JACC in a Flash | In the process of radiofrequency (RF) catheter ablation therapy for atrial fibrillation (AF), lesion formation involving the pulmonary veins (PV) is monitored as electrogram diminution and impedance drop during application. However, an understanding of electrode-to-tissue interaction is missing from this equation.

While studies have shown a correlation between electrode-tissue contact and lesion generation, it has been suggested that using a contact force (CF)—sensing catheter during ablation correlates with clinical outcome in AF patients. Recently, SMART-AF was conducted to evaluate the safety and effectiveness of this catheter during standard ablation procedures.

In a recent issue of JACC, Andrea Natale, MD, and colleagues examined the use of an irrigated, CF-sensing catheter for treating of drug-refractory symptomatic paroxysmal atrial fibrillation (PAF) in a total of 172 patients in this prospective, nonrandomized study. The investigational catheter was inserted into 161 patients, and RF energy was delivered to 160 of these. (Of note, the CF catheter used in the present study was developed using a small spring connecting the ablation tip electrode to the catheter shaft with a magnetic transmitter and sensors to measure microdeflection of the spring.)

All 161 patients comprised the safety cohort, while one patient was discontinued and 38 patients were "calibration roll-in" subjects, leaving 122 patients in the effectiveness cohort. At enrollment, each patient had PAF with at least three symptomatic AF episodes during the previous 6 months, and had failed to improve after taking at least one class I or III anti-arrhythmic agent or an atrioventricular nodal-blocking drug. Patients were followed via serial clinic visits and transtelephonic monitoring for 1 year.

Average procedural time was 3.7±1.4 hours; the average ablation time from first to last ablation was 2.0 hours, and the average fluoroscopy time was 41.5±26 minutes. PV isolation was required during all ablation procedures, and half of the cases required more extensive ablation procedures targeting lines, focal targets, and/or nonfocal targets.

The 12-month success rate (meaning freedom from AF/atrial flutter/atrial tachycardia recurrence) was 72.5%, with an average CF of 17.9±9.4 g. A majority of operators used a target CF range between 5 g and 40 g; when the CF during a procedure was within the desired CF range ≥80% of the time, efficacy was significantly higher, compared to when it was not (81% vs. 66%; TABLE). However, average CF during the procedure was not found to correlate with increased procedural success and procedure-related serious adverse events, such as cardiac tamponade.

TABLE. Outcomes Comparison with Various Types and Forces of Ablation Catheters

In terms of safety, among the 161 patients included in the safety cohort, four (2.5%) had cardiac tamponade and four had vascular complications—two of which required surgical repair.

As shown by the study results, Dr. Natale and colleagues concluded, "A CF-sensing catheter helps obtain stable catheter-to-cardiac tissue contact during AF ablation, substantially improving 12-month freedom from AF recurrence." The results are encouraging; however, the mechanism of improved outcomes derived from the use of this catheter requires further investigation—specifically the interaction between contact force, catheter stability, duration, and efficacy of ablation.

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Natale A, Reddy VY, Monir G, et al. J Am Coll Cardiol. 2014;64:647-56.

Keywords: CardioSource WorldNews Interventions

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