Computer Modeling of Radiofrequency Cardiac Ablation including Heartbeat-Induced Electrode Displacement

Background: The state of the art in computer modeling of radiofrequency catheter ablation (RFCA) only considers a static model, i.e. it does not allow modeling ablation electrode displacements induced by tissue movement due to heartbeats. This feature is theoretically required, since heartbeat-induced changes in contact force can be detected during this clinical procedure. Methods: We built a 2D RFCA model coupling electrical, thermal and mechanical problems and simulated a standard energy setting (25 W - 30 s). The mechanical interaction between the ablation electrode and tissue was dynamically modeled to reproduce heartbeat-induced changes in the electrode insertion depth from 0.86 to 2.05 mm, which corresponded with contact forces between 10 and 30 g when cardiac tissue was modeled by a hyperelastic Neo-Hookean model with a Young's modulus of 75 kPa and Poisson's ratio of 0.49. Results: The dynamic model computed a lesion depth of 5.86 mm, which is within the range of previous experimental results based on a beating heart for a similar energy setting and contact force (5.6-6.7 mm). Lesion size was practically identical (differences less than 0.02 mm) to that using a static model with the electrode inserted to an average depth (1.46 mm, equivalent to 20 g contact force). Conclusions: The RFCA dynamic model including heartbeat-induced electrode displacement predicts lesion depth reasonably well compared to previous experimental results based on a beating heart model, however this is true only at a standard energy setting and moderate contact force.

THE EFFECTIVENESS OF COMPOMER AND GIC AGAINST PREVENTION IN ENAMEL DEMINERALIZATION

Background: Several studies showed that fluoride interferes in the dynamics involved in the development of caries and could present an antimicrobial effect or provide demineralization inhibition or dental remineralization. The development of fluoride-releasing materials can contribute to a preventive of demineralization. GIC and Compomer are restorative materials containing fluoride which can prevent demineralization. Purpose: To analyze the effectiveness of Compomer and GIC against prevention in enamel demineralization. Method: The cavities were made on 18 bovine teeth which grouped into 3 groups, each group consisting of 6 bovine teeth. After the restorative procedures, the teeth were submitted to demineralization and remineralization cycling during 14 days. The sections of the teeth were examined under scanning electron microscope after undergoing pH cycling. The data were analyzed using the Kruskal-Wallis and Tukey Test (p<0.05). Results: GIC group showed the lowest lesion depth of demineralization (10.9883 ± 0.74333) followed by Compomer group (25.4183 ± 3.44268) and Control group (88.9783 ± 3.02495). Conclusion: GIC restorative materials have a better enamel demineralization prevention effect than Compomer. Keywords: compomer, demineralization, fluoride, GIC, remineralization

Quantification of irrigated lesion morphology using near-infrared spectroscopy

There are currently limited means by which lesion formation can be confirmed during radiofrequency ablation procedures. The purpose of this study was to evaluate the use of NIRS-integrated RFA catheters for monitoring irrigated lesion progression, ex vivo and in vivo. Open-irrigated NIRS-ablation catheters with optical fibers were fabricated to sample tissue diffuse reflectance. Spectra from 44 irrigated lesions and 44 non-lesion sites from ex vivo swine hearts (n = 15) were used to train and evaluate a predictive model for lesion dimensions based on key spectral features. Additional studies were performed in diluted blood to assess NIRS signatures of catheter-tissue contact status. Finally, the potential of NIRS-RFA catheters for guiding lesion delivery was evaluated in a set of in vivo pilot studies conducted in healthy pigs (n = 4). Model predictions for lesion depth (R = 0.968), width (R = 0.971), and depth percentage (R = 0.924) correlated well with measured lesion dimensions. In vivo deployment in preliminary trials showed robust translational consistency of contact discrimination (P < 0.0001) and lesion depth parameters (< 3% error). NIRS empowered catheters are well suited for monitoring myocardial response to RF ablation and may provide useful intraprocedural feedback for optimizing treatment efficacy alongside current practices.

Catheter contact angle influences local impedance drop during radiofrequency catheter ablation: insight from a porcine experimental study

Background Local impedance (LI) at a distal tip of the ablation catheter can indirectly measure catheter contact and tissue temperature during radiofrequency catheter ablation (RFCA). LI decreases by RFCA, and a degree of LI drop is correlated with lesion size. However, data on the effects of catheter contact angle on lesion size and LI drop were scarce. This study aimed to evaluate the influence of catheter contact angle on lesion size and LI drop in a porcine experimental study. Methods Lesions were created on porcine myocardial left ventricles by the LI-sensing ablation catheter (IntellaNav MiFi OI®). Contact force (CF) was measured using pressure to current transducer (load cell). Radiofrequency ablation was performed with a power of 30 Watt and a duration of 30 seconds. CF (0g, 5g, 10g, 20g, and 30g) and catheter angle (30°, 45°, and 90°) were changed in each set (total 120 lesions, n=8 each). LI rise, LI drop by RF application, and lesion size (maximum lesion width, maximum surface width, and maximum lesion depth) were evaluated. Results There was no angular dependence in LI rise in all CF. The values of LI rise increased as CF increased. The LI drop also increased as CF increased in all contact angles. Regarding the difference of catheter angles, LI drop with 90° was lower than those with 30° and 45°in CF 10g, 20g, and 30g, respectively. Maximum lesion width and surface width were larger in 30° and 45° than those in 90°, whereas there were no differences in maximum lesion depth. Conclusion LI drop in 90° were significantly lower than those in 45° and 30°. Although lesion depths were not different among the three angles, the absolute values of LI drop were different. Caution should be exercised to comprehend the LI drop with catheter angles. FUNDunding Acknowledgement Type of funding sources: None.

Enamel Demineralization and Remineralization Detection Using Non-invasive Optical Imaging

Introduction: Optical Coherence Tomography (OCT), is one of the most emerging diagnostic imaging technique. It is capable of producing 3D images using optical scattering media. The fast signal acquisition quality has made it a promising tool to detect early in vivo and in vitro lesions. The aim of this study was to reproduce previous demineralization results and to detect remineralization using OCT. Methodology: Bovine enamel discs were used thoroughly in this study. The study was done using the flow cell for detecting demineralization and remineralization following 96 hours demineralization and 192 hours remineralization. A time lapse monitoring was done and the lesions were assessed visually. ImageJ software was used to process the images produced through OCT. The lesion depth and intensity was measured across the images produced which helped in assessing the difference between remineralization and demineralization. Results: OCT B-scan images result in increased backscattering light which is considered the main principle to measure lesion depth and mineral loss. Whereas, in remineralization decreased band of light appeared with reduction in porosity during mineral precipitation. The results for remineralization were diverse and could not be assessed. Conclusion: OCT is favorable technique to detect demineralization and remineralization but it still needs a lot of improvement especially regarding remineralization there are limitations which need to be improved.

Catheter contact area strongly correlates with lesion area in radiofrequency cardiac ablation: an ex vivo porcine heart study

Purpose Our previous study confirmed that not only force but also the catheter contact angle substantially impacted the contact area and its morphology. Therefore, in this study, we aimed to further investigate the relationship between the catheter contact area and the dimensions of the ablation lesion area as a function of catheter contact angle and force in radiofrequency catheter ablation. Methods The radiofrequency catheter ablation test was performed for 5 contact angles and 8 contact forces at a fixed ablation time of 30 s. The initial impedance was 92.5 ± 2.5 Ω, the temperature during ablation was 30 °C, and the power was 30 W. The irrigation rate during ablation was set to 17 mL/min. Each experiment was repeated 6 times. Results The catheter contact area showed a strong correlation with the ablation lesion area (r = 0.8507). When the contact area was increased, the lesion area also increased linearly in a monotonic manner. The relationships between catheter contact force and ablation lesion area and between catheter contact force and ablation lesion depth are logarithmic functions in which increased contact force was associated with increased lesion area and depth. The catheter contact angle is also an important determinant of the lesion area. The lesion area progressively increased when the contact angle was decreased. In contrast, the lesion depth progressively increased when the contact angle was increased. Conclusions The catheter contact area was strongly correlated with the ablation lesion area. Additionally, catheter contact force and contact angle significantly impacted the dimensions of the lesion in radiofrequency catheter ablation procedures.

820 EFFICACY AND SAFETY OF ENDOSCOPIC SUBMUCOSAL DISSECTION FOR SUPERFICIAL ESOPHAGEAL SQUAMOUS CELL CARCINOMA AND PRECANCEROUS LESIONS

With the development of endoscopic technology, endoscopic mucosal dissection (ESD) has become one of the standard treatments for superficial esophageal squamous cell carcinoma and precancerous lesion (SESCC-PL). However, the efficacy and safety of ESD in some special SESCC-PL patients is still unclear. The purpose of this study was to analyze the efficacy and safety of ESD in patients with SESCC-PL, especially for some special patients. Methods Firstly, according to the depth of lesions, all patients were divided into three groups: the epithelium and lamina propria group (M1-M2), the muscularis mucosae and submucosal superficial layer group (M3-SM1) and the submucosal deep layer group (≥SM2). Secondly, according to the age of patients, all patients were divided into two groups: elderly group (≥ 65 years old) and non-elderly group (&lt;65 years old). Finally, all patients were divided into two groups: patients with liver cirrhosis group and patients without liver cirrhosis group. The efficacy and safety of ESD for these patients were analyzed. Results There was no significant difference in operation time, resection speed, en bloc resection rate, bleeding rate, muscularis propria injury rate, perforation rate and intraoperative esophageal stricture rate in three groups with different depths of lesion. However, the R0 resection rate among the three groups decreased with the increase of lesion depth (P &lt; 0.001). There was no significant difference in all surgical indexes between the non-elderly group and the elderly group (all P &gt; 0.05). And there was also no significant difference in all surgical indexes including bleeding rate between the patients with liver cirrhosis and without liver cirrhosis (all P &gt; 0.05). Conclusion This study proved that ESD is safe and effective for all kinds of patients with SESCC-PL, especially for patients with lesion depth ≥ M3, elderly patients and patients with liver cirrhosis, ESD can still achieve a satisfactory treatment effect and a good survival prognosis. Liver cirrhosis is not a contraindication to ESD.

Pulsed-Field Ablation in Ventricular Myocardium Using a Focal Catheter: The Impact of Application Repetition on Lesion Dimensions

Background - Pulsed-field ablation (PFA) is a rapid and nonthermal energy with higher selectivity to myocardial tissue in comparison to radiofrequency ablation (RFA). However, its effects on ventricular myocardium, and titration of lesion dimensions have not been well studied. This study examined the effect of PFA on ventricular myocardium, and the influence of application repetition on lesion dimensions. Methods - An 8Fr lattice catheter with a compressible 9 mm nitinol tip was used with a PFA generator (Affera Inc) applying a bipolar and biphasic waveform (±1.3-2.0 kV, 4 sec per application). We examined the impact of single applications (1x) vs four repetitive applications (4x) interspaced by 10 seconds. The latter was performed to determine whether repetitions of a similar electrical field can increase lesion dimensions. Experiments were performed in an in-vivo porcine model and a survival period of 24 hours (n=6) or 23±5.4 days (n=6) for evaluation of early and late histopathological effects. Results - PFA in ventricular myocardium showed repetition dependency. Acute lesion depth and volume increased from 5.6±1.43mm and 860±362mm 3 to 8.8±0.74mm and 2383±548mm 3 for 1x and 4x applications, respectively (P<0.001 for both comparisons). This effect was maintained in the chronic lesion phase with lesion depth and volume of 3.9±0.92mm and 655±286mm 3 compared with 7.3±0.83mm and 2170±488mm 3 , respectively (P<0.001 for both comparisons). Acute lesions showed well demarcated necrotic core without coagulation necrosis while chronic lesions showed tissue thinning with fibro-fatty replacement. Conclusions - PFA in ventricular myocardium exhibits repetition dependency as lesion dimension increases with consecutive applications of a similar electrical field.