Steam Pops Research Articles

One-year outcomes in patients undergoing very high-power short-duration temperature-controlled ablation for atrial fibrillation

Abstract Funding Acknowledgements Type of funding sources: None. Background The very high-power short-duration (vHPSD) temperature-controlled ablation (vHPSD) improves the efficiency of pulmonary vein isolation (PVI) procedures. Aims We evaluated the procedural and 12-months outcomes in atrial fibrillation (AF) patients undergoing PVI by means of vHPSD ablation. In patients with AF or atrial tachy-arrythmia (AT) recurrence undergoing a redo procedure the durability of the PVI was investigated. Methods Consecutive paroxysmal/persistent AF patients undergoing PVI with the vHPSD ablation strategy (90 W, for 4 s) were enrolled. The rate of PVI, first pass isolation, acute reconnection, and procedural complications were evaluated. Follow-up examinations and EKG were scheduled at 1,6, and 12 months. In case of AF/AT recurrence, patients underwent a redo procedure. Results Overall, 163 AF patients (29 persistent and 134 paroxysmal) were enrolled. The PVI was reached in 100% of patients (88% at first pass). The rate of acute reconnection was 2%. The radiofrequency, fluoroscopy and procedural times were respectively 5,5±1 min, 9±1 min and 75±20 min. No death, tamponade nor steam pops occurred, however 5 patients had vascular complications. The 12-months freedom from AF/AT recurrence was 84% in paroxysmal patients and 71% in persistent. Overall, 9 patients underwent a redo procedure, and in 4 all veins were still isolated, whereas in 5 pulmonary vein reconnections were found. The PVI durability was 83%. No overt complications were observed in the follow-up. Conclusions The vHPSD ablation represents an effective and safe ablation strategy to achieve PVI. The 12-months follow-up showed high freedom from AF/AT recurrence and a good safety profile.

Evaluation of force time integral, force time current integral and lesion size index in a new force sensing catheter

Abstract Funding Acknowledgements Type of funding sources: None. Background Radiofrequency current remains one of the most important ablation techniques in the EP lab. Creating durable lesions is key to successful ablation. Evaluating lesion quality and progression of lesion growth is difficult as many parameters influence lesion formation. Therefore, several approaches were developed, as monitoring RF duration, power and contact force seems insufficient in clinical practice. Force-time-integral (FTI) and force-time-current-integral (FTCI), as well as the ablation index (AI) and lesion size index (LSI) showed decent results in past studies. Recently, a new force sensing catheter (NFSC) was released. By now, data about lesion formation and correlation with the FTI, FTCI and LSI is lacking with this NFSC. This study aimed to further investigate lesion formation with the NFSC in an ex vivo model. Methods 30 RF-lesions were created using an ex vivo porcine cardiac model with the NFSC catheter. The experimental setup consisted of a saline-filled container, a dispersive electrode, a heated thermostat and a circulation pump to imitate in vivo conditions. Global impedance was kept at 120 Ohm as well as the temperature at 37°C. In a first set of lesions, CF was varied (1g, 5g, 10g, 20g). Three lesions were created in each CF-level with 30W. In a second set of lesion, CF was kept at 10 – 15 g, but ablation power was set to 20W, 30W, 40W, 50W, 60W and 70W. In every power level, three lesions were created. All parameters (power, temperature, global impedance, contact force, lesion size) were measured constantly during application of RF-current, enabling real-time correlation of RF parameters and lesion size. In case of an audible steam pop, RF application was stopped. Results 1640 measurement in 30 lesions were included into the analysis. Mean lesion diameter was 7.82 ± 1.52 mm, mean lesion depth 4.80 ± 1.08 mm. Baseline global impedance (GI) was 138.10 ± 10.93 Ω, mean GI-drop 28.10 ± 8.00 Ω. In average, CF of 12.10 ± 5.87 g was used. Correlations of lesion size, FTI and FTCI are shown in table 1. Interestingly, LSI correlated best with lesion size (r = 0.851 and r = 0.852 for lesion depth and diameter; p<0.001). Figure 1 illustrates a scatter plot of LSI and lesion depth (Figure 1a) and lesion diameter (Figure 1b). Figure 2 shows dynamic changes in lesion depth compared to changes in LSI and FTCI. During RF-application, development of lesion formation and LSI is comparable from approximately second 7 onwards. FTCI is rising in a linear manner, whereas lesion formation increases monoexponentially. Conclusion In the NFSC, lesion size correlates strongest with the LSI in power levels up to 70 Watts. FTI and FTCI also showed decent correlations. Regarding dynamic changes in lesion size, LSI is best comparable to actual lesion growth.

Fluoroless vs. conventional catheter ablation of supraventricular tachycardia - retrospective single-centre analysis

Abstract Funding Acknowledgements Type of funding sources: None. Introduction Radiofrequency (RF) catheter ablation of supraventricular tachycardia (SVT) is a gold-standard therapy that offers excellent results. Conventional approach using fluoroscopy has been challenged by the increasing use of electroanatomical mapping (EAM) systems and intracardiac echosonography (ICE) which eliminate the radiation hazard for the patient and medical personnel. They offer good results without compromising safety or efficacy but also require further research. (1, 2) Their widespread use is limited by their cost but is steadily increasing. Purpose To compare the acute outcomes of fluoroless SVT ablation to those of conventional procedures since widespread introduction of this novel technology in our institution. Methods Data about patients with AV-node reentry tachycardia (AVNRT), atrio-ventricular reentry tachycardia (AVRT), atrial tachycardia and atrial flutter (AFL) who were treated with ablation were retrospectively collected using hospital medical records. 80 consecutive patients who underwent fluoroless SVT ablation formed the fluoroless (FL) group. Last 80 patients who previously underwent conventional SVT ablation using fluoroscopy served as a control group. Two different EAM systems were used in the FL group (Abbot Ensite and Biosense Webster CARTO). All procedures were performed by 3 different experienced operators. Results The fluoroless and control group were similar regarding age, sex and comorbidities. Approximately half of all patients in both groups suffered from AVNRT. AVRT was more common in the FL group and AFL in the control group (23.4% vs. 10.0% and 20.8% vs. 37.5% respectively). This was responsible for the difference in the use of ICE and need for transseptal puncture between the groups. Detailed group characteristics are shown in Table 1. Procedure duration was similar in both groups (58.0 ± 25.5 min vs. 63.9 ± 25.3 min in FL and control group respectively, p=0.12). Ablation time, calculated as duration of RF energy delivery, tended to be shorter in the FL group (396 ± 44 vs. 575 ± 636 s) but failed to reach the level of statistical significance (p=0.06). Acute success, defined as non-inducibility of arrhythmia or, in case of AFL, cavotricuspid isthmus conduction block, was achieved in 98.8% and 97.5% of cases in FL and control group respectively. There were no cross-overs from FL group to fluoroscopy. In the control group, mean fluoroscopy duration was 9.7 ± 7.5 min and radiation dose 14.6 ± 21.6 mGy. One steam pop occurred in the FL group but the patient suffered no acute or chronic consequences. There were no other complications. Conclusion Technologies for fluoroless SVT ablation have been widely implemented in our institution with very good acute results and safety profile that is non-inferior to conventional approach. By eliminating risks inherent to fluoroscopy they could be beneficial for patients and physicians likewise. Follow-up data are needed to confirm these results.

Local impedance changes are a suitable real time surrogate for lesion formation in RF-ablation

Abstract Funding Acknowledgements Type of funding sources: None. Background Radiofrequency current remains one of the most important techniques for catheter ablation. Creating durable lesions is key for sufficient and safe procedures. Several possibilities were tested for estimating the progress of lesion formation. For instance, force-time-integral, ablation index and lesion size index are used to assess quality of RF-application and, therefore, lesion size and durability. Nevertheless, recovered conduction after acute conduction block remains an issue in RF-ablation. The aim of this study was to evaluate local impedance (LI) changes as real time surrogate for lesion formation. Methods RF-lesions were created using an ex vivo porcine cardiac model and a force and local impedance sensing catheter. The experimental setup consisted of a saline-filled container, a dispersive electrode, a heated thermostat and a circulation pump to imitate in vivo conditions. Global impedance was kept at 120 Ohm as well as the temperature at 37°C. RF-lesions were created using identic values of RF duration and contact force. RF power (20W, 30W, 40W, 50W) and level of electrode-tissue-coupling were also systematically varied between minor and full coupling. In minor ETC-level, only the distal end of the catheter is in contact with the tissue. In full ETC-level, the whole catheter tip is in contact with the tissue. All parameters (power, temperature, global and local impedance, contact force, ETC, lesion size) were measured constantly during application of RF-current, enabling real-time correlation of RF parameters and lesion size. In case of an audible steam pop, RF application was stopped. Results Including a total of 8654 measurements into the analysis, maximum diameter and depth were 9.51 ± 1.91 mm and 7.29 ± 2.50 mm in average. Local impedance correlated well with lesion depth (r= 0,78, p<0,001), as well as lesion diameter (r=0,652, p<0,001, Figure 1). After significant declines of LI at the beginning of RF-application, it slowly approximates a minimum. Lesion size on the other hand, rises exponentially in first seconds and gets closer to a maximum after more than 25 seconds. This relationship is illustrated in Figure 2. With decreasing lesion growth at the end of RF-application, LI changes decrease to low level (Figure 3). Conclusion Lesion formation in RF-ablation is not linear during application of RF current. Local impedance changes seem to be a suitable real-time surrogate for assessing changes in lesion size during ablation.

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-02-076 AN INVESTIGATION OF LESION EFFICACY AND SAFETY WITH THE TACTIFLEX™ SE ABLATION CATHETER

Treatment of cardiac arrhythmias by the creation of myocardial lesions utilizing RF current is well established as an effective mode of therapy in the clinical electrophysiology laboratory. Efficacy, however, should be evaluated in concert with safety considerations, as passive resistance in the cardiac tissue creates heating that can lead to adverse events (e.g., steam pops). A bench top bovine tissue model allows for comparative testing of RF ablation with the TactiFlex™ SE Ablation Catheter (test device) and a commercially available solid-tip RF ablation catheter with uniform irrigation profile (control device), analyzed with respect to both efficacy and safety. To generate comparative statistics for lesion dimension (maximum width and depth) and steam pop likelihood for the TactiFlex™ SE and control RF catheter designs. In this bench ablation model, recently harvested bovine ventricles were sectioned and placed in a body-temperature saline solution (∼37oC). A catheter in a holding fixture was placed in contact with the tissue at a predefined contact force using an independent force gauge. RF energy was applied to the tissue; lesions (N=288 trials) were created at three different power levels (30W at 30s or 50s, 40W at 12s or 20s, 50W at 6s and 10s), steam pop occurrences were noted. Applied contact force levels were fixed at either 5g or 20g. After ablation, the tissue was stained with 1% Triphenyltetrazolium chloride (TTC). Lesions were measured with respect to maximum width and depth. A linear regression model was applied for lesion width and depth vs. catheter design, power, duration, contact force and orientation. The trials did not result in significantly different widths between catheter designs (p = 0.137); refer to Figure 1 for dimensions vs. RF power and duration. Trials with the TactiFlex™ SE yielded shallower lesions (p=0.018) compared to the control device, but with a regression bias of only 0.2mm. Logistic regression demonstrated that steam pops were significantly less likely with the TactiFlex™ SE (p=0.002). Steam pops occurred in only 1.4% of trials with the TactiFlex™ SE Ablation Catheter (2/144 trials) versus 9.7% of trials with the control catheter design (14/144 trials). RF lesions can be created with the TactiFlex™ SE Ablation Catheter that are clinically similar in size to those created with the control device, with a significant reduction in steam pop likelihood.

PO-05-098 CAN INTRACARDIAC ECHO HELP AVOID STEAM POPS DURING HALF NORMAL SALINE IRRIGATED VENTRICULAR ARRHYTHMIAS ABLATION?

Irrigated radiofrequency ablation (RFA) with half-normal saline (HNS) can potentially increase lesion size, but may increase the risk of steam pops and with possible emboli or perforation. Intracardiac ultrasound (ICE) allows observation of pops, and tissue whitening and spontaneous contrast (bubbles) that may be markers of heating. We assessed the relation between audible pops and ICE observations during HNS irrigation during ventricular arrhythmia RFA in a prospective study. In 100 consecutive patients undergoing endocardial ventricular arrhythmia RFA with HNS we attempted to observe the ablation site with ICE. RFA power was titrated by the operator to a 15 - 20 Ohm impedance fall and could be adjusted for tissue whitening and increasing bubble formation on ICE. Steam pops were defined as audible or on ICE, a sudden explosion of bubbles. Of 2,210 ablation applications in 100 procedures (63.2 ± 14.5 years, 75.0% men, 82% structural heart disease, 51.0% sustained VT, LVEF 39.8 ± 15.2%), the ablation site was visualized on ICE during RFA in 1,334 (60.4%), and was not seen during 876 (39.6%) applications; 38 pops (1.7%) occurred in 21 patients; 31 were audible and 7 (18%) were visible but not audible. Fewer pops occurred when ICE visualization of the RFA site was achieved (1.0%) compared to RF applications in which the site was not visualized (2.7%, p=0.004). Of the 11 ICE-visible pops, 11 (100%) were preceded by tissue whitening and 9 (81.8%) were preceded by an increase in bubble formation. There were no embolic events or cardiac perforations. Acute success was not different for patients with vs without pops (100% vs 89.9%, p=0.140). Steam pops occurred in fewer than 2% of HNS RF applications titrated to an impedance fall but occurrence without an audible pop is common, suggesting that they are under-recognized without ICE. On ICE pops are usually preceded by tissue whitening and increased bubble formation. Pops were less frequent when the operator was able to observe the site on ICE and adjust power, but some sites are difficult to image. Use of ICE may help reduce pops which could potentially improve safety.

PO-02-182 OCCURRENCE OF PERICARDIAL AND INTRA-PERICARDIAL SPACE EFFUSIONS WITH PROTON BEAM ABLATION

With large lesion formation, there is a possibility of perforation or other cardiac related tissue changes. These have not been well evaluated in a in situ model. The purpose of this study was to evaluate the pericardial effusion after pencil-beam scanned proton therapy on normal myocardium in swine in MRI. Therefore, 32 domestic swine underwent proton beam ablation to the left ventricle anterior wall, posterior wall, and apex. Each swine was subjected to monthly contrast-enhanced cardiac MRI to evaluate the post-irradiation effects. Importantly, the typical dose delivered after contouring, simulations, and treatment planning was between 30 and 40 Gy. With these deliveries, a pericardial effusion was seen in 18 swine. These were first seen 4 weeks after the radiation and showed resolution in 87% within 14 days. Actual pericarditis was seen in 2 pigs after the ablation. There was no evidence of dissection of myocardial tissue, nor steam pops or their equivalent with particle therapy. The animals appeared to show no distress or irritation. With the pathology at the time of study showed no presence of pericarditis and no other complications. Also, there was significant correlation between animals with mean dose to myocardium and the grade of PE. As such, pericardial effusions may occur in the setting of particle therapy. Of note, these are minor however and do not appear to be of clinical significance. Still, this suggests the need for careful monitoring of animals in the post-procedure setting.

PO-04-199 CHARACTERISTICS AND SAFETY OF A NOVEL CONTACT-FORCE SENSING IRRIGATED CATHETER WITH A FLEXIBLE TIP WITH LASER-CUT KERFS

The Tactiflex™ SE catheter has a laser-cut 8Fr 4-mm flexible tip irrigated through laser-cut kerfs with a contact-force sensor. We investigated the characteristics of lesion formation and superiority in this catheter to the TactCathTM SE. RF applications at a range of powers (30 W, 40 W, and 50 W), contact forces (10g and 20 g), durations (10–60 s) using perpendicular/parallel catheter orientation with half- or normal-saline irrigation were performed in excised porcine hearts. Lesion characteristics and incidence of steam pops were compared. Incidence of steam-pops were also examined in the clinical setting. A total of 576 RF-lesions were examined. The Tactiflex™ SE catheter demonstrated significantly a lower risk of steam-pops (5(1.7%) vs 59(205%), P<0.0001). Tactiflex™ SE generally produced smaller lesion volume (193 [98-554]mm3 vs 263 [139-436]mm3, p<0.0001), and this difference was mainly due to the differencnt lesion size in perpendicular catheter placement (249 [126-414]mm3 vs 162 [78-309]mm3, P<0.0001). Although Half-saline irrigation tended to increase the lesion volume in both catheters, incidence of steam-pops was also increased with TactCathTM SE, but not with Tactiflex™ SE. %impedance-drop (=absolute impedance-drop/initial impedance) of 20%, predicted steam-pops with a sensitivity and specificity of 100% and 89.6%, respectively (Figure 1). All 1977 RF-applications in the initial 30 patients treated with Tactiflex™ SE catheter for 17AFs, 1AVNRT, 10PVCs, and 2VTs were displayed in the Figure 2. Median RF-energy and power, contact force, and %impedance drop was 692[489-916]J, 36[30-45]W, 12[8-16]g, and 13[11-16]%, and 3 (0.5%) RF-applications were related to pericardial effusion without audible steam-pops with a %impedance-drop of 28%, 34%, and 35%. The FlexAbility™ SE catheter reduced the risk of steam-pops but produced smaller lesions with perpendicular catheter placement compared to the TactiCath™ SE catheter. %impedance-drop<20% may be a reasonable values to safely apply RF-applications with the FlexAbility™ SE.

PO-03-064 BASELINE LOCAL IMPEDANCE AND CHANGES IN LOCAL IMPEDANCE ARE PREDICTORS OF ELECTRODE TISSUE COUPLING IN RF-ABLATION

Radiofrequency (RF) current remains the most used ablation technology in the EP lab. Durable lesion formation without collateral tissue damage is key for obtaining efficient and safe procedures. RF power, duration and contact force (CF) are considered as main determinants of lesion size. Recently published data show that electrode tissue coupling (ETC) is another important parameter of lesion formation. This ex vivo model was created to investigate local impedance (LI) changes and lesion size when alternating ETC-levels. RF-lesions were created using a CF and LI sensing catheter in an ex vivo porcine cardiac model. The experimental setup consisted of a saline-filled container, a dispersive electrode, a heated thermostat and a circulation pump to imitate in vivo conditions. Global impedance was kept at 120 Ohm as well as the temperature at 37°C. RF-lesions were created using identic values of RF duration and contact force. RF power of 20W, 30W, 40W, and 50W was used. The ETC levels were systematically varied between minor and full coupling. In minor ETC-level, only the distal end of the catheter is in contact with the tissue. In full ETC-level, the whole catheter tip is in contact with the tissue. All parameters (power, temperature, global and local impedance, CF, ETC, lesion size) were measured constantly during RF-application, enabling real-time correlation of all parameters and lesion size. 8654 measurements of lesion depth and diameter were analyzed after creating 72 lesions. Lesion depth and diameter in full ETC-level were significantly higher compared to minor ETC-level (s. Table 1). Interestingly, lesions in lower power levels (20-30 Watt), but full ETC-level became wider and deeper than lesions in high power levels (40-50 Watts), but minor ETC-level (s. Figure 1). These observations were made despite shorter RF-duration (54.00 ± 13.07 s vs. 47.11 ± 17.57 s, p=0.032) in lesions with full ETC-level due to higher incidence of steam pops (14 vs. 6 steam pops, p = 0.032). Baseline LI and LI-drop were significantly higher in full ETC-level (Figure 1), but no relevant difference was observed in baseline GI. Baseline LI and LI changes during ablation provide information about ETC-levels and interaction of the RF ablation catheter with cardiac tissue. ETC-levels, as predicted by LI, had a significantly higher impact on RF lesion size than RF power or RF-duration. Therefore, LI should be monitored during RF ablation for estimating ETC-levels and lesion formation.Tabled 1Table 1. Lesion size and impedance changes in different ETC-levels.Minor ETC (n=36)Full ETC (n=36)p-valueMaximum diameter [mm]8.48 ± 1.6110.54 ± 1.63<0.001Maximum depth [mm]5.13 ± 0.999.45 ± 1.45<0.001Start LI [Ω]236.89 ± 26.42300.67 ± 21.61<0.001Start GI [Ω]150.61 ± 21.61151.33 ± 23.680.893LI-drop [Ω]-53.61-125.53<0.001GI-drop [Ω]-21.33-33.44<0.001 Open table in a new tab

PO-04-094 RELEVANCE OF MICROBUBBLE FORMATION WITH PULSED FIELD ABLATION SHOWING IRREVERSIBLE ELECTROPORATION IN A CANINE MODEL

With ablation using a saline flow catheter tips, occasionally microbubbles will be seen, either from excessive heating or steam pops. The occurrence and implications of microbubble formation with PFA/IRE ablation has not been determined. This study aim was to clarify the means of microbubble during PFA/IRE ablation. Therefore, a total of 4 dogs underwent evaluation with the delivery of 34 ablated lesions in the right and left atrium. During PFA/IRE ablation, we monitored by the ICE imaging whether microbubble formation occurred. With these, microbubbles were seen in 82% of deliveries. The microbubbles were class I in 25 %, class II in 25 %, and class III in 50 %. There appeared to be no untoward effect of class I microbubbles. However, with the others, a suggested biophysical property was seen. In those with catheter positioning directly perpendicular to the endocardial surface, microbubbles were less common. On the other hand, with more parallel tip positioning, or with lowere contact force, microbubbles could reach the class II or III level. These were different than past studies showing simple heat related microbubbles. With PFA the heat is not present. Nevertheless, the process of electrophoresis appeared to create the microbubbles to a greater extent than the irrigation catheter’s flow. The concern with this is a decrease in the effectiveness of delivery as judged by high-density mapping. With this study, no actual perforations were seen, but there was an energy loss with the electrophoretic effects. Actually, in gross pathology, the lesion length and width ranged from 16.5 to 24.1 mm and from 11.9 to 21.8 mm in the RA. Class II or III microbubbles are readily seen in PFA/IRE ablation. These appear to be different from that seen with irrigation-tip catheters. The marked occurrence of microbubbles suggests an electrophoretic process, which like incomplete contact could result in a substantial loss of energy rendering ablation lesions less effective. Even with enough contact PFA/IRE, the effect could be substantial. While few complications are seen with PFA/IRE ablation, the marked electrophoretic effect producing microbubbles, also seen with high output pacing could result in a diminution of the actual lesion formation as judged by histology.

PO-01-120 SAFETY AND EFFICACY OF VERY HIGH-POWER SHORT-DURATION ABLATION FOR PULMONARY VEIN ISOLATION: 1-YEAR OUTCOME

The very high-power short-duration (vHPSD) temperature-controlled ablation (vHPSD) improves the efficiency of pulmonary vein isolation (PVI) procedures. We evaluated the procedural and 12-months outcomes in atrial fibrillation (AF) patients undergoing PVI by means of vHPSD ablation. In patients with AF or atrial tachy-arrythmia (AT) recurrence undergoing a redo procedure the durability of the PVI was investigated. Consecutive paroxysmal/persistent AF patients undergoing PVI with the vHPSD ablation strategy (90 W, for 4 s) were enrolled. The rate of PVI, first pass isolation, acute reconnection, and procedural complications were evaluated. Follow-up examinations and EKG were scheduled at 1,6, and 12 months. In case of AF/AT recurrence, patients underwent a redo procedure. Overall, 163 AF patients (29 persistent and 134 paroxysmal) were enrolled. The PVI was reached in 100% of patients (88% at first pass). The rate of acute reconnection was 2%. The radiofrequency, fluoroscopy and procedural times were respectively 5,5±1 min, 9±1 min and 75±20 min. No death, tamponade nor steam pops occurred, however 5 patients had vascular complications. The 12-months freedom from AF/AT recurrence was 86% both in paroxysmal and persistent patients. Overall, 9 patients underwent a redo procedure, and in 4 all veins were still isolated, whereas in 5 pulmonary vein reconnections were found. The PVI durability was 83%. No overt complications were observed in the follow-up. The vHPSD ablation represents an effective and safe ablation strategy to achieve PVI. The 12-months follow-up showed high freedom from AF/AT recurrence and a good safety profile.

PO-03-066 LOCAL IMPEDANCE CHANGES ARE A SUITABLE REAL TIME SURROGATE FOR LESION FORMATION IN RF-ABLATION

Radiofrequency current remains one of the most important techniques for catheter ablation. Creating durable lesions is key for sufficient and safe procedures. Several possibilities were tested for estimating the progress of lesion formation. For instance, force-time-integral, ablation index and lesion size index are used to assess quality of RF-application and, therefore, lesion size and durability. Nevertheless, recovered conduction after acute conduction block remains an issue in RF-ablation. The aim of this study was to evaluate local impedance (LI) changes as real time surrogate for lesion formation. RF-lesions were created using an ex vivo porcine cardiac model and a contact force and LI sensing catheter. The experimental setup consisted of a saline-filled container, a dispersive electrode, a heated thermostat and a circulation pump to imitate in vivo conditions. Global impedance was kept at 120 Ohm as well as the temperature at 37°C. RF-lesions were created using identic values of RF duration and contact force. RF power (20W, 30W, 40W, 50W) and level of electrode-tissue-coupling were also systematically varied between minor and full coupling. All parameters (power, temperature, global and local impedance, contact force, ETC, lesion size) were measured constantly during 60 seconds of RF-application, enabling real-time correlation of RF parameters and lesion size. In case of an audible steam pop, RF application was stopped. Including a total of 8654 measurements into the analysis, maximum diameter and depth were 9.51 ± 1.91 mm and 7.29 ± 2.50 mm in average. LI correlated well with lesion depth (r= 0,78, p<0,001), as well as lesion diameter (r=0,652, p<0,001). After significant declines of LI at the beginning of RF-application, it slowly approximates a minimum. Lesion size on the other hand, rises exponentially in first seconds and gets closer to a maximum after more than 25 seconds. With decreasing lesion growth at the end of RF-application, LI changes decrease to low level (Figure 1). Lesion formation in RF-ablation is not linear during application of RF current. Local impedance changes seem to be a suitable real-time surrogate for assessing changes in lesion size during ablation.

Silent steam pop detected by transesophageal echocardiography for premature ventricular contractions originating from the aortomitral continuity

Silent steam pop detected by transesophageal echocardiography for premature ventricular contractions originating from the aortomitral continuity

Detailed analysis of the lesion formation using a diamond tip catheter in an ex vivo experimental model

BackgroundA novel Diamond Temp™ (DT; Medtronic, Minneapolis, MN, USA) catheter has enabled performing a surface temperature-controlled ablation. The chemical vapor deposition diamond of the ablation catheter acts as a thermal radiator and is useful for effective cooling of the ablation catheter tip. However, a detailed analysis of the lesion formation with this catheter remains unknown. MethodsDT catheters were used in an excised swine heart experimental model. A cross-sectional analysis of 60-s lesions [a combination of various energy power settings (30, 40, and 50 W), and various contact forces (CF) (10, 30, and 50 g)] and a longitudinal analysis [a combination of various powers (40 W or 50 W), various CFs (10, 30, and 50 g), and various ablation times (5 s, 10 s, 15 s, 20 s, 25 s, 30 s, and 60 s)] of the DT catheter were analyzed. ResultsThe maximum lesion depth, maximum diameter, and lesion volume with a 10 g ablation were significantly lower than those with a 30 g or 50 g ablation. There were no significant differences in the lesion formation between the 30 g ablation and 50 g ablation under each radiofrequency (RF) power setting. The impedance drops with steam pops were significantly greater than those without steam pops (pop (+) vs. pop (−), 26.2 ± 6.6 Ohm vs. 18.4 ± 7.1 Ohm, p = 0.0001).A non-linear, time-dependent increase in the lesion depth and diameter was observed for all power and CF settings. Comparing the lesion depth and diameter between 40 W and 50 W under the same CF setting and same ablation time, most of the settings had no significant difference. ConclusionAblation lesions created with the DT catheter were similar to other catheters. Similar ablation lesions were created with the 40 W or 50 W ablation under the same CF setting and same ablation time. Regardless of the ablation power, monitoring the general impedance during the RF application was indispensable for a safe procedure.

One-year outcomes in patients undergoing very high-power short-duration ablation for atrial fibrillation

BackgroundThe very high-power short-duration (vHPSD) temperature-controlled ablation (vHPSD) improves the efficiency of pulmonary vein isolation (PVI) procedures.We evaluated the procedural and 12-months outcomes in atrial fibrillation (AF) patients undergoing PVI by means of vHPSD ablation. In patients with AF or atrial tachyarrythmia (AT) recurrence undergoing a redo procedure the durability of the PVI was investigated.MethodsConsecutive paroxysmal/persistent AF patients undergoing PVI with the vHPSD ablation strategy (90 W, for 4 s) were enrolled. The rate of PVI, first-pass isolation, acute reconnection, and procedural complications were evaluated. Follow-up examinations and EKG were scheduled at 3,6, and 12 months. In case of AF/AT recurrence, patients underwent a redo procedure.ResultsOverall, 163 AF patients (29 persistent and 134 paroxysmal) were enrolled. The PVI was reached in 100% of patients (88% at the first pass). The rate of acute reconnection was 2%. The radiofrequency, fluoroscopy and procedural times were respectively 5.5 ± 1 min, 9 ± 1 min and 75 ± 20 min. No death, tamponade nor steam pops occurred; however, 5 patients had vascular complications. The 12-months freedom from AF/AT recurrence was 86% in both paroxysmal and persistent patients. Overall, 9 patients underwent a redo procedure, and in 4 all veins were still isolated, whereas in 5 pulmonary vein reconnections were found. The PVI durability was 78%. No overt clinical complications were observed in the follow-up.ConclusionsThe vHPSD ablation represents an effective and safe ablation strategy to achieve PVI. The 12-months follow-up showed high freedom from AF/AT recurrence and a good safety profile.

Ambient circulation surrounding an ablation catheter tip affects ablation lesion characteristics.

The association between ambient circulating environments (CEs) and ablation lesions has been largely underexplored. Viable bovine myocardium was placed in a saline bath in an ex vivo endocardial model. Radiofrequency (RF) ablation was performed using three different ablation catheters: 3.5 mm open irrigated (OI), 4, and 8 mm. Variable flow rates of surrounding bath fluids were applied to simulate standard flow, high flow, and no flow. For in vivo epicardial ablation, 24 rats underwent a single OI ablation and performed with circulating saline (30 ml/min; n = 12), versus those immersed in saline without circulation (n = 12). High flow reduced ablation lesion volumes for all three catheters. In no-flow endocardial CE, both 4 mm and OI catheters produced smaller lesions compared with standard flow. However, the 8 mm catheter produced the largest lesions in a no-flow CE. Ablation performed in an in vivo model with CE resulted in smaller lesions compared with ablation performed in a no-flow environment. No statistically significant differences in steam pops were found among the groups. A higher endocardial CE flow can decrease RF effectiveness. Cardiac tissue subjected to no endocardial CE flow may also limit RF for 4 mm catheters, but not for OI catheters; these findings may have implications for RF ablation safety and efficacy, especially in the epicardial space without circulating fluid or in the endocardium under varying flow conditions.

Efficiency and safety of high-power ablation guided by Lesion size index: An ex vivo porcine heart study.

Although Lesion size index (LSI) has been reported to highly predict radiofrequency lesion size in vitro, its accuracy in lesion size and steam pop estimation has not been well investigated for every possible scenario. Initially, radiofrequency ablations were performed on porcine myocardial slabs at various power, CF, and time settings with blinded LSI. Subsequently, radiofrequency power at 20, 30, 40, 50, and 60W was applied at CF values of 5, 10, 20, and 30g to reach target LSIs of 4, 5, 6, and 7. Lesion size and steam pops were recorded for each ablation. Lesion size was positively correlated with LSI regardless of power settings (p<0.001). The linear correlation coefficients of lesion size and LSI decreased at higher power settings. At high power combined with high CF settings (50W/20 g), lesion depth and LSI showed an irrelevant correlation (p=0.7855). High-power ablation shortened ablation time and increased the effect of resistive heating. LSI could predict the risk of steam pops at high-power settings with the optimal threshold of 5.65 (sensitivity, 94.1%; specificity, 46.1%). The ablation depth of the heavy heart was shallower than that of the light heart under similar ablation settings. LSI could predict radiofrequency lesion size and steam pops at high power settings in vitro, while synchronous high power and high CF should be avoided. Lighter hearts require relatively lower ablation settings to create appropriate ablation depth.

Detailed investigation of the lesion formation with a novel contact force sensing catheter with a mesh-shaped irrigation tip.

Recently, a novel contact force (CF) sensing catheter with mesh-shaped irrigation tip (TactiFlex SE, Abbott) was invented and is expected to be useful for safe and effective radiofrequency ablation. However, this catheter's detailed characteristics of the lesion formation are unknown. With an in vitro model, TactiFlex SE and its predecessor, FlexAbility SE, were used. A cross-sectional analysis of 60 s lesions (combination of various energy power settings [30, 40, and 50 W], and CFs [10, 30, and 50 g]) and longitudinal analysis (combination of various powers [40 or 50 W], CFs [10, 30, and 50 g] and ablation times [10, 20, 30, 40, 50, and 60 s]) of both catheters were analyzed and compared. One hundred eighty RF lesions were created in protocol 1 and 300 in protocol 2. The lesion formation, impedance changes, and steam pops characteristics were similar between the two catheters. Higher CFs were related to higher incidences of steam pops. A nonlinear, time-dependent increase in the lesion depth and diameter was observed for all power and CF settings, and linear, positive correlations between the RF delivery time and lesion volume were observed for all power settings. Compared with 40 W, a 50 W ablation created greater lesions. Longer durations with higher CF settings had a higher steam pop incidence. The lesion formation and incidence of steam pops with TactiFlex SE and FlexAbility SE were similar. A 40 or 50 W ablation with careful CF control not to exceed 30 g in addition to monitoring impedance drops was required to safely create transmural lesions.

First clinical experience using the DiamondTemp catheter and a novel omnipolar high-resolution mapping system for atrial fibrillation ablation.

The DiamondTemp (DT) radiofrequency ablation (RFA) catheter has been introduced as a new tool for atrial fibrillation (AF) ablation. The new technology allows for temperature-controlled irrigated ablation and real-time lesion assessment. Recently, the EnSite X mapping system became commercially available allowing for omnipolar and ultra-high-resolution mapping. We aimed to assess the feasibility of the new DT RFA catheter in performing AF ablation procedures in conjunction with the novel EnSite X system under routine clinical conditions. We analyzed data from 10 consecutive patients who underwent AF ablation using the DT RFA catheter guided by EnSite X. Procedural data and short-term follow-up were assessed as well as potential technical issues. Nine out of 10 patients underwent de-novo pulmonary vein isolation (PVI), and 1 patient underwent repeat ablation. First-pass isolation was observed in 7/10 patients. Total procedure duration (skin-to-skin) was 88.9 ± 30.1 min, and left atrium dwell time was 70 ± 22.3 min. The mean number of RF applications needed for PVI and additional ablation was 70.52 ± 26.70. The HD Grid SE mapping catheter was utilized in 8 patients and the Advisor SE in 2 patients. Bidirectional block of the applied lines was achieved in all patients. No steam pops were observed, and no intraprocedural complications occurred. This first clinical series demonstrated that temperature-controlled irrigated ablation in combination with the novel omnipolar and high-resolution mapping system resulted in rapid, efficient, and durable lesion formation under routine clinical conditions. Randomized controlled trials are needed to elucidate the impact on lesion formation, long-term outcomes, and reproducibility of our initial findings.