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

Organization of atrial fibrillation using a pure sodium channel blocker: Implications of rotor ablation therapy

Background

Rotors are the source of atrial fibrillation (AF). However, the ablation of rotors for persistent AF is challenging. The purpose of this study was to identify the dominant rotor by accelerating the organization of AF using a sodium channel blocker and detecting the rotor's preferential area that governs AF.

Methods

Overall, 30 consecutive patients with persistent AF who underwent pulmonary vein isolation and still sustained AF were enrolled. Pilsicainide 50 mg was administered. An online real-time phase mapping system (ExTRa Mapping™) was used to identify the meandering rotors and multiple wavelets in 11 left atrial segments. The time ratio of non-passive activation (%NP) was evaluated as the frequency of rotor activity in each segment.

Results

Conduction velocity became slower-from 0.46 ± 0.14 to 0.35 ± 0.14 mm/ms (p = .004)-and the rotational period of the rotor was significantly prolonged-156 ± 21 to 193 ± 28 ms/cycle (p < .001). AF cycle length was prolonged from 169 ± 19 to 223 ± 29 ms (p < .001). A decrease in %NP was observed in seven segments. Additionally, 14 patients had at least one complete passive activation area. Of them, the use of high %NP area ablation resulted in atrial tachycardia and sinus rhythm in two patients each.

Conclusions

A sodium channel blocker organized persistent AF. In selective patients with a wide organized area, high %NP area ablation could convert AF into atrial tachycardia or terminate AF.

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.

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.

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.