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Radiofrequency cardiac ablation (RFCA) consists of introducing an intravascular catheter until it reaches the target site. RF power is then applied through a metal electrode at the catheter tip (active electrode). RF current circulates between the active electrode and a large dispersive electrode on the patient's skin, causing the irreversible thermal destruction of the cells causing the arrhythmia or blocking the conduction of action potentials associated with arrhythmia (in case of linear lesions in the atrial fibrillation ablation).
Source publication
This review begins with a rationale of the importance of theoretical, mathematical and computational models for radiofrequency (RF) catheter ablation (RFCA). We then describe the historical context in which each model was developed, its contribution to the knowledge of the physics of RFCA and its implications for clinical practice. Next, we review...
Context in source publication
Context 1
... (RF) catheter ablation (RFCA), also known as RF cardiac ablation, is a minimally invasive procedure that can cure cardiac arrhythmias by using RF electrical energy to cause irreversible thermal destruction of the arrhythmia focus or create linear lesions to block the conduction of action potentials associated with arrhythmia. Fig. 1 shows the overall scenario during RFCA, when an intravascular catheter is introduced until it reaches the target site in the heart. Once there, RF power is applied through a metal electrode at the catheter tip (active electrode). RF current circulates between the active electrode and a large dispersive electrode on the patient's skin ...
Citations
... The controller takes the error as input and modulates an output voltage (in volts) applied between the active electrodes and the ground terminal using PID actions. Generally, the control loop is composed of two parts, in terms of TF relating the input and output signals: the controller itself, given in (7), and the system plant, given in (16). The plant is obtained from the SI and has the voltage modulated by the controller as input and the tissue impedance as output: ...
... The step response exhibits a rise time of 0.0364 s, a peak amplitude of 33.6, a settling time of 15.2 s, and a final value of 1.61. From the characteristic equation in (16), it can be observed that the system has nine poles in the left-half plane of the complex plane, indicating stability. However, dominant complex conjugate poles close to the imaginary axis are present. ...
... The performance of the PID controller was estimated using the PSO algorithm, and the results are shown in Fig 10 and Table 3. Points A, B and C in the step response graph indicate the rise time, overshoot and settling time, respectively. The step response illustrate the behavior of the PID controller described in (7), applied to the plant described in (16). ...
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.
... Another approach uses a two-state Arrhenius model [20,26] to model the transition of the cells from native to denaturated state. Despite being widely used, in particular in RFA [6], it is well known that this model greatly overpredicts the shoulder region at low temperatures, where the dynamics of the thermal damage are slower [14,17,20]. This shortcoming is particularly relevant for thermal damage of myocytes, since it is known that at 48 • C the damage is reversible for all treatment times [35], while irreversible damage is expected between 50 and 56 • C for up to 60 s of ablation [9]. ...
Objective.
Thermal cellular injury follows complex dynamics and subcellular processes can heal the inflicted damage if insufficient heat is administered during the procedure. This work aims to the identification of irreversible cardiac tissue damage for predicting the success of thermal treatments.
Approach.
Several approaches exist in the literature, but they are unable to capture the healing process and the variable energy absorption rate that several cells display. Moreover, none of the existing models is calibrated for cardiomyocytes. We consider a three-state cell death model capable of capturing the reversible damage of a cell, we modify it to include a variable energy absorption rate and we calibrate it for cardiac myocytes.
Main results.
We show how the thermal damage predicted by the model response is in accordance with available data in the literature on myocytes for different temperature distributions. When coupled with a computational model of radiofrequency catheter ablation, the model predicts lesions in agreement with experimental measurements. We also present additional experiments (repeated ablations and catheter movement) to further illustrate the potential of the model.
Significance.
We calibrated a three-state cell death model to provide physiological results for cardiac myocytes. The model can be coupled with ablation models and reliably predict lesion sizes comparable to experimental measurements. Such approach is robust for repeated ablations and dynamic catheter-cardiac wall interaction, and allows for tissue remodeling in the predicted damaged area, leading to more accurate in-silico predictions of ablation outcomes.
... Although it is generally accepted that tissue temperatures !50 C in RFCA cause irreversible thermal injury [2], it is also known that hyperthermia-induced thermal damage is dependent not only on temperature but also on exposure time [1]. Both the 50 C isotherm and the damage index X have traditionally been used to estimate lesion size in computer modeling of RFCA [3]. The goal of RFCA is to eliminate the focus of the arrhythmia, i.e., the group of cells involved in the irregular heartbeat. ...
... While all the previous RFCA computer models focused on assessing the temperature distributions and predicting lesion size [3], no previous computational or experimental study has so far focused on estimating the area of tissue subjected to sublethal heating capable of causing transient electrophysiological changes. Despite the limitations inherent in computational models, an initial estimation is certainly relevant scientific information with practical clinical implications. ...
... Most RFCA studies that used computer modeling have estimated the lesion zone using either a lethal isotherm (50-55 C) or a mathematical function to take the 'thermal history' at each point in the tissue into account [3]. The most frequently used function models the tissue damage as an irreversible first-order chemical reaction, with the rate constant following the Arrhenius relationship [7], specifically, with the thermal injury index X, which relates the number of undamaged cells C(0) present before heating to the number of undamaged cells remaining at time t, indicated by C(t) as follows: ...
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.
... The metabolic heat is negligible compared to the energy dissipation and was hence ignored [36]. The perfusion heat was given by: ...
Background
Proactive cooling with a novel cooling device has been shown to reduce endoscopically identified thermal injury during radiofrequency (RF) ablation for the treatment of atrial fibrillation using medium power settings. We aimed to evaluate the effects of proactive cooling during high-power short-duration (HPSD) ablation.
Methods
A computer model accounting for the left atrium (1.5 mm thickness) and esophagus including the active cooling device was created. We used the Arrhenius equation to estimate the esophageal thermal damage during 50 W/ 10 s and 90 W/ 4 s RF ablations.
Results
With proactive esophageal cooling in place, temperatures in the esophageal tissue were significantly reduced from control conditions without cooling, and the resulting percentage of damage to the esophageal wall was reduced around 50%, restricting damage to the epi-esophageal region and consequently sparing the remainder of the esophageal tissue, including the mucosal surface. Lesions in the atrial wall remained transmural despite cooling, and maximum width barely changed (<0.8 mm).
Conclusions
Proactive esophageal cooling significantly reduces temperatures and the resulting fraction of damage in the esophagus during HPSD ablation. These findings offer a mechanistic rationale explaining the high degree of safety encountered to date using proactive esophageal cooling, and further underscore the fact that temperature monitoring is inadequate to avoid thermal damage to the esophagus.
... During this treatment, cardiac tissue that allows the transmission of abnormal electrical signals in the heart which can lead to AF is thermally damaged by delivering a radiofrequency (RF) current using a percutaneous ablation catheter [3]. Computer models are now being widely used to analyze and understand the characteristics of heat transfer and lesion formation during RFCA, which facilitate the fundamental contribution of AF treatment [4,5]. In addition to the essential electrical and thermal problems requiring solutions for modeling ablation procedures, solving the cooling effect experienced by the cardiac tissue and electrode through blood flow is also required for the simulation of RFCA. ...
Background
Highly consistent cardiac ablation outcomes through radiofrequency catheter ablation (RFCA) under pulsatile and constant flow profiles (PP&CP) of intracardiac blood were previously indicated by computer modeling, with simplified geometry and lossless receipt of inflow for ablation catheters. This study aimed to further investigate the effects of intracardiac blood pulsatility in an anatomy-based atrium model.
Methods
Four pulmonary veins were blood inflows at 10 mm Hg. The mitral valve was the outflow, with PP based on pulsatile velocity curve from clinical measurements, and CP was obtained by averaging the velocity curve under PP over an ablation time of 30 s. A numerical comparison between ablation results under PP and CP, without experimental validation, was performed.
Results
Temperature fluctuations persisted in mid-myocardium, and most clearly in blood and endocardium under PP. At a constant power of 20 W, marked differences in ablation outcome between PP and CP occurred in the middle of unilateral pulmonary veins and the posterior wall of the left atrium (LA) where the blood velocities were significantly decreased under CP. The mid-myocardial, blood and endocardial temperatures, as well as the effective lesion volume at the former position, were decreased by 4.1%, 15%, 13.6%, and 13.8%, respectively under PP. The extents for the latter position were 11%, 22%, 22.5%, and 55.6%, respectively.
Conclusion
Intracardiac flow pulsatility causes a greater reduction in blood and endocardial temperatures at ablation sites away from the main bloodstream, effective cooling of which is more likely to rely on blood velocities approaching peak PP values.
... Our objective was to use in-silico modeling to study temperature distribution and lesion size during two repeated applications of RF power on the same site, determine the role of the interval between RF pulses, and provide a physical explanation of the phenomena involved. In-silico modeling has demonstrated to be a fine tool to study RF ablation in different medical fields, such as tumor [5] and cardiac ablation [6] . ...
... About model validation, i.e. the process of determining if a mathematical model of a physical event represents the actual physical event with sufficient accuracy [23] , we have to emphasize that we used a numerical model broadly used in past modeling studies and validated in different occasions (such as in [15] ), providing prediction errors around 3 − 7 ºC and 1 − 2 mm for tissue temperature and lesion size, respectively [6] . In fact, no new features were incorporated in our study in terms of geometry, governing equations, boundary conditions and output variables. ...
Background and objectives
To study temperature distribution and lesion size during two repeated radiofrequency (RF) pulses applied at the same point in the context of RF cardiac ablation (RFCA).
Methods
An in-silico RFCA model accounting for reversible and irreversible changes in myocardium electrical properties due to RF-induced heating. Arrhenius damage model to estimate lesion size during the application of two 20 W pulses at intervals (INT) of from 5 to 70 s. We considered two pulse durations: 20 s and 30 s.
Results
INT has a significant effect on lesion size and maximum tissue temperature (TMAX). The shorter the INT the greater the increase in lesion size after the second pulse but also the greater the TMAX. If the second pulse is applied almost immediately (INT=5 s), depth increases 1.4 mm and 1.5 mm for pulses of 20 s and 30 s, respectively. If INT is longer than 30 s it increases 1.1 mm and 1.3 mm for pulses of 20 s and 30 s, respectively. While a single 20 s pulse causes TMAX=79 ºC, a second pulse produces values of from 92 and 96 ºC (the higher the temperature the shorter the INT). For 30 s pulses, TMAX=93 ºC for a single pulse, and varied from 98 to 104 ºC for a second pulse.
Conclusions
Applying a second RF pulse at the same ablation site increases lesion depth by 1−1.5 mm more than a single pulse and could lead to higher temperatures (up to 17 ºC). Both lesion depth and maximum tissue temperature increased at shorter inter-pulse intervals, which could cause clinical complications from overheating such as steam pops.
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.
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.
Radiofrequency ablation is a nominally invasive technique to eradicate cancerous or non-cancerous cells by heating. However, it is still hampered to acquire a successful cell destruction process due to inappropriate RF intensities that will not entirely obliterate tumorous tissues, causing in treatment failure. In this study, we are acquainted with a nanoassisted RF ablation procedure of cardiac tumor to provide better outcomes for long-term survival rate without any recurrences. A three-dimensional thermo-electric energy model is employed to investigate nanothermal field and ablation efficiency into the left atrium tumor. The cell death model is adopted to quantify the degree of tissue injury while injecting the Fe3O4 nanoparticles concentrations up to 20% into the target tissue. The results reveal that when nanothermal field extents as a function of tissue depth (10 mm) from the electrode tip, the increasing thermal rates were approximately 0.54362%, 3.17039%, and 7.27397% for the particle concentration levels of 7%, 10%, and 15% compared with no-particle case. In the 7% Fe3O4 nanoparticles, 100% fractional damage index is achieved after ablation time of 18 s whereas tissue annihilation approach proceeds longer to complete for no-particle case. The outcomes indicate that injecting nanoparticles may lessen ablation time in surgeries and prevent damage to adjacent healthy tissue.
