Atrial fibrillation is the most common cardiac arrhythmia. In the United States, there are approximately more than 2 million patients with atrial fibrillation and approximately 400,000 hospitalizations for atrial fibrillation each year. The epidemiology of atrial fibrillation in China is not well understood, and it is estimated that there are more than 10 million patients with atrial fibrillation nationwide. A study of nearly 30,000 people in China showed that the prevalence of atrial fibrillation in China is about 0.77%, with a higher prevalence in men (0.9%) than in women (0.7%), and the prevalence tends to increase significantly with age, with a prevalence of 7.5% in people over 80 years of age. From an epidemiological point of view, atrial fibrillation occurs mainly in elderly people with cardiovascular disease. Thus the aging of the population and the increased survival rates of cardiovascular diseases such as myocardial infarction and heart failure have set the stage for the prevalence of atrial fibrillation. Over the next 50 years, atrial fibrillation is thought to become one of the most prevalent cardiovascular diseases. The structure of the normal heart and the processes involved in the generation and conduction of the electrical impulses of a normal heartbeat have been mentioned in the overview section of this chapter. In atrial fibrillation, different parts of the atrial muscle “go their own way” and no longer accept the dominant effect of the electrical impulses generated by the sinus node, resulting in a large number of abnormal electrical impulses, the overall effect of which is extremely fast and disordered. The overall effect of these electrical impulses is extremely fast and disordered. The fast and disordered atrial electrical impulses are transmitted through the AV node to the ventricles, resulting in a heartbeat that is often irregular and fast. Because of the innate protection of the atrioventricular node, although the atrial electrical impulses are extremely fast, only a small percentage of the electrical impulses are transmitted through the atrioventricular node to the ventricles, so that the ventricles are beating rapidly but not “extremely fast”, which could otherwise be fatal. If the atrioventricular node is diseased and conduction is reduced, then only a very small percentage of the electrical impulses are transmitted through it to the ventricles, and the ventricles beat very slowly. Thus, patients with atrial fibrillation tend to have a fast and irregular heartbeat, but it can also be slow or even very slow, depending on the function of the atrioventricular node. In some patients, atrial fibrillation can stop on its own without treatment and return to a normal rhythm, resulting in a period of atrial fibrillation and a period of normal rhythm; this is called “paroxysmal atrial fibrillation”. In some patients, atrial fibrillation requires treatment to change to a normal rhythm, and this is called “persistent” atrial fibrillation. Other patients who are always in atrial fibrillation, even after appropriate treatment, are called “permanent atrial fibrillation”. The atrial muscles are “fragmented” and the electrical impulses are extremely fast, so the atria do not contract as regularly as the normal sinus node delivers impulses to control the heartbeat. The loss of contractile function in the atria makes it easy for blood to stagnate and become clotted, which can block small blood vessels (embolism) as the blood flows. The most common site of embolism is the brain (stroke). Because the heart beats quickly in most cases and the atria lose their normal contractile function in atrial fibrillation, patients may experience enlarged atria and heart failure over time. Atrial fibrillation may worsen heart failure in those who already have heart failure before atrial fibrillation. Atrial fibrillation is relatively easy to diagnose, and an experienced physician can sometimes make a definitive diagnosis of atrial fibrillation simply by auscultating the heart. In persistent or permanent atrial fibrillation, a routine electrocardiogram can confirm the diagnosis. In paroxysmal atrial fibrillation, the diagnosis is relatively difficult if the patient does not seek medical attention or an electrocardiogram in time for the attack; to increase the likelihood of diagnosis, a 24-hour electrocardiogram (Holter) can be performed, but if no episode of atrial fibrillation occurs within 24 hours of the test, the diagnosis cannot be made definitively. The overall treatment of patients with atrial fibrillation consists of three components, including control of the number of heartbeats to reduce the impact of a rapid heart rate on cardiac function and the discomfort it causes the patient; antithrombotic (anticoagulation) therapy to reduce the risk of thromboembolism due to atrial fibrillation; and cardioversion to convert atrial fibrillation to a normal sinus rhythm. Prior to the widespread availability of radiofrequency ablation for atrial fibrillation, it was shown that the two treatment strategies of diverting atrial fibrillation with medications to maintain sinus rhythm and not diverting atrial fibrillation with just controlling the number of heartbeats and anticoagulation to mitigate the consequences of atrial fibrillation did not have a significant impact on the ultimate survival of patients. The results of this study are partly explained by the fact that the negative effects of prolonged use of antiarrhythmic drugs to maintain sinus rhythm offset the benefits of maintaining sinus rhythm itself. If sinus rhythm is maintained in patients with atrial fibrillation by ablation, the negative effects of using medications to maintain sinus rhythm may be avoided. It is currently believed that sinus rhythm should be maintained in patients with atrial fibrillation as long as their condition and medical condition (maintenance of sinus rhythm by ablation) allow. Modern ablation therapy for atrial fibrillation was developed based on the understanding of the mechanism of atrial fibrillation episodes, first reported in 1998, and is a major advance in the field of atrial fibrillation treatment in recent years. The vast majority of patients develop atrial fibrillation in association with the pulmonary veins. The pulmonary veins collect blood from both lungs and return it to the left atrium, where it continues to circulate throughout the body. In humans, there are four pulmonary veins that open in the posterior wall of the left atrium. The pulmonary veins may produce a very rapid number of disorganized electrical impulses, and once these impulses are conducted to the atria, atrial fibrillation occurs in the atrial region. Just as the ignition of a car can start the engine, the pulmonary veins in pathological cases can deliver electrical impulses to start (trigger) atrial fibrillation. Other large veins connected to the heart, such as the superior vena cava, inferior vena cava, and coronary sinus, can also act as ignitors in a small percentage of patients with AF. Ablation therapy for atrial fibrillation involves damaging the tissues that connect the pulmonary veins to the atria so that abnormal electrical impulses from the pulmonary veins can no longer be transmitted to the atria and initiate atrial fibrillation. The “damage” here does not affect the function of the pulmonary veins as normal blood channels, but merely blocks electrical conduction. The initial ablation strategy for atrial fibrillation is to isolate the “initiator” in one of the four pulmonary veins for ablation, or even further in one pulmonary vein to locate the “enemy” (the abnormally excited foci delivering the electrical impulses) for ablation. These methods are called “single pulmonary vein ablation” and “focal ablation of pulmonary veins”. This method still has a high recurrence rate, and later studies have revealed that multiple foci can exist in different pulmonary veins, and that multiple foci can exist in a single pulmonary vein, and that the timing of the function of these different foci, i.e., the delivery of abnormal electrical impulses to initiate AF, can be different. Therefore, a more common approach to the ablation of atrial fibrillation is now “circumferential pulmonary vein ablation therapy”, which means that instead of searching for potentials (electrical pulses) in the pulmonary veins, all pulmonary veins are directly ablated and isolated, guided by the anatomy. It is common practice to ablate two pulmonary veins on the left side and two on the right side in a group, forming a circular ablation line around each pulmonary vein. This results in a total of two circumferential ablation lines on the left and right. In paroxysmal atrial fibrillation, ablation of two circumferential ablation lines is sufficient, whereas in persistent atrial fibrillation, ablation of the posterior atrial wall and other areas is required to reduce the relatively high recurrence rate. Because of the complex local anatomy of the pulmonary veins and atria, ablation of the circumferential pulmonary veins involves a wide range of sites, so it is often necessary to establish a three-dimensional anatomical model of the left atrium and pulmonary veins using a three-dimensional calibration system to guide the treatment. The establishment of a three-dimensional anatomical model facilitates more precise ablation sites and also reduces the dose of radiation (X-rays) that must be used intraoperatively, protecting the patient and the surgeon and nurses. The ablation catheter used for circumferential pulmonary vein ablation using the 3D scaler system is generally a cold saline infused ablation catheter, which ablates point after point, eventually forming a line with the points. This “point after point” ablation method is often time-consuming, and in response to this, technicians have invented cold balloon ablation catheters and “pulmonary vein ablation catheters” (circumferential ablation catheters) specifically for pulmonary veins. These new catheters are linear ablation catheters, which can reduce the operation time and theoretically can ablate isolated pulmonary veins more effectively and reduce some complications, but most of these new catheters are currently used only for ablation of pulmonary veins and cannot ablate the posterior wall of the left atrium, so they are mostly used for ablation treatment of paroxysmal atrial fibrillation. To reduce the likelihood of stroke before and after the ablation procedure, a period of anticoagulation is required before and after ablation. The success rate of atrial fibrillation treatment is currently reported differently and varies widely from place to place. This is related to the ablation technique used and the technical proficiency of individual cardiac centers, the duration of postoperative study follow-up, and the definition of procedural success. It is generally accepted that a relatively mature atrial fibrillation ablation center has a treatment success rate of 60% to 70%, with a somewhat higher success rate for paroxysmal atrial fibrillation surgery, which may be able to reach 70% to 80%. For patients with postoperative AF recurrence, secondary ablation therapy can be considered. After secondary ablation therapy, the overall AF ablation success rate will be improved and may reach more than 70%, and even more than 90% for paroxysmal AF. The number of repeat ablations that can be performed in patients with atrial fibrillation ablation is determined by a variety of factors, such as the surgeon’s expectation of the likelihood of maintaining sinus rhythm after the procedure, the patient’s own condition, and possibly economic factors in domestic patients. The number of atrial fibrillation ablation before and after reaching 4 to 5 times has been reported abroad. Successful atrial fibrillation ablation therapy not only enables patients to maintain normal sinus rhythm, but also reverses the enlarged left atrium. Many studies have shown that the left atrial internal diameter can be shortened by 10% to 20% after atrial fibrillation ablation therapy; in addition, in an observational study of heart failure patients after atrial fibrillation ablation, 70% of patients showed significant improvement in left ventricular systolic function after one year. There are no definitive conclusions about the population for which AF ablation is indicated, and professional recommendations are being developed and updated. Overall, the indications for AF ablation therapy are expanding as the technique continues to mature and improve. In paroxysmal atrial fibrillation with frequent episodes, ablation therapy can be the first choice; it can also be preferred in relatively young patients with atrial fibrillation to avoid long-term use of antiarrhythmic drugs; in persistent atrial fibrillation with significant symptoms; in persistent atrial fibrillation with insufficient effect of drug therapy; and in atrial fibrillation with insignificant structural changes in the heart (left atrial internal diameter less than 55 mm). Although the effectiveness of ablation therapy for atrial fibrillation is clear, it is, after all, an invasive treatment and the possibility of procedural complications exists. Possible complications include pericardial tamponade (incidence 1.2%-6%), pulmonary vein stenosis (incidence less than 10%, incidence of pulmonary vein stenosis requiring management is about 0.6%), atrioventricular esophageal fistula (extremely rare, incidence less than 0.25%), phrenic nerve injury (0-0.48%), and thromboembolism (0-7%). In some large hospitals, experienced atrial fibrillation ablation therapists are often able to minimize the occurrence of complications.