Lesion Geometry Research Articles

Effect of Interlesion Time on Lesion Geometry in the Creation of Radiofrequency Linear Lesions.

Effect of Interlesion Time on Lesion Geometry in the Creation of Radiofrequency Linear Lesions.

A Deep Cascade Architecture for Stroke Lesion Segmentation and Synthetic Parametric Map Generation over CT St

Stroke is the second leading cause of mortality worldwide. Immediate attention and diagnosis play a crucial role in patient prognosis. Nowadays, computed tomography (CT) is the most utilized diagnostic imaging for early analysis and lesion stroke detection. Nonetheless, acute lesions are not visible on CT, and it is only possible to use this modality in screening analysis, discarding other neurological affectations. Expert radiologists can observe stroke lesions in advanced stages (subacute and chronic), as hypodense regions, but with limited sensibility and remarked subject variability. Computational strategies have been addressed to support lesion segmentation, following deep autoencoders and multimodal inputs. However, these strategies remain limited due to the high variability in the appearance and geometry of stroke lesions. This work introduces a novel deep representation that uses multimodal inputs from CT studies and parametric maps, computed from perfusion (CTP), to retrieve stroke lesions. The architecture follows an autoencoder deep representation, that forces attention on the geometry of stroke through additive cross-attention modules. Besides, a cascade train is herein proposed to generate synthetic perfusion maps that complement multimodal inputs and help with stroke lesion refinement at each stage of processing. The proposed approach brings saliency maps that support observational expert analysis, about lesion localization, but also lead with automatic shape estimation of the stroke. The proposed approach was validated on the ISLES 2018 public dataset with a total of 92 studies that include the annotation of an expert radiologist. The proposed approach achieves a Dice score of 0.66 and a precision of 0.67, outperforming classical autoencoder approximations.

Three-dimensional optical coherence tomography for guidance of percutaneous coronary intervention for coronary bifurcation disease: a review of current clinical applications.

Percutaneous coronary intervention (PCI) for coronary bifurcation disease remains one of the most challenging situations in interventional cardiology in terms of procedural success rates and long-term cardiac events. Optical coherence tomography (OCT), with a higher signal-to-noise ratio and the ability to distinguish plaque components, can display the true condition of bifurcation lesions without overlapping or shortening and achieve detailed visualization of vascular structures, which is superior to those of other imaging modalities. Three-dimensional (3D) reconstruction of OCT images (3D-OCT) helps to gain a more informed understanding of the geometry and morphology of bifurcation lesions and provide additive information on plaque distribution. Following stent implantation, 3D-OCT can also guide the re-crossing of guide wires through stent struts jailing the side branch (SB) ostium and more clearly display the jailing strut configuration, as well as the ideal position of the guidewire recrossing point and stent struct link connection, to confirm the optimal guidewire position and understand interactions between stents and vessel walls, which may improve clinical results after PCI. The present review provides an up-to-date overview of the clinical use of 3D-OCT for accurate assessment of bifurcation anatomy, guiding the optimal guidewire rewiring into SB during bifurcation stenting, and evaluation of post-PCI results, offering novel information about atherosclerotic disease or stenting process.

Efficacy of balloon-expandable extreme-low-temperature ventricular epicardial cryoablation: A preclinical proof of concept evaluation

BackgroundCurrent epicardial ablation technologies are limited by the inability to create adequate depth lesions and risk of collateral injury to extracardiac structures. ObjectiveThe purpose of this study was to evaluate the feasibility and efficacy of ventricular epicardial ablation with a novel balloon-expandable extreme-low-temperature (XLT) cryoablation catheter with an embedded insulation pontoon for protection of extracardiac structures, which has been specifically designed for epicardial ablation. MethodsTen healthy swine underwent surgical (n = 6) and subxiphoid percutaneous (n = 4) epicardial access. A total of 3–6 sites were targeted in the right and left ventricular wall for different exposure durations. Ablation was performed with a large footprint (surgical) and smaller footprint (percutaneous) version of the HeartPad (Corfigo Inc., Montclair, NJ) XLT system. The system consists of the balloon-expandable cryoablation catheter and a console. The console vaporizes liquid helium (–269°C) and controls continuous delivery of extremely cold helium gas at high flow rates through a high-efficiency ablation element mounted on an expandable insulation pontoon to protect extracardiac structures. Ablation lesions were assessed by gross pathology and histologic examination. ResultsA total of 42 epicardial lesions were created. Mean lesion depth increased progressively with ablation time (surgical catheter: 11 ± 2 mm at ≤30 seconds, 13 ± 4 mm at 60 seconds, 15 ± 3 mm at ≥120 seconds, P = .001; percutaneous catheter: 10 ± 2 mm at 30 seconds, 14 ± 2 mm at 60 seconds, 16 ± 2 mm at 120 seconds, P = .001). Lesion geometry seemed unaffected by presence and thickness of epicardial fat. One episode of ventricular fibrillation occurred after ablation over the atrioventricular groove and 2 adjacent obtuse marginal arteries. ConclusionSurgical or percutaneous epicardial ablation using the HeartPad XLT cryoablation system is feasible and can efficiently produce deep ventricular lesions in different epicardial locations.

Rapid and Precise Computation of Fractional Flow Reserve from Routine Two-Dimensional Coronary Angiograms Based on Fluid Mechanics: The Pilot FFR2D Study.

Objective: To present a novel pipeline for rapid and precise computation of fractional flow reserve from an analysis of routine two-dimensional coronary angiograms based on fluid mechanics equations (FFR2D). Material and methods: This was a pilot analytical study that was designed to assess the diagnostic performance of FFR2D versus the gold standard of FFR (threshold ≤ 0.80) measured with a pressure wire for the physiological assessment of intermediate coronary artery stenoses. In a single academic center, consecutive patients referred for diagnostic coronary angiography and potential revascularization between 1 September 2020 and 1 September 2022 were screened for eligibility. Routine two-dimensional angiograms at optimal viewing angles with minimal overlap and/or foreshortening were segmented semi-automatically to derive the vascular geometry of intermediate coronary lesions, and nonlinear pressure-flow mathematical relationships were applied to compute FFR2D. Results: Some 88 consecutive patients with a single intermediate coronary artery lesion were analyzed (LAD n = 74, RCA n = 9 and LCX n = 5; percent diameter stenosis of 45.7 ± 11.0%). The computed FFR2D was on average 0.821 ± 0.048 and correlated well with invasive FFR (r = 0.68, p < 0.001). There was very good agreement between FFR2D and invasive-wire FFR with minimal measurement bias (mean difference: 0.000 ± 0.048). The overall accuracy of FFR2D for diagnosing a critical epicardial artery stenosis was 90.9% (80 cases classified correctly out of 88 in total). FFR2D identified 24 true positives, 56 true negatives, 4 false positives, and 4 false negatives and predicted FFR ≤ 0.80 with a sensitivity of 85.7%, specificity of 93.3%, positive likelihood ratio of 13.0, and negative likelihood ratio of 0.15. FFR2D had a significantly better discriminatory capacity (area under the ROC curve: 0.95 [95% CI: 0.91-0.99]) compared to 50%DS on 2D-QCA (area under the ROC curve: 0.70 [95% CI: 0.59-0.82]; p = 0.0001) in predicting wire FFR ≤ 0.80. The median time of image analysis was 2 min and the median time of computation of the FFR2D results was 0.1 s. Conclusion: FFR2D may rapidly derive a precise image-based metric of fractional flow reserve with high diagnostic accuracy based on a single two-dimensional coronary angiogram.

Proof-of-principle of a lung sealant based on functionalized polyoxazolines: experiments in an ovine acute aerostasis model.

More effective lung sealants are needed to prevent prolonged pulmonary air leakage (AL). Polyoxazoline-impregnated gelatin patch (N-hydroxysuccinimide ester functionalized poly(2-oxazoline)s; NHS-POx) was promising for lung sealing ex vivo. The aim of this study is to confirm sealing effectiveness in an in vivo model of lung injury. An acute aerostasis model was used in healthy adult female sheep, involving bilateral thoracotomy, amputation lesions (bronchioles Ø > 1.5 mm), sealant application, digital chest tube for monitoring AL, spontaneous ventilation, obduction and bursting pressure measurement. Two experiments were performed: (i) 3 sheep with 2 lesions per lung (N = 4 NHS-POx double-layer, N = 4 NHS-POx single-layer, N = 4 untreated) and (ii) 3 with 1 lesion per lung (N = 3 NHS-POx single-layer, N = 3 untreated). In pooled linear regression, AL was analysed per lung (N = 7 NHS-POx, N = 5 untreated) and bursting pressure per lesion (N = 11 NHS-POx, N = 7 untreated). Baseline AL was similar between groups (mean 1.38-1.47 l/min, P = 0.90). NHS-POx achieved sealing in 1 attempt in 8/11 (72.7%) and in 10/11 (90.9%) in >1 attempt. Application failures were only observed on triangular lesions requiring 3 folds around the lung. No influences of methodological variation between experiments was detected in linear regression (P > 0.9). AL over initial 3 h of drainage was significantly reduced for NHS-POx [median: 7 ml/min, length of interquartile range: 333 ml/min] versus untreated lesions (367 ml/min, length of interquartile range: 680 ml/min, P = 0.036). Bursting pressure was higher for NHS-POx (mean: 33, SD: 16 cmH2O) versus untreated lesions (mean: 19, SD: 15 cmH2O, P = 0.081). NHS-POx was effective for reducing early AL, and a trend was seen for improvement of bursting strength of the covered defect. Results were affected by application characteristics and lesion geometry.

Head-to-head comparison of pulsed field ablation, very high power-short duration, cryoballoon and conventional radiofrequency ablation by LGE-MRI-based ablation lesion assessment

Abstract Background Novel concepts for pulmonary vein isolation (PVI) like pulsed field ablation (PFA) or high power-short duration ablation (HPSD) promise favourable profiles of safety and efficacy. However, clinical comparisons of ablation lesion quality are lacking. Purpose To systematically investigate lesion characteristics of novel ablation concepts, we performed a prospective head-to-head comparison between PFA, HPSD, conventional RF and latest generation cryoballoon ablation using late gadolinium enhancement (LGE)-MRI-based ablation lesion assessment. Methods This study included patients that underwent first-time PVI-only atrial fibrillation ablation - either by ablation index-guided RF ablation, cryoballoon ablation (Arctic Front Advance Pro), HPSD ablation (QDOT micro catheter, QMODE+, 90W, 4s) or PFA (Farapulse PFA system). All patients received an LGE-MRI 3 months post-ablation. LGE was quantified based on the signal intensity ratio of each voxel relative to the blood pool, applying a previously validated threshold of &amp;gt;1.2 to define LGE indicative of ablation-induced scarring using a dedicated software. LGE discontinuations of &amp;gt;3 mm were considered as gaps, and complete lesions were defined as LGE covering &amp;gt;90% of the peri-antral circumference of ipsilateral pulmonary vein (PV) pairs. Results Post-ablation LGE-MRIs from 120 patients were analysed (40 RF, 40 cryoballoon, 20 PFA, 20 HPSD). The proportion of complete PV-encircling LGE lesions was significantly higher with conventional RF than with cryoballoon ablation (50% vs. 34%; p=0.023). Importantly, HPSD ablation resulted in even more complete lesions than conventional RF (68%, p=0.004), whereas the proportion of complete LGE lesions was lowest with PFA (21%). Accordingly, the total number of gaps was lower with HPSD ablation (1.9 gaps/patient) compared to the other ablation concepts (conventional RF 2.7, cryoballoon 3.2, PFA 3.4 gaps/patient; p=0.034). As expected, large-area ablation with the cryoballoon (13.8 mm) and PFA (12.8 mm) single-shot devices resulted in the widest lesions. Of note, HPSD lesions were significantly wider than conventional RF lesions (11.1 mm vs. 8.9 mm; p=0.004). Conclusions HPSD ablation resulted in the most continuous lesions, translating in the lowest number of gaps. Of note, HPSD lesions were also significantly wider than conventional RF lesions, thus corroborating the concept of a shallower HPSD lesion geometry from experimental studies. Interestingly, conventional RF showed a higher proportion of complete PV-encircling lesions than cryoballoon ablation. While PFA lesions cover relatively large areas, comparable to cryoballoon ablation, lesions are more inhomogeneous. However, it remains to be determined, to what extent LGE discontinuities in PFA lesions indicate ineffective ablation or only reflect a different kind of remodeling compared to thermal ablation, which may be less detectable by LGE-MRI.

Technical principles of ablation therapy

Catheter ablation is astandard procedure in modern cardiology. It can significantly improve the quality of life and life expectancy of cardiac arrhythmia patients. Besides cardiac mapping, ablation itself is afundamental step tosuccessfully treat cardiac arrhythmias. There are various ablation technologies at hand: In traditional radiofrequency (RF) ablation, electrical current flow generates coagulation necrosis. When understanding the biophysical principles of RF ablation, the investigator is capable to adapt lesion geometry and size to the requirements of the procedure and vary them individually. In addition, lesion metric indices evaluate and integrate important parameters such as power, duration, impedance and contact force to standardize and control RF lesions. Cryoablation induces ice crystals within myocardial tissue, which lead to destruction and electrical scarring of the treated tissue. Histologically, cryolesions are well-delineated with preserved tissue architecture and intact endocardium. Pulsed field ablation (PFA) is anovel rising technology, particularly used for pulmonary vein isolation. In contrast to classic thermal technologies (RF and cryoablation), PFA uses pulsed electrical fields to electroporate cardiac tissue and thereby creates damage on acellular level only.

A Convolutional-Transformer Model for FFR and iFR Assessment From Coronary Angiography.

The quantification of stenosis severity from X-ray catheter angiography is a challenging task. Indeed, this requires to fully understand the lesion's geometry by analyzing dynamics of the contrast material, only relying on visual observation by clinicians. To support decision making for cardiac intervention, we propose a hybrid CNN-Transformer model for the assessment of angiography-based non-invasive fractional flow-reserve (FFR) and instantaneous wave-free ratio (iFR) of intermediate coronary stenosis. Our approach predicts whether a coronary artery stenosis is hemodynamically significant and provides direct FFR and iFR estimates. This is achieved through a combination of regression and classification branches that forces the model to focus on the cut-off region of FFR (around 0.8 FFR value), which is highly critical for decision-making. We also propose a spatio-temporal factorization mechanisms that redesigns the transformer's self-attention mechanism to capture both local spatial and temporal interactions between vessel geometry, blood flow dynamics, and lesion morphology. The proposed method achieves state-of-the-art performance on a dataset of 778 exams from 389 patients. Unlike existing methods, our approach employs a single angiography view and does not require knowledge of the key frame; supervision at training time is provided by a classification loss (based on a threshold of the FFR/iFR values) and a regression loss for direct estimation. Finally, the analysis of model interpretability and calibration shows that, in spite of the complexity of angiographic imaging data, our method can robustly identify the location of the stenosis and correlate prediction uncertainty to the provided output scores.

Can three-dimensional models enhance understanding and knowledge of rotator cuff tears?

ObjectivesMagnetic resonance imaging (MRI) is currently the standard diagnostic tool for rotator cuff tears. However, its two-dimensional (2D) output, displayed on a monitor, can complicate the interpretation of anatomy. Three-dimensional (3D) imaging may offer a solution to this issue. This study aimed to demonstrate the diagnostic and interpretive value of a 3D model in assessing lesion anatomy. The hypothesis was that 3D models, compared to 2D MRI, can enhance the comprehension and knowledge of rotator cuff injuries, improve the application of classifications for total tears, and provide a more precise definition of the size and type of tear. MethodsA prospective single-centre study was conducted. 3D models for rotator cuff tears were created and analysed in conjunction with preoperative MRI for each patient up to 2 months before surgery. The 3D models were based on the preoperative MRI. Collected data included 2D plane measurements by MRI in coronal and sagittal planes, descriptions of 3D lesion geometry (new shapes), 3D measurements in coronal and sagittal planes, arthroscopic classifications of rotator cuff injuries, and arthroscopic measurements in coronal and sagittal planes. ResultsAfter examining 25 cases, 3D imaging demonstrated similar arthroscopic values post-bursectomy in the sagittal plane (16.70 ​mm for 3D and 18.28 ​mm for post-bursectomy, p-value ​= ​0.189), although these measurements did not align with those of MRI (which underestimated measurements, p-value ​= ​0.010). Both MRI measurement and 3D imaging showed similar measurement accuracy in the coronal plane when compared to arthroscopic measurements taken before and after bursectomy. The creation of 3D objects enabled the analysis of new geometries, including the length, width, and depth of each lesion. These geometries included the rectangle, rectangular trapezoid, scalene trapezoid, irregular pentagon, and irregular hexagon. Conclusions3D models can enhance the understanding and knowledge of rotator cuff injuries. They can be a promising tool for diagnosing and interpreting the anatomy of the injury, particularly in the sagittal plane. The new 3D understanding of the pathological process has led to the description of new geometric features not visible in conventional 2D MRI. Level of evidenceII – Development of diagnostic criteria on consecutive patients (all compared to “gold” standard).

Anterior Capsulotomy for Refractory Obsessive-Compulsive Disorder: A Tractography and Lesion Geometry study

Introduction: A bilateral anterior capsulotomy effectively treats refractory obsessive-compulsive disorder (OCD). We investigated the geometry of lesions and disruption of white matter pathways within the anterior limb of the internal capsule (ALIC) in patients with different outcomes. Methods: In this retrospective study, we analyzed data from 18 patients with refractory OCD who underwent capsulotomies. Patients were grouped into “responders” and “nonresponders” based on the percentage of decrease in the Yale-Brown Obsessive-Compulsive Scale (YBOCS) after surgery. We investigated neurobehavioral adverse effects and analyzed the overlap between lesions and the ventromedial prefrontal (vmPFC) and dorsolateral prefrontal (dlPFC) pathways. Probabilistic maps were constructed to investigate the relationship between lesion location and clinical outcomes. Results: Of the 18 patients who underwent capsulotomies, 12 were responders (>35% improvement in YBOCS), and six were nonresponders. The vmPFC pathway was more involved than the dlPFC pathway in responders (p = 0.01), but no significant difference was observed in nonresponders (p = 0.10). The probabilistic voxel-wise efficacy map showed a relationship between ventral voxels within the ALIC with symptom improvement. Weight gains occurred in 11/18 (61%) patients and could be associated with medial voxels within the ALIC. Conclusion: The optimal outcome after capsulotomy in refractory OCD is linked to vmPFC disruption in the ALIC. Medial voxels within the ALIC could be associated with weight gains following capsulotomy.

Computational fluid dynamics validated by micro particle image velocimetry to estimate the risk of hemolysis in arteries with atherosclerotic lesions

We aimed to verify the relationship between blood vessel shape and hemolysis risk by using a blood rheological model that reflects the physiological processes related to blood flow. Blood rheology depends on many factors including the red blood cell concentration and local shear stress, which affect the hemolysis process. We introduced a rheology model suitable for modeling hemolysis flows observed in arteries with atherosclerotic lesions in vivo based on the population balance. The model predicts the concentration of single red blood cells and the concentration and size of red blood cell agglomerates, which affect blood rheology and hemolysis. Atherosclerotic lesion geometries were obtained based on image reconstructions from tomographic projections. Computational fluid dynamics (CFD) simulation results were compared with particle image velocimetry measurements of the geometries printed with a 3D printer. Based on the CFD simulation data, a correlation function was established by combining the essential parameters of vessel shape and flow rate with the maximum shear stress, which governs the hemolysis. The chemical engineering methodology was successfully applied to the analysis of biological systems. In future, the model can be implemented in image reconstruction software using tomographic projections to quickly analyze hemolysis risk in medical practice.

Novel protocol for optimal utilization of HPSD approach for pulmonary vein isolation.

The efficiency of pulmonary vein isolation (PVI) depends on the durability of RF lesions. Recent studies documented sustained continuity of ablation lines, improvements in durability, and expected clinical outcomes through altered settings in duration and power. However, the ablation strategy has not been adapted to this new approach and different biophysics of lesion formation. The aim of this study was to demonstrate that by adjusting the ablation approach to the broader geometry of lesions by increasing the minimal spacing between adjacent RF, a further significant reduction of procedural time while maintaining sufficient long-term outcomes is achievable. The presented study was a prospective, observational multi-center trial. The periprocedural data were compared with data from a consecutively collected historical cohort. In total, 196 patients were included (mean age 62 ± 11 years, male 64.3%). Procedural duration, RF time, and LA dwelling time were significantly shorter in the HPSD group compared with the standard group (73 ± 26 min vs. 98 ± 36 min, p < .001; 14 ± 7 min vs. 33 ± 12 min, p < .001; and 59 ± 21 min vs. 77 ± 32 min, p < .001, respectively). Mean AF-free survival in the first year of follow-up was 304 ± 14 days in the HPSD group versus 340 ± 10 days in the standard group (log-rank p = .403). There were no statistically significant differences in the complication rates between the groups. Increasing the minimal distance between individual application points simplifies AF ablation and further reduces procedure time without negative effects on efficacy and safety. Larger studies are needed to optimally utilize this approach.

PO-04-041 EFFICACY OF BALLOON EXPANDABLE EXTREME-LOW TEMPERATURE "XLT" VENTRICULAR EPICARDIAL CRYOABLATION: A PRE-CLINICAL DOSE RANGING STUDY

Lack of transmural lesion formation with catheter or surgical ablation for ventricular tachycardia (VT) can be an important determinant of arrhythmia recurrence. The aim of this study was to evaluate the feasibility and efficacy of a novel balloon expandable extreme-low temperature (XLT) cryoablation device for epicardial ventricular ablation. A total of six healthy Yorkshire swine (63 ± 6 kg) underwent surgical epicardial access. Four-to-five right (RV) and left (LV) ventricular epicardial targets were identified: anterior (1-2), lateral (1-2), summit (1-2). Ablation was performed with the novel 'XLT-cryo' device (HeartPad®Mini, Corfigo, Montclair, NJ), a balloon-expandable epicardial device that circulates extremely cold helium (∼ -253C) at a high flow rate through a flat pad with dimensions of ∼15 x 15mm. It is mounted onto the surface of an ∼30mm insulation balloon with blunted ends for fixation and parietal pericardial protection. At the end of each timed ablation, a thaw cycle was initiated to warm the device and allow repositioning to the next target. Ablation lesion size was measured using TTC staining. A total of 27 epicardial lesions were created (RV: n=2; LV: n = 25). The average lesion depth increased with time and reached complete transmurality with a plateau at 1 minute (time [T; sec] and mean depth±stdv [mm]; T15=11±0.5, T30=12±1, T60=15±1, T120=16±0.5, T240=17±0.5; Figure). Lesion transmurality was achieved in all lesions with ablation time ≥2 min. Lesion geometry was similar across different RV/LV locations, including the LV summit. Ventricular fibrillation (which is common in Yorkshire swine) occurred during/following 3 applications out of 27. Our results indicate that epicardial cryoablation using the novel balloon expandable HeartPad® device with extremely low temperature applications can efficiently produce transmural ventricular lesions in different epicardial locations. This technology holds potential for both surgical and catheter-based VT ablation in humans.

CarveMix: A simple data augmentation method for brain lesion segmentation

Brain lesion segmentation provides a valuable tool for clinical diagnosis and research, and convolutional neural networks (CNNs) have achieved unprecedented success in the segmentation task. Data augmentation is a widely used strategy to improve the training of CNNs. In particular, data augmentation approaches that mix pairs of annotated training images have been developed. These methods are easy to implement and have achieved promising results in various image processing tasks. However, existing data augmentation approaches based on image mixing are not designed for brain lesions and may not perform well for brain lesion segmentation. Thus, the design of this type of simple data augmentation method for brain lesion segmentation is still an open problem. In this work, we propose a simple yet effective data augmentation approach, dubbed as CarveMix, for CNN-based brain lesion segmentation. Like other mixing-based methods, CarveMix stochastically combines two existing annotated images (annotated for brain lesions only) to obtain new labeled samples. To make our method more suitable for brain lesion segmentation, CarveMix is lesion-aware, where the image combination is performed with a focus on the lesions and preserves the lesion information. Specifically, from one annotated image we carve a region of interest (ROI) according to the lesion location and geometry with a variable ROI size. The carved ROI then replaces the corresponding voxels in a second annotated image to synthesize new labeled images for network training, and additional harmonization steps are applied for heterogeneous data where the two annotated images can originate from different sources. Besides, we further propose to model the mass effect that is unique to whole brain tumor segmentation during image mixing. To evaluate the proposed method, experiments were performed on multiple publicly available or private datasets, and the results show that our method improves the accuracy of brain lesion segmentation. The code of the proposed method is available at https://github.com/ZhangxinruBIT/CarveMix.git.

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

A novel irrigation catheter (QDOT MICRO™) has been introduced, which enables a surface temperature-controlled ablation combined with tip cooling. However, the detailed description of its complex behavior and effect on the incidence of pops and lesion formation remains elusive. This study aimed to systematically investigate the ablation characteristics, feedback behavior, and incidence of steam pops in a simplified ex vivo swine model. Using swine ventricular tissue perfused with saline at 37°C, we systematically created lesions with 4×3 combinations of the wattage (20, 30, 40, and 50W) and contact force (CF, 10, 30, and 50g). Ablation was continued for either 120s or until a steam pop occurred and repeated 10 times with each setting. The lesion geometry, ablation index, feedback dynamics, and conditions underlying the steam pops were measured and analyzed. Steam pops occurred particularly frequently in combinations of a low CF and high power (10g vs. 30g+50g [p<.0001]; 40W+50W vs. 20W+30W [p<.0001]). Failure to activate a feedback process was associated with a 5.1 times higher incidence of steam pops (21/109vs.11/11, [95% CI 3.499-7.716], p<.0001). The wattage feedback was particularly evident with a high CF (30 and 50g) and high initial wattage (40 and 50W). The average delivered wattage at 27W predicted the occurrence of steam pops. The temperature-controlled ablation with the QDOT MICRO™ demonstrated a complex feedback behavior, which contributed to a reduced incidence of steam pops and prolonged lead time to the pops.

MRI-based numerical modeling of cardiac pulsed field ablation (PFA) with sub-microsecond pulses

Abstract Background The use of irreversible electroporation (IRE) for cardiac ablation in the management of cardiac arrhythmias, known as Pulsed Field Ablation (PFA), has gained the attention of many researchers, physicians and companies. Despite the demonstrated efficacy and safety profiles of the technique, there are still many open questions. One of them deals with the effective electric field thresholds necessary for cardiac tissue ablation. Contrary to radiofrequency (RF) ablation, where the thermotemporal thresholds for tissue damage are well established, the electric field thresholds for effective IRE are uncertain and depend on the tissue type and the waveform characteristics of the delivered electric field. Purpose The use of numerical models to understand the electric field distribution and the corresponding lesion for a specific electrode geometry are widely used in IRE for cancer treatment. Models can predict ablation volumes when the field thresholds are known or can be used to estimate the field thresholds when the lesion geometry is established post-treatment. The goal of the present study was to build a subject-specific realistic 3D numerical model to assess the ability of modeling to predict PFA lesions. Methods PFA experiments were performed in male mongrel dogs following a protocol approved by the Mayo Clinic Institutional Animal Care and Use Committee. Briefly, animals were sedated and intubated, and two non-irrigated deflectable catheters with an 8-mm tip were positioned on both sides of the interventricular septum under fluoroscopy guidance. Submicrosecond pulses were delivered in a bipolar fashion across both catheters. Sequences of pulses of 300 ns duration (or other durations in that range) were repetitively applied with voltage levels in the kV range. 30 days after the procedure, MRI with late gadolinium enhancement (LGE) were acquired to assess the presence of ablation lesions in the treated tissue. Ventricular areas were segmented from MRI images and 3D volumes were created. The generated 3D geometries were imported into software COMSOL Multiphysics. Realistic 3D geometries of the catheters were placed in the same positions than during the experiments, fluoroscopy videos recorded during the procedures were used as a guidance. The computed electric field intensity distributions were compared to the LGE areas to extract the range of electric field thresholds where the predicted lesion size was compatible with the real size of the LGE areas for each application site and pulsing protocol. Results and conclusions Our results show how the numerical model is able to reproduce the shape of the LGE fibrotic lesion areas observed 30 days after the procedure. Additionally, the model clearly confirms the dose-dependent lesion sizes observed experimentally. This study supports that numerical modeling is a valuable tool for understanding PFA treatments and that it could be used as patient-specific treatment planning tool. Funding Acknowledgement Type of funding sources: Public grant(s) – EU funding. Main funding source(s): European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie

Optimized lesion geometry using very high-power short-duration ablation in catheter ablation adjacent to the phrenic nerve.

Optimized lesion geometry using very high-power short-duration ablation in catheter ablation adjacent to the phrenic nerve.

Morphological and Physiological Characteristics of Ruptured Plaques in Native Arteries and Neoatherosclerotic Segments: An OCT-Based and Computational Fluid Dynamics Study.

BackgroundIntravascular imaging has been used to assess the morphology of lesions causing an acute coronary syndrome (ACS) in native vessels (NV) and identify differences between plaques that ruptured (PR) and caused an event and those that ruptured without clinical manifestations. However, there is no data about the morphological and physiological characteristics of neoatherosclerotic plaques that ruptured (PR-NA) which constitute a common cause of stent failure.MethodsWe retrospectively analyzed data from patients admitted with an acute myocardial infarction that had optical coherence tomography (OCT) imaging of the culprit vessel before balloon pre-dilation. OCT pullbacks showing PR were segmented at every 0.4 mm. The extent of the formed cavity, lipid and calcific tissue, thrombus, and macrophages were measured, and the fibrous cap thickness (FCT) and the incidence of micro-channels and cholesterol crystals were reported. These data were used to reconstruct a representative model of the native and neoatherosclerotic lesion geometry that was processed with computational fluid dynamics (CFD) techniques to estimate the distribution of the endothelial shear stress and plaque structural stress.ResultEighty patients were included in the present analysis: 56 had PR in NV (PR-NV group) and 24 in NA segments (PR-NA group). The PR-NV group had a larger minimum lumen area (2.93 ± 2.03 vs. 2.00 ± 1.26 mm2, p = 0.015) but similar lesion length and area stenosis compared to PR-NA group. The mean FCT (186 ± 65 vs. 232 ± 80 μm, p = 0.009) and the lipid index was smaller (16.7 ± 13.8 vs. 25.9 ± 14.1, p = 0.008) while the of calcific index (8.3 ± 9.5 vs. 2.2 ± 1.6%, p = 0.002) and the incidence of micro-channels (41.4 vs. 12.5%, p = 0.013) was higher in the PR-NV group. Conversely, there was no difference in the incidence of cholesterol crystals, thrombus burden or the location of the rupture site between groups. CFD analysis revealed higher maximum endothelial shear stress (19.1 vs. 11.0 Pa) and lower maximum plaque structural stress (38.8 vs. 95.1 kPa) in the PR-NA compared to the PR-NV model.ConclusionWe reported significant morphological and physiological differences between culprit ruptured plaques in native and stented segments. Further research is needed to better understand the causes of these differences and the mechanisms regulating neoatherosclerotic lesion destabilization.

PO-718-08 PREDICTING TISSUE CONDUCTANCE CHANGES AND ABLATION LESION PATTERNS USING A QUASI-DYNAMIC PULSED FIELD ELECTROPORATION NUMERICAL MODEL FOR CARDIAC ABLATION

Pulsed field ablation (PFA) is proposed as a useful modality in AF treatment, but factors determining the field distribution, and lesion transmurality and geometry have not been fully characterized. To understand the physics behind the tissue response to PSA, we propose a quasi-dynamic PFA model that can predict the tissue conductivity when electroporation equilibrium is achieved, and identify tissue regions that undergo fully irreversible electroporation (IRE) Model parameters include: tissue conductivity at baseline (0.2 S/m) and after complete electroporation (0.8 S/m), critical depth of the electric field for reversible electroporation (RE, 200 V/m and IRE, 450 V/m), and the applied pulsed voltage amplitude. The iterative model yields the steady-state solution with a tissue conductivity map, clearly identifying regions of IRE. The model employed a circular catheter with 9 - 3 mm electrodes fired sequentially using a 1500 V and 3000 V pulse. The steady-state IRE regions are shown (figure) with an estimated IRE lesion surface area and volume of 780 mm2 and 1411 mm3, respectively, at 1500 V, and 1178 mm2 and 2760 mm3, respectively, at 3000 V. Lesion discontinuity is observed at 5.0 mm depth with 1500 V and 7.2 mm with 3000 V. Transverse views through the lesions show maximum lesion depth at each voltage amplitude. The tissue conductivity profiles through predicted lesions show the formation of gaps in the lesion pattern. (Figure 1) The proposed quasi-dynamic model yields steady-state tissue conductivity maps, shows full IRE tissue regions, and confirms larger lesions with higher pulse amplitudes. Future work will predict time-based tissue response given specific pulse duration and delivery of sequential pulses and compare numerical and experimental results.