Atrial fibrillation (AF) is the most common arrhythmia diagnosed in clinical practice and the prevalence is increasing as the US population ages [1, 2]. Without treatment, AF is associated with significant morbidity and mortality, including stroke, embolism, and heart failure [3‐5]. In patients with paroxysmal atrial fibrillation (PAF) refractory to drug treatment, radiofrequency (RF) catheter ablation is an important treatment option that has been shown to be superior to antiarrhythmic drug treatment [6, 7].

The THERMOCOOL SMARTTOUCH® SF Catheter (STSF), a recently developed contact force (CF) catheter, enables real-time sensing of the catheter-to-tissue contact during RF ablation [8]. A 56-hole porous tip has been incorporated in the original CF-sensing catheter design to produce more uniform cooling with less fluid delivery [9, 10]. Compared with the traditional six-hole irrigation system, the porous tip catheter improves procedural efficiency and reduces fluid delivery [11, 12], while maintaining the safety profile for PAF ablation [9].

The acute data from the SMART SF study showed the STSF catheter to be safe with high early effectiveness [11]. A low primary adverse event (AE) rate of 2.5% (4/159) was observed, which is comparable with complication rates for traditional irrigated catheters [7, 8]. There were no unexpected serious AEs related to the study device. Acute effectiveness, defined as confirmation of entrance block for all targeted pulmonary veins (PVs), was 96.2% for subjects who undergone RF ablation. Fluid delivered via the STSF catheter was 44.7% lower than previously reported with the traditional 6-hole non-CF irrigated THERMOCOOL® catheter [7] and 52.2% lower than with the 6-hole irrigated CF THERMOCOOL SMARTTOUCH® catheter [8, 11].

To obtain data on long-term performance, a 12-month extension of the SMART SF study across multiple centers was conducted.

This prospective multicenter study has demonstrated safety and efficacy of STSF for the treatment of patients with drug-refractory symptomatic PAF. The Kaplan-Meier estimate of 12-month effectiveness success was 74.9% with a low incidence of SAEs (7.7%) reported between days 30 and 360, the majority (87%) of which were unrelated to the device/procedures.

Compared with traditional 6-hole contact force-sensing catheters, the THERMOCOOL SMARTTOUCH® SF catheter has a 56-hole porous tip and delivers uniform cooling at half the flow rate. This prior study showed that the reduction in flow rate resulted in an overall decrease in fluid delivery of 44.7 to 52.2%, a significant consideration to patients with existing comorbidities, in which fluid overload could adversely affect cardiac function. The positive safety and short-term effectiveness observations in the initial safety phase presented in Chinitz et al. [11] were also associated with improved procedural efficiency with respect to procedure and fluoroscopy times.

Reports of the long-term outcomes of AF ablation with STSF are limited. Previous studies reported 12-month success rates between 80 and 90% in PAF populations (including short-term persistent AF in one study) from single-center or limited multicenter evaluations [12, 13]. Our results represent the experience of a large number of centers (13), therefore likely representative of broader real-world practice. Overall, 12-month effectiveness with STSF was comparable with a previous PAF ablation study (SMART AF) of similar study design using the predecessor 6-hole irrigated CF catheters [8]. Compared with the original THERMOCOOL AF IDE study, conducted almost a decade ago, the current success rates in the SMART AF and SMART SF studies are substantially higher (74–75% vs. 66%) [7]. This finding is further supported by a previous meta-analysis across CF vs non-CF studies showing a decrease in 12-month AF recurrence with the use of CF technology [14‐16]. The upward trend in long-term success over time and over CF vs. non-CF ablation studies is encouraging and consistent with the expectation of improved outcomes due to advancement in technologies and catheter ablation experience. Safety of PAF ablation with STSF is further confirmed from long-term safety monitoring of this trial. More recently, a real-world multicenter Italian registry utilizing STSF/Visitag reported higher 12-month success of 90% with lower procedure time (100 min) and fluoroscopy time (6 min) [13].

Compared with those who elected not to be included in the study extension through 12 months of follow-up (non-EP), patients in the EP group tended to have higher percentage of female patients and higher proportion with coronary artery disease. This is reflective of real-world patient decision-making in that patients with symptoms are more likely to seek continue treatment in contrast to patients who feel better who are more likely to exit treatment follow-up. In addition, both gender (being female) and advanced age have previously been shown to be risk factors for recurrence after catheter ablation [17‐19]. It is possible that the 12-month success rate observed in the effectiveness evaluation period of this study represented a more symptomatic or sicker patient population than that of the original study, and thus that the success rate in a more representative population would have been higher than what was observed.

This study is limited by the single-arm design and the need for patients to re-consent in order to continue in the effectiveness evaluation phase. Of the 165 patients in the initial safety study, 135 were invited to participate in the effectiveness phase of the study and 80 consented to continue in the study. As such, study participation was not randomized and could have been biased, as observed with some differences in baseline patient characteristics and comorbidities between EP and non-EP patients.

The SMART SF 12-month evaluation confirms the effectiveness of PAF ablation with STSF. One-year success is high (74.9%) and is coupled with a good long-term safety profile.