**Abstract**

Various treatment methods have been used for atrial fibrillation (AF), which has long been a cause of cerebral infarction and heart failure. Antiarrhythmic drug, the first developed treatment, was not effective in maintaining sinus rhythm and did not improve prognosis. In contrast, pulmonary vein (PV) isolation is effective in paroxysmal AF, expected to maintain sinus rhythm by 70–80% in the first session. Therefore, catheter ablation is the first-line treatment for patients with drug-resistant paroxysmal AF. For PV isolation, radiofrequency ablation was developed first, followed by cryoballoon ablation, which was shown to be not inferior to radiofrequency ablation. In contrast, for persistent AF, PV isolation alone has been found to result in a low rate of maintenance of sinus rhythm. However, there has been no impact of the additional radiofrequency application on AF recurrence rate. Recently, a number of the predictive factors of AF recurrence after AF ablation have been reported. Among them, AF duration, defibrillation threshold, left atrial volume are considered useful as predictors of atrial fibrillation recurrence after ablation. In order to improve the outcome of AF ablation, it is desirable to select patients with AF in consideration of the predictive factors of AF recurrence after AF ablation.

**Keywords:** atrial fibrillation, catheter ablation, pulmonary vein isolation, atrial fibrillation recurrence, defibrillation threshold

#### **1. Introduction**

Atrial fibrillation (AF), the most common sustained cardiac arrhythmia, causes cerebral infarction or heart failure. For this reason, treatment strategies for it have been studied for several years. The Atrial Fibrillation Follow-up Investigation of Rhythm Management study [1] published in 2002 reported that, compared with a rate control strategy, a rhythm control–induced strategy with medications does not help improve AF prognosis. In contrast, in catheter ablation, a nonpharmacological therapy for AF reported in 1998 by Haïssaguerre et al. [2], frequent ectopic beats arising from the pulmonary veins (PVs) contribute to AF development, while PV electrical isolation can maintain sinus rhythm. The Catheter Ablation vs. Antiarrhythmic Drug Therapy for Atrial Fibrillation (CABANA) trial [3] showed that AF recurrence occurred less frequently in the ablation group than in the standard medical therapy group. The ablation group in the same trial showed improved quality of life among patients with AF compared with the standard medical therapy group. Furthermore, the Catheter Ablation

for Atrial Fibrillation with Heart Failure (CASTLE-AF) trial demonstrated that, among patients with congestive heart failure, ablation therapy prevented more events than medical therapy [4]. Based on the European Society of Cardiology Guidelines, catheter ablation is the first-line treatment for patients with drug-resistant paroxysmal AF. The FIRE AND ICE trial, which compared the efficacy and safety of radiofrequency ablation versus cryoballoon ablation for drug-resistant paroxysmal AF, determined that the cryoballoon ablation invented in recent years was not inferior to radiofrequency ablation [5]. However, compared with paroxysmal AF, persistent AF has a higher recurrence rate after ablation. To improve the prognosis of persistent AF, the ablation of atrial substrates, including linear ablation [6], complex fractionated atrial electrogram (CFAE) ablation [7], CARTOFINDER [8], ExTRa Mapping [9], and non-PV foci ablation [10], has been performed in addition to pulmonary vein isolation (PVI). A report of whether these procedures can further prevent AF recurrence is expected in the future.

AF development is orchestrated by many risk factors, including hypertension, overweight/obesity, dyslipidemia, diabetes, tobacco smoking, and excessive drinking [11, 12]. Thus, managing these risk factors is important for its prevention.

In addition, patient selection is considered important for improving treatment outcomes; therefore, it is necessary to identify a new index that correlates with patient prognosis.
