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Background and aims: The safety evaluation of TactiFlex, a novel contact‐force sensing catheter with a flexible 4‐mm tip irrigated through laser‐cut kerfs, has been ongoing. This study aimed to verify the safety of this type of catheter. Methods: Study 1: Radiofrequency (RF) applications at a range of powers (30–50 W), contact forces (10–20 g), and durations (10–60 s) using perpendicular/parallel catheter orientation with half‐normal (HNS) or normal saline irrigation were compared between TactiFlex (4‐mm tip) and TactiCath (3.5‐mm tip) with temperature‐controlled mode in excised porcine hearts. Study 2: The relation between RF applications using TactiFlex and the incidence of steam‐pops in the real clinical cases were examined. Results: Study‐1: 576 RF lesions were examined. TactiFlex demonstrated a significantly lower risk of steam‐pops (5[1.7%] vs. 59[20.5%], p <.0001). Compared to 3.5‐mm‐tip catheter (TactiCath), 4‐mm‐tip catheter (TactiFlex) produced smaller lesion volume at perpendicular (193[98–554]mm3 vs. 263[139–436]mm3, p <.0001), but relatively similar lesion volume at parallel contact (243[105–443]mm3 vs. 278[180–440]mm3, p =.06). HNS‐irrigation tended to increase the lesion volume in both catheters and to increase the incidence of steam‐pops with TactiCath, but not with TactiFlex. The cut‐off value of %impedance‐drop (= absolute impedance‐drop/initial impedance) of 20% predicted steam‐pops with a sensitivity = 100% and specificity = 89.6% in TactiFlex. Study‐2: 5496 RF applications in 84 patients (51AFs/8ATs/3AVNRTs/4AVRTs/17PVCs/4VTs) using TactiFlex were analyzed. Four steam‐pops (0.07%) in three patients with pericardial effusion were observed (%impedance‐drop = 24%/26%/29%/35%, respectively). The cut‐off value of %impedance‐drop = 20%, derived from ex‐vivo study, showed sensitivity = 100% and specificity = 90.1% in detecting steam‐pops. Conclusion: TactiFlex reduced the risk of steam‐pops than TactiCath. %impedance‐drop ≤ 20% may be reasonable for safely use with a sufficient safety margin. For 4‐mm‐tip catheter, parallel‐contact may be recommended for larger lesion creation. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Objectives: The aims of this study were to distinguish between behavioral compensation and behavioral recovery and to determine the role of stroke lesions and the optimal timing of rehabilitation in true recovery. Design: Single pellet reaching test has been performed to analyze both quantitative and qualitative measures of forelimb function in a stroke animal model with lesions in the motor cortex, somatosensory cortex, or sensorimotor cortex. The four gestures of compensatory movement patterns that comprised a reach were head lift, limb withdrawal, pellet chasing, and phantom grasp. Results: Functional recovery improved in all the stroke groups after rehabilitation (P < 0.001). However, the compensatory movement patterns of the motor cortex and somatosensory cortex stroke groups initially increased and subsequently decreased (P = 0.0054), whereas those of the sensorimotor cortex stroke group increased and persisted (P = 0.0063). In the sensorimotor cortex stroke group, compensatory movement patterns significantly decreased when training was initiated 5 and 14 days after stroke (P = 0.0083, P = 0.0226, respectively), while they increased and persisted when training was initiated 1 day after stroke. Conclusions: These findings suggest that true recovery by task-specific training after stroke depends, probably, on the lesion size and the timing of rehabilitation. [ABSTRACT FROM AUTHOR]

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 two 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 W and a duration of 30 s. The contact force (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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Background: Steam pops are a rare complication associated with radiofrequency (RF) ablation and are hard to predict. The aim of this study was to assess the influence of coverage between the RF ablation electrode and cardiac tissue on steam pop incidence and lesion size. Methods and results: An ex vivo model using porcine cardiac preparations and contact force sensing catheters was designed to perform RF ablations at different coverage levels between the RF electrode and cardiac tissue. During coverage level I, only the distal part of the ablation electrode was in contact with tissue. During coverage level II half of the ablation electrode, and during coverage level III the entire ablation electrode was embedded in tissue. RF applications (n = 60) at different coverage levels I–III were systematically performed using the same standardized ablation protocol. Ablations during coverage level III resulted in a significantly higher rate of steam pops (100%) when compared to ablations during coverage level II (10%) and coverage level I (0%), log rank p <.001. Coverage level I ablations resulted in significantly smaller lesion depths, diameters, and impedance drops when compared to higher coverage level ablations, p <.001. In the controlled ex vivo model, there was no difference in applied contact force or energy between different coverage levels. Conclusions: The level of coverage between RF electrode, cardiac tissue, and the surrounding fluid significantly influenced the incidence of steam pops in an ex vivo setup. Larger coverage between RF electrode and tissue resulted in significantly larger lesion dimensions. [ABSTRACT FROM AUTHOR]

Introduction: The influence of power (Watt [W]) and total energy (Joule [J]) on lesion size and the optimal overlap ratio remain unclear in laser balloon (LB) ablation for atrial fibrillation. We aimed to evaluate lesion size and visible gaps after LB ablation with various energy settings and different overlap ratios in vitro model. Methods and Results: Chicken muscles were cauterized using the first‐generation LB with single applications of full and a half duration of six energy settings (5.5 W/30 seconds [165 J] to 12 W/20 seconds [240 J]) and varying power (5.5‐12 W) at the constant total energy (160 J). Three overlapped ablations with different ratios (25% and 50%) for each energy setting were also performed to evaluate the visible gap degree categorized from 1 (perfect) to 3 (poor). Twenty lesions were evaluated for each energy setting. In single applications of full duration, lesion depth, lesion volume, and maximum lesion diameter increased according to the total energy (all, P < .001) and were greater than in those of half duration in each energy setting (all, P < .05). However, applications with larger power created larger lesion volume and maximum lesion diameter at constant total energy (P < .05). The visible gap degree was better in all energy settings with 50% overlapped ablation than in those with 25% (all, P < .001). Conclusion: Lesion size depends not only on power but also on total energy in the LB ablation. Sufficiently overlapped ablations allow continuous lesion formation. [ABSTRACT FROM AUTHOR]

Environmental Impedance and Ablation Lesions Introduction The electrical conductivity of the environment surrounding a catheter electrode may affect radiofrequency (RF) current. A higher impedance environment enveloping a catheter tip can be insulating and thus direct RF preferentially into targeted cardiac tissue. We sought to evaluate whether different environmental impedances will affect RF lesions. Methods An ex vivo model using bovine myocardium, load cell, and 4 mm ablation catheter was tested using a circulating bath of normal (0.9%; NS) and half normal (0.45%; HNS) saline. Ablations were performed at 50 W. In addition, using a porcine thigh prep model, warmed heparinized blood was circulated at 350 mL/min. Prior to ablation, circulating bath impedance was altered with NS and HNS. RF was applied at 30 W with a force-sensing, open irrigated catheter. Results Ex vivo RF with a 4 mm catheter using an HNS bath led to larger lesions, 286.7 ± 64 mm³ versus 198.9 ± 61 mm³ (P < 0.001), compared to an NS bath. In the porcine thigh prep, for RF in the high impedance (HNS) bath, initial and final impedances were higher, and the measured impedance reductions during ablation were larger, compared to RF in the low impedance (NS) bath. In vivo ablation within a higher impedance bath created larger lesion sizes, compared to a lower impedance bath, 222.4 ± 63.4 mm3 versus 135.4 ± 61.7 mm3 (P < 0.001). Conclusions A higher impedance surrounding an RF catheter can facilitate more effective RF and thereby increase lesion size. This may have implications for RF safety and efficacy, especially in the epicardium where pericardial fluid can be altered with infusion of ionic solutions. [ABSTRACT FROM AUTHOR]

In Vitro Comparison of Open-Irrigated Catheters Introduction Open-irrigated radiofrequency ablation catheters with slight differences in tip architecture are widely used, although limited comparative data are available. The purpose of this study was to compare the lesion size and potential complications produced by commercially available open-irrigated catheters in an in vitro porcine heart model. Methods and Results Six catheters were tested (Biosense Webster Thermocool, Boston Scientific Open irrigated, St. Jude CoolPath, St. Jude CoolPath Duo, Biosense Webster Thermocool SF, St. Jude Cool Flex) at 20 and 35 W power-control, under 2 different blood flows (0.1 and 0.5 m/s) and at 2 target durations (30 and 60 seconds). A total of 601 lesions were made in 26 in vitro preparations. The tip temperature profile showed significant differences between the catheters (P < 0.001) with the Thermocool SF registering the lowest. Only the surface diameter and the depth at maximum diameter of the lesion were influenced by the design of the ablation electrode. The lesion volume did not show significant differences between catheters for any power, application duration or blood flow condition. Char and pops occurred more often at 35 W with only slight differences between the catheters. Conclusions Tip design of the 6 different irrigated catheters does not affect the lesion total volume, although a slight difference in lesion geometry in terms of surface diameter and depth at maximum diameter is present. The catheters show a slight different in vitro safety profile [ABSTRACT FROM AUTHOR]