Personalized Atrial Fibrillation Ablation With the QDOT Catheter - The QDOT-by-LAW Trial

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.