Prediction of radiofrequency ablation lesion formation using a novel temperature sensing technology incorporated in a force sensing catheter

The effect of half-normal saline irrigation on lesion characteristics in temperature-flow-controlled ablation

PURPOSE

Radiofrequency (RF) ablation with half-normal saline (HNS) irrigation is reported to potentially enlarge local lesion compared to normal saline (NS) in power-controlled ablation (PC-Abl). However, the effect of HNS-irrigation in temperature-flow-controlled ablation (TFC-Abl) on lesion characteristics is unknown. We compared this between TFC-Abl with QDOT-Micro™ catheter and PC-Abl with Thermocool SmartTouch SF™ catheter (STSF).

METHODS

RF-application with NS (n = 480) and HNS (n = 480) irrigation were performed on swine myocardium placed in a circulating saline bath. Lesion characteristics without steam-pops under various conditions (target AI, 400/550; ablation power, 30/50 W; contact force, 10/20/30 g; catheter orientation, perpendicular/parallel) were assessed and compared between two irrigants.

RESULTS

After matching, 343 lesions without steam-pops in each group were evaluated. In PC-Abl, lesion size did not differ between two groups (NS, 188 ± 97 vs. HNS, 200 ± 95 mm3, p = 0.28 in volume; 33.9 ± 7.3 vs. 34.8 ± 9.5 mm2, p = 0.34 in surface area; and 4.0 ± 1.0 vs. 4.0 ± 1.0 mm, p = 0.81 in depth), but steam-pops were more frequently observed with HNS-irrigation (23.8% vs. 37.9%, p = 0.001). Contrary, in TFC-Abl, HNS-irrigation produced significantly larger (214 ± 106 vs. 243 ± 128 mm3, p = 0.017) and deeper (4.0 ± 1.0 vs. 4.3 ± 1.1 mm, p = 0.002) lesions without increasing the risk of steam-pops (15.0% vs 15.0%, p = 0.99). Automatic temperature-guided titration was more frequently observed in HNS-irrigation (54.8% vs. 78.5%, p < 0.001).

CONCLUSIONS

TFC-Abl with QDOT-Micro™ catheter utilizing HNS-irrigation might increase volume and depth of local lesion without increasing the risk of stem-pops compared to NS-irrigation.

A Review of Recent Advancements in Sensor-Integrated Medical Tools

A medical tool is a general instrument intended for use in the prevention, diagnosis, and treatment of diseases in humans or other animals. Nowadays, sensors are widely employed in medical tools to analyze or quantify disease-related parameters for the diagnosis and monitoring of patients' diseases. Recent explosive advancements in sensor technologies have extended the integration and application of sensors in medical tools by providing more versatile in vivo sensing capabilities. These unique sensing capabilities, especially for medical tools for surgery or medical treatment, are getting more attention owing to the rapid growth of minimally invasive surgery. In this review, recent advancements in sensor-integrated medical tools are presented, and their necessity, use, and examples are comprehensively introduced. Specifically, medical tools often utilized for medical surgery or treatment, for example, medical needles, catheters, robotic surgery, sutures, endoscopes, and tubes, are covered, and in-depth discussions about the working mechanism used for each sensor-integrated medical tool are provided.

Very high-power short-duration catheter ablation for treatment of cardiac arrhythmias: Insights from the FAST and FURIOUS study series

The QDOT MICRO™ Catheter is a novel open-irrigated contact force-sensing radiofrequency ablation catheter. It offers very high-power short-duration (vHPSD) ablation with 90 W for 4 s to improve safety and efficacy of catheter ablation procedures. Although the QDOT MICRO™ Catheter was mainly designed for pulmonary vein isolation (PVI) its versatility to treat atrial fibrillation (AF) and other types of arrhythmias was recently evaluated by the FAST and FURIOUS study series and other studies and will be presented in this article. Available study and registry data as well as case reports concerning utilization of the QDOT MICRO™ Catheter for the treatment of cardiac arrhythmias including AF, focal and macroreentry atrial tachycardia, typical atrial flutter by cavotricuspid isthmus block, premature ventricular contractions, and accessory pathways were reviewed and summarized. In summary, the QDOT MICRO™ Catheter showed safety and efficacy for PVI and is able to treat also other types of arrhythmias as is was recently evaluated by case reports and the FAST and FURIOUS studies.

Characterization of radiofrequency ablated myocardium with optical coherence tomography

Certain types of cardiac arrhythmias are best treated with radiofrequency (RF) ablation, in which an electrode is inserted into the targeted area of the myocardium and then RF electrical current is applied to heat and destroy surrounding tissue. The resulting ablation lesion usually consists of a coagulative necrotic core surrounded by a rim region of mixed viable and non-viable cells. The characterization of the RF ablated lesion is of potential clinical importance. Here we aim to elaborate optical coherence tomography (OCT) imaging for the characterization of RF-ablated myocardial tissue. In particular, the underlying principles of OCT and its polarization-sensitive counterpart (PS-OCT) are presented, followed by the knowledge needed to interpret their optical images. Studies focused on real-time monitoring of RF lesion formation in the myocardium using OCT systems are summarized. The design and development of various hybrid probes incorporating both OCT guidance and RF ablation catheters are also discussed. Finally, the challenges related to the transmission of OCT imaging systems to cardiac clinics for real-time monitoring of RF lesions are outlined.

Ablation characteristics and incidence of steam pops with a novel, surface temperature-controlled ablation system in an ex vivo experimental model

BACKGROUND

A novel irrigation catheter (QDOT MICRO™) has been introduced, which enables a surface temperature-controlled ablation combined with tip cooling. However, the detailed description of its complex behavior and effect on the incidence of pops and lesion formation remains elusive. This study aimed to systematically investigate the ablation characteristics, feedback behavior, and incidence of steam pops in a simplified ex vivo swine model.

METHODS

Using swine ventricular tissue perfused with saline at 37°C, we systematically created lesions with 4×3 combinations of the wattage (20, 30, 40, and 50 W) and contact force (CF, 10, 30, and 50 g). Ablation was continued for either 120 s or until a steam pop occurred and repeated 10 times with each setting. The lesion geometry, ablation index, feedback dynamics, and conditions underlying the steam pops were measured and analyzed.

RESULTS

Steam pops occurred particularly frequently in combinations of a low CF and high power (10 g vs. 30 g+50 g [p < .0001]; 40 W+50 W vs. 20 W+30 W [p < .0001]). Failure to activate a feedback process was associated with a 5.1 times higher incidence of steam pops (21/109 vs.11/11, [95% CI 3.499-7.716], p < .0001). The wattage feedback was particularly evident with a high CF (30 and 50 g) and high initial wattage (40 and 50 W). The average delivered wattage at 27 W predicted the occurrence of steam pops.

CONCLUSION

The temperature-controlled ablation with the QDOT MICRO™ demonstrated a complex feedback behavior, which contributed to a reduced incidence of steam pops and prolonged lead time to the pops.

Monitoring of irrigated lesion formation with single fiber based multispectral system using machine learning

In radiofrequency ablation (RFA) treatment of cardiac arrhythmias, intraprocedural assessment of treatment efficacy relies on indirect measures of adequate tissue destruction. Direct sensing of diffuse reflectance spectral changes at the ablation site using optically integrated RFA catheters has been shown to enable accurate prediction of lesion dimensions, ex vivo. Challenges of optical guidance can be due to obtaining reliable measurements under various catheter-tissue contact orientations. In this work, addressed this limitation by assessing the feasibility of monitoring lesion progression using single-fiber reflectance spectroscopy (SFRS). A total of 110 endocardial lesions of various sizes were generated in freshly excised swine right ventricular tissue using a custom-built, irrigated SFRS-RFA catheter. Models were developed for assessing catheter-tissue contact, the presence of nontransmural or transmural lesions and lesion depth percentage. These results support the use of SFRS-based catheters for irrigated lesion assessment and motivate further exploration of using multi-SFRS catheters for omnidirectionality.

Cardiac endocardial left atrial substrate and lesion depth mapping using near-infrared spectroscopy

Atrial fibrillation (AF) is a rapid irregular electrical activity in the upper chamber and the most common sustained cardiac arrhythmia. Many patients require radiofrequency ablation (RFA) therapy to restore sinus rhythm. Pulmonary vein isolation requires distinguishing normal atrial wall from the pulmonary vein tissue, and atrial substrate ablation requires differentiating scar tissue, fibrosis, and adipose tissue. However, current anatomical mapping methods for strategically locating ablation sites by identifying structural substrates in real-time are limited. An intraoperative tool that accurately provides detailed structural information and classifies endocardial substrates could help improve RF guidance during RF ablation therapy. In this work, we propose a 7F NIRS integrated ablation catheter and demonstrate endocardial mapping on ex vivo swine (n = 12) and human (n = 5) left atrium (LA). First, pulmonary vein (PV) sleeve, fibrosis and ablation lesions were identified with NIRS-derived contrast indices. Based on these key spectral features, classification algorithms identified endocardial substrates with high accuracy (<11% error). Then, a predictive model for lesion depth was evaluated on classified lesions. Model predictions correlated well with histological measurements of lesion dimensions (R = 0.984). Classified endocardial substrates and lesion depth were represented in 2D spatial maps. These results suggest NIRS integrated mapping catheters can serve as a complementary tool to the current electroanatomical mapping system to improve treatment efficacy.

Outcome of High-power Short-duration Radiofrequency Ablation in Combination with Half-Normal Saline Irrigation for the Treatment of Atrial Fibrillation

BACKGROUND

Data regarding the use of high-power short-duration (HPSD) radiofrequency (RF) in combination with half-normal saline irrigation for catheter irrigation is limited.

OBJECTIVES

This study investigated the safety and efficacy of using HPSD RF ablation in combination with half-normal saline irrigation for the treatment of AF.

METHODS

 One hundred consecutive patients with AF underwent RF ablation using HPSD combined with half-normal saline for catheter irrigation. In addition, the following ablation strategies were used: 1 mm tags for the display of ablation lesions on the mapping system, high-frequency jet ventilation (HFJV), low contact force, pacing after ablation to verify areas of noncapture, atrial/ventricular pacing at 500 to 700 ms to aid in catheter stability, use of two skin electrodes to reduce impedance, and post-ablation adenosine infusion. Power was started at 40-45 W and was modulated manually based on impedance changes.

RESULTS

 The average age of patients was 65.2 years and 70% were male. Forty-seven percent had paroxysmal AF and the average CHA₂ DS₂ -VASc score was 2.1±1.6. The average power and lesion duration were 38.1 ± 3.3 W and 8.1 ± 2.3 seconds, respectively. During a median follow-up period of 321 ± 139 days, 89% of the patients remained free from any atrial arrhythmias after a single RF ablation procedure. No procedure-related death, stroke, pericardial effusion, or atrioesophageal fistula occurred during follow-up.

CONCLUSIONS

 Catheter ablation using HPSD RF lesions in combination with half-normal saline irrigation and is safe and effective, and results in high rate of freedom from AF. This article is protected by copyright. All rights reserved.

Quantification of irrigated lesion morphology using near-infrared spectroscopy

There are currently limited means by which lesion formation can be confirmed during radiofrequency ablation procedures. The purpose of this study was to evaluate the use of NIRS-integrated RFA catheters for monitoring irrigated lesion progression, ex vivo and in vivo. Open-irrigated NIRS-ablation catheters with optical fibers were fabricated to sample tissue diffuse reflectance. Spectra from 44 irrigated lesions and 44 non-lesion sites from ex vivo swine hearts (n = 15) were used to train and evaluate a predictive model for lesion dimensions based on key spectral features. Additional studies were performed in diluted blood to assess NIRS signatures of catheter-tissue contact status. Finally, the potential of NIRS-RFA catheters for guiding lesion delivery was evaluated in a set of in vivo pilot studies conducted in healthy pigs (n = 4). Model predictions for lesion depth (R = 0.968), width (R = 0.971), and depth percentage (R = 0.924) correlated well with measured lesion dimensions. In vivo deployment in preliminary trials showed robust translational consistency of contact discrimination (P < 0.0001) and lesion depth parameters (< 3% error). NIRS empowered catheters are well suited for monitoring myocardial response to RF ablation and may provide useful intraprocedural feedback for optimizing treatment efficacy alongside current practices.

High-power, short-duration ablation for atrial fibrillation: Pros and cons

This article reviews and compares the rationale and evidence supporting high-power, short-duration radiofrequency (RF) ablation with those of conventional-power, conventional-duration RF ablation for atrial fibrillation (AF). The pros and cons of each approach, biophysics of ablation, pre-clinical studies informing clinical utilization, and the accumulated clinical evidence are presented. Both conventional-power, conventional-duration RF ablation and high-power, short-duration ablation are similarly safe, and effective approaches for AF ablation. Theoretical advantages of high-power, short-duration ablation, including greater procedure efficiency and limited conductive heating of collateral structures, must be weighed against the narrower safety margin related to rapid energy delivery during high power ablation.

Novel concepts in atrial fibrillation ablation-breaking the trade-off between efficacy and safety

Despite substantial technological and procedural advances that have improved the efficacy and safety of AF ablation in recent years, the long-term durability of ablation lesions is still not satisfactory. There also remains concern regarding rare but potentially life-threatening procedure-related complications like cardiac tamponade and atrioesophageal fistulae. Current ablation strategies are aiming to optimize the trade-off between efficacy and safety, where more extensive ablation appears to inevitably increase the risk of collateral injury. However, new forms of energy application may have the potential to resolve this quandary. The emerging concept of high power-short duration radiofrequency ablation features a more favorable lesion geometry that appears ideally suited to create contiguous lesions in the thin-walled atrium. Moreover, novel non-thermal ablation methods based on electroporation appear to provide a unique selectivity for cardiomyocytes and to spare surrounding tissues composed of other cell types. Both, high power-short duration and electroporation ablation might have the potential to break the trade-off between effective lesions and collateral damage and to substantially improve risk-benefit ratios in AF ablation. In addition, both approaches lead to considerable reductions in ablation times. However, their putative benefits regarding efficacy, efficiency, and safety remain to be proven in randomized controlled trials.

Impact of the combined use of intracardiac ultrasound and a steerable sheath visualized by a 3D mapping system on pulmonary vein isolation

BACKGROUND

A novel steerable sheath visualized on a three-dimensional mapping system has become available in this era in which a durable pulmonary vein (PV) isolation (PVI) with reduced fluoroscopy is required.

METHODS

In 60 patients who underwent a PVI with a visualized sheath (n = 30) and non-visualized conventional sheath (n = 30), the fluoroscopic time and catheter stability during the PVI were analyzed.

RESULTS

The fluoroscopic time during the transseptal access (0 [0, 0.1] vs. 1.4 [0.8, 2.3] minutes, P < .001) and PVI (0 [0, 0.1] vs. 0.4 [0.2, 1.1] minutes, P < .001) were shorter in the visualized sheath group than conventional sheath group. The procedure time during the PVI (32.0 [26.8, 36.3] vs. 41.0 [31.8, 47.3] minutes, P = .01), particularly during the right PVI (15.0 [12.8, 18.0] vs. 23.0 [15.8, 26.3] minutes, P = .009), was shorter in the visualized sheath group than conventional sheath group, however, that during the other steps was equivalent. The standard deviation of the catheter contact force during each radiofrequency application was smaller in the visualized sheath group than conventional sheath group (4.5 ± 2.7 vs. 4.9 ± 3.1 g, P = .001). The impedance drop for each lesion was larger in the visualized sheath group than conventional sheath group (10.7 ± 6.5 vs. 9.8 ± 5.5 ohms, P < .001). The incidence of acute PV reconnections per patient (30% vs. 23%, P = .56) and per PV segment (2.5% vs. 2.3%, P = .83) were similar between the two groups. No major complications occurred in either sheath group.

CONCLUSIONS

The use of visualized sheaths may reduce the fluoroscopic time and improve the catheter stability during the PVI.

Advanced fully integrated radiofrequency/optical-coherence-tomography irrigated catheter for atrial fibrillation ablation

The inability of current catheter ablation procedures to accurately monitor lesion formation limits their safety and efficacy. An advanced fully integrated radiofrequency (RF)/optical coherence tomography (OCT) ablation catheter is developed, which enables real-time monitoring during ablation. An OCT fiber array is especially designed, developed and integrated into an off-the-shelf irrigated RF ablation catheter. In-vitro experimental studies performed on poultry and ovine hearts demonstrate the ability of the integrated RF/OCT system to provide information on the quality and orientation of catheter/wall contact. Experimental results show that adipose tissue can be accurately identified from normal myocardial tissue with 94% accuracy and lesion formation is monitored with an overall accuracy of 93%. The ability to predict pop events is also demonstrated, with an accuracy of 86%.

Impact of catheter-tissue contact force on lesion size during right ventricular outflow tract ablation in a swine model

Background

The catheter-tissue contact force (CF) is one of the significant determinants of lesion size and thus has a considerable impact on the effectiveness of ablation procedures. This study aimed to evaluate the impact of CF on the lesion size during right ventricular outflow tract (RVOT) ablation in a swine model.

Methods

Twelve Guangxi Bama miniature male pigs weighing 40 to 50 kg were studied. After general anesthesia, a ThermoCool SmartTouch contact-sensing ablation catheter was introduced to the RVOT via the femoral vein under the guidance of the CARTO 3 system. The local ventricular voltage amplitude and impedance were measured using different CF levels. We randomly divided the animals into the following four groups according to the different CF levels: group A (3–9 g); group B (10–19 g); group C (20–29 g); and group D (30–39 g). Radiofrequency ablations were performed at three points in the free wall and septum of the RVOT in power control mode at 30 W for 30 s while maintaining the saline irrigation rate at 17 mL/min. At the end of the procedures, the maximum depth, surface diameter, and lesion volume were measured and recorded. A linear regression analysis was performed to determine the relationship between continuous variables.

Results

A total of 72 ablation lesions were created in the RVOT of the 12 Bama pigs. The maximum depth, surface diameter, and volume of the lesions measured were well correlated with the CF (free wall: β = 0.105, β = 0.162, β = 3.355, respectively, P < 0.001; septum: β = 0.093, β = 0.150, β = 3.712, respectively, P < 0.001). The regional ventricular bipolar voltage amplitude, unipolar voltage amplitude, and impedance were weakly positively associated with the CF (β = 0.065, β = 0.125, and β = 1.054, respectively, P < 0.001). There was a significant difference in the incidence of steam pops among groups A, B, C, and D (free wall: F = 7.3, P = 0.032; septum: F = 10.5, P = 0.009); and steam pops occurred only when the CF exceeded 20 g. Trans-mural lesions were observed when the CF exceeded 10 g in the free wall, while the lesions in the septum were non-trans-mural even though the CF reached 30 g.

Conclusions

CF seems to be a leading predictive factor for the size of formed lesions in RVOT ablation. Maintaining the CF value between 3 and 10 g may be reasonable and effective for creating the necessary lesion size and reducing the risk of complications, such as steam pops and perforations.

Rapid pacing and high-frequency jet ventilation additively improve catheter stability during atrial fibrillation ablation

INTRODUCTION

Catheter stability during atrial fibrillation ablation is associated with higher ablation success rates. Rapid cardiac pacing and high-frequency jet ventilation (HFJV) independently improve catheter stability. Simultaneous modulation of cardiac and respiratory motion has not been previously studied. The objective of this study was to determine the effect of simultaneous heart rate and respiratory rate modulation on catheter stability.

METHODS

Forty patients undergoing paroxysmal atrial fibrillation ablation received ablation lesions at 15 prespecified locations (12 left atria, 3 right atria). Patients were randomly assigned to undergo rapid atrial pacing for either the first or the second half of each lesion. Within each group, half of the patients received HFJV and the other half standard ventilation. Contact force and ablation data for all lesions were compared among the study groups. Standard deviation of contact force was the primary endpoint defined to examine contact force variability.

RESULTS

Lesions with no pacing and standard ventilation had the greatest contact force standard deviation (5.86 ± 3.08 g), compared to lesions with pacing and standard ventilation (5.45 ± 3.28 g; P < .01) or to lesions with no pacing and HFJV (4.92 ± 3.00 g; P < .01). Lesions with both pacing and HFJV had the greatest reduction in contact force standard deviation (4.35 ± 2.81 g; P < .01), confirming an additive benefit of each maneuver. Pacing and HFJV together was also associated with a reduction in the proportion of lesions with excessive maximum contact force (P < .001).

DISCUSSION

Rapid pacing and HFJV additively improve catheter stability. Simultaneous pacing with HFJV further improves catheter stability over pacing or HFJV alone to optimize ablation lesions.

Combined local impedance and contact force for radiofrequency ablation assessment

BACKGROUND

The combination of contact force (CF) and local impedance (LI) may improve tissue characterization and lesion prediction during radiofrequency (RF) ablation.

OBJECTIVE

The purpose of this study was to evaluate the utility of LI combined with CF in assessing RF ablation efficacy.

METHODS

An LI catheter with CF sensing was evaluated in swine (n = 11) and in vitro (n = 14). The relationship between LI and CF in different tissue types was evaluated in vivo. Discrete lesions were created in vitro and in vivo at a range of forces, powers, and durations. Finally, an intercaval line was created in 3 groups at 30 W: 30s, Δ20Ω, and Δ30Ω. In the Δ20Ω and Δ30Ω groups, the user ablated until a 20 or 30 Ω LI drop. In the 30s group, the user was blinded to LI.

RESULTS

In vivo, distinction in LI was found between the blood pool and the myocardium (blood pool: 122 ± 7.02 Ω; perpendicular contact: 220 ± 29 Ω; parallel contact: 207 ± 31 Ω). LI drop correlated with lesion depth both in vitro (R = 0.84) and in vivo (R = 0.79), informing sufficient lesion creation (LI drop >20 Ω) and warning of excessive heating (LI drop >65 Ω). When creating an intercaval line, the total RF time was significantly reduced when using LI guidance (6.4 ± 2 minutes in Δ20Ω and 8.1 ± 1 minutes in Δ30Ω) compared with a standard 30-second workflow (18 ± 7 minutes). Acute conduction block was achieved in all Δ30Ω and 30s lines.

CONCLUSION

The addition of LI to CF provides feedback on both electrical and mechanical loads. This provides information on tissue type and catheter-tissue coupling; provides feedback on whether volumetric tissue heating is inadequate, sufficient, or excessive; and reduces ablation time.

Cardiac Mapping Systems: Rhythmia, Topera, EnSite Precision, and CARTO

Novel cardiac mapping systems allow a safe and highly accurate 3-D reconstruction of cardiac structures as well as fast and accurate visualization of cardiac arrhythmias. In addition, they are increasingly reducing the need for fluoroscopy in these procedures. The current state of the art, as well as the presentation of possible uses of individual systems and their limitations, is presented in this article. Cardiac mapping systems can significantly contribute to an optimal therapeutic decision making in invasive electrophysiology. This article introduces new developments of Rhythmia, Topera, EnSite Precision, and CARTO systems and provides a look ahead to the future.

High-power, Short-duration Radiofrequency Ablation for the Treatment of AF

High-power, short-duration (HPSD) ablation for the treatment of AF is emerging as an alternative to ablation using conventional ablation generator settings characterised by lower power and longer duration. Although the reported potential advantages of HPSD ablation include less tissue oedema and collateral tissue damage, a reduction in procedural time and superior ablation lesion formation, clinical studies of HPSD ablation validating these observations are limited. One of the main challenges for HPSD ablation has been the inability to adequately assess temperature and lesion formation in real time. Novel catheter designs may improve the accuracy of intra-ablation temperature recording and correspondingly may improve the safety profile of HPSD ablation. Clinical studies of HPSD ablation are on-going and interpretation of the data from these and other studies will be required to ascertain the clinical value of HPSD ablation.

Real-time photoacoustic assessment of radiofrequency ablation lesion formation in the left atrium

In interventional electrophysiology, catheter-based radiofrequency (RF) ablation procedures restore cardiac heart rhythm by interrupting aberrant conduction paths. Real-time feedback on lesion formation and post-treatment lesion assessment could overcome procedural challenges related to ablation of underlying structures and lesion gaps. This study aims to evaluate real-time visualization of lesion progression and continuity during intra-atrial ablation with photoacoustic (PA) imaging, using clinically deployable technology. A PA-enabled RF ablation catheter was used to ablate and illuminate porcine left atrium, both excised and intact in a passive beating heart ex-vivo, for photoacoustic signal generation. PA signals were received with an intracardiac echography catheter. Using the ratio of PA images acquired with excitation wavelengths of 790 nm and 930 nm, ablation lesions were successfully imaged through circulating saline and/or blood, and lesion gaps were identified in real-time. PA-based assessment of RF-ablation lesions was successful in a realistic preclinical model of atrial intervention.

Novel Measure of Local Impedance Predicts Catheter–Tissue Contact and Lesion Formation

Background:

Coupling between the ablation catheter and myocardium is critical to resistively heat tissue with radiofrequency ablation. The objective of this study was to evaluate whether a novel local impedance (LI) measurement on an ablation catheter identifies catheter–tissue coupling and is predictive of lesion formation.

Methods and Results:

LI was studied in explanted hearts (n=10 swine) and in vivo (n=10; 50–70 kg swine) using an investigational electroanatomic mapping system that measures impedance from an ablation catheter with mini-electrodes incorporated in the distal electrode (Rhythmia and IntellaNav MiFi OI, Boston Scientific). Explanted tissue was placed in a warmed (37 °C) saline bath mounted on a scale, and LI was measured 15 mm away from tissue to 5 mm of catheter–tissue compression at multiple catheter angles. Lesions were created with 31 and 50 W for 5 to 45 seconds (n=90). During in vivo evaluation of LI, measurements of myocardium (n=90) and blood pool (n=30) were guided by intracardiac ultrasound while operators were blinded to LI data. Lesions were created with 31 and 50 W for 45 seconds in the ventricles (n=72). LI of myocardium (119.7 Ω) was significantly greater than that of blood pool (67.6 Ω; P <0.01). Models that incorporate LI drop (ΔLI) to predict lesion size had better performance than models that incorporate force-time integral ( R 2 =0.75 versus R 2 =0.54) and generator impedance drop ( R 2 =0.82 versus R 2 =0.58). Steam pops displayed a significantly higher starting LI and larger ΔLI compared with successful radiofrequency applications ( P <0.01).

Conclusions:

LI recorded from miniature electrodes provides a valuable measure of catheter–tissue coupling, and ΔLI is predictive of lesion formation during radiofrequency ablation.

Contact force facilitates the achievement of an unexcitable ablation line during pulmonary vein isolation

AIMS

Contact force (CF) catheters provide catheter-tissue contact information to improve outcome of pulmonary vein isolation (PVI) in paroxysmal atrial fibrillation (PAF). We evaluated different target-CF values for achievement of the additional endpoint of an unexcitable ablation line.

METHODS

A total of 106 patients undergoing PVI were randomized into three groups (G) (G1: target-CF 15 g, G2: target-CF 10 g, G3: CF concealed from operator). The PVI encircling line was divided into predefined sections. Excitable tissue along the PVI-line identified by high output pacing (10 V, 2 ms) was targeted for further ablation.

RESULTS

Mean average CF was 17.4 ± 4.7 g (G1) vs. 12.3 ± 6.0 g (G2) vs. 11.1 ± 6.5 g (G 3) (p < 0.001). Primary unexcitable ablation lines were found in 38.6, 19.4 and 5.7% (G1, G2, G3 respectively; G1 vs. G2 p < 0.05, G1 vs. G3 p < 0.001, G2 vs. G3 ns). Additional radiofrequency (RF)-energy to achieve unexcitability was lowest in G1 (3.6 ± 3.1 kJ vs. 8.6 ± 7.2 kJ (G2) and 10.4 ± 6.7 (G3), p ≤ 0.001, G2 vs. G3 ns) with accordingly lowest additional RF applications in G1 (3.0 ± 2.6 vs. 7.0 ± 5.4 in G2 and 8.4 ± 4.0 in G3; G1 vs. G2 and G3, p < 0.001, G 2 vs. G 3 ns). Sections along ablation lines with low initial CF were most likely to reveal excitability. Single procedure success was 81.9 vs. 73.5 vs. 71.4% (G 1, 2 and 3, p = 0.6) during 437 ± 254 day follow-up.

CONCLUSION

Higher tip-to-tissue CF during PVI facilitates the achievement of an unexcitable ablation line, requiring less additional RF-energy.

Pacing Mediated Heart Rate Acceleration Improves Catheter Stability and Enhances Markers for Lesion Delivery in Human Atria During Atrial Fibrillation Ablation

OBJECTIVES

This study sought to investigate the effect of pacing mediated heart rate modulation on catheter-tissue contact and impedance reduction during radiofrequency ablation in human atria during atrial fibrillation (AF) ablation.

BACKGROUND

In AF ablation, improved catheter-tissue contact enhances lesion quality and acute pulmonary vein isolation rates. Previous studies demonstrate that catheter-tissue contact varies with ventricular contraction. The authors investigated the impact of modulating heart rate on the consistency of catheter-tissue contact and its effect on lesion quality.

METHODS

Twenty patients undergoing paroxysmal AF ablation received ablation lesions at 15 pre-specified locations (12 left atria, 3 right atria). Patients were assigned randomly to undergo rapid atrial pacing for either the first half or the second half of each lesion. Contact force and ablation data with and without pacing were compared for each of the 300 ablation lesions.

RESULTS

Compared with lesion delivery without pacing, pacing resulted in reduced contact force variability, as measured by contact force SD, range, maximum, minimum, and time within the pre-specified goal contact force range (p < 0.05). There was no difference in the mean contact force or force-time integral. Reduced contact force variability was associated with a 30% greater decrease in tissue impedance during ablation (p < 0.001).

CONCLUSIONS

Pacing induced heart rate acceleration reduces catheter-tissue contact variability, increases the probability of achieving pre-specified catheter-tissue contact endpoints, and enhances impedance reduction during ablation. Modulating heart rate to improve catheter-tissue contact offers a new approach to optimize lesion quality in AF ablation. (The Physiological Effects of Pacing on Catheter Ablation Procedures to Treat Atrial Fibrillation [PEP AF]; NCT02766712).