Overview of Cryoballoon Pulmonary Vein Catheter Ablation of Atrial Fibrillation
Atrial fibrillation (AF), or an irregular heartbeat, is the most commonly experienced heart rhythm disorder in the United States, with approximately 3 million people diagnosed with the condition. This issue becomes more common as people get older, and as our population is living longer and we’re seeing more risk factors like high blood pressure and obesity, we can expect the number of cases to continue to rise.
People who live with AF often suffer from a range of health problems, including strokes, heart failure, mental decline, kidney failure, a higher risk of death, and a reduced quality of life. So, it is crucial to control this irregular heartbeat as it can significantly impact a patient’s quality of life and their health outlook.
Since the last few decades, we’ve known that the source of AF mostly lies in a region called the posterior left atrium, which is near where the veins carrying oxygen-rich blood from the lungs enter the heart. A common treatment has been to carry out a procedure known as catheter ablation, which aims to stop the faulty electrical signals causing the irregular heartbeat. This can be done either through medicine or surgery, depending on the patient’s specific situation and their preferences.
There are a couple of methods used for ablation—radio-frequency and cryoenergy. The radio-frequency technique uses heat like a tiny soldering iron to interrupt the faulty electrical signals, while cryoenergy uses extreme cold which freezes and destroys the area causing the problem. Both techniques have been used during heart surgery with good success.
Now, catheter ablation, by using radio-frequency energy, has been the main method to isolate the problematic veins. But, one issue with this approach is that it needs a large number of burn points (ablation lesions) to completely encircle the problematic vein. The results may also vary, as uneven or incomplete blocks can lead to potential injuries to adjacent structures like the food pipe.
In 2012, the FDA approved a new method using something called a cryoballoon, which uses cold temperatures to create a burn and can be applied to the tissues in a complete circle. This makes the application of the freeze burn much more consistent, reducing the chance of any gaps in the treatment. This means that the treatment is less likely to damage deeper tissues in the heart, therefore increasing safety. A significant clinical study in Europe suggested that both the radio-frequency and cryoballoon methods were similarly effective in treating AF. The purpose of this paper is to further examine this technique, exploring both the expected outcomes and the potential risks associated with its use.
Anatomy and Physiology of Cryoballoon Pulmonary Vein Catheter Ablation of Atrial Fibrillation
To understand the processes used to isolate the pulmonary veins electrically, one must know how the left part of the heart and the pulmonary veins are structured and how these structures relate to the heart’s electrical system. Oxygen-rich blood returns to the heart and enters a chamber called the left atrium via the pulmonary veins.
Most people, around 60%, have 4 separate openings into the pulmonary veins. The most common variations include a left pulmonary vein trunk or a right middle pulmonary vein. The right pulmonary veins are positioned behind the right atrium (a chamber of your heart), while the left ones are located between the descending aorta (the large artery that carries blood away from your heart) and a small pouch in the heart, the left atrial appendage.
The right and left superior pulmonary veins (the ones at the top) point upward and forward, while the right and left inferior veins (the ones at the bottom) typically point backward and downward. There are a sort of sleeves of heart tissue around the pulmonary veins, made up of fiber bundles that run around the openings of the veins and form a structure similar to a sphincter.
These fiber bundles extend a bit up the veins, contributing to the formation of these sleeves of heart tissue. These sleeves play an important role in beating your heart in a synchronized manner. It is believed that the cells of the pulmonary veins may predispose to irregular heartbeats due to their shorter refractory periods (the time it takes for the cells to reset and be able to respond to a new signal) and increased triggered activity.
There are also several nerve clusters at the junction of the pulmonary veins and the left atrium. These nerve clusters have been shown to cause irregular heart rhythms in mice when stimulated, suggesting an overly active nervous system may play a role in an irregular heart rhythm, also known as atrial fibrillation. A process called catheter ablation, used to electrically isolate the pulmonary veins, could help prevent atrial fibrillation by stopping the irregular electrical activity from spreading.
Why do People Need Cryoballoon Pulmonary Vein Catheter Ablation of Atrial Fibrillation
The main reason to choose catheter ablation, a treatment to resolve irregular heartbeats, for atrial fibrillation or AF (a heart condition that causes an irregular and often abnormally fast heart rate) is when AF symptoms are present. According to the 2017 Expert Consensus Document on Catheter Ablation of Atrial fibrillation, this treatment is strongly recommended for those cases of AF that show no improvement even after being treated with at least one type of antiarrhythmic medication – medicines that are used to restore a normal heart rhythm.
The usage of ablation as an initial treatment for intermittent or persistent AF has less agreement among experts. It is given a class IIa recommendation, which means it is generally considered effective but less recommended. For long-term persistent AF, which is a continuous irregular heartbeat lasting for more than a year, catheter ablation gets a class IIB recommendation because there’s less proof of its long-term effectiveness.
For AF patients who have not been treated with any antiarrhythmic drugs, catheter ablation as a first-line treatment is also class II recommendation because the evidence about the benefits of this approach is weaker. Recent research showed some benefits to using first-line catheter ablation in patients under 75 years, and in minorities. However, there was no difference seen after 5 years regarding survival or heart-related events when catheter ablation was compared to drug treatment.
Other reasons (Class II recommendations) to choose catheter ablation may include being younger than 75, having heart failure or hypertrophic cardiomyopathy (a disease where the heart muscle becomes abnormally thick), having a rare type of arrhythmia called “tachycardia-bradycardia syndrome” which might otherwise need a pacemaker, and being a competitive athlete.
Even patients without symptoms of AF can discuss with their doctor the possibility of getting catheter ablation, though there’s no strong data to suggest it extends life. We anticipate more research and data will help clarify these issues based on the findings of the CABANA trial – a study comparing catheter ablation and drug treatment for patients with atrial fibrillation.
When a Person Should Avoid Cryoballoon Pulmonary Vein Catheter Ablation of Atrial Fibrillation
If there’s a blood clot (also known as a ‘thrombus’) in the left upper chamber of your heart (the ‘left atrium’), you should not have ‘catheter ablation’ for atrial fibrillation (AF). Catheter ablation for AF is a procedure where a thin tube (a ‘catheter’) is used to destroy the area causing the irregular heartbeat. This is because the procedure might move the clot into your bloodstream, which can be very dangerous.
So far, there’s no solid evidence that this procedure reduces the risk of stroke. So, if you can’t take medicines to prevent blood clots (known as ‘anticoagulants’), it might be a reason not to have this procedure.
How is Cryoballoon Pulmonary Vein Catheter Ablation of Atrial Fibrillation performed
Doctors conduct Cryoballoon catheter pulmonary vein electrical isolation as part of a full diagnostic cardiac electrophysiology study. This step-by-step process to diagnose and treat heart rhythm problems is usually carried out in a specially equipped heart laboratory. The lab should have equipment for capturing images and recording the patient’s heart activity. The lab should also be able to inject IV contrast dye and record pressure waveforms to facilitate the catheterization procedure. Here, an ultrasound of the heart is used to assist in the catheterization procedure and rule out blood clots in the atrium of the heart as well as provide real-time images of the patient’s left atrium anatomy. This can guide the procedure.
The lab could also have facilities to get preoperative CT or MR angiograms. However, these need to be obtained in real-time during the procedure because the volume of the left atrium can change significantly with changes in patient hydration and heart rhythm. An intraoperative ultrasound can also reduce the need for contrast dye. Recent studies show it is possible to do the cryoballoon pulmonary vein isolation without using any fluoroscopy at all.
There is a second-generation cryoballoon catheter that was approved by the FDA for the use of percutaneous catheter ablation in 2012. The catheter is inserted through the femoral vein and passed through the heart to reach the pulmonary veins. The patient will be premedicated with oral anticoagulation medications, either warfarin or a direct oral anticoagulant, for at least 2 weeks before the procedure. The medications stop a day before the procedure. During the procedure, the patient will be treated with heparin to prevent clot formation. An ultrasound or fluoroscope is used to guide the insertion of the catheterization needle and confirm the proper location. Once the needle is across the septum, other steps follow before the procedure ends.
All through the procedure, heparin is continuously administered to the patient. If any catheter remains in the heart, the ACT (a measure of the time it takes for the blood to clot) is checked every 15 minutes. When this is done, the chosen cryoballoon (either 23mm or 28mm in diameter) based on the diameter of the PV ostia taken via ICE, is inserted.
Usually, the 28-mm balloon is used except when one of the veins has a very shallow bifurcation that hinders the larger balloon from sitting adequately, thereby preventing complete occlusion of the vein. After selecting the appropriate balloon size, the balloon is flushed manually, forward and backward, to ensure that all air bubbles have been eliminated. The insertion of the balloon and other steps continue until no more air bubbles are detected on the balloon in the sheath before it is further passed in.
Possible Complications of Cryoballoon Pulmonary Vein Catheter Ablation of Atrial Fibrillation
In a global study of 7000 patients who underwent a procedure called catheter ablation, some experienced complications. These complications included cardiac tamponade (pressure on the heart due to fluid accumulation), thromboembolism (a blood clot blocking a blood vessel) which led to stroke, atrioesophageal fistula (an abnormal connection between the heart’s upper chamber and the esophagus), narrowing of the pulmonary veins, and nerve damage, either affecting the diaphragm or the vagus nerve near the esophagus. It’s worth noting though, the death rate was rather low, at just under 1 patient per 1000.
The study also described some rarer causes of death, including heart attacks, a specific kind of irregular heart rhythm called torsades de pointes, blood poisoning, sudden stoppage of breathing, punctures in the pulmonary veins outside the heart sac, build-up of blood in the chest, severe allergic reactions, perforations in the esophagus from a surgical probe, and bruising at the point where the catheter was entered.
The catheter ablation procedure can sometimes lead to irregular heartbeat rhythms itself, and other heart rhythm disorders post-procedure. There are a few complications that are specific to a type of catheter ablation called cryoballoon ablation, with the most common complication being damage to the phrenic nerve, which controls the diaphragm. This is due to its closeness to the right upper or lower pulmonary veins.
One way to avoid phrenic nerve damage is to immediately stop the delivering of freezing energy by stopping the machine as soon as there’s a sign of weakening diaphragmatic movement felt by touch or a decrease in C-MAP on ECG (the electric tracing of the heart).
While narrowing of the pulmonary veins is less common with cryoablation, more radiation is often needed during the procedure, as a kind of imaging procedure is used to ensure complete obstruction of the veins, necessary for optimal freezing. Despite this, cryoballoon ablation is generally considered less technically complex than radiofrequency catheter ablation, another method of performing ablations.
What Else Should I Know About Cryoballoon Pulmonary Vein Catheter Ablation of Atrial Fibrillation?
In a medical study called the STOP-AF trial, doctors researched two distinct treatments for Paroxysmal Atrial Fibrillation (PAF) – a type of irregular heartbeat, or heart rhythm. They experimented with a freeze balloon technique (called cryoballoon PV isolation) and regular medicine. 245 patients were split into two groups, each going through one of the treatments. After 12 months, 69.9% of patients who had the freeze balloon treatment did not suffer from the heart rhythm irregularity again, compared to just 7.3% in the group using medicine. They also found that patients in the freeze balloon group had improved quality of life.
In a review of a large number of similar studies, they found that the freeze balloon treatment was successful in 93% of veins targeted. When this treatment was used as a sole strategy, this number rose to 99%. After a 3-month period known as a blanking period (which doctors use to discount any minor or irregular rhythm issues), almost three-quarters of patients (73%) remained free of PAF after one year. Compared to radiofrequency catheter ablation – a kind of heat treatment for heart rhythm irregularity – this is quite high. The latter has a success rate between 50% and 64%.
Traditionally, radiofrequency ablation is the more commonly used treatment to isolate the electrical activity of the lungs (or pulmonary vein isolation). However, cryoballoon ablation, the freeze balloon technique, is becoming increasingly popular. Another study led by a doctor named Kuck showed that the freeze balloon method was just as good as the heat treatment. 1 in 3 patients (34.6%) being treated with the freeze balloon needed further treatment or medicine, compared to 35.9% using the heat treatment.
The freeze balloon technique has clear benefits – it’s quicker, less reliant on the doctor’s skill, safer, and leads to less tissue damage. It also reduces blood clot risk by decreasing injury to the inner lining of blood vessels.
Although the freeze balloon treatment may not be suitable for all PAF patients due to everyone’s lungs being different – this was proven in a research by Dr. Kubala. Meanwhile, other studies by Dr. Khoueiry and Dr. Sorgente revealed that the success of the freeze balloon treatment didn’t vary much when taking into account differences in lung anatomy.
In short, the freeze balloon (cryoballoon) treatment for irregular heart rhythm proves to be an effective, safe, and less doctor-reliant method. It improves patients’ quality of life and can be a great option for those where medicine isn’t helping. Consult your doctor to discuss if this treatment suits your condition.
