Technological Advances for Catheter Ablation of Atrial Fibrillation

Atrial fibrillation (AF) is the most common arrhythmia and its prevalence is still increasing mainly due to the demographic changes of the European population. It is estimated that more than 2% of the general population suffer from AF and that 1 in 4 adults over the age of 40 years old will present the arrhythmia during his lifetime.¹ AF has been characterized as the “shame of cardiology” due to the poor efficacy of available therapies. However, during the last decades the introduction of the novel anticoagulants and of the invasive therapy of AF in the form of catheter ablation has substantially improved our armamentarium towards this disease. Atrial fibrillation not only increases mortality by 2-fold in 10 years as it was shown in the Framingham study but it also increases health costs and significantly worsens the quality of life of our patients.

For many years we lacked convincing qualitative data from specifically designed, properly randomized prospective trials on the efficacy of catheter ablation for AF to reduce the burden of the arrhythmia. Recently, the CASTLE trial proved beyond any doubt that AF ablation is by far more efficacious than amiodarone to preserve normal sinus rhythm.² Notably, patients enrolled at the CASTLE trial had undergone implantation of a device, mainly in the form of CRTD, that could accurately follow the burden of AF. At the end of the 60-month follow up the prevalence of AF was reduced by 38% in the ablation group, all-cause mortality was reduced by 25% and cardiovascular mortality by 49%. Reduction of AF burden was also proved at the larger CABANA trial³ where the prognosis results were significantly affected by the low risk of the study population and the crossover of enrolled patients towards the ablation group. Indeed, nowadays it is troublesome to conduct a properly designed trial on AF ablation efficacy in the future mostly because AF ablation is already an established therapy and thus, patients enrolled in clinical trials tend to systematically crossover from the antiarrhythmic drug therapy to the ablation arm confusing efficacy results.

Taking into consideration the increasing role of AF ablation in the management of AF we shall present in this brief report some of the remarkable new tools that aim to increase efficacy and safety of catheter AF ablation and will be soon available in Europe.

1. The new Cryoballoon

Single shot pulmonary veins isolation modalities, mostly in the form of cryoballoon from Medtronic, are increasingly used throughout Europe. The efficacy of cryoballoon ablation to reduce AF burden has been proved to be at least equal to convention radiofrequency (RF) ablation even in patients with persistent AF where pulmonary vein isolation should be considered as the sole target during the first procedure.⁴ The new cryoballoon has been recently introduced by Boston Scientific and promises better efficacy and safety due to its improved design. However, there are still no data supporting its claimed superiority and CE approval is still pending.

There are some issues that need to be addressed concerning cryoballoon AF ablation. Firstly, it will surely spread because of its fast learning curve and secondly it is preferred by electrophysiologists because it is associated with lower overall time in the lab and lower risk for tamponade. However, clinicians need to keep in mind that cryoballoon ablation cannot cure any of the other arrhythmias that are common in AF patients (e.g. atrial flutter, atrial tachycardia and accessory pathways mediated tachycardias). The incidence of these arrhythmias in AF patients may reach 30%. In addition, cases of complex anatomy (e.g. huge common antrum of pulmonary veins and uncommon angulation of some veins and especially of the right inferior vein) may also have a measurable effect on the efficacy of cryoballoon ablation.

In conclusion we rightfully expect that cryoballoon ablation will be improved with the introduction of new tools. However, clinicians need to be aware that their patients need to be treated in centres that are experienced to the whole spectrum of electrophysiology and in the use of RF ablation that may be needed for some of the patients that had been allocated to cryoballoon ablation.

2. Improved imaging

Recent strides in cardiac imaging have substantially improved efficacy and safety of atrial fibrillation ablation. Pre-procedural imaging has been proved to be useful to detect uncommon anatomy and usage of TEE and intracardial echocardiography is considered common practice during the procedure resulting to reduced incidence of transseptal puncture related complications.

In addition to its current clinical use, imaging is expected to improve catheter AF ablation outcomes through the following applications:

• Risk stratification and selection of candidates for AF ablation through detection of atrial fibrosis by delayed - enhancement MRI.⁵
• Early detection of cerebral emboli after AF ablation with high-resolution diffusion-weighted magnetic resonance imaging.
• Improved safety and reduced contrast agent exposure with integration of electroanatomical mapping with intracardiac echocardiography.
• Improved efficacy and safety with the pre-procedural use of 3D printed models of the left atrium, especially in the case of cryoballoon ablation.

3. 2^nd generation Laser Balloon ablation

Laser balloon has been proved to effective isolate pulmonary veins. The main disadvantage of laser balloon technology was the rather lengthy procedures in comparison to the other balloon technologies. This drawback was abolished with the recent introduction of the 2^nd generation of laser balloon. The 2nd-generation laser balloon offers optimized features for improved tissue contact, visibility and procedural time. The MERLIN registry authors recently published that procedure time, left atrial dwelling time and fluoroscopy time significantly decreased with the 2^nd generation laser balloon after a learning curve of 15 cases.⁶ Laser balloon was the first widespread technology that introduced direct visualization of the veins during AF ablation. Although the results of competition with cryoballoon technologies is uncertain there is little doubt that visualization of pulmonary veins and of the position of the catheters and balloons will be further used in electrophysiology in the future.

4. Radiofrequency Balloons Catheter Ablation

Both these devices have been recently introduced and have not yet received CE mark. But they are going to be soon available for use in Europe and the first clinical data from clinical studies in humans are more than encouraging.⁷ They are both innovative combining balloon simplicity with RF energy but the one presented at the B part of the Figure (Luminize RF balloon) also incorporates direct visualization of the veins and of the RF balloon through microcameras. Both are open-irrigated with saline in order to avoid thrombi formation. 

5. Pulsed Field Ablation for Atrial Fibrillation

 Possibly the most promising new technology is pulsed field ablation (PFA). This is a non-thermal tool that creates irreversible micropores at the cell membranes resulting in cell death. PFA has been used before to treat cancer in the form of solid tumors. It could be proved a uniquely safe modality for AF ablation limiting collateral tissue damage because cardiomyocytes present the lowest threshold to pulse electric fields. The first human trials (IMPULSE and PEFCAT) have been recently published presenting quite promising data regarding both efficacy and safety.⁸ Notably, PFA isolation is ultra-rapid and 3-month durability of pulmonary vein isolation reached 100% in these 2 studies.

Conclusions

This is a turning point for AF ablation. We move towards shorter procedures, increased safety, lower exposure to radiation, faster learning curves and improved outcomes. In this brief report we discussed some of the novel technologies that will help us achieve these targets. But most importantly, it is the general cardiologists’ clinical decisions and appropriate selection of candidates for AF ablation that will dominate the management of AF in the near future. We have better tools, we have accumulating experience but we still have the majority of our patients entering the electrophysiology lab at an advanced stage of their disease.

“Better three hours too soon than a minute too late”

William Shakespeare (1564-1616)

About the author

George K. Andrikopoulos, MD, FESC, PhD

Head of First department of Cardiology / Electrophysiology & Pacing

Henry Dunant Hospital Center, Athens, Greece