Although a well experienced group reported

Although a well experienced group reported a very high success rate of 80% after catheter ablation even in patients with congestive heart failure [40], the evidence described above suggests that catheter ablation alone is not sufficient to treat AF in patients with hemodynamic deterioration. This indicates that pharmacological therapies for heart failure, underlying cardiac pathophysiology, and hypertension, such as angiotensin-converting enzyme inhibitors, beta-blockers, statins, and diuretics, are as important as catheter ablation to decrease susceptibility to AF and to prevent recurrence of AF after ablation. Obesity and sleep pla2 inhibitor also affect hemodynamic status and are associated with the prognosis of AF. Continuous positive air pressure therapy (CPAP) may be effective for maintenance of sinus rhythm after ablation [41–43], but this needs to be tested by randomized prospective trials.
Advances in technology to isolate PVs Standard 4-mm-tip ablation catheters were initially used for LA ablation. Because of the unstable and limited energy delivery of 4-mm-tip catheters due to the temperature-limited setting, 8-mm-tip catheters were introduced. However, one of problems in the use of 8-mm-tip catheters was the ambiguity of local electrograms due to the inclusion of far-field electrograms. Since 2000, irrigated-tip catheters have been used in European countries, and they offer several advantages, including delivery of the desired power independent of local blood flow [44]. The usefulness of this technology has been supported in animal models [45] and in patients undergoing ablation of AF [46,47]. Efforts continue to improve the efficacy and safety of LA ablation. Traditional catheter ablation is performed as a single-tip, point-by-point ablation process. This technique requires a high degree of operator skill, and procedures are lengthy, often lasting more than 4h. Creating reliable continuous transmural lesions with a single-point catheter is difficult. During the past decade, a number of alternative ablation systems have appeared, including cryoablation (with a conventional-tip catheter or a circular catheter or balloon device), ultrasound ablation, laser ablation, and an over-the-wire multi-electrode catheter delivering duty-cycled bipolar and unipolar RF energy. A radiofrequency ablation catheter capable of real-time tissue–tip contact force measurements has recently been developed and has garnered particular attention. The contact force between the catheter tip and the tissue may affect the clinical outcome of RF ablation for the treatment of cardiac arrhythmias [48,49]. Insufficient contact force may result in an ineffective lesion, whereas excessive contact force may result in complications. Preliminary studies have indicated that a contact-force sensing catheter is useful for safe catheter manipulation and reduction of fluoroscopy time. In the future, it may also increase the effectiveness of ablations by allowing better control of the lesion size.
Ablation of persistent AF Because triggers/drivers that originate from the PVs and other thoracic veins appear to be the primary mechanism of paroxysmal AF, ablation strategies that target only thoracic vein arrhythmogenicity have been effective in the majority of patients with paroxysmal AF. Additional linear ablation in combination with circumferential PVI resulted in an increased incidence of LA atrial tachycardia compared with circumferential PVI alone in patients with paroxysmal AF [50]. However, elimination of PV arrhythmogenicity alone has been insufficient to eliminate persistent AF. Although catheter ablation has also evolved into an effective treatment strategy in patients with persistent AF [46,47,51,52], the mechanism of persistent AF is still unclear and ablation efficiency remains low.
The mechanism of persistent AF from the procedural point of view The main explanation for the current disappointing ability to control AF is an incomplete understanding of the mechanism underlying its maintenance, despite many years of research and speculation. Over the past 50 years, the multiple wavelet hypothesis has been the dominant mechanistic model of AF. This hypothesis, first postulated by Moe et al., states that AF is the result of randomly propagating multiple electrical wavelets that interact in very complex ways, with local excitation limited by the heterogeneous distribution of refractory periods throughout the atria [68]. According to this model, the number of wavelets at any point in time depends on the atrial conduction velocity, refractory period, and mass. Perpetuation of AF is favored by slowed conduction, shortened refractory periods, and increased atrial mass. The shorter the wavelength is, the higher the number of wavelets there are. The presence of more wavelets makes perpetuation of AF more stable.