Not all rotors, effective ablation targets for nonparoxysmal atrial fibrillation, are included in areas suggested by conventional indirect indicators of atrial fibrillation drivers: ExTRa Mapping project

Assessing the arrhythmogenic propensity of fibrotic substrate using digital twins to inform a mechanisms-based atrial fibrillation ablation strategy

Atrial fibrillation (AF), the most common heart rhythm disorder, may cause stroke and heart failure. For patients with persistent AF with fibrosis proliferation, the standard AF treatment-pulmonary vein isolation-has poor outcomes, necessitating redo procedures, owing to insufficient understanding of what constitutes good targets in fibrotic substrates. Here we present a prospective clinical and personalized digital twin study that characterizes the arrhythmogenic properties of persistent AF substrates and uncovers locations possessing rotor-attracting capabilities. Among these, a portion needs to be ablated to render the substrate not inducible for rotors, but the rest (37%) lose rotor-attracting capabilities when another location is ablated. Leveraging digital twin mechanistic insights, we suggest ablation targets that eliminate arrhythmia propensity with minimum lesions while also minimizing the risk of iatrogenic tachycardia and AF recurrence. Our findings provide further evidence regarding the appropriate substrate ablation targets in persistent AF, opening the door for effective strategies to mitigate patients' AF burden.

Impact of Atrial Fibrillation Triggers on Long-Term Outcomes of a Second Catheter Ablation of Nonparoxysmal Atrial Fibrillation

Background: Catheter ablation (CA) of atrial fibrillation (AF) triggers, including non-pulmonary vein (PV) foci, contributes to improved procedural outcomes. However, the clinical significance of an AF trigger ablation during second CA procedures for nonparoxysmal AF is unknown. Methods and Results: We enrolled 94 patients with nonparoxysmal AF undergoing a second CA. Intracardiac cardioversion during AF using high-dose isoproterenol was performed to determine the presence or absence of AF triggers. PV re-isolations were performed if PV potentials recurred, and if AF triggers appeared from any non-PV sites, additional ablation was added to those sites. We investigated the incidence of atrial arrhythmia recurrence (AAR) >3 months post-CA. Of the 94 enrolled patients, AF triggers were identified in 65 (69.1%), and of those with AF triggers, successful elimination of the triggers was achieved in 47 patients (72.3%). Multivariate analysis revealed that no observed AF triggers were a significant predictor of AAR (hazard ratio [HR] 1.97, 95% confidence interval [CI] 1.21-3.46, P=0.019). In a subanalysis of the patients with AF triggers, multivariate analysis showed that unsuccessful trigger ablation was significantly associated with AAR (HR 5.84, 95% CI 2.79-12.22, P<0.01). Conclusions: Having no observed AF triggers during a second CA session significantly increased the risk of AAR, as did unsuccessful CA of AF triggers.

Distributions and number of drivers on real-time phase mapping associated with successful atrial fibrillation termination during catheter ablation for non-paroxysmal atrial fibrillation

BACKGROUND

Real-time phase mapping (ExTRa™) is useful in determining the strategy of catheter ablation for non-paroxysmal atrial fibrillation (AF). This study aimed to investigate the features of drivers of AF associated with its termination during ablation.

METHODS

Thirty-six patients who underwent catheter ablation for non-paroxysmal AF using online real-time phase mapping (ExTRa™) were enrolled. A significant AF driver was defined as an area with a non-passively activated ratio of ≥ 50% on mapping analysis in the left atrium (LA). All drivers were simultaneously evaluated using a low-voltage area, complex fractionated atrial electrogram (CFAE), and rotational activity by unipolar electrogram analysis. The electrical characteristics of drivers were compared between patients with and without AF termination during the procedure.

RESULTS

Twelve patients achieved AF termination during the procedure. The total number of drivers detected on the mapping was significantly lower (4.4 ± 1.6 vs. 7.4 ± 3.8, p = 0.007), and the drivers were more concentrated in limited LA regions (2.8 ± 0.9 vs. 3.9 ± 1.4, p = 0.009) in the termination group than in the non-termination group. The presence of drivers 2-6 with limited (≤ 3) LA regions showed a tenfold increase in the likelihood of AF termination, with 83% specificity and 67% sensitivity. Among 231 AF drivers, the drivers related to termination exhibited a greater overlap of CFAE (56.8 ± 34.1% vs. 39.5 ± 30.4%, p = 0.004) than the non-related drivers. The termination group showed a trend toward a lower recurrence rate after ablation (p = 0.163).

CONCLUSIONS

Rotors responsible for AF maintenance may be characterized in cases with concentrated regions and fewer drivers on mapping.

Efficacy and safety of low voltage area ablation for atrial fibrillation: a systematic review and meta-analysis

BACKGROUND

Pulmonary vein isolation is the cornerstone of atrial fibrillation (AF) ablation. However, the recurrence rate of AF after pulmonary vein isolation (PVI) remains high. The efficacy and safety of low voltage area (LVA) ablation in the treatment of AF are uncertain.

METHODS

The studies comparing the efficacy and safety of LVA ablation and LVA non-ablation for AF were systematically reviewed and meta-analyzed. Outcomes of interest included recurrent event, procedure time, and fluoroscopy time. Continuous variables were evaluated with mean deviation (MD) and standard mean difference (SMD). Odds ratio (OR) values and its 95% confidence intervals (CI) were used in meta-analysis of binary variables.

RESULTS

Fourteen studies were eligible for inclusion. The AF recurrence was similar between the two groups, with no statistical difference (25.7% (67/346) vs. 28% (63/225), P = 0.49). LVA ablation did not increase the incidence of AT (8.7% (20/231) vs. 14.5% (28/193), P = 0.66). Fluoroscopy time was longer in the LVA ablation group (31.4 ± 8.4 min vs. 26.3 ± 7.8 min, P < 0.05). Complication rates were similar between the two groups (26.6% (17/64) vs. 21.7% (13/60), P = 0.53). Patients with LVA had higher AT/AF recurrence (32.9% (213/647) vs. 24.2% (229/948), P < 0.05).

CONCLUSIONS

Patients with left atrial LVA have a poor prognosis after catheter ablation. LVA ablation did not reduce the recurrence of AF nor did it increase the recurrence of atrial tachycardia.

Association with the nonparoxysmal atrial fibrillation duration and outcome of ExTRa Mapping-guided rotor ablation

Background

Additional ablation strategies after pulmonary vein isolation (PVI) for patients with nonparoxysmal atrial fibrillation (non-PAF) lasting ≥2 years have not been fully effective. This is presumably because of insufficient identification of non-PAF maintenance mechanisms. In this study, we employed a novel online and real-time phase mapping system, ExTRa Mapping, to identify and modulate rotors as one of the non-PAF maintenance mechanisms in patients with non-PAF sustained after PVI. We investigated the relationship between outcomes of ExTRa Mapping-guided rotor ablation (ExTRa-ABL) and non-PAF duration prior to this procedure.

Methods

This study consisted of 73 non-PAF patients (63 ± 8 years, non-PAF duration 31 ± 37 months) who underwent the first ExTRa-ABL in patients with non-PAF sustained after completion of PVI.

Results

Freedom from non-PAF/atrial tachycardia (AT) recurrence at 12 months after ExTRa-ABL was achieved in 50 (69%) of patients. The non-PAF duration prior to ExTRa-ABL was significantly longer in patients with non-PAF/AT recurrence after ExTRa-ABL compared with those without (56 ± 50 vs. 19 ± 22 months, p = .001). In patients with non-PAF duration of ≤60 months prior to ExTRa-ABL, compared with >60 months, non-PAF/AT-free rate was significantly higher (68.9% vs. 23.1%, p < .001), during the follow-up of 36 ± 18 months.

Conclusions

A non-PAF duration of ≤60 months prior to ExTRa-ABL was associated with a better outcome. The effect of ExTRa-ABL was considered to be limited in patients with >60 months of non-PAF duration.

Atrial fibrillation activation patterns predict freedom from arrhythmias after catheter ablation: utility of ExTRa mapping™

Background

Mechanisms underlying atrial fibrillation (AF) are widely complex and vary tremendously among individuals.

Objectives

This retrospective study aimed to investigate the association between AF activation patterns and clinical outcomes post-ablation.

Methods

Fifty-five AF patients (64.0 ± 12.9 years; 41 men; 17 paroxysmal) underwent bi-atrial endocardial driver mapping during AF pre-ablation with a real-time phase mapping system (ExTRa Mapping). The nonpassively activated ratio (%NP) of meandering rotors and multiple wavelets relative to the recording time was evaluated in 26 atrial segments [15 in the left atrium (LA) and 11 in the right atrium]. Irrespective of the mapping results, all patients underwent standard AF ablation via cryoballoons and/or radiofrequency catheters.

Results

In a median follow-up interval of 27(14-30) months, 69.1% of patients were free from recurrent arrhythmias and antiarrhythmic drugs at one year post-procedure. Patients with recurrent AF were more likely to have non-paroxysmal AF, a significantly larger LA size, and higher LA maximal %NP(LAmax%NP) and LA anterior wall %NP(LAAW%NP) than those without recurrent AF. A multivariate Cox regression analysis showed that both an LAmax%NP (hazard ratio [HR] = 1.075; 95% confidence interval [CI] = 1.02-1.14, p = 0.012) and LAAW%NP (HR = 1.061; 95% CI = 1.01-1.11, p = 0.013) were independent predictors of atrial arrhythmia recurrence. The optimal cutoff points for the LAmax%NP and LAAW%NP for predicting AF recurrence were 64.5% and 60.0%, respectively. A Kaplan-Meier analysis demonstrated that both an LAmax%NP > 64.5% (p = 0.0062) and LAAW%NP > 60.0% (p = 0.014) were associated with more frequent AF recurrences.

Conclusion

Baseline AF activation pattern mapping may aid in predicting freedom from arrhythmias after standard AF ablation procedures.

The spatiotemporal electrogram dispersion ablation targeting rotors is more effective for elderly patients than non-elderly population

Background

Modulating atrial fibrillation (AF) drivers has been proposed as one of the effective ablation strategies for non-paroxysmal AF (non-PAF). However, the optimal non-PAF ablation strategy is still under debate because the exact mechanisms of AF persistence including focal activity and/or rotational activity, are not well-understood. Recently, spatiotemporal electrogram dispersion (STED) assumed to indicate rotors in the form of rotational activity is proposed as an effective target for non-PAF ablation. We aimed to clarify the effectiveness of STED ablation for modulating AF drivers.

Methods

STED ablation plus pulmonary vein isolation was applied in 161 consecutive non-PAF patients not undergoing previous ablation. STED areas within the entire left and right atria were identified and ablated during AF. After the procedures, the STED ablation's acute and long-term outcomes were investigated.

Results

(1) Despite a more effective acute outcome of the STED ablation for both AF termination and non-inducibility of atrial tachyarrhythmias (ATAs), Kaplan-Meier curves showed that the 24-month freedom ratio from ATAs was 49%, which resulted from the higher recurrence ratio of atrial tachycardia (AT) rather than AF. (2) A multivariate analysis showed that the determinant of ATA recurrences was only a non-elderly age, not long-standing persistent AF, and an enlarged left atrium, which were conventionally considered as key factors.

Conclusions

STED ablation targeting rotors was effective in elderly non-PAF patients. Therefore, the main mechanism of AF persistency and the component of the fibrillatory conduction might vary between elders and non-elders. However, we should be careful about post-ablation ATs following substrate modification.

Effect of pulmonary vein isolation on rotor/multiple wavelet dynamics in persistent atrial fibrillation, association with vagal response and implications for adjunctive ablation

Persistent atrial fibrillation (PeAF) may develop arrhythmogenic substrates of rotors/multiple wavelets. However, the ways in which pulmonary vein isolation (PVI) affects the dynamics of rotor/multiple wavelets in PeAF patients remain elusive. Real-time phase-mapping (ExTRa mapping, EXT) in the whole left atrium (LA) was performed during PeAF before and after PVI (n = 111). The percentage of time in which rotor/multiple wavelets (phase singularities) was observed during each 5-s phase-mapping recording (non-passive activation ratio, %NP) was measured as an index of its burden. The mapping areas showing %NP ≥ 50% were defined as rotor/multiple-wavelet substrates (RSs). Before PVI, RSs were globally distributed in the LA. After PVI, %NP decreased (< 50%) in many RSs (PVI-modifiable RSs) but remained high (≥ 50%) in some RSs, especially localized in the anterior/septum/inferior regions (PVI-unmodifiable RSs, 2.3 ± 1.0 areas/patient). Before PVI, vagal response (VR) to high-frequency stimulation was observed in 23% of RSs, especially localized in the inferior region. VR disappearance after PVI was more frequently observed in PVI-modifiable RSs (79%) than in PVI-unmodifiable RSs (55%, p < 0.05), suggesting that PVI affects autonomic nerve activities and rotor/multiple wavelet dynamics. PVI-unmodifiable RSs were adjunctively ablated in 104 patients. The 1-year AT/AF-free survival rate was 70% in those with PVI alone (n = 115), and 86% in patients with the adjunctive ablation (log-rank test = 7.65, p < 0.01). PVI suppresses not only ectopic firing but also rotor/multiple wavelets partly via modification of autonomic nerve activities. The adjunctive ablation of PVI-unmodifiable RSs improved the outcome in PeAF patients and might be a novel ablation strategy beyond PVI.

Instability of rotational activation as atrial fibrillation drivers: assessment by ExTRa Mapping system

BACKGROUND

ExTRa Mapping™ has developed to visualize rotational activation as atrial fibrillation(AF) drivers. The current study was sought to evaluate the instability of AF drivers by ExTRa Mapping™.

METHODS

Variation of non-passively activated ratio(%NP) among 3-time repetitive recordings before and after pulmonary vein isolation(PVI) in left atrium was assessed in 26 persistent AF patients. The recoding time was set at 5 seconds or 8 seconds for the respective patients. The outcome measures included %NP at each recording, mean value of the 3-time recordings, and the instability index, which was defined as maximum difference per mean %NP×100 (%).

RESULTS

Total 683 sites 2049 recordings were assessed. Mean %NP was 33.3(23.3-42.7)%, and higher in sites with severe(≥50%) and patchy low voltage area than those without, but not in those with severe complex fractionated atrial electrogram area. There was significant correlation between actual and mean %NP (R = 0.86, P<0.001), but maximum difference among the repetitive recordings was 16(10-24) %. The instability index of %NP was 55.9(30.9-83.6)%, and significantly lower at the recordings of 8 seconds compared with 5 seconds (50.6[28.6-78.4]% versus 60.4[35.0-90.0]%, P = 0.004). Furthermore, it was higher at sites with lower reliability of the recordings. After PVI, mean %NP significantly decreased (28.7[18.3-36.7]% versus 37.7[28.7-45.7]%, P<0.001), but the instability index significantly increased compared with those before PVI (60.0[35.0-92.7]% versus 48.9[29.1-75.0]%, P = 0.001).

CONCLUSION

Rotational activation as AF drivers assessed by ExTRa Mapping™ is unstable, and repetitive and longer recording is required for the reliable assessment even after PVI. This article is protected by copyright. All rights reserved.

The impact of the atrial wall thickness in normal/mild late-gadolinium enhancement areas on atrial fibrillation rotors in persistent atrial fibrillation patients

Background

Some of atrial fibrillation (AF) drivers are found in normal/mild late-gadolinium enhancement (LGE) areas, as well as moderate ones. The atrial wall thickness (AWT) has been reported to be important as a possible AF substrate. However, the AWT and degree of LGEs as an AF substrate has not been fully validated in humans.

Objective

The purpose of this study was to evaluate the impact of the AWT in normal/mild LGE areas on AF drivers.

Methods

A total of 287 segments in 15 persistent AF patients were assessed. AF drivers were defined as non-passively activated areas (NPAs), where rotational activation was frequently observed, and were detected by the novel real-time phase mapping (ExTRa Mapping), mild LGE areas were defined as areas with a volume ratio of the enhancement voxel of 0% to <10%. The AWT was defined as the minimum distance from the manually determined endocardium to the epicardial border on the LGE-MRI.

Results

NPAs were found in 20 (18.0%) of 131 normal/mild LGE areas where AWT was significantly thicker than that in the passively activated areas (PAs) (2.5 ± 0.3 vs. 2.2 ± 0.3 mm, p < .001). However, NPAs were found in 41 (26.3%) of 156 moderate LGE areas where AWT was thinner than that of PAs (2.1 ± 0.2 mm vs. 2.23 ± 0.3 mm, p = .02). An ROC curve analysis yielded an optimal cutoff value of 2.2 mm for predicting the presence of an NPA in normal/mild LGE areas.

Conclusion

The location of AF drivers in normal/mild LGE areas might be more accurately identified by evaluating AWT.

Distinguishing heat-treated dead cells from viable cells using frequency dependence of electrical impedance

BACKGROUND

There is currently no methodology for evaluating the accuracy of ablation in ablation therapy, and thus normal cells in the surrounding area can be damaged, possibly leading to complications.

OBJECTIVE

The aim of this study was to distinguish heat-treated dead cells from viable cells using the electrical impedance-to-frequency ratio as an evaluation index.

METHODS

Rat heart striated myocytes were cultured in a monolayer on collagen-coated microelectrodes placed in the center of an electrode-loaded chamber. The cells in the chamber were killed by heat treatment for 5 minutes at 50 °C, and the frequency response of the cell impedance was measured before and after heat treatment. The frequency of the input current was varied from 10 to 100 kHz. The measured electrical impedance at each frequency was divided by the value at 100 kHz, and we refer to the resulting values as the impedance ratio.

RESULTS

The impedance ratio was high at low frequencies and low at high frequencies. Furthermore, the impedance ratio was lower at lower frequencies after heat treatment than before heat treatment.

CONCLUSIONS

The electrical impedance ratio can be used to distinguish viable and dead cells after heat treatment.

Predictors of recurrence of atrial tachyarrhythmias after pulmonary vein isolation by functional and structural mapping of nonparoxysmal atrial fibrillation

BACKGROUND

This study aimed to evaluate the predictors of recurrence of atrial tachyarrhythmias by structural and functional mapping: voltage, dominant frequency (DF), and rotor mapping after a pulmonary vein isolation (PVI) in nonparoxysmal atrial fibrillation (AF) patients.

METHODS

A total of 66 nonparoxysmal AF patients were prospectively investigated. After the PVI, an online real-time phase mapping system was used to detect the location of rotors with critical nonpassively activated ratios (%NPs) of ≧50% in each left atrial (LA) segment, and high-DFs of ≧7 Hz were simultaneously mapped. After restoring sinus rhythm, low-voltage areas (LVAs < 0.5 mV) were mapped using the Advisor HD grid catheter (HDG).

RESULTS

Sixty-four of 66 (97%) AF patients had minimum to mild LVAs regardless of an enlarged LAD and LA volume (45 ± 6.0 mm and 141 ± 29 ml). There were no significant differences in the max and mean DF values and %NPs between the patients with and without recurrent atrial tachyarrhythmias. However, there was a significant difference in the LVA/LA surface area between the patients with and without recurrent atrial tachyarrhythmias (p = .004). Atrial tachyarrhythmia freedom was significantly greater in those with LVAs of ≤3.3% than in those >3.3% after one procedure over 11.6 ± 0.8 months of follow-up (77.1% vs. 33.3%, p < .001). In a multivariate analysis, the LVA/LA surface area after the PVI (HR 1.079; CI, 1.025-1.135, p = .003) was an independent predictor of AF recurrence.

CONCLUSIONS

The predictor of atrial tachyarrhythmia recurrence after the PVI was LVAs rather than DFs and rotors in nonparoxysmal AF patients.

Defibrillation threshold of internal cardioversion prior to ablation predicts atrial fibrillation recurrence

BACKGROUND

Many studies have reported the predictors of atrial fibrillation (AF) recurrence after persistent AF (peAF) ablation. However, the correlation between the atrial defibrillation threshold (DFT) for internal cardioversion (IC) and AF recurrence rate is unknown. Here we investigated the relationship between the DFT prior to catheter ablation for peAF and AF recurrence.

HYPOTHESIS

DFT prior to ablation was the predictive factor for AF recurrence after peAF ablation.

METHODS

From June 2016 to May 2019, we enrolled 82 consecutive patients (mean age, 65.0 ± 12.4 years), including 45 with peAF and 37 with long-standing peAF, at Hamamatsu Medical Center. To assess the DFT, we performed IC with gradually increasing energy prior to radiofrequency application.

RESULTS

Forty-nine and 33 patients showed DFT values less than or equal to 10 J (group A) and greater than 10 J or unsuccessful defibrillation (group B). During the mean follow-up duration of 20.5 ± 13.1 months, patients in group B showed significantly higher AF recurrence rates than those in group A after the ablation procedure (p = .017). Multivariate analysis revealed that DFT was the only predictive factor for AF recurrence (odds ratio, 1.07; 95% CI, 1.00-1.13, p = .047).

CONCLUSIONS

The DFT for IC was among the strongest prognostic factors in the peAF ablation procedure.

Late-gadolinium enhancement properties associated with atrial fibrillation rotors in patients with persistent atrial fibrillation

BACKGROUND

A computational model demonstrated that atrial fibrillation (AF) rotors could be distributed in patchy late-gadolinium enhancement (LGE) areas and play an important role in AF drivers. However, this was not validated in humans.

OBJECTIVE

The purpose of this study was to evaluate the LGE properties of AF rotors in patients with persistent AF.

METHODS

A total of 287 segments in 15 patients with persistent AF (long-standing persistent AF in 9 patients) that underwent AF ablation were assessed. Non-passively activated areas (NPAs), where rotational activation (AF rotor) was frequently observed, were detected by the novel real-time phase mapping (ExTRa Mapping). The properties of the LGE areas were assessed using the LGE heterogeneity and the density which was evaluated by the entropy (LGE-entropy) and the volume ratio of the enhancement voxel (LGE-volume ratio), respectively.

RESULTS

NPAs were found in 61 (21%) of 287 segments and were mostly found around the pulmonary vein antrum. A receiver operating characteristic curve analysis yielded an optimal cutoff value of 5.7% and 10% for the LGE-entropy and LGE-volume ratio, respectively. The incidence of NPAs was significantly higher at segments with an LGE-entropy of >5.7 and LGE-volume ratio of >10% than at the other segments (38 [30%] of 126 vs. 23 [14%] of 161 segments; p = .001). No NPAs were found at segments with an LGE-volume ratio of >50% regardless of the LGE-entropy. Of five patients with AF recurrence, NPAs outside the PV antrum were not ablated in three patients and the remaining NPAs were ablated, but their LGE-entropy and LGE-volume ratio were low.

CONCLUSION

AF rotors are mostly distributed in relatively weak and much more heterogenous LGE areas.

Feasibility of catheter ablation in patients with persistent atrial fibrillation guided by fragmented late-gadolinium enhancement areas

BACKGROUND

A computer simulation model has demonstrated that atrial fibrillation (AF) driver can be attached to heterogeneous fibrosis assessed by late gadolinium enhancement magnetic resonance imaging (LGE-MRI). However, it has not been well elucidated in patients with persistent AF. The aim of this study was to investigate whether radiofrequency (RF) applications in the fragmented LGE area (FLA) could terminate AF or convert it to atrial tachycardia (AT) and improve the rhythm outcome.

METHODS

A total of 31 consecutive persistent AF patients with FLAs were enrolled (FLA ablation group, mean age: 69 ± 8 years, mean left atrial diameter: 42 ± 6 mm). A favorable response was defined as direct AF termination or AT conversion during RF applications at the FLA. The rhythm outcome was compared between the FLA ablation group and FLA burden-matched pulmonary vein isolation (PVI) group.

RESULTS

Favorable responses were found in 15 (48%) of 31 patients in the FLA group (AF termination in seven, AT conversion in eight patients), but not in the PVI group. AF recurrence at 12 months follow-up was significantly less in the FLA ablation group than in the PVI group (4 [13%] vs. 12 [39%] of 31 patients, log-rank p = .023). In patients with a favorable response, AT recurred in 1 (7%) of 15 patients, but AF did not.

CONCLUSIONS

FLA ablation could terminate AF or convert it to AT in half of the patients. No AF recurrence was documented in patients with a favorable response.

Spatial phase discontinuity at the center of moving cardiac spiral waves

BACKGROUND

Precise analysis of cardiac spiral wave (SW) dynamics is essential for effective arrhythmia treatment. Although the phase singularity (PS) point in the spatial phase map has been used to determine the cardiac SW center for decades, quantitative detection algorithms that assume PS as a point fail to trace complex and rapid PS dynamics. Through a detailed analysis of numerical simulations, we examined our hypothesis that a boundary of spatial phase discontinuity induced by a focal conduction block exists around the moving SW center in the phase map.

METHOD

In a numerical simulation model of a 2D cardiac sheet, three different types of SWs (short wavelength; long wavelength; and low excitability) were induced by regulating ion channels. Discontinuities of all boundaries among adjacent cells at each instance were evaluated by calculating the phase bipolarity (PB). The total amount of phase transition (PTA) in each cell during the study period was evaluated.

RESULTS

Pivoting, drifting, and shifting SWs were observed in the short-wavelength, low-excitability, and long-wavelength models, respectively. For both the drifting and shifting cases, long high-PB edges were observed on the SW trajectories. In all cases, the conduction block (CB) was observed at the same boundaries. These were also identical to the boundaries in the PTA maps.

CONCLUSIONS

The analysis of the simulations revealed that the conduction block at the center of a moving SW induces discontinuous boundaries in spatial phase maps that represent a more appropriate model of the SW center than the PS point.

Cardiac Spiral Wave Termination by Linear Regional Cooling Toward the Anatomical Boundary of the Heart

Purpose

We hypothesized that linear regional cooling (LRC) toward the atrio-ventricular groove (AV-G) can move the spiral wave (SW) center to the AV-G effectively and terminate SW. The effectiveness of LRC in ex vivo 2D ventricle rabbit experiments was tested.

Methods

We developed an experimental system to operate LRC and optical mapping simultaneously. To realize simultaneous cooling and optical mapping, a transparent cooling device was developed. LRC for 60 s toward 2D subepicardial ventricular myocardium of Langendorff-perfused rabbit hearts (n = 4) was conducted during constant pacing and persistent ventricular tachyarrhythmias (VTs).

Results

Action potential duration at 90% repolarization (APD90) at the cooling area was prolonged by LRC from 187 to 228 ms. 41% of persistent VTs were terminated by LRC (12/29 cases). Cases where the original SW center moved toward the AV-G were observed via optical mapping. However, there were some cases where VT was not terminated by LRC. When the action potential duration (APD) of VT sustained cases were analyzed, LRC prolonged APD, but the APD prolonged area did not move toward the AV-G in most VT sustained cases

Conclusion

Proper LRC toward the AV-G near the original SW center could move this center toward the AV-G and terminate SW excitation.

Successful modulation of atrial fibrillation drivers anchoring to fibrotic tissue after box isolation using an online real-time phase mapping system: ExTRa Mapping

A 41-year-old man with persistent atrial fibrillation (AF) underwent radiofrequency (RF) catheter ablation using an online real-time phase mapping system: ExTRa Mapping. Box isolation could not terminate AF. Subsequently, RF applications on nonpassively activated areas (NPAs), where rotational activations were frequently observed, at the posterior bottom of left atrium outside of box lesion could convert AF to common atrial flutter. Of interest, the NPA near the posterior bottom were located on the patchy fibrotic tissue area assessed by the late-gadolinium enhancement magnetic resonance imaging. This indicated the possibility of the critical AF rotor meandering through the fibrotic tissue area.

Effects of additional ablation of low-voltage areas after Box isolation for persistent atrial fibrillation

BACKGROUND

Previous studies reported that ablation of low-voltage areas (LVAs) after pulmonary vein isolation (PVI) improves the success rate in persistent atrial fibrillation (PerAF) patients with LVAs. However, the need for LVA ablation in addition to the posterior left atrial isolation, Box isolation (BOXI), for PerAF is unclear. We evaluated the effects of LVA ablation after BOXI for PerAF with LVAs.

METHODS

In 115 patients with PerAF (75 longstanding PerAF), LA voltage maps were created during sinus rhythm after PVI. Subsequently, BOXI was performed. In 61 patients without LVAs (<0.5 mV), BOXI alone was performed. Fifty-four patients with LVAs were randomly assigned to BOXI plus LVA ablation (33 patients) or BOXI alone (21 patients).

RESULTS

The rate of AF termination or cardioversion after BOXI was significantly higher than that after PVI (100% vs 88%, P < 0.001). The inducibility of atrial tachyarrhythmia after BOXI was significantly lower than that after PVI (27% vs 100%, P < 0.001). During 24 ± 9 months of follow-up after a single procedure, atrial tachyarrhythmia-free rate in the patients with LVAs, was significantly lower than that without LVAs (65% vs 82%, P = 0.043). However, the success rate was not significantly different between the BOXI plus LVA ablation group and the BOXI alone group of patients with LVAs (67% vs 62%, P = 0.722).

CONCLUSION

BOXI facilitates AF termination and its non-inducibility. Among patients with PerAF, BOXI alone may be adequate in cases without LVAs. Although cases with LVAs have higher risk of AF recurrence, additional LVA ablation does not improve the outcomes much.