Since the seminal publication by Haissaguerre et al.[
20] in 1998, catheter ablation has become accepted therapy for AF refractory to conventional treatment. Electrical isolation of the pulmonary veins (PVI) was found to prevent AF by effective elimination of triggers, which remains the cornerstone for ablation treatment [
21]. The strategy evolved from focal application of a radiofrequency current inside the veins, to segmental linear ablation, to wide area circular ablation, avoiding damage to the pulmonary veins while aiming at eliminating as much ectopy generating tissue as possible. Initially, freedom of AF was claimed in more than 90% of patients, and technical development led to electroanatomical navigation systems to guide ablation. As these procedures required expensive equipment and remained long and difficult, new catheter technologies were designed for quicker ‘single shot’ PVI. The phased radiofrequency multi-electrode array and the cryoballoon came onto the market[
22,
23] and quickly became the most popular single short ablation strategies, which were as effective as existing single-tip ablation catheter procedures but with much shorter procedure times [
24,
25]. The major adverse event rate during AF ablation procedures has become very low by increased operator skills, mapping and navigation systems, and optimising periprocedural anticoagulation, such that stroke, tamponade, severe groin bleeding and mortality have become rare [
25]. However, during clinical follow-up and by using longer and more intense rhythm monitoring it has become apparent that recurrence of AF is much more frequent than reported in the early days. In the randomised FIRE&ICE trial comparing cryoballoon to irrigated radiofrequency single-tip ablation, freedom of AF after 18 months was less than 70%. The most common finding during redo-ablation remains recurrence of electrical conduction between the left atrium and one or more pulmonary veins, regardless of how extensively the index ablation was performed [
26]. There is, however, still a potential for collateral damage to the oesophagus, the phrenic nerve, stroke due to char or thrombus embolisation, and perforation of the wall. This has urged improvements of existing technologies and strategies. Nowadays, single-tip radiofrequency catheters are irrigated and use contact-force sensing to perform safer, quicker, and more effective wide area ablation around the pulmonary vein, with improved AF freedom of up to 87% in low-risk patients with paroxysmal AF, if applications are done with optimal parameters and in close proximity to each other [
27]. Several companies have developed new tools to create lesions with irrigated high-power output but short duration to retain safety and efficacy while further shortening the ablation time. New tools such as diamond-tip catheters allow similar quick radiofrequency delivery with rapid passive cooling by optimal heat exchange capacity, while a novel lattice-tip mesh-based catheter may allow more continuous lesion creation by conforming better to the tissue surface [
28]. The latest cryoballoon iterations by Medtronic and Boston Scientific may provide more homogeneous circular freezing with improved and quicker isolation and higher reported freedom of AF outcomes. Still, the search for easier, safer, and quicker procedures continues and currently the field of AF ablation is exploding with novel tools and energy forms such as multi-electrode radiofrequency balloons and cryoballoon platforms from Biosense-Webster and Boston Scientific, or Adagio’s ultra-low temperature linear cryoablation with custom-built stylet driven shape optimisation for various ablation targets. One of the most promising new strategies is energy delivery by electroporation which is being developed by various companies. By delivering high voltage electrical field applications of only nanoseconds in the proximity of the tissue, the myocytes become irreversibly damaged without any effect on local temperature and specific to myocardial tissue, thereby avoiding char formation or insufficient energy transmission and collateral damage to surrounding structures. The next 5 years will reveal if all these new technologies can live up to their promise for improvement.
Aside from ablation technology, ablation strategy also needs improvement in those with non-paroxysmal AF or comorbidities with structural left atrial changes including dilatation and fibrosis, as PVI even with extensive left atrial substrate ablation shows freedom of AF in no more than half of the patients [
29]. As the ablation strategy may require a more tailored individual approach, new strategies aim at electroanatomical substrate visualisation. High-resolution MRI may be used to determine left atrial wall fibrosis, which may be incorporated in the ablation strategy beyond PVI [
30]. Several companies have developed systems for high-resolution mapping of electrical activation during AF to determine the individual AF mechanism to guide ablation. While TOPERA, the first in its kind, could not live up to initial high expectations (Brachmann et al. Heart Rhythm Society late-breaking clinical trial 2019; unpublished data), other technologies such as CardioInsight body surface mapping[
31] and ACUTUS dipole density mapping[
32] are still developing and testing sophisticated technologies and algorithms to characterise individualised AF patterns in real time to guide ablation and improve outcomes for those where PVI alone is not enough. New electroanatomical mapping technologies such as KODEX (Philips)[
33] or working in an MRI instead of X‑ray imaging environment (Philips/Imricor) may further help guide and improve transmural lesion creation by real-time tissue evaluation.