Overview of Catheter Ablation
Catheter ablation, especially the type using radio waves, has been a game-changer in treating irregular or rapid heart rhythms, also known as tachyarrhythmia. Over the years, it’s become a top choice of treatment for many who have recurring symptoms that interfere with their day-to-day life. The technique of catheter ablation was first proposed in the late 1960s, originally intended for tracking the heart’s electrical activity when surgery was the main treatment for heart rhythm problems.
In 1967, the idea of triggering heart rhythm issues through planned electrical stimulation came to the fore. By the late 1970s, advancements meant that doctors could carry out this electrical stimulation and record the heart’s electrical signals using more than one recording catheter. The process progressed, evolving towards surgical ablation and better recording of the heart’s activity inside the organ.
Before, heart rhythm issues were often dealt with via surgery, for instance, surgically removing the origin of the irregular beats for some heart rhythm issues, or using cold temperatures to remove a part of the heart’s electrical system in stubborn cases of fast irregular heartbeats occurring above the ventricles. One notable procedure is the Maze procedure, which is often used during a complicated mitral valve surgery when the patient also has a heart rhythm problem, specifically atrial fibrillation.
The idea of the transvenous catheter, which means a catheter inserted through a vein, came about in 1981 in an interesting circumstance. While recording a patient’s heart activity after a defibrillation (an electric shock to the heart to get it back into a normal rhythm), a high-voltage discharge happened when a defibrillator electrode hit the catheter electrode at His (a part of the heart’s electrical system). This discharge damaged the tissue underneath.
Direct current cardioversion, which is a method to restore a normal heartbeat, was initially used in ablation for atrial fibrillation. Here, a direct current was sent between a catheter electrode and a surface electrode on the skin, but the tissue damage produced was uncontrolled. By the 1990s though, radiofrequency ablation replaced the direct current approach. Radiofrequency ablation uses an alternating current (electricity that regularly changes direction) with a specific frequency to cause targeted injury by heat, transmitted from the tip of the catheter electrode to the skin using a big patch. This method helps avoid skin burns.
Tissue in direct contact with the catheter gets damaged by heat, and the tissue deeper and around this point is also damaged by the heat conducted. When looked at under a microscope, the early-stage damage appears as inflammation and bleeding around a central dead tissue area. Sometimes, heart rhythm issues reappear as the damaged areas may still harbor cells capable of causing rhythm problems, which initially don’t conduct electricity during ablation but regain this ability as healing occurs.
Today’s ablation devices can monitor and regulate temperature, which is key during radiofrequency ablation procedures. It gives useful details about tissue heating, reducing abnormal clot formation, and regulating lesion size. Innovations like larger distal electrodes (far end of the catheter) and saltwater cooling have helped to lower the resistance to electricity and enable creating larger, deeper damage zones. Here, we’ve discussed catheter ablation’s role in managing heart rhythm problems, the technical side of the procedure, when it’s recommended, and the risks associated with catheter ablation.
Anatomy and Physiology of Catheter Ablation
Doctors often access the body’s vein system through the right and left femoral veins, which are large veins in the groin area. If they have trouble reaching the coronary sinus, which is a collection of veins that collect blood from the heart muscle, they might use veins in the neck (internal jugular) or near the collarbone (subclavian).
Diagnostic catheters, which are thin, flexible tubes, are put into these veins. These allow the doctor to pace (control the speed of) the heart, stimulate it, and record signals from different parts of the heart. These include the high right atrium (upper right chamber of the heart), right ventricle (lower right chamber), His bundle (an area of specialized cells that transmit electrical signals in the heart), and the coronary sinus.
If they need to access the left side of the heart, doctors may either puncture the septum (the wall that divides the right and left sides of the heart) from the right atrium to the left atrium, or they may take a back route through the aorta, the main artery that carries blood from the heart to the rest of the body.
Why do People Need Catheter Ablation
Catheter ablation is a medical procedure used to treat certain types of abnormal heart rhythms. There are three main reasons for why a doctor may recommend this treatment:
1. To treat an ongoing and bothersome fast heart rhythm problem known as supraventricular tachycardia (SVT). This includes:
– Atrioventricular re-entrant tachycardia (AVRT): a rapid heart rhythm caused by electrical signals moving in a circular pattern in the heart.
– Atrioventricular nodal re-entrant tachycardia (AVNRT): a rapid heart rhythm caused by electrical signals that move in a circular pattern in a region of the heart called the atrioventricular node.
– Unifocal atrial tachycardia: an irregular heart rhythm resulting from a single area in the heart’s upper chambers (the atria) sending out electrical signals too rapidly.
– Atrial flutter: a fast and irregular heart rhythm involving the heart’s upper chambers.
2. To manage symptoms of atrial fibrillation (AF), which is a rapid and irregular heartbeat, in cases where medication doesn’t help. Atrial fibrillation can make daily activities difficult due to feeling shaking sensations in the chest, lightheadedness, or shortness of breath.
3. To treat a rapid and irregular heartbeat originating from the heart’s lower chambers called ventricular tachycardia (VT) when it causes symptoms.
However, in people who have an irregular heart rhythm because of an underlying heart condition, catheter ablation is usually only considered when medication doesn’t work well enough. It may also be used alongside a device called an implantable cardioverter-defibrillator (ICD) that can regulate the heartbeat for people who experience frequent irregular heart rhythms.
When a Person Should Avoid Catheter Ablation
While there are no absolute restrictions to carrying out a catheter ablation (a procedure to correct heart rhythm problems), there are certain circumstances when it could be risky. These include:
When it is difficult to gain access to the blood vessels needed for the procedure. For example, if a patient has a deep vein thrombosis (DVT) in the leg vein where the catheter needs to be inserted, or peripheral arterial disease (PAD, a buildup of plaque in the arteries), or a tear in the aorta (aortic dissection), then these conditions could complicate the procedure.
If a patient has clots inside their heart (intracardiac thrombi), carrying out this procedure might risk moving these thrombi, which can block blood vessels in other parts of the body.
Finally, if a patient has problems with bleeding or blood clotting (termed as bleeding diatheses and coagulopathy), they may not be suitable for catheter ablation. However, the doctor who performs these procedures (an electrophysiologist), can usually still carry out the procedure safely if a patient’s INR (a measure of how quickly blood clots) is up to 3.
Equipment used for Catheter Ablation
A range of catheters (thin tubes) are available for different medical purposes. They typically come with two ring-shaped parts that can be used for sending and receiving signals between parts of the body. These tubes may be made from different materials such as Dacron, a type of polyester, or other synthetic substances like a form of plastic, polyurethane.
Catheters made from Dacron are usually chosen because they are stronger and have better physical characteristics. For instance, they can hold their shape but soften at body temperature, making them flexible enough to adopt various uses inside the body.
On the other hand, synthetic catheters cannot change their shape once inside the body, which makes them less versatile. However, they are cheaper and come in smaller sizes (2 to 3 French). Nowadays, most electrode catheters, which are used to pick up electrical activity from the body, range in size from 3 to 8 French. The smaller ones are used in children while adults typically require 5 to 7 French catheters.
There are two main types of mapping catheters, another kind of catheter used for producing a map indicating the source of abnormal heart rhythms:
- Deflectable catheters for easy positioning and energy delivery
- Catheters with multiple poles for picking up signals from many locations at once
Some versions of ablation catheters (used to eliminate areas of the heart causing abnormal rhythms) have a tip that can be cooled. This prevents the tip from getting too hot and causing harmful effects during a procedure’s tissue heating process.
Another kind is particularly helpful in mapping large areas of the heart. They have up to 24 poles and can be redirected or “deflected” to different areas of the heart. Recently, a new type of catheter after this type has been developed. It’s a 64-pole roving catheter, a kind of specialised mapping device with flexible sections containing four electrodes each, which can pick up 20 individual activation sites.
The doctor uses a tool called a junction box that collects the signals from the catheters and links to a recorder. The recorder then captures, displays, and saves both the inner and surface recordings of the body. Signals picked up by it are usually weak and therefore amplified for better viewing and recording. The recorder usually includes filters to remove unnecessary signals that could distort the main signals.
A stimulator is used to get more information than just simple measurement of conduction time (the time it takes for a signal to get from one point to another). This device can generate a wide range of modes of electrical signals used for various procedures. It can generate variable levels of current, from 0.1 mA to 10 mA.
Finally, a cardioverter/defibrillator, a machine that can restore a normal heart rhythm by sending an electric shock to the heart, should be available all the time during EP (Electrophysiology) studies. It works by delivering energy in a form that has been proven to be very effective in restoring the heart’s normal rhythm. The patient is connected via defibrillation pads to the machine, which is electrically grounded.
Who is needed to perform Catheter Ablation?
For a test called an electrophysiology study/ablation, which checks the electrical activity of your heart and can treat certain heart rhythm problems, several healthcare professionals are needed. These include a cardiac electrophysiologist – a doctor who specializes in heart rhythm problems, a cardiac electrophysiology laboratory technician – a skilled person who operates special machines and helps the doctor during the procedure, and nursing staff whose job is to administer drugs to the patient.
Furthermore, a radiographer is required, who is an expert in using imaging technology needed in the procedure. In rare and complex cases, an anesthesiologist – a doctor who administers medication to ensure you don’t feel any pain – may also be involved.
Preparing for Catheter Ablation
The main part of preparing for the procedure is explaining to the patient what will happen. This can help the patient understand and feel more comfortable.
Doctors will do several tests before the procedure. These tests check the patient’s blood, kidney, and liver. These tests are needed even more if the patient is currently taking medicine to control an irregular heartbeat (antiarrhythmic drugs).
Doctors also need to test the patient’s blood to make sure it clots properly. This is especially important for patients taking blood thinners (anticoagulation).
When the patient is ready to have the procedure, doctors will clean the area where the treatment will be performed with a special disinfectant. This is the same for most heart-related procedures.
How is Catheter Ablation performed
The process of evaluating heart rhythm disorders involves recording and analyzing a variety of heart events under different conditions. For this evaluation to be accurate, we need to understand various techniques and concepts, such as the types of heart recording, calculating the time it takes for signals to pass from the upper to the lower chambers of the heart (A-V conduction intervals), mapping the heart’s electrical activities, and observing the patient’s reaction to programmed electrical stimulation. What’s important here is understanding the meaning of these responses, as they guide the doctors in their treatment decisions.
The placement of the catheter – a thin, flexible tube – depends on the type of procedure being done. Some common procedures include AVNRT/AVRT, Atrial Flutter, Atrial Fibrillation, and VT Ablation. The placement of the catheter differs for each procedure, but what’s common among all procedures is the use of a catheter to get a better picture of the activities inside the heart.
The recordings made by the catheter either come in two forms: Unipolar signals or Bipolar signals. The unipolar signals help in figuring out the exact point of activation and movement, while bipolar signals are good at removing unnecessary signals and focusing on particular ones. In simple terms, these recordings are like maps, guiding the doctors during the procedure.
In addition to traditional mapping, there is an advanced mapping system which provides a 3D image of the heart. By using magnetic fields and special sensors, doctors can see and record the heart’s structure in 3 dimensions, which increases the accuracy of the procedure. Other technologies also allow doctors to create a visual map of the heart’s electrical activities, reducing radiation exposure and providing a detailed view of the heart.
The doctors then measure the time it takes for signals to pass from various parts of the heart. This gives them a clearer understanding of how the patient’s heart is functioning.
Radiofrequency Ablation is a technique used to correct heart rhythm abnormalities. It uses a current to deliver energy to the heart muscle, causing the tissue to break down. To ensure the treatment is safe and effective, the procedure’s time, power, and impedance are closely monitored.
Possible Complications of Catheter Ablation
During a procedure called catheter ablation, where we use heat to treat abnormal heart rhythms, there can be further health risks. However, these risks largely depend on the type of irregular heart rhythm you have and where in the heart the treatment is applied.
There’s a very slight chance (0.05% to 0.01%) that the procedure might cause severe problems like death, heart attack, or stroke, especially when treating a kind of irregular heartbeat called atrial fibrillation. A slightly higher chance (0.5%) exists that the heart’s normal rhythm could be disrupted, meaning you have to have a pacemaker fitted. The risk here mainly increases if the treated area is near a part of the heart called the atrioventricular node, which helps control heartbeat.
Further potential issues include heart damage or the heart being punctured during the procedure, potentially leading to a life-threatening condition called tamponade, where fluid builds up around the heart (affecting around 1-2% of people). Likewise, there is a risk of blood clots forming and blocking blood flow (thromboembolic complications), the risk of which can change depending on the exact procedure.
Complications linked to the point where the catheter is inserted into the body are more common (2% to 4%). These can include an abnormal connection between an artery and a vein (arteriovenous fistula), bulges in blood vessels (aneurysms), and serious internal bleeding (retroperitoneal bleeding). For those undergoing catheter ablation to treat atrial fibrillation, there are specific complications like pulmonary vein stenosis (a narrowing of the veins that take blood from the lungs to the heart) and damage to the phrenic nerve which controls the diaphragm (the muscle you use to breathe). But these complications can often be prevented by taking care to identify the location of this nerve during the operation.
Issues with blood clots happening during the procedure (thromboembolic events) are fairly common, especially if more time is spent using heat during the procedure to treat a connection between the heart and esophagus (atrial-esophageal fistula). Pulmonary vein stenosis along with atrial-esophageal fistulae, however, are uncommon complications of the procedure.
What Else Should I Know About Catheter Ablation?
Catheter ablation is currently the main method used to treat most irregular heart rhythms, known as arrhythmias. This procedure could be a better option for people who keep experiencing heart rhythm problems. Catheter ablation is considered a long-term solution, with a success rate of over 90% in treating two specific types of rapid heart rhythms referred to as AVRT and AVNRT.
Catheter ablation is often the best treatment for abnormal pathways in the heart that cause symptoms, a type of fast, twitchy heartbeat called atrial flutter, and a common and serious type of arrhythmia, known as atrial fibrillation. Also, it’s generally the best choice for people suffering from resistant types of heart rhythm disturbances (VT) or conditions caused by premature ventricular contractions (PVCs), which are extra, abnormal heartbeats, that aren’t effectively managed with medication.
