Atrial Fibrillation Ablation and Contact Force

The number of patients with atrial fibrillation (AF) continues to grow in the United States. Catheter ablation is now a well-established treatment option for patients. The cornerstone for AF ablation is achievement of complete isolation of the pulmonary veins (PVs). Since the development of this procedure, much progress has been made, with improvement in long-term success and decreases in complication rates in experienced centers. 

There is, however, continued opportunity to increase success rates in patients undergoing catheter ablation, as one of the known limitations has been the rate of recurrences — almost invariably associated with electrical reconnection of the PVs. Over the past decade, a large body of clinical research has been dedicated to the development of a more efficacious tool. 

It is well known that durable and transmural lesions are needed to achieve long-term success. Catheter stability and good tissue contact as well as power delivered by radiofrequency catheters are the variables needed to achieve that goal. Optimization of electrode-tissue contact can produce better lesions (with greater transmurality) while preventing complications secondary to excessive force.¹ Up until recently, electrophysiologists were left with surrogate measures of contact, such as intracardiac electrograms and impedance changes during ablation.²

The ThermoCool^® SmartTouch^® Catheter (ST Catheter; Biosense Webster, Inc., a Johnson & Johnson company) is the first FDA-approved catheter in the U.S. that directly measures contact force (CF) continuously, providing the data in real time and allowing electrophysiologists to have an objective measure of tissue contact. This technology has allowed us to focus on electrode-tissue contact, keeping CF at a safe yet effective level. This increases the chances that transmural and durable lesions will be created, and in turn that we will achieve better outcomes. In this article we will discuss our experience with this technology at St. Vincent’s Birmingham.

Clinical Data 

The safety and effectiveness of the ST Catheter has been evaluated both in prospective multicenter and smaller single-center studies. The catheter has been available clinically since 2012 in Europe, where a growing body of evidence has demonstrated a link between contact force and better outcomes.^3,4 In the United States, the SMART-AF Trial randomized patients to either the ST Catheter or the ThermoCool^® Catheter. One-year results from the trial showed that patients experienced a 74 percent overall success rate when the ST Catheter was used, with higher success rates the longer physicians stayed within an investigator-selected CF range. Results from a sub-analysis of the SMART-AF data recently presented at Heart Rhythm 2014, the Heart Rhythm Society’s 35th Annual Scientific Sessions, showed that across all subjects and centers, the success rate was consistently greater than 80 percent when investigators stayed within a pre-selected CF range. The trial demonstrated the importance of CF stability and its impact on clinical outcomes.

Many other studies have shown that AF ablation guided by CF is more effective both acutely and long term.⁵ When contact forces were kept at 10-20g, there was a significantly lower chance of acute vein reconnection,⁶ while better long-term success rates were seen. Interestingly, use of the ST Catheter while diligently keeping CF between 10-20 was also associated with lower procedural, ablation and fluoroscopy times because more efficacious lesions were delivered. The data from the ST Catheter provides us with objective data that good lesions were delivered in first pass.

Fluoroscopy Use and Contact Force Catheters

Fluoroscopy is traditionally used in electrophysiology for catheter manipulation. Catheter ablation typically requires extended fluoroscopy times, which can carry short- and long-term risks to physicians, lab staff, and patients. With the diligent use of 3D mapping systems, as well as various devices leveraging ultrasound technology, electrophysiologists have been able to significantly reduce fluoroscopy utilization. At our laboratory, the average fluoroscopy time for catheter ablation of atrial fibrillation is less than one minute. We believe that CF is the ultimate tool that can be used by electrophysiologists in reducing fluoroscopy use. By providing real-time measurement of CF, one can manipulate the catheter guided only by a 3D mapping system in a much safer way. The need for fluoroscopy during some portions of the procedure is greatly minimized.

Our Experience

In our laboratory, we have worked on reducing fluoroscopy for quite a while. New technologies were incorporated in a stepwise fashion, which allowed a progressive decrease in fluoroscopy times to current levels:

1. Greater reliability on 3D mapping for catheter navigation.
2. Shaft visualization, which allowed easier and safer non-fluoroscopic catheter manipulation.
3. The CartoUnivu^™ Module (Biosense Webster, Inc., a Johnson & Johnson company), which uses fluoroscopic images (e.g., either still frames or cine loops of angiograms) as the background picture of the 3D mapping system. 

The ST Catheter was initially used at our EP laboratory in March 2014. Since then, we have performed over 50 ablations of atrial fibrillation using the new device.

AF ablations are performed using a wide area ablation technique and the catheter is moved every 15 seconds while radiofrequency is on. The contact force is kept at >10 grams, while each ablation point is automatically annotated by the VisiTag Module (Biosense Webster, Inc.). As each ipsilateral vein is encircled, we usually stop to analyze the data collected by the VisiTag Module. The ablation points are then color-coded based on CF, force time integral (FTI) and lesion times. Sites where we had not obtained CF >10g or high FTI are targeted for further ablation. After ablation is complete, we use adenosine and isoproterenol to attempt to reinduce acute vein reconnection. Since the introduction and diligent use of the ST Catheter, we have noticed a much lower number of acute reconnections using this technique. The ST Catheter has also led to a lower procedural time with no changes in complication rates. 

Conclusion

Atrial fibrillation ablation is a now considered the treatment of choice for patients with drug refractory symptomatic paroxysmal AF. Recurrence of AF, commonly associated with vein reconnection and complications, are some of the major problems we face. In the quest for a safer and more effective procedure, the ST Catheter is a great addition to our armamentarium. Research shows better acute and long-term success rates when CF is measured and kept within a certain range. The addition of the ST Catheter has made catheter navigation safer and has led to a significant decrease in ablation and procedural times at our institution.

Disclosures: The authors have no conflicts of interest to report. Outside the submitted work, Dr. Osorio reports consultancy with Biosense Webster.

References

1. Marijon E, Fazaa S, Narayanan K, et al. Real-Time Contact Force Sensing for Pulmonary Vein Isolation in the Setting of Paroxysmal Atrial Fibrillation: Procedural and 1-Year Results. J Cardiovasc Electrophysiol. 2013 Oct 8. doi: 10.1111/jce.12303. [Epub ahead of print].
2. Nakagawa H, Kautzner J, Natale A, et al. Locations of high contact force during left atrial mapping in atrial fibrillation patients: electrogram amplitude and impedance are poor predictors of electrode-tissue contact force for ablation of atrial fibrillation. Circ Arrhythm Electrophysiol. 2013;6(4):746-753.
3. Stabile G, Solimene F, Calo L, et al. Catheter-tissue contact force for pulmonary veins isolation: a pilot multicentre study on effect on procedure and fluoroscopy time. Europace. 2014;16(3):335-340.
4. Kuniss M, Lehinhant S, DPajitnev, Zaltsberg S, Greiss H, Berkowitsch A. Clinical success of conventional vs. contact force-controlled radiofrequency catheter ablation of atrial fibrillation: clinical outcome after 12 months. Heart Rhythm Society. 2013; (abstract # AB35-04).
5. Kimura M, Sasaki S, Owada S, et al. Comparison of lesion formation between contact force-guided and non-guided circumferential pulmonary vein isolation: A prospective, randomized study. Heart Rhythm. 2014 Mar 18. [Epub ahead of print]
6. Sotomi Y, Kikkawa T, Inoue K, et al. Regional Difference of Optimal Contact Force to Prevent Acute Pulmonary Vein Reconnection during Radiofrequency Catheter Ablation for Atrial Fibrillation. J Cardiovasc Electrophysiol. 2014 Apr 24. doi: 10.1111/jce.12443. [Epub ahead of print].