Ablation Surgery For Atrial Fibrillation - A Brief Introduction
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This hub is a brief introduction on ablation surgery, which is widely used in treating heart diseases such as atrial fibrillation. The hub is just a summary of what I have learned about ablation surgery or maze procedure, patient is recommeded to formally consult a surgeon before the operation.
What is atrial fibrillation?
Heartbeat in a healthy person begins from the sinus node (a tissue located near the right atrium of the heart). Sinus node is a complicated body tissue that works as the source of heartbeat by generating electrical impulses rhythmically (about 60 to 100 beats per minute), and conducting the impulses through atria to atrioventricular node (or AV node for short, it is located between the atria and the ventricles of the heart) and then to ventricles, so that the entire heart can contract repeatedly and pump blood throughout the blood vessels. That way, the human body's need for blood and oxygen can be satisfied, and the above normal beating of the heart is also called sinus rhythm. Sinus rhythm is a main characteristic of a healthy heart.
However, If the normal rhythmic movement of the heart has some problems, it will produce unsystematic electrical impulses of various frequencies and directions, thus leading to heart beat disorder and fast quivering of the atria, or what is typically called atrial fibrillation. In atrial fibrillation, the contraction of heart muscle is no longer synchronized and effective, this usually results in decreased pump function, and blood clots due to a large number of blood deposition on the atrial trabecular muscle wall. These small blood clots are easily to flow throughout the whole body and have a 20% incidence rate of cerebral infarction (50% of the patients have died). Moreover, the heart muscle lost its normal movement, has decreased overall function and eventually leads to heart failure.
What are the dangers of atrial fibrillation?
Atrial fibrillation is one of the most common arrhythmia in the general population. Its incidence rate increase significantly with age, there is a 5% to 10% chance of having the disease among people aged 60 and over. The main dangers of atrial fibrillation are listed below:
- Patients have irregular heartbeat and rapid heart rate that is difficult to control, they will always experience discomfort, palpitation, and psychological anxiety.
- The loss of coordination in atrioventricular conduction has a strong impact on the cardiac contractile function, the patient's heart will have decreased stroke volume and different degrees of heart failure.
- The atrial blood stagnation will easily lead to atrial thrombus, which will greatly increase the incidence rate of thromboembolic complications in various organs, especially the possibility of cerebral embolism.
What is ablation surgery and what's its principle?
The mechanism of atrial fibrillation is very complicated, until today, there are many assumptions in regard to what its main causes are. The most commonly accepted theory states that there exists pacemaker cells (similar to the sinus node) in the muscle sleeve of pulmonary veins (veins that carry blood from the lungs to the left atrium), which might work as a potential ectopic pacemaker. An ectopic pacemaker is a potential threat to the normal heart beat as it may rule over the heart rhythm of sinus node on occasions. This reason, together with various unknown factors, may lead to a phenomenon called "reentry" of the electrical impulse, which forms multiple reentrant circuits in the heart, and these reentrant circuits are considered to be the main reasons of atrial fibrillation. Accordingly, based upon the above theory, surgical treatment of atrial fibrillation is done by cutting off the abnormal tissues to stop the influence of ectopic pacemaker and blocking the pathways of reentrant circuits to prevent the occurrence of atrial fibrillation.
You may also have heard of "maze surgery" in the treatment of atrial fibrillation. So what's the relationship between maze surgery and ablation surgery? Actually, "maze" refers to the new pathways surgeons have created to let electrical impulses travel easily through the heart. While "ablation" refers to the methods surgeons have used in the operation to create the "maze". So generally speaking, ablation surgery can be divided into the following types based on different methods used, they are, standard maze procedure, modified maze procedure and the newly emerged minimally invasive surgical ablation surgery.
The purpose of ablation surgery is to restore sinus rhythm and normal pump function, to reduce complications and eliminate the risk of thromboembolism.
Standard maze procedure (cut and sew)
Standard maze procedure was developed by Dr. James Cox in 1980s. it is based on the multiple reentry theory which has been widely accepted and used to explain the occurrence of atrial fibrillation. The theory, as introduced above, also states that, for the multiple reentrant circuits to exist, a certain mass of atrial tissue needs to be maintained, and maze procedure uses several linear incisions to separate atria tissues, so that each separated tissue is smaller than the required critical mass to trigger reentrant circuits. Or, the principle can be simplified as: these tiny cuts in the heart can block the pathway where abnormal electrical impulses travel and restore new pathway through which the sinus node impulse can not be returned, and all electrical activities terminate immediately upon arrival at the suture line. The above complicated pathway is designed like a labyrinth, that's why it is often called maze procedure.
Pros: In addition to restoration of sinus rhythm, the most important benefit of maze procedure is that it can eliminate the risks of stroke and blood clots.
Cons: The repeated cutting of the atrium will bring some damages to the heart, what's more, due to its complexity, standard maze procedure requires long time of operation, accurate positioning of the tiny cuts and the support of extracorporeal circulation (blood circulation outside the body). Standard maze procedure also has many complications such as atrial flutter and sinus node dysfunctions.
Generally, surgeons are not willing to perform standard maze procedure just for the purpose of curing atrial fibrillation because of the uncertainty of the surgery.
Modified maze procedure
Standard maze procedure uses "cut and sew" method to eliminate atrial fibrillation, however, it has many disadvantages as stated above. To simplify the operation and reduce the incision length, modified maze procedure has been introduced to improve the procedure. Modified maze procedure abandons physical incision approach but uses other ablation methods to make tiny cuts in the heart. This not only significantly reduces operating time but also reduces the risks of the incision and suture.
Currently, the ablation methods used in the surgery include cryotherapy, radio frequency waves, microwaves, laser beams and confocal ultrasounds. Take cryotherapy, or the freezing ablation surgery, as an example, usually, liquid nitrogen, carbon dioxide, argon or helium is used through a probe to act on the heart muscle and cut clear boundaries in the atria tissues. The freezing ablation method is less likely to cause postoperative inflammations and thrombosis, it is a safe surgery especially in ablation of vascular tissues as it is unlikely to lead to vascular stenosis.
Pros: Modified maze procedure is more convenient and more secure than the standard surgical procedure. It can significantly simplify the surgical procedure, in particular, shorten the operation time and extracorporeal circulation time, thus significantly reducing the incidence of complications.
Minimally invasive ablation surgery
With the development of minimally invasive surgery, ablation surgery has improved to become a safer and more reliable surgery in the treatment of atrial fibrillation. Currently, there have been many minimally invasive techniques combined with ablation surgeries, among which Wolf Mini Maze ablation surgery (minimally invasive maze surgery) is the most successful one. The general features of these minimally invasive ablation technologies are small incisions, accurate and fast operation and fewer complications.
The general procedure of Wolf Mini Maze ablation surgery include isolation of all the pulmonary veins, linear ablation in the left atrium, excision of left atrial appendage, and denervation of part of the epicardium. In the operation, surgeons will make two small holes and a tiny incision (about 3 to 5 cm) on each side of the chest wall, the operation is done through these holes and incision. The ablation surgery usually takes 2 to 4 hours to complete, and it is done without opening the chest, stopping the heart beat and using cardiopulmonary bypass, so the postoperative recovery is much faster than the traditional ablation surgeries. The average postoperative hospital stay may be shortened to 4 to 7 days.
After the Mini Maze ablation surgery, some anti-arrhythmia drugs and anticoagulant drugs will be prescribed by the surgeon based on the situation of patients. After discharge, patients will need to do periodic electrocardiogram review etc..