a heart specialist who does non-surgical procedures on the heart), and a cardiac surgeon (a doctor who does heart surgery). These professionals are there as a backup for the patient’s safety, ready to manage unlikely but serious complications that might occur during the procedure.
Preparing for Electrophysiologic Study Interpretation
Before a certain medical procedure, a patient is required to avoid eating or drinking anything for a minimum of six hours. Certain medications should be paused or adjusted accordingly as per doctor’s instructions. For example, if you’re taking a medication to control your heartbeat, called antiarrhythmic therapy, you might need to stop it for a certain period. Similarly, those on treatment for blood clots (anticoagulation therapy) will usually be asked to temporarily stop taking their medication. This mainly includes warfarin for 3-4 days, and other types of anticoagulant drugs for 1-2 days. In some cases, other anticoagulants may continue to be taken. Each person’s plan might vary based on their risk of developing blood clots and the chances of bleeding.
Before arriving in the doctor’s office where the procedure will be performed, the patient should be prepared with an intravenous (IV) line so that fluids can be readily given if needed during the procedure. The purpose here is to prevent dehydration (a state when the body doesn’t have as much water as it should).
Once in the procedure room, the patient will be hooked up to several machines. These machines will help monitor the patient’s heart activity (through a mechanism known as 12-lead surface ECG). Other monitors include a device to measure the oxygen level in the blood (pulse oximeter), a cuff to check blood pressure, and pads to regulate heart beats if needed (external defibrillation pads).
Even though deep sleep-inducing medicines (known as intravenous sedation) are usually avoided because they can interfere with the procedure, light relaxation medicines are given to a majority of patients. These could be a combination of benzodiazepines (drugs that can help decrease anxiety), opiates (pain-relieving drugs), and antiemetics (medications that help control nausea and vomiting). These help with the discomfort of the initial needle stick and to ease anxiety.
How is Electrophysiologic Study Interpretation performed
Interpreting a heart’s electrical activity involves analyzing the shape and timing of the electronic signals produced by your heart at rest and after a programmed simulation of your heart. Special machines record these signals generated by the heart. ECG, which is an abbreviation for electrocardiogram, is a regular hospital test that records the electrical activity of the heart. But in a detailed examination like this, we use a faster recording speed to capture more details.
Understandably, the signals coming from the upper (atrial) and lower (ventricular) chambers of the heart are easy to pick because they coincide with specific patterns seen in a routine ECG. However, capturing the His bundle’s electrical signals (a part of the heart’s electrical system) needs additional measures. The recording equipment should be directed towards the septum (a wall in the heart) at the level of the tricuspid valve ring. In this region, the His bundle’s electrical signals show a two or three phased sharp variation.
The recording can also collect signals from a special equipment – the multipolar CS catheter. The CS (coronary sinus) runs in the atrioventricular groove; this grove lies between the heart’s upper and lower chambers. The catheter records signals from both chambers. It’s worthy of note that signals taken from the catheter’s tip pair of electrodes are coming from the left side of the heart, while those from the pairs closer to the body come from the right side. This provides important differentiation between the right and left heart chamber signals.
Here are some important terms involved in this study:
– Cycle Length: It’s the time duration (in milliseconds) between two consecutive events like two heartbeats or pulses. The shorter the cycle length, the faster your heart is beating. For example, a cycle length of 600 ms corresponds to a heart rate of 100 beats/min, while 400 ms corresponds to 150 beats/min.
– Programmed Stimulation: Stimulating heart tissue through a catheter as per a planned protocol.
– Incremental pacing: This is when a specific number of pacing stimuli (train) are introduced at progressively shorter cycle lengths. In this case, one or more early impulses, usually up to three, are introduced at specific intervals after a natural impulse or after a train of eight impulses stimulated at a fixed cycle.
– Coupling interval: The time measured in milliseconds between a natural heart impulse and an early impulse introduced through programmed stimulation.
– Effective Refractory Period: This is the longest interval at which an early impulse fails to propagate through the heart tissue or structure.
The analysis begins with the measurement of time intervals between signals in relation to the normal activation sequence of the heart. Following the electrical impulses from their origin to the end, several time intervals are measured, these mainly include:
– PA Interval: This is the time required for the impulse to move within the upper chamber of the heart (normally 25 to 55 ms).
– AH Interval: This is the time that it takes for the impulse to travel from the upper chambers of the heart (the atria) to the His Bundle (normally 55 to 125 ms).
– H Time: This indicates the time taken for the electrical activity to travel the His bundle (normally less than 30 ms).
– HV Interval: This represents the time it takes for the conduction to pass from the His bundle to activate the muscle of the ventricles (the lower chambers) of the heart (normally 35 to 55 ms).
All these measurements provide a clear picture of the functioning of your heart’s electrical system.
Possible Complications of Electrophysiologic Study Interpretation
Having an electrophysiological study performed by a skilled doctor and a trained team specializing in heart rhythm problems (arrhythmias) generally has a low risk of complications. However, the risks can go up with the use of radiofrequency ablation (a technique that uses heat to disrupt the source of the abnormal rhythm) or with increasing age. The most common issue that arises during such a study is the creation of a persistent, fast heart rhythm (known as sustained ventricular tachycardia) that requires immediate attention to return the heart to normal rhythm.
There are other, less common complications that include damage to local blood vessels, inflammation of veins related to a blood clot (thrombophlebitis), blockage in one of the arteries in the lungs (pulmonary embolism), blockage in an artery in another part of the body (systemic arterial embolism), puncture or damage to the heart that leads to fluid build-up around it (cardiac perforation and tamponade), blockage in the heart caused by the catheter (catheter-induced AV block), and the creation of not-so-harmful irregular heart rhythm (nonclinical atrial fibrillation).
Severe life-threatening problems like heart attack, stroke, or sudden death are very uncommon, with chances generally being less than 0.5%. But it’s essential that before you agree to the procedure, your doctor fully informs you about both the benefits and all possible risks. You should always be asked to sign a consent form that acknowledges you understand these aspects and agree to proceed with the procedure. Your healthcare provider is responsible for obtaining this consent.
What Else Should I Know About Electrophysiologic Study Interpretation?
Doctors conduct a procedure to learn about different kinds of heart rhythm problems. They’ll examine if you possibly have issues with your sinus node (the natural pacemaker of your heart) not working properly, irregular heart rhythms that start in the upper or lower chambers of your heart, or if they need to analyze your heart function after a successful treatment for a heart rhythm disorder.
Here’s how some of these checks work:
1. Sinus Node Dysfunction: The doctors measure how long it takes for the sinus node to recover and for impulses to travel from the sinus node to the upper chamber of your heart. A normal measurement means your sinus node is working properly. If the measurement is too long, there might be some issues.
2. Atrioventricular Conduction Abnormalities: The doctors evaluate how well electricity travels from the upper chambers of your heart (atria) to the lower chambers (ventricles). If the travel time is prolonged, it may suggest blockage that could potentially lead to serious problems like fainting or sudden cardiac death. If such blocking is detected, a pacemaker (a small device that helps your heart beat at a normal rhythm) might need to be implanted.
3. Supraventricular Tachyarrhythmias: Doctors look into issues relating to rapid heart rhythms that start in the atria. The heart can start beating too fast due to two main reasons: an unusual initiation of the electrical impulse from cells other than the sinus node or issues with the impulse’s propagation leading to abnormally fast circulating impulse in the heart.
Understanding the cause helps doctors decide the best treatment. For example, if the issue is with the propagation of the impulse, medication or an invasive intervention to block the electrical activity might be needed. Or if the problem is due to an extra electrical pathway in the heart, a specialized form of heart surgery might be the best solution.
Each case is unique and the doctor employs these methods to understand the heart’s rhythm problems better and choose the most suitable treatment based on individual patient needs.
