Proactive esophageal cooling during laser cardiac ablation: A computer modeling study.

BACKGROUND AND OBJECTIVES: Laser ablation is increasingly used to treat atrial fibrillation (AF). However, atrioesophageal injury remains a potentially serious complication. While proactive esophageal cooling (PEC) reduces esophageal injury during radiofrequency ablation, the effects of PEC during laser ablation have not previously been determined. We aimed to evaluate the protective effects of PEC during laser ablation of AF by means of a theoretical study based on computer modeling. METHODS: Three-dimensional mathematical models were built for 20 different cases including a fragment of atrial wall (myocardium), epicardial fat (adipose tissue), connective tissue, and esophageal wall. The esophagus was considered with and without PEC. Laser-tissue interaction was modeled using Beer-Lambert's law, Pennes' Bioheat equation was used to compute the resultant heating, and the Arrhenius equation was used to estimate the fraction of tissue damage (FOD), assuming a threshold of 63% to assess induced necrosis. We modeled laser irradiation power of 8.5 W over 20 s. Thermal simulations extended up to 250 s to account for thermal latency. RESULTS: PEC significantly altered the temperature distribution around the cooling device, resulting in lower temperatures (around 22°C less in the esophagus and 9°C in the atrial wall) compared to the case without PEC. This thermal reduction translated into the absence of transmural lesions in the esophagus. The esophagus was thermally damaged only in the cases without PEC and with a distance equal to or shorter than 3.5 mm between the esophagus and endocardium (inner boundary of the atrial wall). Furthermore, PEC demonstrated minimal impact on the lesion created across the atrial wall, either in terms of maximum temperature or FOD. CONCLUSIONS: PEC reduces the potential for esophageal injury without degrading the intended cardiac lesions for a variety of different tissue thicknesses. Thermal latency may influence lesion formation during laser ablation and may play a part in any collateral damage.

How far the zone of heat-induced transient block extends beyond the lesion during RF catheter cardiac ablation.

PURPOSE: While radiofrequency catheter ablation (RFCA) creates a lesion consisting of the tissue points subjected to lethal heating, the sublethal heating (SH) undergone by the surrounding tissue can cause transient electrophysiological block. The size of the zone of heat-induced transient block (HiTB) has not been quantified to date. Our objective was to use computer modeling to provide an initial estimate. METHODS AND MATERIALS: We used previous experimental data together with the Arrhenius damage index (Ω) to fix the Ω values that delineate this zone: a lower limit of 0.1-0.4 and upper limit of 1.0 (lesion boundary). An RFCA computer model was used with different power-duration settings, catheter positions and electrode insertion depths, together with dispersion of the tissue's electrical and thermal characteristics. RESULTS: The HiTB zone extends in depth to a minimum and maximum distance of 0.5 mm and 2 mm beyond the lesion limit, respectively, while its maximum width varies with the energy delivered, extending to a minimum of 0.6 mm and a maximum of 2.5 mm beyond the lesion, reaching 3.5 mm when high energy settings are used (25 W-20s, 500 J). The dispersion of the tissue's thermal and electrical characteristics affects the size of the HiTB zone by ±0.3 mm in depth and ±0.5 mm in maximum width. CONCLUSIONS: Our results suggest that the size of the zone of heat-induced transient block during RFCA could extend beyond the lesion limit by a maximum of 2 mm in depth and approximately 2.5 mm in width.

Relationship between luminal esophageal temperature and volume of esophageal injury during RF ablation: In silico study comparing low power-moderate duration vs. high power-short duration.

OBJECTIVE: To model the evolution of peak temperature and volume of damaged esophagus during and after radiofrequency (RF) ablation using low power-moderate duration (LPMD) versus high power-short duration (HPSD) or very high power-very short duration (VHPVSD) settings. METHODS: An in silico simulation model of RF ablation accounting for left atrial wall thickness, nearby organs and tissues, as well as catheter contact force. The model used the Arrhenius equation to derive a thermal damage model and estimate the volume of esophageal damage over time during and after RF application under conditions of LPMD (30 W, 20 s), HPSD (50 W, 6 s), and VHPVSD (90 W, 4 s). RESULTS: There was a close correlation between maximum peak temperature after RF application and volume of esophageal damage, with highest correlation (R2 = 0.97) and highest volume of esophageal injury in the LPMD group. A greater increase in peak temperature and greater relative increase in esophageal injury volume in the HPSD (240%) and VHPSD (270%) simulations occurred after RF termination. Increased endocardial to esophageal thickness was associated with a longer time to maximum peak temperature (R2 > 0.92), especially in the HPSD/VHPVSD simulations, and no esophageal injury was seen when the distances were >4.5 mm for LPMD or >3.5 mm for HPSD. CONCLUSION: LPMD is associated with a larger total volume of esophageal damage due to the greater total RF energy delivery. HPSD and VHPVSD shows significant thermal latency (resulting from conductive tissue heating after RF termination), suggesting a requirement for fewer esophageal temperature cutoffs during ablation.

Effect of intracardiac blood flow pulsatility during radiofrequency cardiac ablation: computer modeling study.

PURPOSE: To assess the effect of intracardiac blood flow pulsatility on tissue and blood distributions during radiofrequency (RF) cardiac ablation (RFCA). METHODS: A three-dimensional computer model was used to simulate constant power ablations with an irrigated-tip electrode and three possible catheter orientations (perpendicular, parallel and 45°). Continuous flow and three different pulsatile flow profiles were considered, with four average blood velocity values: 3, 5.5, 8.5 and 24.4 cm/s. The 50 °C contour was used to assess thermal lesion size. RESULTS: The differences in lesion size between continuous flow and the different pulsatile flow profiles were always less than 1 mm. As regards maximum tissue temperature, the differences between continuous and pulsatile flow were always less than 1 °C, with slightly higher differences in maximum blood temperature, but never over 6 °C. While the progress of maximum tissue temperature was identical for continuous and pulsatile flow, maximum blood temperature with the pulsatile profile showed small amplitude oscillations associated with blood flow pulsatility. CONCLUSIONS: The findings show that intracardiac blood pulsatility has a negligible effect on lesion size and a very limited impact on maximum tissue and blood temperatures, which suggests that future experimental studies based on ex vivo or in silico models can ignore pulsatility in intracardiac blood flow.

High-power short-duration vs. standard radiofrequency cardiac ablation: comparative study based on an in-silico model.

PURPOSE: While the standard setting during radiofrequency catheter ablation (RFCA) consists of applying low power for long times, a new setting based on high power and short duration (HPSD) has recently been suggested as safer and more effective. Our aim was to compare the electrical and thermal performance of standard vs. HPSD settings, especially to assess the effect of the catheter orientation. METHODS: A 3D computational model was built based on a coupled electric-thermal-flow problem. Standard (20 W-45 s and 30 W-30 s) and HPSD settings (70 W-7 s and 90 W-4 s) were compared. Since the model only included a cardiac tissue fragment, the power values were adjusted to 80% of the clinical values (15, 23, 53 and 69 W). Three catheter-tissue orientations were considered (90°, 45° and 0°). Thermal lesions were assessed by the Arrhenius equation. Safety was assessed by checking the occurrence of steam pops (100 °C in tissue) and thrombus formation (80 °C in blood). RESULTS: The computed thermal lesions were in close agreement with the experimental data in the literature, in particular with in vivo studies. HPSD created shallower and wider lesions than standard settings, especially with the catheter at 45°. Steam pops occurred earlier with HPSD, regardless of catheter orientation. CONCLUSION: HPSD seems to be more effective in cases that need shallow and extensive lesions, especially when the catheter is at 0° or at 45°, as used in pulmonary vein isolation.

Differences in applied electrical power between full thorax models and limited-domain models for RF cardiac ablation.

Purpose: Most modeling studies on radiofrequency cardiac ablation (RFCA) are based on limited-domain models, which means the computational domain is restricted to a few centimeters of myocardium and blood around the active electrode. When mimicking constant power RFCA procedures (e.g., atrial fibrillation ablation) it is important to know how much power is absorbed around the active electrode and how much in the rest of the tissues before reaching the dispersive electrode.Methods: 3D thorax full models were built by progressively incorporating different organs and tissues with simplified geometries (cardiac chamber, cardiac wall, subcutaneous tissue and skin, spine, lungs and aorta). Other 2D limited-domain models were also built based on fragments of myocardium and blood. The electrical problem was solved for each model to estimate the spatial power distribution around the active electrode.Results: From 79 to 82% of the power was absorbed in a 4 cm-radius sphere around the active electrode in the full thorax model at active electrode insertion depths of between 0.5 and 2.5 mm, while the impedance values ranged from 104 to 118 Ω, which were consistent with those found (from 83 to 103 Ω) in a 4 cm radius cylindrical limited domain model.Conclusion: The applied power in limited-domain RFCA models is approximately 80% of that applied in full thorax models, which is equivalent to the power programed in a clinical setting.

Thermal impact of balloon occlusion of the coronary sinus during mitral isthmus radiofrequency ablation: an in-silico study.

Purpose: Although experimental data have suggested that temporary occlusion of the coronary sinus (CS) can facilitate the creation of transmural lesions across the atrial wall (AW) during mitral isthmus radiofrequency (RF) ablation, no computer modeling study has yet been made on the effect of the blood flow inside the epicardial vessels and its stoppage by an occlusion balloon.Methods: Computer simulations using constant power were conducted to study these phenomena by two methods: (1) by setting blood velocity in the CS to zero, which mimics a distal occlusion; and (2) by including a balloon filled with air in the model just below the ablation site, which mimics a proximal occlusion.Results: For short ablations (15 s) and perpendicular electrode/tissue orientation, lesion size was smaller with proximal occlusion compared to distal or no occlusion, regardless of the AW-CS distance (from 0.5 mm to 3.4 mm). For other angulations (0 and 45°) lesion size was almost the same in all cases. For longer ablations (60 s), the internal CS blood flow (no occlusion) considerably reduced lesion size, while stoppage combined with the proximal presence of a balloon produced the largest lesions. This performance was similar for different catheter angulations (0, 45 and 90°). Balloon length (from 10 to 40 mm) was found to be an irrelevant parameter when proximal occlusion was modeled.Conclusions: Using an air-filled balloon to occlude CS facilitates mitral isthmus ablation in long ablations, while proximal occlusion could impede transmural lesions in the case of short ablations (15 s).

Should fluid dynamics be included in computer models of RF cardiac ablation by irrigated-tip electrodes?

BACKGROUND: Although accurate modeling of the thermal performance of irrigated-tip electrodes in radiofrequency cardiac ablation requires the solution of a triple coupled problem involving simultaneous electrical conduction, heat transfer, and fluid dynamics, in certain cases it is difficult to combine the software with the expertise necessary to solve these coupled problems, so that reduced models have to be considered. We here focus on a reduced model which avoids the fluid dynamics problem by setting a constant temperature at the electrode tip. Our aim was to compare the reduced and full models in terms of predicting lesion dimensions and the temperatures reached in tissue and blood. RESULTS: The results showed that the reduced model overestimates the lesion surface width by up to 5 mm (i.e. 70%) for any electrode insertion depth and blood flow rate. Likewise, it drastically overestimates the maximum blood temperature by more than 15 °C in all cases. However, the reduced model is able to predict lesion depth reasonably well (within 0.1 mm of the full model), and also the maximum tissue temperature (difference always less than 3 °C). These results were valid throughout the entire ablation time (60 s) and regardless of blood flow rate and electrode insertion depth (ranging from 0.5 to 1.5 mm). CONCLUSIONS: The findings suggest that the reduced model is not able to predict either the lesion surface width or the maximum temperature reached in the blood, and so would not be suitable for the study of issues related to blood temperature, such as the incidence of thrombus formation during ablation. However, it could be used to study issues related to maximum tissue temperature, such as the steam pop phenomenon.

RF-energised intracoronary guidewire to enhance bipolar ablation of the interventricular septum: in-silico feasibility study.

PURPOSE: Although bipolar radiofrequency (RF) ablation (RFA) is broadly used to eliminate ventricular tachycardias in the interventricular septum wall, it can fail to create transmural lesions in thick ventricular walls. To solve this problem, we explored whether an RF-energised guidewire inserted into the ventricular wall would enhance bipolar RFA in the creation of transmural lesions through the ventricular wall. METHODS: We built three-dimensional computational models including two irrigated electrodes placed on opposing sides of the interventricular septum and a metal guidewire inserted into the septum. Computer simulations were conducted to compare the temperature distributions obtained with two ablation modes: bipolar mode (RF power delivered between both irrigated electrode) and time-division multiplexing (TDM) technique, which consists of activating the bipolar mode for 90% of the time and applying RF power between the guidewire and both irrigated electrodes during the remaining time. RESULTS: The TDM technique was the most suitable in terms of creating wider lesions through the entire ventricular wall, avoiding the hour-glass shape of thermal lesions associated with the bipolar mode. This was especially apparent in the case of thick walls (15 mm). Furthermore, the TDM technique was able to create transmural lesions even when the guidewire was displaced from the midplane of the wall. CONCLUSIONS: An RF-energised guidewire could enhance bipolar RFA by allowing transmural lesions to be made through thick ventricular walls. However, the safety of this new approach must be assessed in future pre-clinical studies, especially in terms of the risk of stenosis and its clinical impact.

Numerical analysis of thermal impact of intramyocardial capillary blood flow during radiofrequency cardiac ablation.

PURPOSE: The thermal effect of the intramyocardial blood perfusion on the size of lesions created by radiofrequency cardiac ablation (RFCA) has not been adequately studied to date. Our objective was to assess the impact of including this phenomenon in RFCA computer modelling in terms of the thermal lesion depth created. METHODS: A computer model was built and computer simulations were conducted to assess the effect of including the blood perfusion term in the bioheat equation. This term mimics the intramyocardial blood flow (i.e., blood perfusion) in the cardiac wall at the site at which the RFCA is being conducted and hence represents a heat removing mechanism. When considered, blood perfusion rates ranged from 609 to 1719 ml/min/kg. Two electrode design and modes were considered: a non-irrigated electrode with constant temperature mode and an irrigated electrode with constant power mode. RESULTS: All the depths computed without including the blood perfusion term were larger than those that did include it, regardless of perfusion rate. The differences in lesion depth between ignoring and including blood perfusion increased over time; for a 60 s RFCA they were 0.45 and 1 mm for minimum and maximum perfusion rate, respectively. The differences were more or less independent of blood flow in the cardiac chamber, electrode type and ablation mode. CONCLUSIONS: The findings suggest that the heat-sink effect of blood perfusion should be taken into account in the case of ablations (>1 minute) such as those conducted in RFCA of the ventricular wall.

Relation between denaturation time measured by optical coherence reflectometry and thermal lesion depth during radiofrequency cardiac ablation: Feasibility numerical study.

BACKGROUND/OBJECTIVE: Radiofrequency (RF) catheter ablation is a minimally invasive medical procedure used to thermally destroy the focus of cardiac arrhythmias. Novel optical techniques are now being integrated into RF catheters in order to detect the changes in tissue properties. Loss of birefringence due to fiber denaturation at around 70°C is related to changes in accumulated phase retardation and can be measured by polarization-sensitive optical coherence reflectometry (PS-OCR). Since irreversible thermal lesions are produced when the tissue reaches 50°C, our goal was to seek the mathematical relationship between both isotherms. MATERIALS AND METHODS: A two-dimensional model based on a coupled electric-thermal problem was built and solved using the finite element method. The model consisted of cardiac tissue, blood, and a non-irrigated electrode with a sensor embedded in its tip to maintain a specific target electrode temperature. Computer simulations were conducted by varying the tissue characteristics. Lesion depth was estimated by the 50°C isotherm, while the denaturation time (TD) was taken as the time at which the 70°C isotherm reached a depth of 0.75 mm (which corresponds to the optical depth reached by PS-OCR technology). RESULTS: A strong correlation (R2 > 0.83) was found between TD and lesion depth and an even stronger correlation (R2 > 0.96) was found between TD and the time required to achieve a specific lesion depth. For instance, the ablation time required to ensure a minimum lesion depth of 3 mm was 1.33 × TD + 3.93 × seconds. CONCLUSIONS: The computer results confirmed the strong relationship between denaturation time and lesion depth and suggest that measuring denaturation time by PS-OCR could provide information on the ablation time required to reach a specific lesion depth. Lasers Surg. Med. 50:222-229, 2018. © 2017 Wiley Periodicals, Inc.

Thermal and elastic response of subcutaneous tissue with different fibrous septa architectures to RF heating: numerical study.

BACKGROUND AND OBJECTIVE: Radiofrequency currents are commonly used in dermatology to treat cutaneous and subcutaneous tissues by heating. The subcutaneous morphology of tissue consists of a fine, collagenous and fibrous septa network enveloping clusters of adipocyte cells. The architecture of this network, namely density and orientation of septa, varies among patients and, furthermore, it correlates with cellulite grading. In this work we study the effect of two clinically relevant fibrous septa architectures on the thermal and elastic response of subcutaneous tissue to the same RF treatment; in particular, we evaluate the thermal damage and thermal stress induced to an intermediate- and a high-density fibrous septa network architecture that correspond to clinical morphologies of 2.5 and 0 cellulite grading, respectively. STUDY DESIGN/MATERIALS AND METHODS: We used the finite element method to assess the electric, thermal and elastic response of a two-dimensional model of skin, subcutaneous tissue and muscle subjected to a relatively long, constant, low-power RF treatment. The subcutaneous tissue is constituted by an interconnected architecture of fibrous septa and fat lobules obtained by processing micro-MRI sagittal images of hypodermis. As comparison criteria for the RF treatment of the two septa architectures, we calculated the accumulated thermal damage that corresponds to 63% loss in cell viability. RESULTS: Electric currents preferentially circulated through the fibrous septa in the subcutaneous tissue. However, the intensity of the electric field was higher within the fat because it is a poor electric conductor. The power absorption in the fibrous septa relative to that in the fat varied with septum orientation: it was higher in septa with vertical orientation and lower in septa with horizontal orientation. Overall, maximum values of electric field intensity, power absorption and temperature were similar for both fibrous septa architectures. However, the high-density septa architecture (cellulite grade 0) had a more uniform and broader spatial distribution of power absorption, resulting in a larger cross-sectional area of thermal damage (≈1.5 times more). Volumetric strains (expansion and contraction) were small and similar for both network architectures. During the first seconds of RF exposure, the fibrous septa were subjected to thermal expansion regardless of orientation. In the long term, the fibrous septa contracted due to the thermal expansion of fat. Skin and muscle were subjected to significantly higher Von Mises stresses (measure of yield) or distortion energy than the subcutaneous tissue. CONCLUSION: The distribution of electric currents within subcutaneous tissues depends on tissue morphology. The electric field is more intense in septum oriented along the skin to muscle (top to bottom) direction, creating lines or planes of preferential heating. It follows that the more septum available for preferential heating, the larger the extent of volumetric RF-heating and thermal damage to the subcutaneous tissue. Thermal load alone, imposed by long-exposure to heating up to 50 °C, results in small volumetric expansion and contraction in the subcutaneous tissue. The subcutaneous tissue is significantly less prone to non-reversible deformation by a thermal load than the skin and muscle.

Radiofrequency cardiac ablation with catheters placed on opposing sides of the ventricular wall: computer modelling comparing bipolar and unipolar modes.

PURPOSE: The aim of this study was to compare the efficacy of bipolar (BM) vs. unipolar (UM) mode of radiofrequency ablation (RFA) in terms of creating transmural lesions across the interventricular septum (IVS) and ventricular free wall (VFW). MATERIALS AND METHODS: We built computational models to study the temperature distributions and lesion dimensions created by BM and UM on IVS and VFW during RFA. Two different UM types were considered: sequential (SeUM) and simultaneous (SiUM). The effect of ventricular wall thickness, catheter misalignment, epicardial fat, and presence of air in the epicardial space were also studied. RESULTS: Regarding IVS ablation, BM created transmural and symmetrical lesions for wall thicknesses up to 15 mm. SeUM and SiUM were not able to create transmural lesions with IVS thicknesses ≥12.5 and 15 mm, respectively. Lesions were asymmetrical only with SeUM. For VFW ablation, BM also created transmural lesions for wall thicknesses up to 15 mm. However, with SeUM and SiUM transmurality was obtained for VFW thicknesses ≤7.5 and 12.5 mm, respectively. With the three modes, VFW lesions were always asymmetrical. In the scenario with air or a fat tissue layer on the epicardial side, only SiUM was capable of creating transmural lesions. Overall, BM was superior to UM in IVS and VFW ablation when the catheters were not aligned. CONCLUSIONS: Our findings suggest that BM is more effective than UM in achieving transmurality across both ventricular sites, except in the situation of the epicardial catheter tip surrounded by air or placed over a fat tissue layer.

Difference between endocardial and epicardial application of pulsed fields for targeting Epicardial Ganglia: An in-silico modelling study.

BACKGROUND: Pulsed Field Ablation (PFA) has recently been proposed as a non-thermal energy to treat atrial fibrillation by selective ablation of ganglionated plexi (GP) embedded in epicardial fat. While some of PFA-technologies use an endocardial approach, others use epicardial access with promising pre-clinical results. However, as each technology uses a different and sometimes proprietary pulse application protocol, the comparation between endocardial vs. epicardial approach is almost impossible in experimental terms. For this reason, our study, based on a computational model, allows a direct comparison of electric field distribution and thermal-side effects of both approaches under equal conditions in terms of electrode design, pulse protocol and anatomical characteristics of the tissues involved. METHODS: 2D computational models with axial symmetry were built for endocardial and epicardial approaches. Atrial (1.5-2.5 mm) and fat (1-5 mm) thicknesses were varied to simulate a representative sample of what happens during PFA ablation for different applied voltage values (1000, 1500 and 2000 V) and number of pulses (30 and 50). RESULTS: The epicardial approach was superior for capturing greater volumes of fat when the applied voltage was increased: 231 mm3/kV with the epicardial approach vs. 182 mm3/kV with the endocardial approach. In relation to collateral damage to the myocardium, the epicardial approach considerably spares the myocardium, unlike what happens with the endocardial approach. Although the epicardial approach caused much more thermal damage in the fat, there is not a significant difference between the approaches in terms of size of thermal damage in the myocardium. CONCLUSIONS: Our results suggest that epicardial PFA ablation of GPs is more effective than an endocardial approach. The proximity and directionality of the electric field deposited using an epicardial approach are key to ensuring that higher electric field strengths and increased temperatures are obtained within the epicardial fat, thus contributing to selective ablation of the GPs with minimal myocardial damage.

Ablation catheter-induced mechanical deformation in myocardium: computer modeling and ex vivo experiments.

Cardiac catheter ablation requires an adequate contact between myocardium and catheter tip. Our aim was to quantify the relationship between the contact force (CF) and the resulting mechanical deformation induced by the catheter tip using an ex vivo model and computational modeling. The catheter tip was inserted perpendicularly into porcine heart samples. CF values ranged from 10 to 80 g. The computer model was built to simulate the same experimental conditions, and it considered a 3-parameter Mooney-Rivlin model based on hyper-elastic material. We found a strong correlation between the CF and insertion depth (ID) (R2 = 0.96, P < 0.001), from 0.7 ± 0.3 mm at 10 g to 6.9 ± 0.1 mm at 80 g. Since the surface deformation was asymmetrical, two transversal diameters (minor and major) were identified. Both diameters were strongly correlated with CF (R2 ≥ 0.95), from 4.0 ± 0.4 mm at 20 g to 10.3 ± 0.0 mm at 80 g (minor), and from 6.4 ± 0.7 mm at 20 g to 16.7 ± 0.1 mm at 80 g (major). An optimal fit between computer and experimental results was achieved, with a prediction error of 0.74 and 0.86 mm for insertion depth and mean surface diameter, respectively.

Particle swarm optimization solution for roll-off control in radiofrequency ablation of liver tumors: Optimal search for PID controller tuning.

The study investigates the efficacy of a bioinspired Particle Swarm Optimization (PSO) approach for PID controller tuning in Radiofrequency Ablation (RFA) for liver tumors. Ex-vivo experiments were conducted, yielding a 9th order continuous-time transfer function. PSO was applied to optimize PID parameters, achieving outstanding simulation results: 0.605% overshoot, 0.314 seconds rise time, and 2.87 seconds settling time for a unit step input. Statistical analysis of 19 simulations revealed PID gains: Kp (mean: 5.86, variance: 4.22, standard deviation: 2.05), Ki (mean: 9.89, variance: 0.048, standard deviation: 0.22), Kd (mean: 0.57, variance: 0.021, standard deviation: 0.14) and ANOVA analysis for the 19 experiments yielded a p-value ≪ 0.05. The bioinspired PSO-based PID controller demonstrated remarkable potential in mitigating roll-off effects during RFA, reducing the risk of incomplete tumor ablation. These findings have significant implications for improving clinical outcomes in hepatocellular carcinoma management, including reduced recurrence rates and minimized collateral damage. The PSO-based PID tuning strategy offers a practical solution to enhance RFA effectiveness, contributing to the advancement of radiofrequency ablation techniques.

Mechanisms of action behind the protective effects of proactive esophageal cooling during radiofrequency catheter ablation in the left atrium.

Proactive esophageal cooling for the purpose of reducing the likelihood of ablation-related esophageal injury resulting from radiofrequency (RF) cardiac ablation procedures is increasingly being used and has been Food and Drug Administration cleared as a protective strategy during left atrial RF ablation for the treatment of atrial fibrillation. In this review, we examine the evidence supporting the use of proactive esophageal cooling and the potential mechanisms of action that reduce the likelihood of atrioesophageal fistula (AEF) formation. Although the pathophysiology behind AEF formation after thermal injury from RF ablation is not well studied, a robust literature on fistula formation in other conditions (eg, Crohn disease, cancer, and trauma) exists and the relationship to AEF formation is investigated in this review. Likewise, we examine the abundant data in the surgical literature on burn and thermal injury progression as well as the acute and chronic mitigating effects of cooling. We discuss the relationship of these data and maladaptive healing mechanisms to the well-recognized postablation pathophysiological effects after RF ablation. Finally, we review additional important considerations such as patient selection, clinical workflow, and implementation strategies for proactive esophageal cooling.

How intramyocardial fat can alter the electric field distribution during Pulsed Field Ablation (PFA): Qualitative findings from computer modeling.

Even though the preliminary experimental data suggests that cardiac Pulsed Field Ablation (PFA) could be superior to radiofrequency ablation (RFA) in terms of being able to ablate the viable myocardium separated from the catheter by collagen and fat, as yet there is no formal physical-based analysis that describes the process by which fat can affect the electric field distribution. Our objective was thus to determine the electrical impact of intramyocardial fat during PFA by means of computer modeling. Computer models were built considering a PFA 3.5-mm blunt-tip catheter in contact with a 7-mm ventricular wall (with and without a scar) and a 2-mm epicardial fat layer. High voltage was set to obtain delivered currents of 19, 22 and 25 A. An electric field value of 1000 V/cm was considered as the lethal threshold. We found that the presence of fibrotic tissue in the scar seems to have a similar impact on the electric field distribution and lesion size to that of healthy myocardium only. However, intramyocardial fat considerably alters the electrical field distribution and the resulting lesion shape. The electric field tends to peak in zones with fat, even away from the ablation electrode, so that 'cold points' (i.e. low electric fields) appear around the fat at the current entry and exit points, while 'hot points' (high electric fields) occur in the lateral areas of the fat zones. The results show that intramyocardial fat can alter the electric field distribution and lesion size during PFA due to its much lower electrical conductivity than that of myocardium and fibrotic tissue.

Low-energy (360 J) radiofrequency catheter ablation using moderate power - short duration: proof of concept based on in silico modeling.

BACKGROUND: Pilot clinical studies suggest that very high power-very short duration (vHPvSD, 90 W/4 s, 360 J energy) is a feasible and safe technique for ablation of atrial fibrillation (AF), compared with standard applications using moderate power-moderate duration (30 W/30 s, 900 J energy). However, it is unclear whether alternate power and duration settings for the delivery of the same total energy would result in similar lesion formation. This study compares temperature dynamics and lesion size at different power-duration settings for the delivery of equivalent total energy (360 J). METHODS: An in silico model of radiofrequency (RF) ablation was created using the Arrhenius function to estimate lesion size under different power-duration settings with energy balanced at 360 J: 30 W/12 s (MPSD), 50 W/7.2 s (HPSD), and 90 W/4 s (vHPvSD). Three catheter orientations were considered: parallel, 45°, and perpendicular. RESULTS: In homogenous tissue, vHPvSD and HPSD produced similar size lesions independent of catheter orientation, both of which were slightly larger than MPSD (lesion size 0.1 mm deeper, ~ 0.7 mm wider, and ~ 25 mm3 larger volume). When considering heterogeneous tissue, these differences were smaller. Tissue reached higher absolute temperature with vHPvSD and HPSD (5-8 °C higher), which might increase risk of collateral tissue injury or steam pops. CONCLUSION: Ablation for AF using MPSD or HPSD may be a feasible alternative to vHPvSD ablation given similar size lesions with similar total energy delivery (360 J). Lower absolute tissue temperature and slower heating may reduce risk of collateral tissue injury and steam pops associated with vHPvSD and longer applications using moderate power.