Value of the LocaLisa Non-fluoroscopic Mapping System in the Ablation of Atrial Fibrillation

Ablation of Atrial Fibrillation

P. S

, P. J

, M. H

, L.-F. H

, G.D. Y

, C. S

, P. K

, M. R

, Y. T

, T. R

, F. S

B. J

, M. S

, M.

H

Background

Achieving and maintaining sinus rhythm in patients with atrial fibrillation (AF) is the optimal therapeutic outcome. While antiarrhythmic therapy to maintain sinus rhythm has been demonstrated to be of limited efficacy [1–3], preliminary evidence suggests a beneficial effect of catheter ablation strategies to achieve and maintain sinus rhythm [4, 5]. The importance of the interaction between the triggers and substrate in the development of AF is well-recognised. Catheter ablation strategies are centred on pulmonary vein (PV) ablation. However, it is becoming evident that most patients with per- manent or persistent AF and 30–40% of those with paroxysmal AF will require additional substrate modification to improve the outcomes of AF ablation [6]. Several modalities of substrate modification have been pro- posed and include linear atrial ablation [7–9], ablation of fractionated elec- trograms [10], ablation at sites of high-frequency activity [11], and attempts at vagal denervation [12]. However, these procedures are technically chal- lenging and associated with prolonged procedural and fluoroscopic dura- tions.

Recently, several localising and three-dimensional mapping tools have emerged to facilitate and reduce the fluoroscopic exposure associated with AF ablation. This review will focus on the use of the LocaLisa (Medtronic) non-fluoroscopic mapping system for anatomical guidance during the abla- tion of AF.

1Hôpital Cardiologique du Haut-Lévêque, and Université Victor Segalen Bordeaux II, Bordeaux, France;²Department of Cardiology, Royal Adelaide Hospital, and Department of Medicine, University of Adelaide, Adelaide, Australia

The LocaLisa Mapping System

The LocaLisa mapping system has been developed to allow three-dimension- al catheter localisation. This is based on externally applied electrical fields and works on the principle that a voltage drop occurs as the current passes through the various body structures. Three orthogonally placed pairs of skin electrodes are used to send small, 1-mA currents between each pair of skin electrodes (each at a slightly different frequency: 30.27 kHz, 30.70 kHz, and 31.15 kHz). Standard intra-cardiac catheters are used as sensors to detect these thoracic electrical fields. By digitally separating the three frequencies, the three-dimensional position (X, Y, and Z directions, respectively) of the catheter can be determined. Each electrode on the system can be used as a sensor and displayed in terms of its relative position. The location accuracy of the system has been demonstrated to be better than 2 mm, with a strong linear correlation with fluoroscopically determined catheter locations (cor- relation coefficient 0.996–0.999) [13].

Pulmonary Vein Isolation

While a number of sites within the atria have been reported to initiate AF, the PVs are recognised as the dominant source of triggers initiating AF in many clinical situations [14]. Spontaneous activity arising from the PVs can manifest in a spectrum of atrial arrhythmias, isolated extrasystoles, slow atrial rhythms, and atrial tachycardia [14]. Rapid sustained focal discharges (sometimes for hours, days, or longer) may drive sustained AF (true ‘focal’

AF), but more commonly short bursts initiate AF in patients with the appro- priate atrial substrate [14]. More recently, it has been suggested that the PVs also have a role in the maintenance of a significant proportion of cases of paroxysmal AF [15, 16].

Circumferential mapping catheters have enabled evaluation of the peri- metric distribution and activation sequence of PV activity to allow their effective isolation. Ablation of the PVs guided by circumferential mapping is performed 1 cm from the ostium of both right-PVs as well as for the poste- rior and superior aspects of the left-PVs, to minimise the risk of PV stenosis.

However, when ablation is required at the anterior portions of the left-PVs, energy is delivered within the first millimetres of the PV (rather than the posterior wall of the appendage) to achieve effective disconnection.

Radiofrequency (RF) energy is delivered for 30 s at each point and this

application is prolonged for 1–2 min when a change occurs in the morphol-

ogy or sequence of the PV potentials, as determined by circumferential map-

ping. The procedural endpoint is the total disconnection or dissociation of

the PV. An immediate procedural success of 94–100% has been reported for this type of circumferential mapping. The long-term success rates for PV electrical isolation have been approximately 70% without antiarrhythmics.

Several mapping tools have been used for anatomical localisation during PV ablation, including for real-time demonstration of catheters and struc- tures, tagging of ablation sites, and mapping of gaps in the ablation lines.

Macle and colleagues prospectively randomised 52 patients undergoing PV ablation for paroxysmal AF to ablation using the LocaLisa mapping system or to fluoroscopy alone [17]. The LocaLisa system was used to visualise in real-time the circumferential mapping catheter positioned at the ostia of each PV and the ablation catheter location relative to this catheter, and to annotate ablated sites. While the total duration of RF energy delivered did not differ significantly between the groups, there was a significant decrease in the fluoroscopic duration (8.4 ± 4.3 min vs 23.7 ± 9.7 min, respective- ly; P < 0.0001) and time to achieve isolation of all four PVs (46.5 ± 12.0 min vs 66.3 ± 18.9 min, respectively; P < 0.0001). These results have recently been confirmed by Rotter et al. using a more advanced mapping sys- tem (NavX, Endocardial Solution) based on the same principles [18]. In this prospective randomised study evaluating the role of NavX in 72 patients with paroxysmal AF, a significant reduction in fluoroscopic duration (15.4 ± 3.4 min vs 21.3 ± 6.4 min, respectively; P < 0.001) and time to isolate all PVs (52 ± 12 min vs 61 ± 17 min; P = 0.02) was observed. Both these studies demonstrated the benefit of continuous real-time visualisation of catheters at the time of ablation to reduce the fluoroscopic exposure and procedural duration for the patient and the physician. While, theoretically, continuous monitoring of the ablation catheter may decrease the delivery of energy within the PV and therefore PV stenosis, neither of these studies were powered to establish this benefit.

Ablation of the Substrate for AF

Surgically created linear compartmentalisation of the atria (the MAZE oper- ation) is associated with long-term suppression of AF. A number of groups have attempted to perform linear ablation to modify the atrial substrate.

These studies have indicated that the most effective linear ablation for the prevention of AF needs to involve the left atrium or both atria [7–9, 19–22].

These procedures to achieve complete linear conduction block have been

technically challenging, with incomplete linear lesions being associated with

the frequent development of left atrial macroreentry and recurrence of

arrhythmia; they were also associated with increased procedural risk and

prolonged procedural and fluoroscopic durations.

Recently, ablation of the mitral isthmus (left inferior PV to the lateral mitral annulus) and the roofline (joining the two superior PVs) has become an increasingly popular approach. Mitral isthmus ablation is particularly attractive as target for substrate modification as it is short in length and its proximity to the coronary sinus allows optimal positioning of catheters to confirm linear conduction block. This short line, when combined with PV ablation results in a contiguous line of conduction block that transects the posterior lateral LA (analogous to the conduction block created by cavotri- cuspid isthmus ablat ion being extended by the cr ista ter minalis).

Conduction block at the mitral isthmus can be achieved in 92% of patients with paroxysmal AF and was associated with 88% of patients being arrhyth- mia-free without the use of anti-arrhythmic agents at 10 ± 5 months of fol- low-up [9]. Importantly, there was no change in atrial activation as a result of mitral isthmus ablation during sinus rhythm. Preliminary data concerning the use of this procedure in patients with chronic AF suggests that at a fol- low-up of 6 ± 5 months, 75% of patients remained in sinus rhythm. Scavee and colleagues presented data evaluating the role of LocaLisa navigation compared to fluoroscopy alone to undertake mitral isthmus ablation [23].

This group randomised 60 patients undergoing ablation of paroxysmal AF after PV isolation and found a significant reduction in the fluoroscopic dura- tion (8 ± 4 min vs 20 ± 11 min, respectively; P < 0.001), procedural time (38 ± 18 min vs 62±38 min, respectively; P = 0.004), and the duration of RF energy to achieve bidirectional conduction block (1166 ± 652 s vs 1811

± 922 s, respectively; P = 0.04). Similar results have been presented with the use of NavX mapping [24]. While the reduction in fluoroscopic and pro- cedural duration is consistent with that observed with PV ablation and reflects the benefit of continuous online visualisation of the catheters, the reduction in the RF duration suggests a benefit in terms of tagging of previ- ously ablated regions (Fig. 1).

Similarly, Rotter et al. evaluated the use of NavX navigation in perform-

ing roofline ablation and found a consistent reduction in the fluoroscopic

(5.6 ± 2.2 min vs 9.9 ± 4.8 min, respectively; P = 0.003) and procedural

durations (14.7 ± 5.5 min vs 26.6 ± 16.9 min; P = 0.007). While these

results have not yet been confirmed using the LocaLisa mapping system,

given the similarities of these systems it is anticipated that the benefit would

extend to this system as well (Fig. 2).

Fig. 1.Mitral isthmus ablation using the LocaLisa navigation system. Left right anterior oblique (RAO), right anterior posterior (AP). The left inferior PV (LIPV) is marked in purple and the mitral annulus (MA) marked through the coronary sinus (CS). The red tags demonstrate the linear ablation line

Fig. 2.Roofline ablation using the LocaLisa navigation system. The two superior PVs are marked in purple. The red tags demonstrate the ablation sequence joining the two superior PVs

Conclusions

The LocaLisa mapping system provides an economical means of continuous online monitoring of multiple catheters, the annotation of anatomic struc- tures, and the tagging of previously ablated regions. These features signifi- cantly reduce the fluoroscopic exposure and procedural duration associated with PV isolation and linear substrate modification for AF.

Acknowledgments

Dr. Sanders is supported by the Neil Hamilton Fairley Fellowship from the National Health and Medical Research Council of Australia and the Ralph Reader Fellowship from the National Heart Foundation of Australia. Dr. Rotter is supported by the Swiss National Foundation for Scientific Research, Bern, Switzerland. Dr. Rostock is sup- ported by the German Cardiac Society. Dr. Stiles is supported by an Overseas Research Fellowship from the National Heart Foundation of New Zealand.

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