Catheter-tissue contact optimizes pulsed electric field ablation with a large area focal catheter

INTRODUCTION

Pulsed electric field (PEF) ablation relies on the intersection of a critical voltage gradient with tissue to cause cell death. Field-based lesion formation with PEF technologies may still depend on catheter-tissue contact (CTC). The purpose of this study was to assess the impact of CTC on PEF lesion formation with an investigational large area focal (LAF) catheter in a preclinical model.

METHODS

PEF ablation via a 10-spline LAF catheter was used to create discrete right ventricle (RV) lesions and atrial lesion sets in 10 swine (eight acute, two chronic). Local impedance (LI) was used to assess CTC. Lesions were assigned to three cohorts using LI above baseline: no tissue contact (NTC: ≤∆10 Ω, close proximity to tissue), low tissue contact (LTC: ∆11-29 Ω), and high tissue contact (HTC: ≥∆30 Ω). Acute animals were infused with triphenyl tetrazolium chloride (TTC) and killed ≥2 h post-treatment. Chronic animals were remapped 30 days post-index procedure and stained with infused TTC.

RESULTS

Mean (± SD) RV treatment sizes between LTC (n = 14) and HTC (n = 17) lesions were not significantly different (depth: 5.65 ± 1.96 vs. 5.68 ± 2.05 mm, p = .999; width: 15.68 ± 5.22 vs. 16.98 ± 4.45 mm, p = .737), while mean treatment size for NTC lesions (n = 6) was significantly smaller (1.67 ± 1.16 mm depth, 5.97 ± 4.48 mm width, p < .05). For atrial lesion sets, acute and chronic conduction block were achieved with both LTC (N = 7) and HTC (N = 6), and NTC resulted in gaps.

CONCLUSIONS

PEF ablation with a specialized LAF catheter in a swine model is dependent on CTC. LI as an indicator of CTC may aid in the creation of consistent transmural lesions in PEF ablation.

Local impedance and contact force guidance to predict successful cavotricuspid isthmus ablation with a zero-fluoroscopy approach

Introduction

A new technology capable of monitoring local impedance (LI) and contact force (CF) has recently been developed. At the same time, there is growing concern regarding catheter ablation performed under fluoroscopy guidance, due to its harmful effects for both patients and practitioners. The aim of this study was to assess the safety and effectiveness of zero-fluoroscopy cavotricuspid isthmus (CTI) ablation monitoring LI drop and CF as well as to elucidate if these parameters can predict successful radiofrequency (RF) applications in CTI ablation.

Methods

We conducted a prospective observational study recruiting 50 consecutive patients who underwent CTI ablation. A zero-fluoroscopy approach guided by the combination of LI drop and CF was performed. In each RF application, CF and LI drop were monitored. A 6-month follow-up visit was scheduled to assess recurrences.

Results

A total of 767 first-pass RF applications were evaluated in 50 patients. First-pass effective RF applications were associated with greater LI drops: absolute LI drops (30.05 ± 6.23 Ω vs. 25.01 ± 5.95 Ω), p = 0.004) and relative LI drops (-23.3 ± 4.9% vs. -18.3 ± 5.6%, p = 0.0005). RF applications with a CF between 5 and 15 grams achieved a higher LI drop compared to those with a CF below 5 grams (29.4 ± 8.76 Ω vs. 24.8 ± 8.18 Ω, p < 0.0003). However, there were no significant differences in LI drop between RF applications with a CF between 5 and 15 grams and those with a CF beyond 15 grams (29.4 ± 8.76 Ω vs. 31.2 ± 9.81 Ω, p = 0.19). CF by itself, without considering LI drop, did not predict effective RF applications (12.3 ± 7.54 g vs. 11.18 ± 5.18 g, p = 0.545). Successful CTI ablation guided by a zero-fluoroscopy approach was achieved in all patients. Only one patient experienced a recurrence during the 6-month follow-up.

Conclusions

LI drop (absolute and relative values) appears to be a good predictor of successful RF applications to achieve CTI conduction block. The optimal CF to achieve a good LI drop is between 5 and 15 g. A zero-fluoroscopy approach guided by LI and CF was feasible, effective, and safe.

The influence of electrode-tissue-coverage on RF lesion formation and local impedance: Insights from an ex vivo model

BACKGROUND

The influence of power, duration and contact force (CF) on radiofrequency (RF) lesion formation is well known, whereas data on local impedance (LI) and electrode-tissue-coverage (ETC) is scarce. The objective was to investigate their effect on lesion formation in an ex vivo model.

METHODS AND RESULTS

An ex vivo model was developed utilizing cross-sections of porcine heart preparations and a force-sensing, LI-measuring catheter. N = 72 lesion were created systematically varying ETC (minor/full), CF (1-5 g, 10-15 g, 20-25 g) and power (20 W, 30 W, 40 W, 50 W). In minor ETC, the distal tip of the catheter was in electric contact with the tissue, in full ETC the whole catheter tip was embedded within the tissue. Lesion size and all parameters were measured once per second (n = 3320). LI correlated strongly with lesion depth (r = -0.742 for ΔLI; r = 0.781 for %LI-drop). Lesions in full ETC were significantly wider and deeper compared to minor ETC (p < .001) and steam pops were more likely. Baseline LI, ΔLI, and %LI-drop were significantly higher in full ETC (p < .001). In lesions resulting in steam pops, baseline LI, and ΔLI were significantly higher. The influence of CF on lesion size was higher in minor ETC than in full ETC.

CONCLUSIONS

ETC is a main determinant of lesion size and occurrence of steam pops. Baseline LI and LI-drop are useful surrogate parameters for real-time assessment of ETC and ΔLI correlates strongly with lesion size.

Higher power achieves greater local impedance drop, shorter ablation time, and more transmural lesion formation in comparison to lower power in local impedance guided radiofrequency ablation of atrial fibrillation

BACKGROUND

Since the local impedance (LI) of the ablation catheter reflects tissue characteristics, the efficacy of higher power (HP) compared to lower power (LP) in LI-guided ablation may differ from other index-guided ablations.

OBJECTIVE

This study aimed to assess the efficacy of HP ablation in LI-guided ablation of atrial fibrillation (AF).

METHODS

A prospective observational study was conducted, enrolling patients undergoing de novo ablation for AF. Pulmonary vein isolation was performed using point-by-point ablation with a RHYTHMIA HDxTM Mapping System and an open-irrigated ablation catheter with mini-electrodes (IntellaNav MIFI OI). Ablation was stopped when the LI drop reached 30 ohms, three seconds after the LI plateaued, or when ablation time reached 30 s. To balance the baseline differences, a unique method was used in which the power was changed between HP (45 W to anterior wall/40 W to posterior wall) and LP (35 W/30 W) alternately for each adjacent point.

RESULTS

A total of 551 ablations in 10 patients were analyzed (HP, n = 276; LP, n = 275). The maximum LI drop was significantly larger (HP: 28.3 ± 5.4 vs. LP: 24.8 ± 6.3 ohm), and the time to minimum LI was significantly shorter (HP: 15.0 ± 6.3 vs. LP: 19.3 ± 6.6 s) in the HP setting. The unipolar electrogram analysis of three patients revealed that the electrogram indicating transmural lesion formation was observed more frequently in the HP setting.

CONCLUSION

In LI-guided ablation, the HP could achieve a larger LI drop and shorter time to minimum LI, which may result in more transmural lesion formation compared to a LP setting.

Impact of baseline pool impedance on lesion metrics and steam pops in catheter ablation

INTRODUCTION

Little is known about the impact of blood-pool local impedance (LI) on lesion characteristics and the incidence of steam pops.

METHODS

Radiofrequency applications at a range of powers (30, 40, and 50 W), contact forces (CF) (5, 15, and 25 g), and durations (15, 30, 45, and 120 s) using perpendicular/parallel catheter orientation were performed in 40 excised porcine preparations, using a catheter capable of monitoring LI (StablePoint©, Boston Scientific). To simulate the variability in blood-pool impedance, the saline-pool LI was modulated by calibrating saline concentrations. Lesion characteristics were compared under three values of saline-pool LI: 120, 160, and 200 Ω.

RESULTS

Of 648 lesions created, steam pops occurred in 175 (27.0%). When power, CF, time, and catheter orientation were adjusted, ablation at a saline-pool impedance of 160 or 200 Ω more than doubled the risk of steam pops compared with a saline-pool impedance of 120 Ω (Odds ratio = 2.31; p = .0002). Lesions in a saline-pool impedance of 120 Ω were significantly larger in surface area (50 [38-62], 45 [34-56], and 41 [34-60] mm2 for 120, 160, and 200 Ω, p < .05), but shallower in depth (4.0 [3-5], 4.4 [3.2-5.3], and 4.5 [3.8-5.5] mmfor 120, 160, and 200 Ω, respectively, p < .05) compared with the other two settings. The correlation between the absolute LI-drop and lesion size weakened as the saline-pool LI became higher (e.g., 120 Ω group (r2  = .30, r2  = .18, and r2  = .16, respectively for 120, 160, and 200 Ω), but the usage of %LI-drop (= absolute LI-drop/initial LI) instead of absolute LI-drop may minimize this effect.

CONCLUSIONS

In an experimental model, baseline saline-pool impedance significantly affects the lesion metrics and the risk of steam pops.

Insight into contact force local impedance technology for predicting effective pulmonary vein isolation

Background

Highly localized impedance (LI) measurements during atrial fibrillation (AF) ablation have the potential to act as a reliable predictor of the durability of the lesions created.

Objective

We aimed to collect data on the procedural parameters affecting LI-guided ablation in a large multicenter registry.

Methods

A total of 212 consecutive patients enrolled in the CHARISMA registry and undergoing their first pulmonary vein (PV) isolation for paroxysmal and persistent AF were included.

Results

In all, 13,891 radiofrequency (RF) applications of ≥3 s duration were assessed. The first-pass PV isolation rate was 93.3%. A total of 80 PV gaps were detected. At successful ablation spots, baseline LI and absolute LI drop were larger than at PV gap spots (161.4 ± 19 Ω vs. 153.0 ± 13 Ω, p < 0.0001 for baseline LI; 22.1 ± 9 Ω vs. 14.4 ± 5 Ω, p < 0.0001 for LI drop). On the basis of Receiver operating characteristic curve analysis, the ideal LI drop, which predicted successful ablation, was >21 Ω at anterior sites and >18 Ω at posterior sites. There was a non-linear association between the magnitude of LI drop and contact-force (CF) (r = 0.14, 95% CI: 0.13-0.16, p < 0.0001) whereas both CF and LI drop were inversely related with delivery time (DT) (-0.22, -0.23 to -0.20, p < 0.0001 for CF; -0.27, -0.29 to -0.26, p < 0.0001 for LI drop).

Conclusion

An LI drop >21 Ω at anterior sites and >18 Ω at posterior sites predicts successful ablation. A higher CF was associated with an increased likelihood of ideal LI drop. The combination of good CF and adequate LI drop allows a significant reduction in RF DT.

Clinical trial registration

http://clinicaltrials.gov/, identifier: NCT03793998.

Estimation of mechanical properties by transcatheter monitoring using local impedance and contact force

The mechanical properties of the myocardium in the left ventricle and right atrium were estimated by simultaneously measuring the local impedance (LI) and contact force (CF) using an ablation catheter. Radiofrequency catheter ablation (RFCA) is a well-established arrhythmia treatment. Monitoring the RF power, CF and properties of myocardium during RFCA are necessary to estimate the effect of ablation. Indices, such as CF, lesion size index and ablation index, do not include the myocardium mechanical properties. Therefore, there is the risk of side effects, such as cardiac tamponade, by excessive catheter indentation into vulnerable areas. We propose the simultaneous measurement of LI and CF for estimating the myocardial mechanical properties to reduce the side effects. In this study, an in vitro experimental system was constructed to measure LI and CF via the catheter. The relationship between the porcine myocardial tissue thickness and CF-LI curve was investigated using the left ventricle and right atrium. Power function coefficients approximating the CF-LI curve increased with thicker left ventricle. The thickness of the myocardium can be estimated by simultaneously measuring LI and CF. Intraoperative measurement of the myocardial mechanical properties can be used to determine the ablation conditions at each site.

Optimal local impedance parameters for successful pulmonary vein isolation in patients with atrial fibrillation

INTRODUCTION

Local impedance (LI) parameters of IntellaNav STABLEPOINT for successful pulmonary vein isolation (PVI) of atrial fibrillation (AF) remain unclear. The purpose of this study was to seek LI data achieving successful PVI.

METHODS

Consecutive AF patients who underwent catheter ablation with STABLEPOINT were prospectively enrolled in two centers. PVI was performed under a constant 35-or 40-watt power, 20-s duration, and >5-g contact force. The operators were blinded to the LI data. The characteristics of all ablation points with/without conduction gaps (Unsuccess or Success tags) after the first-attempt PVI were evaluated for the right/left PVs and anterior/posterior wall (RPV/LPV and AW/PW, respectively), and cutoff values of LI data were calculated for successful lesion formation.

RESULTS

A total of 5257 ablation points in 102 patients (65 [58-72] years old, 65.7% male) were evaluated. The LI drop values were higher in the Success tags than Unsuccess tags on the LPV-AW and RPV-AW/PW (p < .001), except for the LPV-PW (p = .105). The %LI drop values (LI drop/initial LI) were higher for the Success tags in all areas (15.8 [12.2%-19.6%] vs. 11.6 [9.7%-15.6%] in LPV-AW: p < .001, 15.0 [11.5%-19.3%] vs. 11.4 [8.7%-17.3%] in LPV-PW: p = .035, 15.3 [11.5%-19.4%] vs. 9.9 [8.1%-13.7%] in RPV-AW: p < .001, and 13.3 [10.1%-17.4%] vs. 8.1 [6.3%-9.5%] in RPV-PW, p < .001). The LI drop and %LI drop cutoff values were 20.0 ohms and 11.6%, respectively.

CONCLUSIONS

An insufficient LI drop with STABLEPOINT was associated with a gap formation during PVI, and the best cutoff values for the LI drop and %LI drop were 20.0 ohms and 11.6%, respectively.

Biophysical Tissue Characterization of Ventricular Tachycardia Substrate With Local Impedance Mapping to Predict Critical Sites

BACKGROUND

New tools are needed to improve ventricular tachycardia (VT) substrate characterization and optimize outcomes. LI provides biophysical tissue characterization.

OBJECTIVES

The purpose of this study was to test local impedance (LI)-based mapping to predict critical ventricular tachycardia components after myocardial infarction (MI).

METHODS

One month after a nonreperfused anterior MI, endo-epicardial high-density electroanatomic mapping and endocardial LI mapping were performed in 23 Landrace Large X White pigs. LI thresholds were set using the blood pool value to define a 10 Ω range: low (<blood pool -1Ω), intermediate (≥blood pool -1Ω and ≤blood pool +9Ω), and high (normal) tissue resistance (>blood pool +9Ω).

RESULTS

Low LI was detected in low-voltage areas in 100% of cases, but intermediate LI was found in both core (87%) and border zone (12.5%) voltage areas. A total of 17 VTs were induced (VT isthmus identified in 9 animals). VT inducibility was associated with the size of intermediate LI area (OR: 1.19 [95% CI: 1.0-1.4]; P = 0.039) and the presence of specific LI patterns: LI corridor (OR: 15.0 [95% CI: 1.3-169.9]; P = 0.029); LI gradient (OR: 30.0 [95% CI: 2.1-421.1]; P = 0.012), high LI heterogeneity (OR: 21.7 [95% CI: 1.8-260.6]; P = 0.015), and presence of ≥2 low LI regions (OR: 11.3 [95% CI: 1.0-130.2]; P = 0.053). Potential VT isthmuses were in areas of intermediate LI and colocalized to LI patterns associated with VT inducibility in all cases (LI corridors or LI gradient). Low LI regions did not actively participate in the VT circuit (0%).

CONCLUSIONS

LI mapping is feasible and may add useful characterization of the VT substrate. Specific LI patterns (ie, corridors, gradients) were associated with VT inducibility and colocalized with the VT isthmus, thus representing a potential new target for ablation in substrate-based procedures.

Local Impedance Drop Predicts Durable Conduction Block in Patients With Paroxysmal Atrial Fibrillation

OBJECTIVES

This analysis was performed to evaluate the transition of local impedance (LI) drop during pulmonary vein isolation (PVI) to durable block and mature lesion formation based on 3-month mapping procedures.

BACKGROUND

A radiofrequency catheter measuring LI has been shown to be effective for performing PVI in patients with paroxysmal atrial fibrillation. Previous analysis has demonstrated LI drop to be predictive of pulmonary vein segment conduction block during an atrial fibrillation ablation procedure.

METHODS

Fifty-eight patients who had undergone LI-blinded de novo PVI returned for a 3-month mapping procedure. PVI ablation circles were divided into 16 anatomic segments for classification (durable block or gap), and the median LI drop within segments with an interlesion distance of ≤6 mm was compared. A total of 51 data sets met the criteria for segmental analysis of LI performance.

RESULTS

At the 3-month procedure, PV connection was confirmed in at least 1 PV segment in 35 of the included patients. LI drop outperformed generator impedance drop as a predictor of durable conduction block (area under the receiver-operating characteristic curve: 0.79 vs 0.68; P = 0.003). Optimal LI drops were identified by left atrial region (anterior/superior: 16.9 Ω [sensitivity: 69.1%; specificity: 85.0%; positive predictive value for durable conduction block: 97.7%]; posterior/inferior:14.2 Ω [sensitivity: 73.8%; specificity: 78.3%; positive predictive value: 96.9%]). Starting LI before radiofrequency (RF) application was significantly different among healthy, gap, and mature scar tissue and was also a contributing factor to achieving an optimal LI drop (85.2% of RF applications with a starting LI of ≥110 Ω achieved the optimal regional drop or greater).

CONCLUSIONS

LI drop is predictive of durable PV segment isolation. Preablation starting LI is associated with the magnitude of LI drop. These findings suggest that a regional approach to RF ablation guided by LI combined with careful interlesion distance control may be beneficial in patients with paroxysmal atrial fibrillation (Electrical Coupling Information From the Rhythmia HDx System and DirectSense Technology in Subjects With Paroxysmal Atrial Fibrillation [LOCALIZE]; NCT03232645).

Improved procedural workflow for catheter ablation of paroxysmal AF with high-density mapping system and advanced technology: Rationale and study design of a multicenter international study

BACKGROUND

The antral region of pulmonary veins (PV)s seems to play a key role in a strategy aimed at preventing atrial fibrillation (AF) recurrence. Particularly, low-voltage activity in tissue such as the PV antra and residual potential within the antral scar likely represent vulnerabilities in antral lesion sets, and ablation of these targets seems to improve freedom from AF. The aim of this study is to validate a structured application of an approach that includes the complete abolition of any antral potential achieving electrical quiescence in antral regions.

METHODS

The improveD procEdural workfLow for cathETEr ablation of paroxysmal AF with high density mapping system and advanced technology (DELETE AF) study is a prospective, single-arm, international post-market cohort study designed to demonstrate a low rate of clinical atrial arrhythmias recurrence with an improved procedural workflow for catheter ablation of paroxysmal AF, using the most advanced point-by-point RF ablation technology in a multicenter setting. About 300 consecutive patients with standard indications for AF ablation will be enrolled in this study. Post-ablation, all patients will be monitored with ambulatory event monitoring, starting within 30 days post-ablation to proactively detect and manage any recurrences within the 90-day blanking period, as well as Holter monitoring at 3, 6, 9, and 12 months post-ablation. Healthcare resource utilization, clinical data, complications, patients' medical complaints related to the ablation procedure and patient's reported outcome measures will be prospectively traced and evaluated.

DISCUSSION

The DELETE AF trial will provide additional knowledge on long-term outcome following a structured ablation workflow, with high density mapping, advanced algorithms and local impedance technology, in an international multicentric fashion. DELETE AF is registered at ClinicalTrials.gov (NCT05005143).

Catheter contact angle influences local impedance drop during radiofrequency catheter ablation: Insight from a porcine experimental study with 2 different LI-sensing catheters

BACKGROUND

Local impedance (LI) can indirectly measure catheter contact and tissue temperature during radiofrequency catheter ablation (RFCA). However, data on the effects of catheter contact angle on LI parameters are scarce. This study aimed to evaluate the influence of catheter contact angle on LI changes and lesion size with 2 different LI-sensing catheters in a porcine experimental study.

METHODS

Lesions were created by the INTELLANAV MiFi™ OI (MiFi) and the INTELLANAV STABLEPOINT™ (STABLEPOINT). RFCA was performed with 30 watts and a duration of 30 seconds. The CF (0, 5, 10, 20, and 30 g) and catheter contact angle (30°, 45°, and 90°) were changed in each set (n=8 each). The LI rise, LI drop, and lesion size were evaluated.

RESULTS

The LI rise increased as CF increased. There was no angular dependence with the LI rise under all CFs in the MiFi. On the other hand, the LI rise at 90° was lower than at 30° under 5 and 10 g of CF in STABLEPOINT. The LI drop increased as CF increased. Regarding the difference in catheter contact angles, the LI drop at 90° was lower than that at 30° for both catheters. The maximum lesion widths and surface widths were smaller at 90° than at 30°, whereas there were no differences in lesion depths.

CONCLUSION

The LI drop and lesion widths at 90° were significantly smaller than those at 30°, although the lesion depths were not different among the 3 angles for the MiFi and STABLEPOINT. This article is protected by copyright. All rights reserved.

Local impedance for the optimization of radiofrequency lesion delivery: A review of bench and clinical data

INTRODUCTION

Radiofrequency catheter ablation is a cornerstone of treatment for many cardiac arrhythmias. Progression in three-dimensional mapping and contact-force sensing technologies have improved our capability to achieve success, but challenges still remain.

METHODS

In this article, we discuss the importance of overall circuit impedance in radiofrequency lesion formation. This is followed by a review of the literature regarding recently developed "local impedance" technology and its current and future potential applications and limitations, in the context of established surrogate markers currently used to infer effective ablation.

RESULTS

We discuss the role of local impedance in assessing myocardial substrate, as well as its role in clinical studies of ablation. We also discuss safety considerations, limitations and ongoing research.

CONCLUSION

Local impedance is a novel tool which has the potential to tailor ablation in a manner distinct from other established metrics.

Characteristics and optimal ablation settings of a novel, contact-force sensing and local impedance-enabled catheter in an ex vivo perfused swine ventricle model

BACKGROUND

Local impedance (LI) has emerged as a new technology that informs on electrical catheter-tissue coupling during radiofrequency (RF) ablation. Recently, IntellaNav StablePoint, a novel LI-enabled catheter that equips contact force (CF) sensing, has been introduced. Although StablePoint and its predecessor IntellaNav MiFi OI share the common technology that reports LI, distinct mechanics for LI sensing between the two products raise a concern that the LI-RF lesion formation relationship may differ.

METHODS

In an ex vivo swine cardiac tissue model, we investigated the initial level and range of a reduction in LI during a 60-s RF ablation and the resultant lesion characteristics at nine combinations of three energy power (30, 40, and 50 W) and CF (10, 30, and 50 g) steps. Correlations and interactions between CF, LI, wattage, and formed lesions were analyzed. Incidence of achieving LI drop plateau and that of a steam pop were also determined.

RESULTS

Positive correlations existed between CF and initial LI, CF and absolute/relative LI drop, CF and lesion volume, and LI drop and lesion volume. At the same LI drop, wattage-dependent gain in lesion volume was observed. Steam pops occurred in all CF steps and the prevalence was highest at 50 W. LI drop predicted a steam pop with a cutoff value at 89Ω.

CONCLUSION

In StablePoint, wattage crucially affects LI drop and lesion volume. Because 30 W ablation may by underpowered for intramural lesion formation and 50 W often resulted in a steam pop, 40 W appears to achieve the balance between the safety and efficacy.

Local impedance-guided radiofrequency ablation with standard and high power: Results of a preclinical investigation

BACKGROUND

Local impedance (LI) drop measured with microfidelity electrodes embedded in the tip of an ablation catheter accurately reflects tissue heating during radiofrequency (RF) ablation. Previous studies found 15-30 Ω LI drops created successful lesions, while more than 40 Ω drops were associated with steam pops. The objective of this study was to evaluate the safety and efficacy of LI-guided ablation using standard (30 W) and high-power (50 W) in a preclinical model.

METHODS

RF lesions were created in explanted swine hearts (n = 6) to assess the feasibility of LI-guided ablation by targeting 10, 20, or 30 Ω (n = 20/group) drops. Subsequently, LI-guided ablation was evaluated in a chronic animal model (n = 8 Canines, 25-29 kg, 30/50 W). During the index procedure point-by-point intercaval line ablation and left inferior pulmonary vein (PV) isolation were performed. RF duration was at the operators' discretion but discontinued early if a 15-30 Ω drop was achieved. Operators attempted to avoid LI drops of more than 40 Ω. At 1-month, durable conduction block was evaluated with electroanatomic mapping followed by necropsy and histopathology.

RESULTS

In explanted tissue, terminating ablation at 10, 20, or 30 Ω LI drops created statistically larger lesions (p < .05; 1.8 [1.6-2.4] mm, 3.3 [3.0-3.7] mm; 4.9 [4.3-5.5] mm). LI-guided high-power ablation in vivo significantly reduced RF duration per application compared to standard-power (p < .05; intercaval: 8.9 ± 5.2 vs. 18.1 ± 11.0 s, PV: 9.6 ± 5.4 vs. 23.2 ± 10.3 s). LI drops of 15-40 Ω were more readily achievable for high-power (90.1%, 318/353) than standard-power (71.7%, 243/339). All intercaval lines and PV isolations were durable (16/16) at 1-month. Necropsy revealed no major collateral injury to the pericardium, phrenic nerve, esophagus, or lungs. There was no pericardial effusion, stroke, tamponade, or PV stenosis. Vagal nerve injury was found in two 30 W animals after using 19.7 ± 13.9 and 19.5 ± 11.8 s RF applications.

CONCLUSION

LI-guided ablation was found to be safe and efficacious in a chronic animal model. High-power ablation more readily achieved more than 15 Ω drops, reduced RF duration compared with standard-power, and had no major RF collateral injury.

Prevalence, characteristics, and predictors of endocardial and nonendocardial conduction gaps during local impedance-guided extensive pulmonary vein isolation of atrial fibrillation with high-resolution mapping

INTRODUCTION

Local impedance (LI) drops during radiofrequency ablation can predict lesion formation. Some conduction gaps during pulmonary vein isolation (PVI) can be associated with nonendocardial connections. This study aimed to investigate the incidence, characteristics, and predictors of endocardial and nonendocardial conduction gaps during an LI-guided PVI.

METHODS AND RESULTS

We prospectively enrolled 157 consecutive patients undergoing an initial LI-guided extensive PVI of atrial fibrillation (AF). After the first-pass encirclement, the residual conduction gaps and reconnected gaps were mapped using Rhythmia (Boston Scientific) and a mini-basket catheter. Right and left PV (RPV/LPV) gaps were observed in 22.3% and 18.5% of the patients, respectively: 27 endocardial and 49 nonendocardial gaps. The carina regions were common sites for the gaps (51 carina-related vs. 25 noncarina-related). The carina-related gaps consisted of more nonendocardial gaps than endocardial gaps (RPVs: 90.0% vs. 10.0%, p = .001; LPVs: 76.2% vs. 23.8%, p < .001). A univariate analysis revealed that paroxysmal AF and the left atrial (LA) volume index for RPV endocardial gaps (odds ratio [OR]: 8.640 and 0.946; p = .043 and 0.009), minor right inferior PV diameter for RPV nonendocardial gaps (OR: 1.165; p = .028), and major left inferior PV diameter for LPV endocardial gaps (OR: 1.233; p = .028) were significant predictors.

CONCLUSIONS

During the LI-guided PVI, approximately two-thirds of the conduction gaps were nonendocardial. The carina regions had more conduction gaps than noncarina regions, which was due to the presence of nonendocardial connections. Paroxysmal AF, a lower LA volume index, and larger inferior PV diameters may increase the risk of conduction gaps.

The optimal ablation setting for a local impedance guided catheter in an in vitro experimental model

BACKGROUND

The local impedance (LI) reflects the electrical catheter-tissue coupling and correlates with the local tissue temperature. However, there have been few clinical studies showing the recommended method for LI monitoring catheters. This study aimed to investigate the optimal ablation setting for this catheter in an in vitro experimental model.

METHODS

LI monitoring catheters were used in an excised swine heart experimental model. The tissue contact force (CF) was directly monitored from an external weight scale. Radiofrequency ablation was performed with a combination of various energy power settings (30, 40, and 50 W), and various CFs (10, 30, and 50 g) for 60 s. The correlation between the LI-related indexes, power, and CF with the lesion formation was statistically analyzed.

RESULTS

A positive correlation between the LI or lesion formation and CF was observed under all powers. Although the LI drop always correlated with the maximum lesion depth, lesion diameter, and lesion volume, the coefficient of the correlation value was lower under a high CF (lesion depth, diameter, and volume; 10 g, r = 0.8064, r = 0.8389, r = 0.8477; 30 g, r = 0.7590, r = 0.8063, r = 0.8060; 50 g r = 0.5555, r = 0.5701, and r = 0.5678, respectively). Steam pops occurred only under a 50 W ablation and the LI drop cutoff value for steam pops was 46 Ω.

CONCLUSION

The same LI drop did not always lead to the same lesion size when the CF differed. Monitoring the LI and not exceeding 46 Ω would be useful for a safe ablation.

Pulmonary vein isolation in atrial fibrillation patients guided by a novel local impedance algorithm: 1-year outcome from the CHARISMA study

BACKGROUND

Highly localized impedance (LI) measurements during atrial fibrillation (AF) ablation have recently emerged as a viable real-time indicator of tissue characteristics and durability of the lesions created. We report the outcomes of acute and long-term clinical evaluation of the new DirectSense algorithm in AF ablation.

METHODS

Consecutive patients undergoing AF ablation were included in the CHARISMA registry. RF delivery was guided by the DirectSense algorithm, which records the magnitude and time-course of the impedance drop. The ablation endpoint was pulmonary vein isolation (PVI), as assessed by the entrance and exit block.

RESULTS

3556 point-by-point first-pass RF applications of >10 s duration were analyzed in 153 patients (mean age=59 ± 10 years, 70% men, 61% paroxysmal AF, 39% persistent AF). The mean baseline LI was 105 ± 15 Ω before ablation and 92 ± 12 Ω after ablation (p < .0001). Both absolute drops in LI and the time to LI drop (LI drop/τ) were greater at successful ablation sites (n = 3122, 88%) than at ineffective ablation sites (n = 434, 12%) (14 ± 8 Ω vs 6 ± 4 Ω, p < .0001 for LI; 0.73 [0.41-1.25] Ω/s vs. 0.35[0.22-0.59 Ω/s, p < .0001 for LI drop/τ). No major complications occurred during or after the procedures. All PVs had been successfully isolated. During a mean follow-up of 366 ± 130 days, 18 patients (11.8%) suffered an AF/atrial tachycardia recurrence after the 90-day blanking period.

CONCLUSION

The magnitude and time-course of the LI drop during RF delivery were associated with effective lesion formation. This ablation strategy for PVI guided by LI technology proved safe and effective and resulted in a very low rate of AF recurrence over 1-year follow-up.

Incidence and characteristics of silent cerebral embolisms after radiofrequency-based atrial fibrillation ablation: A propensity score-matched analysis between different mapping catheters and indices for guiding ablation

INTRODUCTION

The difference in the incidence and characteristics of silent cerebral events (SCEs) after radiofrequency-based atrial fibrillation (AF) ablation between the different mapping catheters and indices used for guiding radiofrequency ablation remains unclear. This study aimed to compare the incidence and characteristics of postablation SCEs between the following two groups: Group C, Ablation Index-guided ablation using two circular mapping catheters with CARTO (Biosense Webster); Group R, local impedance-guided ablation using one mini-basket catheter and one circular mapping with Rhythmia (Boston Scientific).

METHODS AND RESULTS

Of 211 consecutive patients who underwent an AF ablation and brain magnetic resonance (MR) imaging after the ablation, 120 patients (each group, n = 60) were selected by propensity score matching. SCEs were detected in 37 patients (30.8%). Group R had a higher incidence of SCEs (51.7% vs. 10.0%; p < .001) and more SCEs per patient (median, 3 vs. 1, p = .028) than Group C. A multivariate analysis demonstrated that nonparoxysmal AF and being Group R were independent positive predictors of SCEs (odds ratios, 6.930 and 15.464; both p < .001). On the follow-up MR imaging, all SCEs in Group C and 87.9% of the SCEs in Group R disappeared (p = .537).

CONCLUSIONS

Group R had a significantly higher incidence of SCEs than Group C. Most probably the use of a complexly designed basket mapping catheter is the reason for the difference in the incidence of SCEs but further validation is needed. A nonparoxysmal form of AF may also increase the risk of SCEs during these ablation procedures.

Optimal local impedance drops for an effective radiofrequency ablation during cavo-tricuspid isthmus ablation

PURPOSE

A novel ablation catheter capable of local impedance (LI) monitoring (IntellaNav MiFi OI, Boston Scientific) has been recently introduced to clinical practice. We aimed to determine the optimal LI drops for an effective radiofrequency ablation during cavo-tricuspid isthmus (CTI) ablation.

METHODS

This retrospective observational study enrolled 50 consecutive patients (68 ± 9 years; 34 males) who underwent a CTI ablation using the IntellaNav MiFi OI catheter, guided by Rhythmia. The LI at the start of radiofrequency applications (initial LI) and minimum LI during radiofrequency applications were evaluated. The absolute and percentage LI drops were defined as the difference between the initial and minimum LIs and 100× absolute LI drop/initial LI, respectively.

RESULTS

A total of 518 radiofrequency applications were analyzed. The absolute and percentage LI drops were significantly greater at effective ablation sites than ineffective sites (median, 15 ohms vs 8 ohms, P < .0001; median, 14.7% vs 8.3%, P < .0001). A receiver-operating characteristic analysis demonstrated that at optimal cutoffs of 12 ohms and 11.6% for the absolute and percentage LI drops, the sensitivity and specificity for predicting the effectiveness of the ablation were 66.5% and 88.2%, and 65.1% and 88.2%, respectively. Finally, bidirectional conduction block along the CTI was achieved in all patients.

CONCLUSIONS

During the LI-guided CTI ablation, the effective RF ablation sites exhibited significantly greater absolute and percentage LI drops than the ineffective RF ablation sites. Absolute and percentage LI drops of 12 ohms and 11.6% may be suitable targets for effective ablation.

Clinical utility of local impedance monitoring during pulmonary vein isolation

INTRODUCTION

Local impedance (LI) at the tip of ablation catheter can be measured using a recently available technology. We aimed to explore target LI measurements at each radiofrequency application (RFA) for creating sufficient ablation lesions during pulmonary vein (PV) isolation.

METHODS

This prospective study included 15 consecutive patients scheduled to undergo an initial ablation of paroxysmal atrial fibrillation (AF). Circumferential ablation around both ipsilateral PVs was performed using a 4-mm irrigated ablation catheter with an LI sensor. Point-by-point ablation was used with a 4-mm inter-ablation-point distance. Operators were blinded to LI measurements during the procedure. Creation of sufficient ablation lesions was assessed by the absence of a conduction gap.

RESULTS

After first-pass encircling PV antrum ablation, left atrium to PV conduction remained in 12 of 30 (40%) ipsilateral PVs. Mapping using the minibasket catheter identified 48 ablation points through which the propagation wave entered the PV. At ablation points with a gap, the LI drop during RFA was half that at points without a gap (12 ± 7 vs. 23 ± 12 Ω; p < .001). The generator impedance drop did not differ between ablation points with and without a gap (12 ± 7 vs. 14 ± 10  Ω; p = .10). An LI drop of 13.4 Ω predicted sufficient lesion formation without a gap with a sensitivity of 0.78, specificity of 0.75, and predictive accuracy of 0.75.

CONCLUSION

An LI drop of 13.4 Ω at each RFA under the conditions of a 4-mm inter-ablation-point distance and RFA duration ≥20 s may facilitate creation of sufficient lesions during PV isolation.

A novel local impedance algorithm to guide effective pulmonary vein isolation in atrial fibrillation patients: Preliminary experience across different ablation sites from the CHARISMA pilot study

INTRODUCTION

Recently, a novel technology able to measure local impedance (LI) and tissue characteristics has been made available for clinical use. This analysis explores the relationships among LI and generator impedance (GI) parameters in atrial fibrillation (AF) patients. Characterization of LI among different ablation spots and procedural success were also evaluated.

METHODS AND RESULTS

Consecutive patients undergoing AF ablation from the CHARISMA registry at five Italian centers were included. A novel radiofrequency (RF) ablation catheter with a dedicated algorithm (DIRECTSENSE™) was used to measure LI and to guide ablation. The ablation endpoint was pulmonary vein (PV) isolation. We analyzed 2219 ablation spots created around PVs in 46 patients for AF ablation. The mean baseline tissue impedance was 105.8 ± 14 Ω for LI versus 91.8 ± 10 Ω for GI (p < .0001). Baseline impedance was homogenous across the PV sites and proved higher in high-voltage areas than in intermediate- and low-voltage areas and the blood pool (p < .001). Both LI and GI displayed a significant drop after RF delivery, and absolute LI drop values were significantly larger than GI drop values (14 ± 8 vs. 3.7 ± 5 Ω, p < .0001). Every 5-point increment in LI drop was associated with successful ablation (odds ratio = 3.05, 95% confidence interval: 2.3-4.1, p < .0001). Conversely, GI drops were not significantly different comparing successful versus unsuccessful sites (3.7 ± 5 vs. 2.8 ± 4 Ω, p = .1099). No steam pops or major complications occurred during or after the procedures. By the end of the procedures, all PVs had been successfully isolated in all patients.

CONCLUSIONS

The magnitude of the LI drop was more closely associated with effective lesion formation than the GI drop.

Novel Electrochemical Flow Sensor Based on Sensing the Convective-Diffusive Ionic Concentration Layer

Presented is a novel flow sensor based on electrochemical sensing of the ionic concentration-polarization (CP) layer developed within a microchannel-ion permselective membrane device. To demonstrate the working principle of the electrochemical flow sensor, the effect of advection on the transient and steady-state ionic concentration-polarization (CP) phenomenon in microchannel-Nafion membrane systems is studied. In particular, we focused on the local impedance, measured using an array of electrode pairs embedded at the bottom of the microchannel, as well as the total current across the permselective medium, as two approaches for estimating the flow. We examined both a stepwise application of CP under steady-state flow and a stepwise application of flow under steady-state CP.