Circumferential pulmonary vein isolation (PVI) has become a mainstay in the treatment of atrial fibrillation (AF), particularly in symptomatic patients with paroxysmal AF (PAF) intolerant or refractory to medical treatment. The safety and short-term performance of the novel QDOT® catheter (Biosense Webster, Irvine, CA, USA), that allows for a high-power short-duration (HPSD) ablation, has already been evaluated in the QDOT-FAST clinical study, with favorable data on feasibility and safety, and lowered fluoroscopy and procedure times needed to achieve complete PVI. HPSD ablation was based on immediate heat formation during the resistive phase, affecting a small tissue depth at 90 W/4 s (irrigation at 8 ml/min) with a temperature limit of 65ºC.

However, up to date there are no randomized studies evaluating the real usefulness of the QDOT® catheter. Longer-term follow-up is still required to verify the long-term effectiveness and correlations between short-term follow-up and arrhythmia recurrence when using this catheter. The impact of this novel catheter, when used in conjunction with a personalized ablation protocol that uses the information of left atrial wall thickness (LAWT) to modulate the AI target at each ablation point, compared with a standard ablation protocol following the published CLOSE study criteria is already unknown.

Circumferential pulmonary vein isolation (PVI) has become a mainstay in the treatment of atrial fibrillation (AF), particularly in symptomatic patients with paroxysmal AF (PAF) intolerant or refractory to medical treatment. Dormant conduction and pulmonary vein reconnections are responsible for AF/atrial tachycardia (AT) recurrences owing to incomplete non-transmural ablation lesions that generate gaps on ablation lines.

The advent of contact force (CF) catheters has represented a significant milestone when reaching better efficiency in RF delivery, helping to achieve better PVI rates after AF ablation. The benefits of CF sensing have been already demonstrated in both the SMART AF (THERMOCOOL® SMARTTOUCH® Catheter for the Treatment of Symptomatic Paroxysmal Atrial Fibrillation) and the TOCCASTAR (TactiCath® Contact Force Ablation Catheter Study for Atrial Fibrillation) studies. Moreover, CF stability is also an important predictor of reduced arrhythmia recurrence.

Recently, ablation index (AI) (CARTO3® V4; Biosense Webster, Inc, Diamond Bar, CA, USA) was developed as a novel marker of lesion quality that, for the first time, incorporates CF as well as duration, and power delivery. The recent CLOSE clinical study analyzed the utility of ablation index (AI), a novel formula developed to assess real-time effect of RF delivery and improve the rates of permanent PVI, with 91.3% of the patients free from AF/AT/atrial flutter (AFL) at 12 months follow-up. The CLOSE protocol targeted an interlesion distance (ILD) of 6 mm and AI ≥ 400 at the posterior wall and ≥550 at the anterior wall.

However, another recent study revealed that AI, while being very reliable across a range of CF values, may be 'penalized' by small contact angles and high-power RF applications, which could decrease the lesion size at the same AI. The small lesion size at narrow contact angle may be explained by tip temperature drop due to saline flow from irrigation holes located at the side of the catheter tip during RF application. Bourier et al. reported that extremely high-power RF applications (> 50 W) resulted in significantly smaller lesion depth for short-duration applications (n = 120).

In a swine model, high-power short-duration (HPSD) ablation resulted in 100% contiguous lines with all transmural lesions, whereas standard ablation (25 W for 20 s) had linear gaps in 25% and partial thickness lesions in 29%. The authors of this experimental study used a novel ablation catheter that incorporates 6 thermocouples symmetrically embedded in the circumference of the tip electrode, named QDOT® catheter (Biosense Webster, Irvine, CA, USA). This catheter permits to control the confounding effect of the cold irrigation fluid during ablation, while having an improved irrigation system. In the same study, ablation with HPSD produced wider lesions at similar depth, and improved lesion-to-lesion uniformity with comparable safety endpoints. Given the aforesaid, it can be hypothesized that larger diameter of HPSD lesions might contribute to a complete encirclement of PV, by ensuring better contiguity between adjacent lesions, while the reduced lesion depth may still achieve lesion transmurality in atrial tissue, diminishing the risk of collateral tissue damage.

The safety and short-term performance of the QDOT® catheter (Biosense Webster, Irvine, CA, USA) has already been evaluated in the QDOT-FAST clinical study (Clinical Study for Safety and Acute Performance Evaluation of the THERMOCOOL SMARTTOUCH SF-5D System Used With Fast Ablation Mode in Treatment of Patients With Paroxysmal Atrial Fibrillation), with favorable data on feasibility and safety, and lowered fluoroscopy and procedure times needed to achieve complete PVI. HPSD ablation was based on immediate heat formation during the resistive phase, affecting a small tissue depth at 90 W/4 s (irrigation at 8 ml/min) with a temperature limit of 65ºC.

Up to date, there are no randomized studies evaluating the real usefulness of the QDOT® catheter. Moreover, longer-term follow-up is required to verify the long-term effectiveness and correlations between short-term follow-up and arrhythmia recurrence when using this catheter. The impact of the QDOT® catheter, when used in conjunction with a personalized ablation protocol that uses the information of left atrial wall thickness (LAWT) to modulate the AI target at each ablation point, compared with a standard ablation protocol (CLOSE study criteria) is already unknown.

Our research hypothesis is that QDOT-by-LAW, a personalized protocol that uses a dedicated vHPSD catheter, a multichannel radiofrequency (RF) generator with a vHPSD ablation mode, and integrated LAWT information to adapt the ablation index (AI) target to the subjacent LAWT, is safe, while showing at least the same efficacy and better efficiency than the CLOSE protocol.

Inclusion Criteria:

• Age > 18 years.
• Indication for paroxysmal atrial fibrillation ablation.
• Signed informed consent

Exclusion Criteria:

• Age < 18 years.
• Pregnancy.
• Previous AF redo procedure.
• Impossibility to perform a pre-procedural CT scan.
• Concomitant investigation treatments.
• Medical, geographical and social factors that make study participation impractical, and inability to give written informed consent. Patient's refusal to participate in the study.