Results from the SMART-AF trial, recently published in the Journal of the American College of Cardiology, have shown that the ThermoCool SmartTouch contact force-sensing catheter is safe and effective for the treatment of drug-refractory symptomatic paroxysmal atrial fibrillation.
SMART-AF was a prospective, multicentre, non-randomised trial designed to assess the safety and effectiveness of the ThermoCool SmartTouch catheter (Biosense Webster) to support Food and Drug Administration (FDA) approval in the USA. The device, which enables direct and real-time measurement of contact force during catheter ablation procedures, was subsequently FDA approved in February 2014.
Andrea Natale (Texas Cardiac Arrhythmia Institute at St David’s Medical Center, Austin, Texas) principal investigator of the study, and others, enrolled 172 patients at 21 sites, from June to December 2011. The safety cohort included 161 patients, who had the catheter inserted. The effectiveness cohort included 122 patients who were ablated. Enrolment required at least three symptomatic atrial fibrillation episodes within the six months before enrolment and non-response to at least one antiarrhythmic drug.
The researchers found that the probability of freedom from atrial fibrillation at 12 months-according to the effectiveness cohort and Kaplan-Meier analyses-was 72.5%. In the safety cohort there were not deaths, stroke, cerebrovascular accident, atrioesophageal fistula, myocardial infarction, thromboembolism or pulmonary vein stenosis reported during the study period. Procedural-related serious adverse events occurring within seven days of the procedure included four tamponade, three pericarditis, one heart block (prior to radiofrequency application) and four vascular access complications.
They also found that repeat ablation procedures without recurrence during the effectiveness period was approximately 5%, “which is substantially lower” in comparison to the 20% – 40% reported in the 2012 HRS/EHRA/ECAS expert consensus statement on catheter and surgical ablation of atrial fibrillation (Calkins et al, HeartRhythm 2012;9:632-96.e21). In addition, Natale et al found that patients who underwent radiofrequency ablation showed clinically meaningful improvement in quality of life and symptom severity and frequency.
Natale et al comment that, until now, there were limited animal and human studies suggesting a correlation between electrode-tissue contact and radiofrequency lesion generation. In this study, they report that the contribution of real-time contact force sensing to the ablation outcome “was demonstrated by the significantly higher success rate (probability of freedom from recurrence of 81% (≥80) vs. 66% (<80)) in patients where the investigators stayed within their selected contact force range ≥80% of the time during radiofrequency application.” They write that these patients were 4.25 times more likely to have primary effectiveness success at 12 months. This suggests that consistent and stable catheter-tissue contact is necessary for effective ablation results.
In an accompanying editorial, Hugh Calkins (Department of Cardiology, Johns Hopkins Hospital, Baltimore, USA) questions the results of this trial regarding contact force monitoring during atrial fibrillation ablation, he says: “Although the efficacy of the force-sensing ablation system was superior to that reported in the original ThermoCool AF trial (72.5% vs.66%), this may or may not be the result of contact force monitoring. The ablation field has advanced considerably since 2004 when this prior trial was launched. We now have a better appreciation for the importance of permanent pulmonary vein isolation. We now know that the use of deflectable sheaths improves outcomes. We now have the benefit of nearly a decade of additional experience performing atrial fibrillation ablation. So, is the 10% improvement in efficacy due to force monitoring?”
He continues, “Firm conclusions are challenging, despite the post hoc analysis that revealed that operators who obtained the best results kept contact force in their ideal range at least 80% of the time. Based on this I would anticipate that cardiac tamponade would be avoided by knowing the contact force. But this was not the case.”
Calkins concludes that ablation catheters that allow contact force monitoring “will become the new standard of radiofrequency ablation […] The hope of those involved with radiofrequency ablation is that the incorporation of contact force sensing into radiofrequency ablation catheters will make our dreams come true, including more permanent pulmonary vein isolation, greater efficacy, fewer left atrial flutters due fewer gaps in lines, improved safety, and quicker procedures.”
SMART-AF is “the first study of its kind and the results will need to be confirmed in future randomised, controlled trials against traditional non-contact force-sensing irrigated catheters,” Natale et al write.