Atrial flutter is also a type of tachyarrhythmia that occurs in the atria. Atrial flutter occurs because there is a “loop” of electrical impulses going back and forth within the atria (the folding loop), and the atria are excited every week that the electrical impulses “travel” through the loop. The electrical impulses travel back and forth through the loop at a rapid rate (commonly about 300 beats per minute), and because the atrial flutter loop is generally fixed, the overall frequency of electrical impulses generated in the atria is also relatively constant. The frequency of the heartbeat depends on the proportion of the atrioventricular node that allows the atrial electrical impulses to travel down to the ventricles. If this proportion is constant, then the frequency of the heartbeat is also essentially fixed, and if the proportion of the downward transmission is constantly changing, then the heartbeat will also be irregular. In most cases, patients with atrial flutter have a faster than normal heartbeat and often have a feeling of panic. Because the frequency of atrial excitation is also rapid, atrial flutter, like atrial fibrillation, prevents the atria from contracting effectively, which can and will likely lead to the formation and dislodgement of intra-atrial thrombi to form emboli. By the same token, atrial flutter may cause or worsen heart failure. Atrial flutter is divided into typical and atypical atrial flutter, depending on the location of the folding loop, and is also referred to as type I and type II atrial flutter accordingly. A typical atrial flutter is described when the return loop of the electrical impulse is located in the tricuspid annulus (a structure at the junction of the right atrium and right ventricle) and passes through the isthmus (a structure between the tricuspid annulus and the inferior vena cava). If the regurgitant ring is located elsewhere, either in the left or right atrium, it is called atypical atrial flutter. Typical atrial flutter is more common and is also referred to as isthmus-dependent atrial flutter because the folding loop of the electrical impulse must pass through the isthmus, and accordingly, atypical atrial flutter is also referred to as non-isthmus-dependent atrial flutter. There is also a distinction between paroxysmal and persistent atrial flutter episodes. The diagnosis of atrial flutter is usually not difficult if the ECG recordings of atrial flutter episodes are available, and the diagnosis of typical or atypical atrial flutter can be determined from the surface ECG; however, it is difficult to distinguish atrial tachycardia or atrial fibrillation from the surface ECG in some patients, and intracardiac catheterization is required to identify such cases. The treatment of atrial flutter is similar to that of atrial fibrillation and includes medications to control the number of heartbeats, anticoagulation, and to revert and maintain sinus rhythm. Because slowing the heart rate is more difficult in atrial flutter than in atrial fibrillation, conversion and maintenance of sinus rhythm is generally recommended in patients with atrial flutter. Atrial flutter is caused by electrical impulses going back and forth over a fixed fold loop, which is fixed and easier to treat with ablation than atrial fibrillation. From these two considerations, ablation therapy can be the first choice for the treatment of atrial flutter. The ablation treatment for typical atrial flutter is to ablate the right atrial isthmus and block the regurgitant ring around the tricuspid annulus. The ablation of atypical atrial flutter is more complex than that of typical atrial flutter, as the location of the regurgitant ring in atypical atrial flutter needs to be found before the regurgitant ring can be ablated and blocked. In order to find the folding loop of atypical atrial flutter, a three-dimensional calibration system is required. The application of the 3D scaler system makes the ablation of atypical atrial flutter possible instead of impossible. It not only helps to find the folding ring of atrial flutter, but also helps to discover the critical areas on the folding ring, i.e., the areas suitable for ablation. If the folding loop of atrial flutter is located in the left atrium, an atrial septal puncture is required to allow the ablation catheter to enter the left atrium from the right heart portion. Atrial flutter, like atrial fibrillation, also requires a period of anticoagulation before and after the procedure to reduce the risk of thromboembolism. After successful block of the isthmus during a typical atrial flutter ablation, it is often necessary to continue observation for 20-30 minutes and then revalidate to ensure successful isthmus ablation, as isthmus conduction is easily restored. Even so, atrial flutter recurs in approximately 10% of patients within 1 year. With a second isthmus ablation in this group of recurrent patients, 95% of patients can be successfully treated without recurrence. The vast majority (75%) of recurrences after typical atrial flutter ablation occur within 6 months of the procedure. In a group of studies of ablative treatment of atypical atrial flutter with a mean follow-up of 14-20 months, the recurrence rate of atrial flutter ranged from 14% to 27%. The complication rate of atrial flutter ablation is also lower than that of atrial fibrillation because the area ablated is much smaller than that of atrial fibrillation.