Review: Focal Impulse and Rotor Modulation (FIRM) Ablation

Finding Focal Impulse and Rotor Modulation (FIRM) with the RhythmView^™ 3D Electrophysiological Mapping System (Topera, Inc.) is an innovative approach in atrial fibrillation (AF) ablation, and shows promising results in treatment of AF. The purpose of our article is to review this novel strategy.

BACKGROUND

Atrial fibrillation is the most common cardiac arrhythmia, and its incidence increases with advancing age.¹ The prevalence of AF is between 2.7 million and 6.1 million among American adults, and it is projected to increase to between 5.6 and 12.1 million by 2050.² Patients with AF have a fivefold increased risk of ischemic stroke, and a threefold increased risk of heart failure (HF). In addition, AF is associated with a twofold greater risk of dementia and mortality.³

AF is classified into different categories based on the duration of the arrhythmia episodes. If AF terminates spontaneously or with intervention in a period of 7 days from onset, it is called paroxysmal AF (PAF); AF lasting more than 7 days is defined as persistent AF. Continuous AF that lasts longer than one year is called longstanding persistent AF. Patients with continued AF, for whom all attempts to restore and/or maintain sinus rhythm has been stopped through a joint decision by the patient and physician, are categorized as permanent AF.³

Symptomatic paroxysmal AF, which is refractory or intolerant to at least one class 1 or class 3 antiarrhythmic medication, is the leading driver for the utilization of catheter ablation (Class I recommendation). Additionally, catheter ablation is recommended as a reasonable therapy for symptomatic persistent AF, in which the patient is refractory or intolerant to at least one class 1 or class 3 antiarrhythmic medication, or as a first-line treatment in patients with symptomatic paroxysmal AF (Class IIa recommendation).³

Pulmonary veins (PVs) are the most common sources of rapid ectopic beats that trigger AF; however, up to 28% of AF may be triggered from other sources such as the posterior LA, coronary sinus, ligament of Marshall, interatrial septum, appendages, and vena cava.^3,4

MILESTONES IN THE MANAGEMENT OF AF ABLATION 

In the early 1990s, John Swartz opened the door for catheter ablation in the EP lab when he attempted to replicate the Cox-Maze surgery concept (an open-heart surgical procedure to cure AF by making a maze-like pattern of incisions in the upper chambers of the heart⁵) in the EP lab. However, high complications, long fluoroscopy time, and a very lengthy procedure made his efforts too futile to pursue.

In 1998, a major breakthrough came to AF ablation as Haïssaguerre et al observed that a vast majority of AF was initiated by triggers from a focal source in the PVs and ablation of the focal source in the PV ostium eliminated PAF (segmental PV ostial isolation).⁶  

In 2000, Pappone et al proved the electroanatomic guided circumferential radiofrequency (RF) ablation of the PV ostia to be a safe and effective technique to cure paroxysmal or permanent AF. This technique is known as wide area circumferential ablation (WACA).⁷

Four years later, Nademanee et al described ablation of continuous fractionated electrical activity (CFAEs) as an effective treatment for chronic and paroxysmal AF. CFAEs are defined as fractioned electrograms that display 2 or more deflections with very short cycle length (CL) (≤120 ms), and usually have low voltage (0.05-0.25 mV).

In December 2010, the cryoablation catheter was approved by the U.S. Food and Drug Administration (FDA). Cold temperatures are used in cryoablation to alter the cells that conduct abnormal heart rhythms. Cryoablation is mainly utilized for PAF. The Sustained Treatment of Paroxysmal Atrial Fibrillation (STOP AF) trial confirmed the safety and efficacy of this procedure in the treatment of PAF.⁸

In 2012, Narayan et al demonstrated that a very rapid firing focus drives the atria and maintains AF through short re-entrant circuits (rotors and drivers), and ablation of these sources could terminate AF without pulmonary vein ablation.⁹ Ablation of electrical rotors and focal impulses may have been the most important breakthrough in catheter ablation of AF since Haïssaguerre’s discovery.

FIRM ABLATION

Topera’s RhythmView 3D Electrophysiological Mapping System, which received 510(k) clearance by the FDA in 2014,¹⁰ provides a dynamic representation of the electrical activity of the heart. The electrical signals of the heart are captured by placing Topera’s FIRMap^™ catheter in the left and right upper chambers of the heart. The tip of the FIRMap catheter has a spherical expandable “basket” that consists of 64 evenly-spaced electrodes, which are placed over the eight splines that form the basket and could capture the point-by-point electrical activity of the heart (Figure 3). The RhythmView Workstation analyzes the captured signals and makes a graphical display to show the specific locations in the heart which could sustain an arrhythmia.¹¹ Early data of ablating these locations (electrical rotors) with radiofrequency has shown promising results for AF treatment.⁹ The CONFIRM (Conventional Ablation for Atrial Fibrillation With or Without Focal Impulse and Rotor Modulation) Trial showed higher freedom of AF after a single procedure in FIRM-guided group (82.4%) in comparison to FIRM-blinded cases (44.9%) in a median of 273 days follow-up (interquartile range: 132 to 681 days). In the CONFIRM study, 92 patients with paroxysmal or persistent AF (72%) were recruited and prospectively enrolled to FIRM-guided ablation group (n=36) or conventional ablation group (n=71; FIRM-blinded).⁹ Extended follow-up of the CONFIRM Trial demonstrated that freedom of AF was higher in the FIRM-guided group (77.8% [21 of 27]) versus the convectional ablation group (38.5% [25 of 65]) during a median of 890 days follow-up after 1.2 + 0.4 procedures (median 1; interquartile range: 1 to 1).¹²

CONCLUSION

Mapping of rotors is a new development that may allow us to improve the long-term outcome of AF. Catheter ablation of patient-specific electrical rotor and focal sources shows significant advantage to reduced late recurrence of atrial arrhythmias on approximately three-year follow-up versus the conventional AF ablation approach, in which we only eliminate triggers without finding and eliminating rotors. 

Disclosure: The authors have no conflicts of interest to report regarding the content herein. 

References

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