**2. Prognosis differs among ablation devices**

#### **2.1 AF recurrence rates for radiofrequency ablation versus cryoballoon ablation**

Cryoballoon ablation is a procedure that involves inducing necrosis by exposing the myocardium to ultralow temperatures. PVI using cryoballoon ablation is currently performed in many medical facilities because cryoballoon ablation catheter is relatively easy to handle compared with a radiofrequency ablation catheter. Because the cryoballoon's radius cannot be adjusted, electrical isolation is difficult in some cases; therefore, it is important to confirm the locations of the PV and left atrium using preoperative computed tomography. In the FIRE AND ICE trial, the effectiveness of cryoballoon ablation was not inferior to that of conventional radiofrequency ablation, while the operating time for cryoballoon ablation was significantly shorter.

#### **2.2 Laser balloon ablation**

Laser balloon ablation enables observation of the crimped myocardium through the endoscope following balloon occlusion of the PV. Furthermore, the laser balloon enables free adjustment of the balloon size, target ablation site, and output power. The flexibility of the laser balloon allows an operator to perform a personalized PVI. One previous study reported that treatment outcomes for paroxysmal AF vary widely among patients [13]. Other studies reported the high incidence of phrenic neuropathy.

The isolation success and complication rates involve a learning curve. Laser balloon ablation is expected to have safe and good treatment outcomes if used properly.

#### **2.3 Hot balloon ablation**

In a hot balloon catheter, a compliant balloon made of polyurethane is attached to the end of the catheter, while electrodes for radiofrequency energy and a temperature *Predictors of Atrial Fibrillation Recurrence after Ablation DOI: http://dx.doi.org/10.5772/intechopen.105163*

sensor are placed inside the catheter. In hot balloon ablation, the administration of a contrast–saline mixture causes the balloon to fully expand to the appropriate size and then press against the tissue surrounding the PV. The balloon is heated to 70°C by energizing of the radiofrequency current in the balloon electrode. Compared with cryoballoon, the major difference of hot balloon ablation is to change the balloon size. Furthermore, hot balloon ablation is considered a relatively safe method because the temperature for tissue heating is ≤70°C. For that reason, the steam pop phenomenon does not occur. We are awaiting the results of a multicenter study of its clinical performance [14].

#### **2.4 Pulsed field ablation**

Pores in cell membranes are made using electric pulses, through which substances can enter cells, a phenomenon called electroporation. This method has been used for transformation, by which *Escherichia coli* or animal cells deliver DNA into cells; however, irreversible electroporation, which kills cells via irreversible perforation, has also been developed. The electric pulse frequency that kills cells differs among tissues. When applying the frequency to ablation, it is possible to selectively ablate the atrial muscle without affecting the tissues surrounding the blood vessels, nerves, and esophagus. Although the number of cases is small, the effectiveness and safety of pulsed field ablation have been reported [15].

#### **3. AF recurrence after persistent AF ablation**

Along with the progress of catheter ablation, the proportion of patients cured of AF among those with paroxysmal AF is high in all medical facilities; however, in terms of the ablation of persistent AF, the proportion of patients cured of AF still shows great variability among medical facilities.

According to the CASTLE-AF trial, catheter ablation for AF complicated by heart failure significantly decreases the composite endpoint of hospitalization; thus, its use for persistent AF is becoming increasingly significant. Although persistent AF is associated with non-PV foci ectopy, degeneration of the atrial substrate also contributes greatly to persistent AF. To improve the outcomes of persistent AF, ablations other than PVI targeting the left atrial substrate published in recent reports are described below.

#### **3.1 Complex fractionated atrial electrogram (CFAE)**

Nademanee et al. defined local potentials (cycle length ≤ 120 ms) or continuously fractionated potentials as complex fractionated atrial electrogram (CFAE). According to Nademanee et al., CFAE during AF indicates regions of slow conduction and pivot points, within which ablation can terminate AF. However, CFAE does not always imply a reentry circuit that sustains AF; rather, it sometimes indicates the regions in which the excitable media that underlie fibrillation can be passively propagated or the etiology of AF is not connected. The Substrate and Trigger Ablation for Reduction of Atrial Fibrillation (STAR AF II) trial [16] demonstrated that CFAE showed no significant difference when compared with PVI alone in terms of prevention of AF recurrence. Therefore, this method has not been used in recent years.

#### **3.2 Linear ablation**

Linear ablation has been used previously. The most common linear ablations consist of a "roof line" that creates an ablation line connecting the right and left superior PVs and a "mitral isthmus line" creating an ablation line connecting the posterolateral mitral annulus and the left inferior PV. However, because the linear ablation technique is difficult to perform in many cases, prolonged procedure time and complications occasionally occur. Additionally, residual conduction gaps may cause recurrent arrhythmias.

In the STAR AF II trial, no significant difference was reported between linear ablation and PVI alone in terms of preventing AF recurrence.

#### **3.3 Non-PV foci**

Ablation of PVI and non-PV foci is necessary to improve treatment outcomes. Non-PV foci arise from the superior vena cava, left atrial posterior wall, atrial septum, mitral annulus, ligament of Marshall, coronary sinus, and crista terminalis. Active induction is often required to identify non-PV foci. When AF lasts longer, cardioversion is used to restore sinus rhythm. When AF recurs, it is necessary to identify its triggers. During sinus rhythm, induction is attempted by isoproterenol loading, ATP loading, and atrial pacing. To enable wide mapping, multiple electrodes are placed at various locations, and the region originating from the non-PV foci, which act as AF triggers, is identified from the early electric potentials recorded.

#### **3.4 Ganglionated plexus**

Ganglionated plexuses (GPs), which are mainly embedded within fat pads distributed to the epicardial surface of the atrium, contain the same number of cholinergic and adrenergic neurons. The cell bodies of GP neurons are densely populated by the following five areas of left atrial GPs: superior left GP, Marshall tract GP, anterior right GP, inferior left GP, and inferior right GP. GP ablation makes it possible to inhibit and eliminate both PV firing and fractionated atrial potential. According to Nakagawa et al. [17], among 63 patients with paroxysmal AF who underwent GP ablation and PVI, 90% did not experience AF recurrence at 1 year of follow-up.

#### **3.5 CARTOFINDER™**

The CARTOFINDER™ mapping system for AF catheter ablation, which was developed in recent years, enables the generation of wavefront propagation maps acquired from bipolar and unipolar signals using a 64-pole basket catheter. After filtering the ventricular activation signals, the unipolar signal created between two neighboring bipolar signals is annotated, and the focal and rotational activities are recorded. Ablation is performed on these drivers that terminates AF. The effectiveness of this ablation was reported previously, and future reports on clinical outcomes are expected.

#### **3.6 ExTRa Mapping™**

To completely cure patients with persistent AF using catheter ablation, it is necessary to determine the location of AF drivers in the atria. Ashihara et al. developed the first online real-time clinical arrhythmia visualization system, the ExTRa Mapping™. This system includes specialized artificial intelligence based on intracardiac electrocardiography signals recorded by a 20-pole spiral-shaped catheter inserted into the atrium and visualizes arrhythmia by combining the action potential waveform of the human atrial muscle calculated by computer simulation. Highly intensified rotor sites in the visualized areas are ablated.

#### **3.7 Low-voltage area ablation**

This ablation procedure targets the low-voltage area in AF. However, it has limitations; for example, the definition of low-voltage areas is inconsistent, the low-voltage area can be influenced by map density or mapping catheter, and mapping during AF may overestimate the low-voltage area [18].

#### **3.8 Left atrial appendage isolation**

The left atrial appendage, a known frequent origin of non-PV triggers [19], is likely involved in the sustained form of AF. Left atrial appendage isolation carries the risk of cardiac perforation. Furthermore, patients who undergo isolation must be placed on lifelong anticoagulation therapy or undergo left atrial appendage closure; therefore, indications for this procedure must be carefully considered [20].
