Radiofrequency Ablation Lesions Research Articles

Investigation of Optimal Needle Position for Radiofrequency Ablation-Based Blockade of Interspace between the Popliteal Artery and the Posterior Capsule of the Knee: A Cadaveric Study.

Background and Objectives: The interspace between the popliteal artery and the posterior capsule of the knee (iPACK) block has been widely used in perioperative settings to control posterior knee pain and can additionally be used for chronic knee pain. In this cadaveric study, we aimed to investigate the needle tip position and its proximity to the articular branch of the tibial nerve (ABTN) during an iPACK-targeted radiofrequency procedure. Materials and Methods: An ultrasound-guided iPACK block was performed on 20 knees of 10 cadavers. We injected 0.1 mL each of blue and green gelatinous dye near the tibial artery (point A) and posterior knee capsule (point B), respectively, and evaluated the spread of both around the ABTN. For a hypothetical conventional radiofrequency ablation (RFA) lesion (diameter, 2.95 mm) and cooled RFA lesion (diameter, 4.9 mm), we counted the number of specimens in which the ABTNs would be captured. Results: The percentage of specimens in which the ABTN would be captured by a cooled RFA lesion was 64.71% at point A and 43.75% at point B (p = 0.334). Meanwhile, the percentage of specimens in which the ABTN would be captured by a conventional RFA lesion was 58.82% from point A and 25% from point B (p = 0.065). Conclusions: When performing an RFA-based iPACK block, the needle tip may be positioned either lateral to the tibial artery or in the space between the posterior knee capsule and the tibial artery. However, more studies with larger samples are needed to verify these results before the clinical use of this procedure can be recommended.

Difference in radiofrequency ablation profile between during sinus rhythm and atrial fibrillation: Considerations in this era of high‐power short‐duration strategy

AbstractBackgroundThe concept of ablation index (AI) was introduced to evaluate radiofrequency (RF) ablation lesions. It is calculated from power, contact force (CF), and RF duration. However, other factors may also affect the quality of ablation lesions. To examine the difference in RF lesions made during sinus rhythm (SR) and atrial fibrillation (AF).MethodsSixty patients underwent index pulmonary vein isolation during SR (n = 30, SR group) or AF (n = 30, AF group). All ablations were performed with a power of 50 W, a targeted CF of 5–15 g, and AI of 400–450 using Thermocool Smarttouch SF. The CF, AI, RF duration, temperature rise (Δtemp), impedance drop (Δimp), and the CF stability of each ablation point quantified as the standard deviation of the CF (CF‐SD) were compared between the two groups.ResultsA total of 3579 ablation points were analyzed, which included 1618 and 1961 points in the SR and the AF groups, respectively. Power, average CF, RF duration per point, and the resultant AI (389 ± 59 vs. 388 ± 57) were similar for the two rhythms. However, differences were seen in the CF‐SD (3.5 ± 2.2 vs. 3.8 ± 2.1 g, p < .01), Δtemp (3.8 ± 1.3 vs. 4.0 ± 1.3°C, p < .005), and Δimp (10.3 ± 5.8 vs. 9.4 ± 5.4 Ω, p < .005).ConclusionsDespite similar AI, various RF parameters differed according to the underlying atrial rhythm. Ablation delivered during SR demonstrated less CF variability and temperature increase and greater impedance drop than during AF.

Robust, high-density lesion mapping in the left atrium with near-infrared spectroscopy.

Radiofrequency ablation (RFA) procedures for atrial fibrillation frequently fail to prevent recurrence, partially due to limitations in assessing extent of ablation. Optical spectroscopy shows promise in assessing RFA lesion formation but has not been validated in conditions resembling those in vivo. Catheter-based near-infrared spectroscopy (NIRS) was applied to porcine hearts to demonstrate that spectrally derived optical indices remain accurate in blood and at oblique incidence angles. Porcine left atria were ablated and mapped using a custom-fabricated NIRS catheter. Each atrium was mapped first in phosphate-buffered saline (PBS) then in porcine blood. NIRS measurements showed little angle dependence up to 60deg. A trained random forest model predicted lesions with a sensitivity of 81.7%, a specificity of 86.1%, and a receiver operating characteristic curve area of 0.921. Predicted lesion maps achieved a mean structural similarity index of 0.749 and a mean normalized inner product of 0.867 when comparing maps obtained in PBS and blood. Catheter-based NIRS can precisely detect RFA lesions on left atria submerged in blood. Optical parameters are reliable in blood and without perpendicular contact, confirming their ability to provide useful feedback during in vivo RFA procedures.

Ultrastructural insights from myocardial ablation lesions from microsecond pulsed field vs radiofrequency energy

BackgroundUltrastructural findings immediately after pulsed field ablation (PFA) of the myocardium have not been described. ObjectivesThe purpose of this study was to elucidate ultrastructural characteristics and differences between microsecond PFA at the 1- and 4-hour timepoints after pulse delivery and to compare them to irrigated radiofrequency ablation (RFA) lesions. MethodsHealthy swine underwent endocardial PFA or RFA followed by necropsy. Discrete microsecond PFA and irrigated RFA lesions were created in the ventricles with a lattice tip ablation catheter. Lesions were delivered in a manner so as to allow sampling to occur 1 and 4 hours after ablation. All lesions were located at necropsy, and samples were carefully obtained from within the lesion core, lesion periphery, and adjacent healthy myocardium. Transmission electron microscopic assessment was performed after fixation using paraformaldehyde and glutaraldehyde. ResultsOne hour after microsecond PFA delivery, myocytes were noted to be significantly and uniformly disrupted. Clustered, misaligned, swollen mitochondria coupled with degenerating nuclei and condensed chromatin were visualized. These findings progressed over the subsequent few hours with worsening edema. Similar changes were seen with RFA but reduced in severity. However, there was prominent extravasation of red blood cells with occlusion of capillaries that was not seen in PFA. At the lesion periphery, an abrupt change in the degree of myocyte damage was observed with PFA but not RFA. ConclusionTransmission electron microscopy demonstrates evidence of widespread destruction of myocytes as early as an hour after PFA and corroborates known histologic features such as sparing of vessels and sharp lesion margins.

Bipolar radiofrequency ablation lesion areas and confluence: An exvivo study and technical report.

Radiofrequency ablation (RFA) has been used for nearly 100 years, treating an array of medical conditions including chronic pain. Radiofrequency (RF) energy depolarizes and repolarizes tissues adjacent to a probe producing heat and causing direct thermal injury. When positioned adjacent to neural structures, it leads to neural tissue injury and cell death interrupting pain signaling with the ultimate goal of providing lasting pain relief. Today, RFA is commonly used to treat cervical, thoracic, and lumbar zygapophyseal joints, sacroiliac joint, and more recently large peripheral joint-mediated pain. There are several applications of RFA systems, including bipolar, conventional thermal, cooled, protruding, and pulsed. As yet, no study has determined the best technical practice for bipolar RFA. This exvivo study examines RFA lesion midpoint (LMP) area and lesion confluence comparing three different commonly used gauge (g) probes (18-g, 20-g, and 22-g) with 10-mm active tips at various interprobe distances (IPD) to guide best technical practices for its clinical application. Bipolar RFA lesions were generated in preservative-free chicken breast specimens using three different gauge probes (18-g, 20-g, and 22-g) with 10-mm active tips at various IPD (6, 8, 10, 12, 14, 16, and 18 mm). RF was applied for 105 s (15-s ramp time) at 80°C for each lesion at both room and human physiological temperature. The specimen tissues were dissected through the lesion to obtain a length, width, and depth, which were used to calculate the LMP area (mm2 ). The LMP areas of each thermal ablation were investigated using visualization and descriptive analysis. The Kruskal-Wallis test was performed to compare LMP areas between the two temperature groups and the three different gauge probe subgroups at the various IPDs. Of the 36 RF lesions (14: 18-g, 12: 20-g, and 10: 22-g) performed, 24 demonstrated lesion confluence. The average time to reach 80°C was 16-17 s; therefore, the average time of RF-energy delivery (at goal temperature) was 88-89 s despite varying needle size or IPD. Comparing the 25 and 37°C groups, 18-g probes produced mean LMP areas of 73.7 and 79.2 mm2 , respectively; 20-g probes produced mean LMP areas of 66 and 66.8 mm2 , respectively; 22-g probes produced mean LMP areas of 56.6 and 59.7 mm2 , respectively. There was no statistical evidence to state a difference regarding LMP area between temperature groups; however, the 18-g probes produced consistently larger LMP areas in the 37°C compared to 25°C specimen groups at each IPD. Lesion confluence was lost for 18-g, 20-g, and 22-g probes at IPD of 14, 12, and 10 mm, respectively, in both 25 and 37°C groups. LMP area was similar between 6 and 8 mm IPD in all of the three-gauge groups; however, there was a significant drop in LMP area from 8 mm IPD to 10 mm and greater. The 18-g, 20-g, and 22-g probes all demonstrated a sharp decline in LMP area when increasing the IPD from 8 to 10 mm. This exvivo technical study evaluated bipolar RFA LMP areas and lesion confluence, and determined the recommended IPD of 18-g, 20-g, and 22-g probes to be less than 12, 10, and 8 mm, respectively, for best clinical practice. Placing bipolar probes at an IPD greater than 14, 12, and 10 mm, respectively, risks the loss of lesion confluence and failure to produce a clinically significant treatment response due to lack of nerve capture. In clinical practice, the use of injectate may produce larger lesions than demonstrated in this study. Additionally, invivo factors may impact ablation zone size and ablation patterns. As there are a paucity of studies comparing various RFA applications and conventional RFA needles are least expensive, it is possible that bipolar conventional RFA is more cost-effective than other techniques.

Acute mitral isthmus block during catheter ablation with vein of Marshall ethanol infusion: Angiographic considerations

Achieving bidirectional mitral isthmus block is still challenging. Conventional ablation methods involve radiofrequency applications on the endocardial aspect of the lateral mitral isthmus, and often epicardial applications inside the coronary sinus. To evaluate the impact of the systematic use of ethanol infusion in the vein of Marshall on the achievement of acute mitral isthmus block of additional epicardial component lesion. We evaluated patients referred to two centres for long-standing persistent atrial fibrillation ablation or recurrent peri-mitral flutter. All patients had pulmonary vein isolation and mitral isthmus line using ethanol infusion in the vein of Marshall for the first procedure and additional radiofrequency ablation lesion if necessary. For redo procedures, additional ablations (atrial lines and complex fractionated atrial electrogram ablations, if needed) were also performed. We included 149 patients, and ethanol infusion in the vein of Marshall was not performed in 27 patients (18%). Among 122 patients, 115 had long-standing persistent atrial fibrillation (94.2%) and seven had peri-mitral flutter (5.8%). The mean duration of continuous atrial fibrillation was 53 months before ablation. Acute bidirectional mitral isthmus block was obtained in 115 (94.2%) of the 122 patients who received ethanol infusion in the vein of Marshall (77% when considering the total population). The mean radiofrequency delivery time to obtain mitral isthmus block was 2.6minutes for the endocardial mitral isthmus radiofrequency ablation and 2.6minutes for the epicardial mitral isthmus radiofrequency ablation. Failure to obtain mitral isthmus block was associated with increased mitral isthmus length and left atrial dilation. No major complications related to ethanol infusion in the vein of Marshall were observed. Ethanol infusion in the vein of Marshall, when feasible (82%), was a safe approach to obtaining a high success rate (94%) of acute bidirectional endocardial and epicardial mitral isthmus block.

Surpoint algorithm for improved guidance of ablation for ventricular tachycardia (SURFIRE-VT): a propensity-matched study

Abstract Background Ablation Index (AI) is a novel multiparametric radiofrequency (RF) ablation lesion quality metric, which incorporates contact force, time, and power in a weighted formula. AI guided strategies have been shown to be clinically effective for catheter ablation of atrial arrhythmias. The utility of AI to guide ablation of ventricular tachycardia (VT) in patients with structural heart disease is not known. Objectives To assess RF ablation and procedural characteristics, safety, and long-term clinical outcomes in patients undergoing VT ablation using either an AI guided strategy (maximum AI target value 550) or conventional approach using traditional parameters at a large tertiary medical center. Methods Consecutive patients (n=91) undergoing initial VT ablation for both ischemic (ICM) and non-ischemic (NICM) VT at single tertiary medical center between 2017 and 2022 were examined. Patients were 1:1 propensity matched for baseline characteristics, co-morbid conditions, and antiarrhythmic use depending on whether the ablation was guided by AI or traditional lesion quality parameters. Baseline categorical variables were compared using chi square test or Fisher exact test, and continuous measures were evaluated using Wilcoxon rank sum test. Linear regression was used to assess the impact of the use of AI on ablation characteristics and Cox proportional hazard model was used evaluate clinical outcomes. Results After propensity matching, baseline characteristics were well balanced between AI (n=37) and non-AI (n=37) groups (Table 1). Patients undergoing an AI guided strategy had shorter average procedure duration (-30.9 minutes, 95% CI [-60.4, -1.4], p=0.04) and average time per lesion (-13.7 seconds, 95% CI [-17.9, -9.5], p <0.001), as well as a trend toward significantly lower total RF ablation duration (357 seconds, 95% CI [-776, 61.9] p=0.09) and fewer steam pops (-0.19, 95% CI [-0.40, 0.02] p = 0.08). Lesion sets were similar between AI and non-AI groups (Scar homogenization: 41% vs 27%; p=0.22, Linear: 23% vs 73%; p=0.31, elimination LPs/LAVAs: 50% vs 43%; p=0.25, Scar dechanneling: 19% vs 8%; p=0.19, Core isolation: 5% vs 11%; p=0.4) as was use of epicardial mapping and ablation (11% vs 14%; p=0.73) Inducibility of VT (70% vs 67%; p=0.8) and termination of clinical VT during ablation (11% vs 16%; p=0.17) were also similar between AI and non-AI groups. When compared to a traditional strategy, patients undergoing an AI strategy had similar hazard for VT recurrence (0.97, 95% CI [0.42 – 2.2], p=0.93) and appropriate device therapy (0.79, 95% CI [0.32 – 1.95] p=0.61). Conclusions Compared to a strategy guided by traditional lesion parameters, use of AI of 550 for VT ablation in patients with structural heart disease resulted in shorter procedure time and average time of RF delivery per lesion with similar intermediate term clinical outcomes.Table 1Figure 1

Transcatheter occlusion of the coronary sinus increases radiofrequency ablation lesion size in the left ventricular myocardium: a new approach to improve the efficiency of ventricular tachyarrhythmia substrate destruction

The aim. The results of ventricular tachyarrhythmia catheter ablation in patients with structural heart diseases remains to be improved. Both evolution of the arrhythmia substrate and its deep location are the main reasons for standard endocardial ablation limitations. Theoretically, the reduction of myocardial perfusion rate may improve convective heating of the myocardium during radiofrequency (RF) ablation, expanding the volume of damage. The purpose of this study was to assess the effect of coronary sinus (CS) occlusion in order to reduce myocardial perfusion during RF ablation on the volume of myocardial damage.Methods. The study was performed on 13 pigs. Following vascular access accomplishment, a balloon catheter was inserted into the lumen of the CS. A 3.5-mm open-irrigated RF ablation catheter was inserted into the cavity of the left ventricle. RF applications were applied in an alternate order, with and without CS occlusion (power 30 and 40W, application time 40 and 30 s, respectively). Each ablation point was marked on a three-dimensional electroanatomic map. After euthanasia, myocardial lesions were analyzed.Results. The analysis of 50 RF applications was performed (22 with CS occlusion and 28 without CS occlusion). At the same time, 28 applications (13 with occlusion and 15 without occlusion) were performed at a power of 40W, and 22 applications (9 with occlusion and 13 without occlusion) at a power of 30 watts. There was a trend toward the increase in lesion sizes created during CS occlusion. Significantly larger lesions were detected with 40W applications during CS occlusion when compared with open CS applications: depth 11.6±3.9 vs. 8.8±3.8 mm (p=0.04), diameter 11.7±4.6 vs. 8.5±3.9 mm (p=0.03), volume 504.2±499.5 vs. 183.0±157.5 mm3 (p=0.01). Transmural myocardial lesions were more often encountered during applications with CS occlusion with both power settings, 30 and 40W: 68.2% of transmural lesions versus 39.3%; p=0.046.Conclusion. RF applications with a power of 40W and CS occlusion are characterized by greater depth, diameter, and volume of damage, as well as a greater frequency of transmural necrosis. Temporary transcatheter occlusion of CS can be proposed for ablation of ventricular arrhythmia with extended and deep substrate.

Optimal conditions for high-power, short-duration radiofrequency ablation using a novel, flexible-tipped, force-sensing catheter.

High-power, short-duration (HPSD) radiofrequency ablation (RFA) reduces procedure time; however, safety and efficacy thresholds vary with catheter design. The study sought to determine optimal HPSD ablation conditions with a novel flexible-tipped, contact force-sensing RFA catheter. RFA lesions were created in thigh muscle (16 swine) over a range of conditions (51-82 W, 2-40 g, 8-40 mL/min irrigation). An intracardiac study was performed (12 swine) to characterize steam pop thresholds. Lesions were created in a second intracardiac study (14 swine, n = 290 pulmonary vein isolation [PVI] lesions) with combinations of radiofrequency power, duration, and contact force. PVI was tested, animals were sacrificed, and lesions were measured. The likelihood of coagulation formation in the thigh model was <20% when power was ≤79 W, when contact force was ≤40 g, when duration was ≤11 seconds, and when irrigation rates were 8 to 40 mL/min. The impact of contact force on lesion safety and efficacy was more pronounced using HPSD (60 W/8 seconds) compared with conventional ablation (30 W/45 seconds) (P = .038). During PVI, focal atrial lesions ranged in width from 4.2 to 12.5 mm and were transmural 80.8% of the time. PVI was achieved in 13 of 14 veins. Logistic regression identified that the optimal parameters for radiofrequency application were 60 to 70 W with a duration <8 seconds and <15 g contact force. Optimal HPSD lesions with this this flexible-tipped, force-sensing RFA catheter were created at 60 to 70 W for <8 seconds with <15 g contact force. Chronic studies are ongoing to assess radiofrequency parameter refinements and long-term lesion durability using these conditions.

ID: 209893 The Effect of Local Anesthetics and Contrast Agents on Radiofrequency Ablation Lesion Size

Radiofrequency ablation (RFA) is a validated treatment option for the treatment of chronic pain in patients with lumbar spondylosis. Lesion size is suggested to correlate with good clinical outcomes. This has created an abundance of scientific interest to develop products with larger lesion characteristics. Needle characteristics, energy transfer, and heat rate are known to modify lesion size. Here, we demonstrate that common intra-operative solutions such as Lidocaine, Iodine and Gadolinium-based products can also affect lesion shape.

AB-453068-4 BENCH EVALUATION OF OVERLAPPING LESION STEAM POP RATES

Sequentially delivered, overlapping radiofrequency (RF) ablation lesions pose a risk of creating steam pops due to heat stacking. The relationship between inter-lesion distance and heat stacking is presently unknown. Therefore, the smallest inter-lesion distance for safe therapy delivery needs to be determined. The study objective was to quantify steam pop rates when creating sequential, adjacent, potentially overlapping RF ablation lesions at various inter-lesion distances in a non-perfused bovine cardiac tissue model with the intention of identifying the safest minimum inter-lesion distance. In a saline filled tank at clinically relevant conductivity and temperature, a TactiCath SE RF ablation catheter created sets of 2 lesions on isolated, non-perfused bovine right ventricular tissue. At 15g force and 40W, successive 10s lesions were created (transition time less than 1s between lesions) at center-to-center distances of 1, 2, 3, 4, 5, and 10 mm, and steam pop frequency was determined. If a steam pop occurred during the first 10s lesion prior to the drag, the trial was excluded and repeated. Using pilot data, it was determined a minimum of 49 samples at each inter-lesion distance would provide a robust sample size for statistical analysis. Steam pop rate at an inter-lesion distance of 10mm was used as the control for analysis as there was no lesion overlap at this center-to-center distance. Steam pop rates at 1 and 2 mm were significantly greater (p=0.002 and p<0.001) than at 10mm. Using a 2-proportions, 2-sample non-inferiority (NI) test, with a NI margin of 20%, statistical equivalence was claimed between steam pop rates at 10mm and 5mm (p=0.009), 4mm (p=0.005), 3mm (p=0.003). Lesions spaced closer than 3mm apart have a greater risk of resulting in steam pops. Therefore, a minimum of 3mm inter-lesion distance would be recommended as it has shown to have a similar steam pop rate to focal lesions.

PO-05-146 AN UNUSUAL ATRIOVENTRICULAR REENTRY TACHYCARDIA: SUCCESSFUL ABLATION OF NOVEL SLOW PATHWAY AT SUPERIOR SEPTAL PERIMITRAL LEFT ATRIUM

Atrioventricular nodal reentrant tachycardia (AVNRT) is a common supraventricular tachycardia (SVT), treated with catheter ablation of slow pathway. The right and left inferior slow pathway (SP) extensions of the AV node are widely recognized, but other SPs are very rare. We present a case of atypical AVNRT that was successfully ablated at the superior septal perimitral left atrium. N/A A 75-year-old man with history of coronary artery disease status post coronary artery bypass grafting and recurrent episodes of symptomatic SVT despite diltiazem and metoprolol presented for catheter ablation. Mid RP SVT (cycle length, CL 350 ms) with concentric atrial activation was inducible with atrial and ventricular extrastimulation. Synchronized premature ventricular complexes and ventricular entrainment excluded AV reentry. Very late coupled premature atrial complex from coronary sinus (CS) delivered synchronous to septal A activation delayed next A and reset SVT indicating AVNRT and excluding ectopic junctional (JT) or atrial tachycardia (AT). Further, AH interval during SVT was much longer than AH with atrial pacing at same CL excluding AT. We concluded mechanism to be atypical AVNRT. On activation mapping of right atrium, earliest A was recorded in the fast pathway region, earlier than locations of right and left slow pathways in the triangle of Koch and CS respectively. Radiofrequency ablation lesions anatomically targeting both slow pathways were delivered at base of triangle of Koch and inside CS without affecting SVT. High density activation maps of both right and left atria were created during SVT using Orion basket catheter and Rhythmia (Boston Scientific) mapping system. Earliest A was recorded in the superior septal perimitral left atrium, superior to the location of His bundle electrogram, and anatomically adjacent to aortic sinuses of Valsalva (not mapped). We concluded this to be an unusual left superior extension of the AV node. Radiofrequency ablation lesion using IntellaNav MiFi catheter at this site promptly terminated SVT. Consolidation lesions were delivered and anchored to the mitral annulus. The tachycardia was no longer inducible on programmed electrical stimulation despite isoproterenol. The patient has remained symptom free for 6 months since ablation. With activation mapping we identified the retrograde slow pathway participating in an unusual atypical AVNRT at superior septal perimitral left atrium.

PO-01-119 CATHETER STABILITY ANALYSIS IN ABLATION OF PAROXYSMAL ATRIAL FIBRILLATION: IMPACT OF A NOVEL FLEXIBLE ELECTRODE TIP

Catheter electrode stability is a key factor of a successful radiofrequency (RF) ablation lesion formation. Current techniques to enhance or monitor catheter stability include the use of steerable introducers, high-frequency jet ventilation, and the incorporation of objective lesion marker placement via Electroanatomic Mapping (EAM) Systems. In addition to automatic lesion marker placement, the EnSite™ AutoMark Module records catheter location during RF energy delivery, providing insight into catheter electrode stability during ablation. To demonstrate improved stability during ablation with a flexible laser cut tip electrode vs. a solid-6-hole electrode tip during de novo PVI ablation for the treatment of PAF and concomitant CTI-lines for the treatment of typical AFL. AutoMark™ ablation data gathered during the TactiFlex AF IDE NCT04356040 (flex tip catheter) and TactiSense IDE NCT03354663 (solid tip catheter) trials was analyzed (FIGURE). Both trials were prospective, non-randomized multicenter clinical studies which enrolled 355 and 150 subjects worldwide, respectively. PVI and CTI lesions from point-by-point ablation style operators with discrete lesions were included. Anatomic region assignment of each RF episode was accomplished using machine learning. Average distance and standard deviations of the ablation electrode movement from the mean positional centroid were calculated for each RF episode. Stability was evaluated as the percent of time during an RF episode where the ablation electrode remained within 2.5mm of the ablation lesion centroid. A total of 10285 flexible tip and 2141 solid tip RF episodes were analyzed from 112 and 21 cases, respectively. The average RF episode duration for the flexible tip and solid tip lesions, was 10.6 ± 4.8 and 17.1 ± 9.8 seconds, respectively. The flexible tip and solid tip catheters remained positionally stable within a 2.5 mm sphere for 85.3% ± 22.7 and 79.9% ± 26.1 of the RF episode duration, respectively, (p <0.001) (FIGURE). In the subset of lesions <10 seconds, the difference in stability was even more pronounced (TABLE). A flexible tip ablation catheter (TactiFlex™ SE) demonstrated greater stability than a solid tip ablation catheter (TactiCath™ SE) during ablation of atrial fibrillation and CTI-dependent atrial flutter. Greater stability during lesion formation may result in more durable lesions and better patient outcomes.Tabled 1Catheter# RF EpisodesRF Episode Duration, sec (SD)Mean (SD)Median [Q1, Q3]p-valueAll RF EpisodesFlexible Tip1028510.6 (4.8)85.3% (22.7)96.9% [79.9, 100]< 0.001Solid Tip214817.1 (9.8)79.9% (26.1)92.6% [66.7, 100]< 0.001RF Episodes < 10 secFlexible Tip43406.4 (2.8)85.0% (24.2)98.7% [80.7, 100]< 0.001Solid Tip5427.3 (2.3)73.6% (32.9)89.8% [51.7, 100]< 0.001Stability of a solid tip (TactiCath™ Contact Force Ablation Catheter, Sensor Enabled™) versus flexible tip (TactiFlex™ Contact Force Ablation Catheter, Sensor Enabled™), reported as the percent time the catheter tip remained within a 2.5 mm radius sphere. Open table in a new tab

PO-03-065 PULSED FIELD ABLATION IS MORE EFFECTIVE THAN RADIOFREQUENCY ABLATION FOR THE RETREATMENT OF CHRONIC ABLATION SUBSTRATE

There are known limitations of radiofrequency ablation (RFA) in extending and homogenizing prior ablation. The effect of pulsed field ablation (PFA) following prior RFA is not known. To evaluate the differential ability of PFA versus RFA to penetrate chronic RFA lesions. A two step in-vivo study was designed to simulate a retreatment scenario. Step I : Six Yorkshire swine underwent intentional ineffective RFA using IntellaNav StablePoint catheter in three sites: I.1) Right atrium: intercaval line with multiple intentional gaps, I.2) Left atrium: right superior and inferior common pulmonic veins with intentional gaps, and I.3) Left ventricle: discrete lesions. Step II: Following a survival period of ≈5 weeks animals were remapped. Chronic RFA was identified via voltage mapping. Next, animals were retreated as following: II.1) Right atrium: PFA over prior intercaval line using a focal PFA catheter (FARAPOINT), II.2) pulmonic vein isolation using a single shot PFA catheter (FARAWAVE), and II.3) Left ventricle: animals were randomized into two arms, PFA or RFA. In each arm, two types of sub-chronic lesions were performed: PFA and RFA on chronic RFA scar or PFA and RFA on healthy myocardium. PFA was applied with 4 applications of 2.0kV. RFA was applied with 30W, 60s or a local impedance drop >50Ω. After 2-5 day survival, atrial electrical block was assessed via electroanatomical mapping. All lesions were measured sub-gross for the extent of the chronic and sub-chronic zones. Right and left atria: Retreatment with focal PFA resulted in complete intercaval block (width: 16-28mm) and isolation of all targeted pulmonic veins, expanding and homogenizing the disparate chronic RFA lesions. Left ventricle: the mean depth for chronic RFA was 4.8±1.4mm. When RFA was performed on healthy substrate, the mean depth of the sub-chronic zone was 7.6±1.3mm, compared to 3.9±1.6mm when RFA was applied on chronic RFA scar (p<0.01). In contrast, the mean depth for sub-chronic PFA on healthy substrate was 7.0±1.6mm, similar to the sub-chronic PFA zone on chronic RFA (7.1±1.3mm; p=0.94) demonstrating that PFA has the ability to penetrate chronic RFA scar. PFA may be advantageous for ablation following prior RFA, producing lesions that, unlike RFA retreatment, are not significantly impeded by the presence of scar from the prior RFA.

Evaluating temperature gradients across the posterior left atrium with radiofrequency ablation.

Esophageal injury is a well-known complication associated with catheter ablation. Though novel methods to mitigate esophageal injury have been developed, few studies have evaluated temperature gradients with catheter ablation across the posterior wall of the left atrium, interstitium, and esophagus. To investigate temperature gradients across the tissue, we developed a porcine heart-esophageal model to perform ex vivo catheter ablation on the posterior wall of the left atrium(LA), with juxtaposed interstitial tissue and esophagus. Circulating saline (5 L/min) was used to mimic blood flow along the LA and alteration of ionic content to modulate impedance. Thermistors along the region of interest were used to analyze temperature gradients. Varying time and power, radiofrequency (RF) ablation lesions were applied with an externally irrigated ablation catheter. Ablation strategies were divided into standard approaches (SAs, 10-15 g, 25-35 W, 30 s) or high-power short duration (HPSD, 10-15 g, 40-50 W, 10 s). Temperature gradients, time to the maximum measured temperature, and the relationship between measured temperature as a function of distance from the site of ablation was analyzed. In total, fiveexperiments were conducted each utilizing new porcine posterior LA wall-esophageal specimens for RF ablation (n = 60 lesions each for SA and HPSD). For both SA and HPSD, maximum temperature rise from baseline was markedly higher at the anterior wall (AW) of the esophagus compared to the esophageal lumen (SA: 4.29°C vs. 0.41°C, p < .0001 and HPSD: 3.13°C vs. 0.28°C, p < .0001). Across ablation strategies, the average temperature rise at the AW of the esophagus was significantly higher with SA relative to HPSD ablation (4.29°C vs. 3.13°C, p = .01). From the start of ablation, the average time to reach a maximum temperature as measured at the AWof the esophagus with SA was 36.49 ± 12.12 s, compared to 16.57 ± 4.54 s with HPSD ablation, p < .0001. Fit to a linear scale, a 0.37°C drop in temperature was seen for every 1 cm increase in distance from the site of ablation and thermistor location at the AW of the esophagus. Both SA and HPSD ablation strategies resulted in markedly higher temperatures measured at the AW of the esophagus compared to the esophageal lumen, raising concern about the value of clinical intraluminal temperature monitoring. The temperature rise at the AW was lower with HPSD. A significant time delay was seen to reach the maximum measured temperature and a modest increase in distance between the site of ablation and thermistor location impacted the accuracy of monitored temperatures.

Quantitative late gadolinium enhancement cardiac magnetic resonance analysis of the relationship between ablation parameter and left atrial tissue lesion following pulmonary vein isolation.

The impact of ablation parameters on acute tissue lesion formation after pulmonary vein isolation (PVI) has not been sufficiently evaluated in patients with atrial fibrillation. Radiofrequency ablation lesion can be visualized by late gadolinium enhancement cardiac magnetic resonance (LGE-CMR). We sought to quantitatively analyze the relationship between ablation parameter and tissue lesion following PVI at different segments of pulmonary vein (PV) using LGE-CMR. Twenty-one patients with atrial fibrillation who underwent PVI procedure were retrospectively enrolled. All patients underwent LGE-CMR examination within 3 days after radiofrequency ablation. Ablation parameters during PVI were documented, including lesion size index (LSI), force-time integral (FTI), power, contact force, temperature, and time of duration. The ablation point was projected onto 3-dimensional (3D) left atrial shell constructed base on LGE-CMR and corresponding image intensity ratio (IIR) was calculated on the same shell. A tissue lesion point was defined when the LGE-CMR IIR was > 1.2. In total, 1,759 ablation points were analyzed. The ablation parameters and IIRs for each PV segment were significantly different (P < 0.0001). IIRs corresponding to ablation points at posterior of PV tended to be higher than those at non-posterior of PV when similar ablation parameters were applied during ablation. LSI was a better predictor of tissue lesion existence following PVI than FTI, contact force, power, temperature, and duration time at non-posterior wall of PV. The IIR showed positive correlation with LSI at non-posterior wall of PV (non-posterior of right PV, r = 0.13, P = 0.001, non-posterior of left PV, r = 0.26, P < 0.0001). When similar ablation parameters were applied during PVI, the posterior wall of PV had more severe tissue lesion than non-posterior wall of PV. Therefore, it was reasonable to decrease ablation energy at posterior wall of PV. Moreover, LSI was a better index to reflect tissue lesion quality following PVI at non-posterior of PV.

Safe and effective delivery of high-power, short-duration radiofrequency ablation lesions with a flexible-tip ablation catheter.

High-power, short-duration (HPSD) radiofrequency ablation (RFA) may reduce ablation time. Concerns that catheter-mounted thermocouples (TCs) can underestimate tissue temperature, resulting in elevated risk of steam pop formation, potentially limit widespread adoption of HPSD ablation. The purpose of this study was to compare the safety and efficacy of HPSD and low-power, long-duration (LPLD) RFA in the context of pulmonary vein isolation (PVI). An open-irrigated ablation catheter with a contact force sensor and a flexible-tip electrode containing a TC at its distal end (TactiFlexTM Ablation Catheter, Sensor EnabledTM, Abbott) was used to isolate the left pulmonary veins (PVs) in 12 canines with HPSD RFA (50 W for 10 seconds) and LPLD RFA (30 W for a maximum of 60 seconds). PVI was assessed at 30 minutes and 28 ± 3 days postablation. Computed tomographic scans were performed to assess PV stenosis after RFA. Lesions were evaluated with histopathology. A total of 545 ablations were delivered: 252 with LPLD (0 steam pops) and 293 with HPSD RFA (2 steam pops) (P = .501). Ablation time required to achieve PVI was >3-fold shorter for HPSD than for LPLD RFA (P = .001). All 24 PVs were isolated 30 minutes after ablation, with 12/12 LPLD-ablated and 11/12 HPSD-ablated PVs still isolated at follow-up. Histopathology revealed transmural ablations for HPSD and LPLD RFA. No major adverse events occurred. An investigational ablation catheter effectively delivered RFA lesions. Ablation time required to achieve PVI with HPSD with this catheter was >3-fold shorter than with LPLD RFA.

High-density mapping improves detection of conduction gaps after pulmonary vein isolation ablation with a circular mapping catheter.

High-density (HD) mapping of the pulmonary vein (PVs) has been hypothesized to improve the detection of conduction gaps in the radiofrequency ablation lesions set after pulmonary vein isolation (PVI) for the treatment of atrial fibrillation (AF). We aimed to compare the incidence of gaps after PVI with a standard 20-pole circumferential mapping catheter (CMC-20) and an HD mapping catheter (HD Grid). This prospective study included patients scheduled for high-power short-duration PVI. Acute PVI was defined as an entrance and exit block using the CMC-20 after ≥ 20min waiting period. The left atrium was then remapped using the HD Grid high-density mapping catheter to identify residual conduction gaps in the PVI lines by voltage and activation criteria. The primary endpoint was the number of gaps identified per patient by the HD Grid catheter. A total of 20 patients were included (mean age 59.9 ± 10.8years, 15% female, 70% paroxysmal AF). The new map with the HD Grid identified 6 gaps in 4 patients (20%) or 0.3 ± 0.7 gaps per patient (p = 0.055 when compared to CMC-20). Five gaps (83%) were located at the right PVs. There was no difference in mapping time (CMC-20 12.2 ± 2.6min vs HD Grid 11.7 ± 3.4min, p = 0.452); however, the number of points was significantly higher in the HD Grid map (1662.7 ± 366.1 vs 1171.6 ± 313.6, p < 0.001). HD mapping during AF ablation identified PVI gaps in 1 out of 5 patients. Therefore, HD mapping may have the potential to improve AF ablation success rates in the long term. ClinicalTrials.gov NCT04850508 on April 20, 2021.

Comparison of gross pathology inspection and 9.4T magnetic resonance imaging in the evaluation of radiofrequency ablation lesions in the left ventricle of the swine heart.

Aims: Gross pathology inspection (patho) is the gold standard for the morphological evaluation of focal myocardial pathology. Examination with 9.4T magnetic resonance imaging (MRI) is a new method for very accurate display of myocardial pathology. The aim of this study was to demonstrate that lesions can be measured on high-resolution MRI images with the same accuracy as on pathological sections and compare these two methods for the evaluation of radiofrequency (RF) ablation lesion dimensions in swine heart tissue during animal experiment. Methods: Ten pigs underwent radiofrequency ablations in the left ventricle during animal experiment. After animal euthanasia, hearts were explanted, flushed with ice-cold cardioplegic solution to relax the whole myocardium, fixed in 10% formaldehyde and scanned with a 9.4T magnetic resonance system. Anatomical images were processed using ImageJ software. Subsequently, the hearts were sliced, slices were photographed and measured in ImageJ software. Different dimensions and volumes were compared. Results: The results of both methods were statistically compared. Depth by MRI was 8.771 ± 2.595mm and by patho 9.008 ± 2.823 mm; p = 0.198. Width was 10.802 ± 2.724mm by MRI and 11.125 ± 2.801mm by patho; p = 0.049. Estuary was 2.006 ± 0.867mm by MRI and 2.001 ± 0.872mm by patho; p = 0.953. The depth at the maximum diameter was 4.734 ± 1.532mm on MRI and 4.783 ± 1.648mm from the patho; p = 0.858. The volumes of the lesions calculated using a formula were 315.973 ± 257.673mm3 for MRI and 355.726 ± 255.860mm3 for patho; p = 0.104. Volume directly measured from MRI with the "point-by-point" method was 671.702 ± 362.299mm3. Conclusion: Measurements obtained from gross pathology inspection and MRI are fully comparable. The advantage of MRI is that it is a non-destructive method enabling repeated measurements in all possible anatomical projections.

Real-time electrophysiological characterization of acute and chronic radiofrequency ablation lesions

Abstract Background Assessment of lesion formation remains one of the most important goals to guide radiofrequency (RF) procedures in the cardiac electrophysiology laboratory. Cardiac navigation systems use specific algorithms to predict the effective lesion size, but these metrics are based only on ablation parameters and ignore local electric tissue characteristics. [1] Recent studies show that local multiparametric impedance is influenced by the intrinsic structural characteristics of the tissue. [2] Purpose This study aimed to assess the ability of local multiparametric impedance to characterize acute and chronic RF ablation lesions in the right atrium of pigs. Methods Four anesthetized closed-chest pigs were submitted to two interventions. The first intervention aimed at creating RF ablation lesions (30W, 60s, 55°) in the right atrium using an electrocatheter connected to a conventional cardiac navigation system, while mapping the local multiparametric impedance (LMI), the generator impedance (GI) and the bipolar voltage (BiV). All RF ablation lesions were performed with a stable contact force. Four weeks later, the second intervention aimed at mapping again the previous ablation sites. After the second intervention animals were euthanized and the hearts were removed and processed to identify the presence of fibrosis in the previously ablated lesions (Figure). Results We performed 19 ablations (5±2 per animal) with an average contact force of 14.2±4.6g. Four weeks later, 14/19 (74%) ablation lesions were identified as fibrotic points in the explanted heart (Figure 1). These showed decreased acute LMI and BiV values that persisted low after 4 weeks (Table 1). The remaining 5/19 ablations that did not present fibrosis had lower baseline LMI and bipolar values that resulted in lower LMI and BiV drops (Table 1). The absolute drop in LMI between effective and non-effective lesions was around 50%, while GI drop was only 21% (LMI drop @51KHz: From −3.0±1.4° to −1.5±0.3°, T-TEST p&amp;lt;0.05; GI drop: From 12.7±27.6Ω to 10.5±21.3Ω, T-TEST p=0.89). Conclusion The local baseline electrical properties of atrial myocardium are directly related to the effectiveness of RF ablation lesions. RF ablation sites that resulted into persistent fibrosis points had larger LMI and BiV values, with higher absolute drops than non-effective lesions. The use of LMI in clinical practice could improve the outcome of the procedures of arrhythmia ablation in the electrophysiology lab. Funding Acknowledgement Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Supported by grants from ISCI-MINECO (FIS PI21/00392), FEDER, CIBERCV (CB16/11/00276)