Successful catheter ablation for a dominant atrial fibrillation driver manifested after box isolation using a novel mapping system in a patient with persistent atrial fibrillation

Several mapping systems have been developed to analyze substrates of persistent atrial fibrillation (AF). The ability to analyze arrhythmogenic substrates is essential to improving the outcome of catheter ablation for persistent AF. There is ongoing disagreement over the AF mechanism, including whether a local AF driver maintains fibrillatory conduction in the atrium, because identifying an exact AF rotor core is challenging in the vast area of the human atrium. CARTOFINDER (Biosense Webster, Diamond Bar, CA) is a novel mapping system that can identify AF drivers by visualizing excitation propagation during the 30-second recording of unipolar electrograms. Here we report a case in which the CARTOFINDER mapping system clearly showed a potential driver with a repetitive focal activation pattern for persistent AF maintained within the limited region of the left atrial (LA) posterior wall after box isolation. Subsequent radiofrequency (RF) applications targeting focal activation sites successfully terminated AF.

A 75-year-old man with symptomatic persistent AF was referred to our institution for further treatment with catheter ablation. He had a history of lung cancer, hypertension, and dyslipidemia. The patient initially was diagnosed with AF based on palpitations 1 year ago, which persisted even after administration of bisoprolol. Three-dimensional computed tomography revealed an enlarged LA volume of 201 mL with advanced remodeling. After informed consent was obtained from the patient, catheter ablation was scheduled for symptomatic persistent AF.

The ablation procedure was performed using a 3-dimensional navigation system (CARTO3, Biosense Webster). After obtaining access from the right femoral and right subclavian veins, a deflectable 20-pole, 6F catheter (BeeAT®, Japan Lifeline Co., Tokyo, Japan) was placed into the coronary sinus (CS). After a transseptal puncture was performed under intracardiac echocardiography, a multipolar electrode catheter (PentaRay, Biosense Webster) was advanced to the LA, and high-density electroanatomic mapping of the LA and 4 pulmonary veins (PVs) was performed during AF rhythm. The low-voltage area (0.10–0.50 mV) was extended in the anterior wall and was also scattered in the posterior wall on the LA bipolar voltage map (Figure 1). Before ablation, mean AF cycle length of the LA posterior wall and right PV was 158 ms with fragment potentials between 170 and 176 ms, which were shorter than those of the left PV (192–195 ms) and right atrium (RA) (220 ms). We conducted box isolation as an ablation strategy, including all PVs without posterior vertical lesions, due to the characteristics of the patient with persistent AF and the presence of a low-voltage area in the posterior wall. An ablation application was initiated at the anterior wall of the left PVs in a point-by-point manner using an irrigated-tip, contact force–sensing ablation catheter (ThermoCool SmartTouch, Biosense Webster). Subsequently, ablation proceeded to the bottom line from the left to the right PV side and ascended to the anterior wall of the right PVs. Finally, roof line ablation resulted in connection to the starting point and encircling of the posterior wall and 4 PVs (Figure 2A). RF energy power was adjusted by 40 W for each lesion, with a target temperature of 40°C. The target ablation index in the CARTO system was set to 500 and 400–450 in the LA anterior wall and roof and the bottom line, respectively. During box isolation, the cycle length of the CS gradually increased, suggesting that the ablation of box isolation was effective and that the cause of AF might be within the area of the box line (Figure 2B). AF suddenly terminated outside the box line when box isolation was presumed to compete, but the AF continued within the region of the box isolation line (Figure 2C). Because of this unusual phenomenon, a CARTOFINDER map was generated on the isolated region within the box line. The CARTOFINDER map in the LA posterior wall identified a repetitive focal activation pattern on the unipolar electrograms, showing a regular QS pattern morphology with mean cycle length of 181 ms and maximum of 22 focal QS patterns per assessment (Figures 3A and 3B). These focal activation areas overlapped with the low-voltage area on the voltage map before ablation (Figure 1). No other site demonstrated focal or rotational activity in the mapping system. Internal cardioversion was attempted for AF termination using an electrode catheter placed in the high RA and CS equipped in the cardioversion system (commercially available in Japan [BeeAT, Japan Lifeline Co.; and SHOCK AT α, Japan Lifeline Co.]) to observe the occurrence and initiation mode of AF within the box isolation area. Automaticity and continuous firing occurred at the site where focal activations were observed (Figure 3C). Pacing stimulation from the same site repeatedly induced AF. Considering the strong presence of a possible AF driver in this area, we decided to apply RF ablation in the area where focal activations were observed on CARTOFINDER mapping. AF cycle length gradually increased after ablation, and AF termination was achieved (Figure 3D). These focal activation areas overlapped with the low-voltage area on the voltage map before ablation and were located in proximity to complex fractionated atrial electrogram areas (Figure 3E). Bidirectional block of the box isolation was confirmed by pacing from outside the box isolation, as well as the disappearance of pacing capture in the posterior wall via high-output pacing (10 V) during sinus rhythm. Rapid pacing stimulation from the RA and CS did not induce any sustained AF, nor did infusion of isoproterenol and adenosine triphosphate. The procedure was completed without complications. The patient had no recurrence of atrial tachyarrhythmias 1 year after the procedure or detection of asymptomatic AF on 24-hour Holter monitoring postoperatively.

The present case demonstrated maintenance of AF within a limited area of the LA posterior wall and PVs after successful ablation of the box isolation. CARTOFINDER mapping for persistent AF in the box region detected repetitive focal activation in the LA posterior wall, and subsequent ablation of the focal activations successfully terminated the AF.

The CARTOFINDER map system analyzes the propagation of AF excitation based on unipolar potentials and determines the location where repeated local QS patterns are recorded as focal activations. Repeated local QS excitation patterns in the unipolar electrogram may indicate the origin or termination of electrical conduction to the atrial surface. Termination of AF was achieved in 12 of 19 patients (63%) with persistent AF after undergoing CARTOFINDER-guided ablation of the AF driver. Ablation for focal activation identified by CARTOFINDER has been associated with termination of AF in the acute stage.^, In the present case, the repetitive focal activation in the LA posterior wall detected on the CARTOFINDER may strongly suggest the presence of an AF driver. However, because the CARTOFINDER map was performed after box isolation but not before ablation, whether the AF rotor documented in the posterior wall dominated the entire AF process in the atrium from the beginning is unknown. It is possible that focal activations manifested increasingly after box isolation due to elimination of an effect of activation from outside of the bottom line. In addition, the local focal activation detected by CARTOFINDER may indicate the presence of microreentrant drivers as well as automaticity or triggered activity. Analysis of optical mapping has reported that the AF driver is microreentry based in pectinate muscles caused by endo–epicardial muscle misalignment, and this micro-reentry consisted of 3-dimensional circuits across the endo–epicardial substrate. Moreover, AF is caused by rapid regular activity, as shown in this case, which subsequently converts to fibrillatory conduction toward surrounding tissue. Although we did not obtain epicardial LA information contrary to the focal activation area on the endocardium in the present case, the electrical characteristics of local activation on the damaged LA body and persistent AF support this speculation, as the focal activation may correspond to the exit of a microreentrant circuit. The CARTOFINDER algorithm may be useful for identifying a potential AF driver conjunctive to further effective treatment and may elucidate the mechanism and characteristics of the AF rotor.

The CARTOFINDER mapping system identified repetitive focal activations in the LA posterior wall in a patient with persistent AF maintained within the box isolation area. RF applications to the focal activation sites successfully terminated the AF, which may have been caused by a microreentrant driver.