Onset Of Ablation Research Articles

Findings at repeat ablation after complex left atrial pulsed field ablation for longstanding persistent atrial fibrillation

Abstract Background There is a limited knowledge on atrial arrhythmias recurring after complex left atrial (LA) pulsed field ablation (PFA) for longstanding persistent atrial fibrillation (LSPAF). Purpose To present recurrent atrial arrhythmias and their sources found at repeat ablation following PFA for LSPAF. Methods and results Of 214 patients with LSPAF (age 65±8, 53 females, continuous AF for 30±27 months) with complex LA PFA (Farapulse) in 10/2021-10/2023, 19 patients (64±8 years, 5 females) underwent repeat ablation for recurrent AF or arial tachycardia (AT) in 20 procedures. First PFA procedure included pulmonary vein isolation (PVI), roof/posterior wall, and mitral isthmus/coronary sinus/Ligament of Marshal region (LOM) ablation. At repeat ablation, 3D activation and entrainment mapping and ablation identified the AF/AT sources; ATs sources were classified as macroreentry (MRAT) (perimitral, roof-dependent, typical flutter) or localized (LOCAT) in case of smaller reentry or ectopic origin. Results The clinical recurrent arrhythmias included paroxysmal AF (n=1), persistent AF (n=2), paroxysmal AT (n=1) or persistent AT (n=16). At the onset of repeat ablation, persistent AF/AT was present (n=15) or had to be induced (n=5). AF was finally present during the procedure in 8 patients, and was terminated by ablation directly into SR (n=3) or into intermediate AT (n=3) (conversion sites included LA ridge/LOM region 2x, RA septum 1x, RA low lateral 2x, CTI 1x), or required DCC (n=2). Primary recurrent or from AF converted AT was present in 15 patients; only MRAT in 6 patients, only LOCAT in 3 patients, and both AT types in 6 (patients). Of MRAT (N. ATs = 16), there were 12 perimitral ATs, 0 roof-dependent AT, and 2 typical flutters. Of LOCATs, sources were located at LA anterior wall 4x, LA septum 2x, LA roof 1x, LA ridge/LOM 1x, persistent left vena cava 1x, and RA – para SA node 1x. Recurrent AF/AT sources were targeted by radiofrequency or PFA in 16 and 4 cases, respectively, all spontaneous and induced AF/AT were finally terminated into SR in 16 cases, subsequent noninducibility by atrial pacing up to 300 bpn was achieved in 13 cases, and recurrent AF/AT occurred in 3 patients. Conclusion At repeat ablation PFA (Farapulse) for LSPAF, recurrent AT dominated over AF, MRAT slightly prevailed over LOCAT, mostly constituted by perimitral AT, while roof-dependent AT recurrence was reduced to zero. A majority of AF/AT sources were located outside prior PFA lesions at the LA anterior wall, septum and the right atrium.

Dynamics of phase transformations in Si and Ge upon strong excitation with UV femtosecond laser pulses

Femtosecond laser processing of semiconductors has evolved into a mature, high-precision fabrication technique, enabling a wide range of applications. While initially most studies have employed pulses at near infrared wavelengths, the interest in using UV laser pulses is constantly increasing due to the different excitation conditions as a consequence of the much shorter optical penetration depth, leading to an improved resolution. In this context, fundamental studies on the temporal dynamics of phase transformations triggered by such pulses are necessary in order to comprehend and eventually control the complex phase transformation pathways. Here, we report a detailed time-resolved study on the phase transformation dynamics of crystalline silicon and germanium upon irradiation with single 400 nm, 100 fs laser pulses in the moderate and high excitation regime. To this end, we have employed fs-resolved optical microscopy with a probe wavelength of 800 nm to study the reflectivity evolution of the irradiated surface over a temporal window ranging from 100 fs up to 20 ns. At moderate excitation fluence, the data reveals the entire sequence of laser-induced processes, starting from the generation of a free-electron plasma, non-thermal melting, ablation onset and expansion of a semi-transparent ablation layer with sharp interfaces. At excitation with peak fluences more than 30 times the ablation threshold, an anomalous transient high-reflectivity state is observed, which might be indicative of a recoil pressure-induced liquid–liquid phase transition. Moreover, 70 nm-thick amorphous surface layers are formed in both materials after irradiation at moderate fluences. Overall, our results provide relevant information on both, transformation dynamics and final state of both materials for fs-pulse excitation in the near-UV wavelength range.

Multi-shot near-infrared femtosecond laser tuning of silicon microring resonators

We studied multi-shot femtosecond laser surface modification as a permanent tuning technique for obtaining the desired resonance wavelengths for silicon microring resonators. In this multi-shot tuning approach, each microring resonator was irradiated with 10 or 100 laser pulses in the same location of the waveguide with selected laser fluence. The laser beam has 800 nm wavelength, 130 fs pulse duration, a Gaussian spatial profile with a beam waist radius of 13.1μm, and pulse energies of 12 nJ to 186 nJ to generate the applied range of laser fluences. The silicon microring resonators used in the study have a 15μm diameter and are coupled to a waveguide of 500 nm in width with a gap of 260 nm. We found that the multi-shot tuning curves (resonance wavelength shifts as a function of laser fluences) do not monotonically increase with laser fluences: they first increase, then plateau, and finally decrease. We observed that the laser energies required for the multi-shot case to obtain the onset of crystalline modifications and ablation are several times below the single-shot case because of the incubation effect. With proper control we can achieve both positive and negative resonance wavelength shifts with acceptable induced roundtrip waveguide losses.

Abstract 18088: Survival After Ventricular Tachycardia Onset in Left Ventricular Assist Device Recipients

Introduction: Left Ventricular Assist Devices (LVADs) revolutionized the care of patients with heart failure. However, the burden of ventricular tachycardia (VT) increases after LVAD insertion. The role of ablation in treating VT in LVAD recipients is unclear. Hypothesis: The incidence of VT following LVAD insertion is associated with worse survival, but this association is ameliorated by VT ablation. Methods: This is a single-center retrospective review of 549 LVAD recipients. LVADs implanted elsewhere, LVADs prior to 2011, and patients with inadequate follow up were excluded. Endpoints were transplantation, explantation, and last date of follow up. Event failure was defined as patient death. Cox and Kaplan-Meier survival analysis was performed with STATA and reported as hazard ratio with 95% confidence interval (HR [95% CI]). Results: Pre-LVAD VT was seen in 52% of patients: 33% had a prior ICD shock and 12% had a prior VT ablation. At study conclusion, 57% had died, 22% were transplanted, 9% were explanted, and 12% remained alive. Regardless of VT incidence, worse survival was seen in ischemic cardiomyopathy (HR 2.0 [1.5-2.7]), RV failure necessitating RVAD (HR 2.6 [1.9-3.6]), and pre-LVAD ICD shocks (HR 1.3 [1.0-1.7]). While post-LVAD VT overall was not associated with worse survival (HR 1.1 [0.8-1.3]), VT within 1 year of LVAD insertion demonstrated worse survival (HR 1.9 [1.3-2.6]; Figure 1). Incremental years between LVAD insertion and VT onset improved survival (HR 0.8 [0.7-0.9]). Among those with post-LVAD VT, ablation was not associated with a survival difference (IRR 0.9 [0.6-1.4]) regardless of the timing of ablation or VT onset. Conclusions: The incidence of VT within 1 year of LVAD insertion is associated with worse survival. However, mortality was not improved by VT ablation. This study is limited by its retrospective design, and further prospective studies would better determine the impact of VT ablation on survival in LVAD recipients.

Increase of the energy available for snow ablation in the Pyrenees (1959–2020) and its relation to atmospheric circulation

Mid-latitude mountain snowpacks are highly vulnerable to climate warming. Past and future hydroclimate changes require a thorougout knowledge of snow ablation physical processes and the associate climate drivers. In this work we provide the first spatio-temporal characteritzation of the energy available for snow ablation (Qm) in the Pyrenees for the period 1959–2020, during the main ablation season (March to June) for low (1200 m), mid (1800 m) and high (2400 m) elevations. We analyze the role of the the main Circulation Weather Types (CTs) in the Qm components for the entire mountain range. Finally, we train and tune a machine learning algorithm, the Random Forest, with atmospheric data (Surface Level Pressure and 500 hPa Geopotential Height) as an independent variable and Qm as the dependent one, in order to determine how much of the observed changes in Qm can be related with atmospheric circulation variability. The largest contribution of Qm is Net Radiation (Rn), increasing with elevation. Qm has shown a statistically significant increase since the 1980s. The comparison between the period 1959–1980 and the 2000–2020 revealed that positive Qm fluxes have been anticipated 22 and 12 days at mid and high elevations, respectively, showing evidence of an advance in the timing of the ablation season and faster snow ablation in high-elevation areas of the Pyrenees. The Qm is principally driven by Rn during the prevailing antyciclonic situations, characterized by the extension of high-pressure systems, low-barometric gradients and the SE advection of hot and dry air masses. The positive frequency of these anticyclonic CTs explains the majority (75%) of the Qm variability, the upward Qm trends and the earlier snow ablation onset since the 1980s.

Localized Myocardial Anti-Inflammatory Effects of Temperature-Sensitive Budesonide Nanoparticles during Radiofrequency Catheter Ablation.

Radiofrequency (RF) catheter ablation has emerged as an effective alternative for the treatment of atrial fibrillation (AF), but ablation lesions will result in swelling and hematoma of local surrounding tissue, triggering inflammatory cell infiltration and increased release of inflammatory cytokines. Some studies have shown that the inflammatory response may be related to the early occurrence of AF. The most direct way to inhibit perioperative inflammation is to use anti-inflammatory drugs such as glucocorticoids. Here, we prepared polylactic-co-glycolic acid (PLGA) nanoparticles loaded with budesonide (BUD) and delivered them through irrigation of saline during the onset of ablation. Local high temperature promoted local rupture of PLGA nanoparticles, releasing BUD, and produced a timely and effective local myocardial anti-inflammatory effect, resulting in the reduction of acute hematoma and inflammatory cell infiltration and the enhancement of ablation effect. Nanoparticles would also infiltrate into the local myocardium and gradually release BUD ingredients to produce a continuous anti-inflammatory effect in the next few days. This resulted in a decrease in the level of inflammatory cytokine IL-6 and an increase of anti-inflammatory cytokine IL-10. This study explored an extraordinary drug delivery strategy to reduce ablation-related inflammation, which may prevent early recurrence of AF.

Gender associated disparities in atrioventricular nodal reentrant tachycardia: A review article.

Atrioventricular nodal reentrant tachycardia (AVNRT) is the most common sustained supraventricular arrhythmias. An understanding of gender-related differences in AVNRT epidemiology, diagnosis, treatment, outcome, and complications can help guide a more effective diagnosis and treatment of the condition. The study aimed to perform a review of the available literature regarding all aspects of gender-related differences of AVNRT. We focused on all aspects of gender-related differences regarding AVNRT between men and women. A literature search was performed using Google Scholar, PubMed, Springer, Ovid, and Science Direct. Many investigations have demonstrated that the prevalence of AVNRT exhibited a twofold women-to-men predominance. The potential mechanism behind this difference due to sex hormones and autonomic tone. Despite being more common in women, there is a delay in offering and performing the first-line therapy (catheter ablation) compared to men. There were no significant gender-related discrepancies in patients who underwent ablation therapy for AVNRT, regarding the acute success rate of the procedure, long-term success rate, and recurrence of AVNRT. AVNRT is more common in women due to physiological factors such as sex hormones and autonomic tone. Catheter ablation is equally safe and efficacious in men and women; however, the time between the onset of symptoms and ablation is significantly prolonged in women. It is important for the medical community to be aware of this discrepancy and to strive to eliminate such disparities that are not related to patients' choices.

Cryoablation for atrial fibrillation.

Cryoballoon ablation for the treatment of atrial fibrillation has established itself as an effective and efficient modality for achieving pulmonary vein isolation. Over the past 13 years more than 100,000 Cryoballoon ablation procedures have been performed with the first to fourth generation cryoballoons. Over that time there have been significant advances in our understanding regarding the optimal procedural techniques. The purpose of this "topic in review" is to focus on the practical aspects of performing a Cryoballoon ablation procedure, within the context of the contemporary literature. Specifically there is a focus on how contemporary studies can inform clinical decision making and ensure operators are able to perform a safe and effective procedure.

Predictive modeling of brain tumor laser ablation dynamics.

Laser interstitial thermal therapy (LITT) is a novel MR thermometry-guided thermoablative tool revolutionizing the clinical management of brain tumors. A limitation of LITT is our inability to estimate a priori how tissues will respond to thermal energy, which hinders treatment planning and delivery. The aim of this study was to determine whether brain tumor LITT ablation dynamics may be predicted by features of the preoperative MRI and the relevance of these data, if any, to the recurrence of metastases after LITT. Intraoperative thermal damage estimate (TDE) map pixels representative of irreversible damage were retrospectively quantified relative to ablation onset for 101 LITT procedures. Raw TDE pixel counts and TDE pixel counts modelled with first order dynamics were related to eleven independent variables derived from the preoperative MRI, demographics, laser settings, and tumor pathology. Stepwise regression analysis generated predictive models of LITT dynamics, and leave-one-out cross validation evaluated the accuracy of these models at predicting TDE pixel counts solely from the independent variables. Using a deformable atlas, TDE maps were co-registered to the immediate post-ablation MRI, allowing comparison of predicted and actual ablation sizes. Brain tumor TDE pixel counts modelled with first order dynamics, but not raw pixel counts, are correlated with the independent variables. Independent variables showing strong relations to the TDE pixel measures include T1 gadolinium and T2 signal, perfusion, and laser power. Associations with tissue histopathology are minimal. Leave-one-out analysis demonstrates that predictive models using these independent variables account for 77% of the variance observed in TDE pixel counts. Analysis of metastases treated revealed a trend towards the over-estimation of LITT effects by TDE maps during rapid ablations, which was associated with tumor recurrence. Features of the preoperative MRI are predictive of LITT ablation dynamics and could eventually be used to improve the clinical efficacy with which LITT is delivered to brain tumors.

Suprathreshold laser injuries in excised porcine skin for millisecond exposures at 1070 nm

Skin injury response to near-infrared (NIR) laser radiation between the minimum visible lesion threshold and ablation onset is not well understood. This study utilizes a 1070-nm diode-pumped Yb-fiber laser to explore the response of excised porcine skin to high-energy exposures in the suprathreshold injury region without inducing ablation. Concurrent high-speed videography is employed to determine a dichotomous response for three progressive damage categories: observable surface distortion, surface bubble formation due to contained intracutaneous water vaporization, and surface bubble rupture during exposure. Median effective dose (ED50) values are calculated in these categories for 3- and 100-ms pulses with beam diameters (1 / e2) of 3mm (28, 35, and 49 J / cm2) and 7mm (96, 141, and 212 J / cm2), respectively. Double-pulse cases are secondarily investigated. Experimental data are compared with the maximum permissible exposure limits and ablation onset simulated by a one-dimensional multiphysics model. Logistic regression analysis predicted injury events with ∼90 % of accuracy. The distinction of skin response into progressive damage categories expands the current understanding of high-energy laser safety while underlining the unique biophysical effects during induced water phase change in tissue. These results prove to be useful in the diagnosis and treatment of NIR laser injuries.

Observation of particle assisted nano-ring, bump, pit structures on semiconductor substrates by dry laser exposure

We report on the generation of nano-structures on semiconductor substrates through particle assisted dry laser exposure technique. Of particular interest is the formation of nano rings in case of Silicon substrate following exposure with sub nano-second laser pulse at 532 nm wavelength. Usage of such a laser pulse enabled us to realise a condition wherein the dominating thermo-capillary force allowed the formation of nano rings. With gradual increase in the laser fluence the nano rings gave way to formation of nano bumps and nano pits. In case of GaAs, on the other hand, nano rings could be observed for irradiation at 1064 nm at substantially higher value of fluence, in line with its poor absorption in the substrate. For exposure to 532 nm wavelength, onset of ablation even for low incident fluence precluded the formation of rings or bumps.

What have we learned in the last 20 years? A comparison of a modern era pediatric and congenital catheter ablation registry to previous pediatric ablation registries

Since the onset of pediatric catheter ablation, the pediatric electrophysiology community has reported outcomes via various registries (PAPCA [Prospective Assessment After Pediatric Cardiac Ablation], PCAR [Pediatric Catheter Ablation Registry]). Most recently, a modern era pediatric and congenital ablation registry (MAP-IT [Multicenter Pediatric and Congenital EP Quality Initiative]) was developed for eventual incorporation into the National Cardiovascular Data Registry (NCDR) IMPACT (Improving Pediatric and Adult Congenital Treatment) registry. The purpose of this study was to describe initial findings from the MAP-IT pilot registry and to compare these findings to earlier registries. Before entering the NCDR IMPACT registry, MAP-IT was active at 12 centers (11 in the United States) between October 2014 and April 2016. All electrophysiological studies for patients younger than 21 years and for patients of all ages with structural congenital heart disease were included. We compared the acute success, fluoroscopy and procedural times, and frequency of complications between MAP-IT and the earlier registries. Acute success rates have improved from the initial PCAR registry for both accessory and slow pathway substrates. Both fluoroscopy and procedural times have significantly decreased across the time periods (fluoroscopy time 47.6 ± 40 minutes to 7.0 ± 9.2 minutes; P <.001; procedural time 257 ± 157 minutes to 166 ± 84 minutes; P <.001). Acute success rates and fluoroscopy and procedural times in pediatric ablation all have improved over the last 25 years.

Satellite and Ground Observations of Snow Cover in Tibet during 2001–2015

The seasonal snow cover of the Tibetan Plateau exerts a profound environmental influence both regionally and globally. Daily observations of snow depth at 37 meteorological stations in Tibet and MODIS eight-day snow products (MOD10A2) during the period 2001–2015 are analyzed with respect to the frequency and spatial distribution of snow cover for each season and for various altitude ranges. The results show that the average snow cover percentage was 16%. Snow cover frequency was less than 21% for 70% of the Tibetan area, while it was more than 40% in eastern Tibet and in the Himalayas. We also estimated the variations in the starting times of snow accumulation and ablation. During the 15 years, both datasets revealed a significant trend of earlier onset of ablation, but no evident trend for the start of accumulation. The two datasets differed slightly with respect to the seasonal variation of snow cover. MODIS data showed more snow in winter than in other seasons, but the ground data showed most snow in early spring. For the station locations, the correlation between ground and MODIS snow cover percentage (number of snow-covered stations/number of cloud-free stations) is 0.77. Combining the advantages of remote sensing data and ground observation data is the best way to investigate snow in Tibet.

Controlling the oxidation processes of Zn nanoparticles produced by pulsed laser ablation in aqueous solution

We used online UV-VIS optical absorption and photoluminescence spectra, acquired during and after pulsed laser ablation of a Zinc plate in aqueous solution, to investigate the effect of the laser repetition rate and liquid environment on the oxidation processes of the produced nanoparticles. A transient Zn/ZnO core-shell structure was revealed by the coexistence of an absorption peak around 5.0 eV due to Zn surface plasmon resonance and of an edge at 3.4 eV coming from wurtzite ZnO. The growth kinetics of ZnO at the various repetition rates, selectively probed by the excitonic emission at 3.3 eV, began immediately at the onset of laser ablation and was largely independent of the repetition rate. In addition, we detected an emission at 2.3 eV related to oxygen vacancies, which began to grow after a number of pulses increasing with the used repetition rate. Optical absorption spectra during and after ablation in a mixture of water and ethanol (0%–100%) revealed that the oxidation kinetics of Zn nanoparticles slows down from about 900 s in pure water to at least one week in pure ethanol.

Fabrication of CVD graphene-based devices via laser ablation for wafer-scale characterization

Selective laser ablation of a wafer-scale graphene film is shown to provide flexible, high speed (1 wafer/hour) device fabrication while avoiding the degradation of electrical properties associated with traditional lithographic methods. Picosecond laser pulses with single pulse peak fluences of 140 mJ cm−2 for 1064 nm, 40 mJ cm−2 for 532 nm, and 30 mJ cm−2 for 355 nm are sufficient to ablate the graphene film, while the ablation onset for Si/SiO2 (thicknesses 500 μm/302 nm) did not occur until 240 mJ cm−2, 150 mJ cm−2, and 135 mJ cm−2, respectively, allowing all wavelengths to be used for graphene ablation without detectable substrate damage. Optical microscopy and Raman Spectroscopy were used to assess the ablation of graphene, while stylus profilometery indicated that the SiO2 substrate was undamaged. CVD graphene devices were electrically characterized and showed comparable field-effect mobility, doping level, on–off ratio, and conductance minimum before and after laser ablation fabrication.

Are some meteoroids rubble piles?

AbstractThe possibility that some meteoroids in the size range 1 – 20 meters are rubble piles i.e. assembles of boulders of various sizes held together only by small van der Waals forces, is investigated. Such meteoroids are expected to start disrupting into individual pieces during the atmospheric entry at very low dynamic pressures of ~ 25 Pa, even before the onset of ablation. The heterogeneous bodies as Almahata Sitta (asteroid 2008 TC3) and Benešov are primary candidates for rubble piles. Nevertheless, by analyzing the deceleration, wake, and light curve of the Benešov bolide, we found that the meteoroid disruption started only at a height of 70 km under dynamic pressure of 50 kPa. No evidence for a very early fragmentation was found also for the Chelyabinsk event.

Oxidation of Zn nanoparticles probed by online optical spectroscopy during nanosecond pulsed laser ablation of a Zn plate in H2O

We report online UV-Visible absorption and photoluminescence measurements carried out during and after pulsed laser ablation of a zinc plate in water, which clarify the events leading to the generation of ZnO nanoparticles. A transient Zn/ZnO core-shell structure is revealed by the coexistence of the resonance absorption peak around 5.0 eV due to Zn surface plasmon resonance and the edge at 3.5 eV of ZnO. The growth kinetics of ZnO, selectively probed by the exciton luminescence at 3.3 eV, begins only after a ∼30 s delay from the onset of laser ablation. We also detect the luminescence at 2.3 eV of ZnO oxygen vacancies, yet rising with an even longer delay (∼100 s). These results show that the oxidation of Zn nanoparticles mainly occurs out of the ablation plume region and proceeds as a sequence of two stages: the earliest oxidation is only superficial and forms a defect-free ZnO shell around a Zn core, whereas core oxidation is driven by comparatively slower diffusion of water through the ZnO shell and leaves behind a defective ZnO material rich of oxygen vacancies.

Inducible forebrain-specific ablation of the transcription factor Creb during adulthood induces anxiety but no spatial/contextual learning deficits.

The cyclic AMP (cAMP)-response element binding protein (CREB) is an activity-dependent transcription factor playing a role in synaptic plasticity, learning and memory, and emotional behavior. However, the impact of Creb ablation on rodent behavior is vague as e.g., memory performance of different Creb mutant mice depends on the specific type of mutation per se but additionally on the background and learning protocol differences. Here we present the first targeted ablation of CREB induced during adulthood selectively in principal forebrain neurons in a pure background strain of C57BL/6 mice. All hippocampal principal neurons exhibited lack of CREB expression. Mutant mice showed a severe anxiety phenotype in the openfield and novel object exploration test as well as in the Dark-Light Box Test, but unaltered hippocampus-dependent long-term memory in the Morris water maze and in context dependent fear conditioning. On the molecular level, CREB ablation led to CREM up regulation in the hippocampus and frontal cortex which may at least in part compensate for the loss of CREB. BDNF, a postulated CREB target gene, was down regulated in the frontal lobe but not in the hippocampus; neurogenesis remained unaltered. Our data indicate that in the adult mouse forebrain the late onset of CREB ablation can, in case of memory functionality, be compensated for and is not essential for memory consolidation and retrieval during adulthood. In contrast, the presence of CREB protein during adulthood seems to be pivotal for the regulation of emotional behavior.

Characterization of radiofrequency ablation lesion development based on simulated and measured intracardiac electrograms.

Radiofrequency ablation (RFA) therapy is the gold standard in interventional treatment of many cardiac arrhythmias. A major obstacle is nontransmural lesions, leading to recurrence of arrhythmias. Recent clinical studies have suggested intracardiac electrogram (EGM) criteria as a promising marker to evaluate lesion development. Seeking for a deeper understanding of underlying mechanisms, we established a simulation approach for acute RFA lesions. Ablation lesions were modeled by a passive necrotic core surrounded by a borderzone with properties of heated myocardium. Herein, conduction velocity and electrophysiological properties were altered. We simulated EGMs during RFA to study the relation between lesion formation and EGM changes using the bidomain model. Simulations were performed on a three-dimensional setup including a geometrically detailed representation of the catheter with highly conductive electrodes. For validation, EGMs recorded during RFA procedures in five patients were analyzed and compared to simulation results. Clinical data showed major changes in the distal unipolar EGM. During RFA, the negative peak amplitude decreased up to 104% and maximum negative deflection was up to 88% smaller at the end of the ablation sequence. These changes mainly occurred in the first 10 s after ablation onset. Simulated unipolar EGMs reproduced the clinical changes, reaching up to 83% negative peak amplitude reduction and 80% decrease in maximum negative deflection for transmural lesions. In future studies, the established model may enable the development of further EGM criteria for transmural lesions even for complex geometries in order to support clinical therapy.

Serendipitous induction of ventricular tachycardia during pace-mapping: Should we ablate?

Case presentation A 63-year-old man with ischemic cardiomyopathy, severely impaired left ventricular systolic function, and an implantable defibrillator presented with multiple episodes of protracted slow ventricular tachycardia (VT). He was brought to the electrophysiology laboratory for catheter ablation. Initial programmed stimulation induced VT at 154 bpm that was associated with hemodynamic instability necessitating cardioversion. Subsequently, a substrate-based mapping approach was undertaken with pacing from the right ventricle (RV) at 50 bpm. An electroanatomic voltage map (using CARTO-3 mapping system, Biosense Webster, Diamond Bar, CA) was created with tagging of late potentials/late abnormal ventricular activity along with pace-mapping where appropriate. Figure 1A shows the intracardiac electrogram (IEGM) seen during mapping within the scar in the mid-anterior wall of the left ventricle and with RV pacing. Figure 1B shows the IEGMs and surface QRS morphology during pace-mapping from the ablation catheter at 600 ms at this site. Figure 2A shows the last 3 beats of pacing from the ablation catheter and onset of VT immediately after pacing. Radiofrequency ablation was then performed at 50 W (NaviStar catheter, Biosense Webster) at this site. Figure 2B shows the response after 15 seconds of ablation. Based on these observations, what is the mechanism of initiation of VT? Crucially, where is this site in relation to the VT circuit, and is this an optimal site for ablation? Finally, was VT initiated during or after pacing?