Maximum Tissue Temperature Research Articles

Abstract 15220: The Thermal Characteristics to Phrenic and Esophageal Injuries During Ablation of QDOTMICRO (50w-Qmode and 90w/4sec-Qmode+) vs 50w-TactiCath SE vs 50w-Thermocool Smart Touch: Findings From an In-Vivo Porcine Study

Introduction: Recently, there have been numerous strategies for treating atrial fibrillation, including the choice of catheters However, the thermal characteristics of each catheter, particularly in terms of safety, have not been fully understood. Hypothesis: Our aim was to characterize the thermal damage to collateral tissues during 50W-HPSD ablation and 90W/4sec-vHPSD ablation using three different ablation catheters. Methods: In 28 pigs, we implanted thermocouples on the superior vena cava, close to the phrenic nerve, and on the esophageal, close to the inferior vena cava. We performed endocardial ablation near the fiducial markers of the thermocouples using three different RF catheters: ablation index (AI)-guided HPSD (Qmode) and vHPSD ablation (Qmode+) with QDOTMICRO, lesion size index-guided HPSD ablation (targeting 5.0) with TactiCath Sensor Enabled (Tacti), and AI-guided HPSD ablation (targeting 400) with Thermocool Smart Touch (STSF). We measured tissue temperatures during ablation, including maximum tissue temperature (Tmax), time to maximum tissue temperature (t-Tmax), time to achieve a lethal temperature of 50°C (t-50°C), and time to return to baseline from Tmax (t-Tbase). Results: In terms of the frequency of esophageal injury, there were no significant differences among the different catheters. However, the depth of esophageal injury from the adventitia showed a significant difference. In terms of phrenic nerve injury, Tacti had the highest frequency compared to the other catheters (100%, p=0.0012). Tmax, t-Tmax, t-50°C, and t-Tbase showed significant differences, as shown in figure. Conclusions: The thermal effects on collateral tissues differ among the three different catheters and settings. STSF and Qmode result in a gradual increase in tissue temperature, while Tacti and Qmode+ lead to a rapid temperature increase. These distinct thermal distributions may contribute to the risk of phrenic nerve and esophageal injuries.

Characteristics of tissue temperature during ablation with THERMOCOOL SMARTTOUCH SF versus TactiCath versus QDOT MICRO catheters (Qmode and Qmode+): An in vivo porcine study.

High-power short-duration (HPSD) ablation at 50 W, guided by ablation index (AI) or lesion size index (LSI), and a 90 W/4 s very HSPD (vHPSD) setting are available for atrial fibrillation (AF) treatment. Yet, tissue temperatures during ablation with different catheters around venoatrial junction and collateral tissues remain unclear. In this porcine study, we surgically implanted thermocouples on the epicardium near the superior vena cava (SVC), right pulmonary vein, and esophagus close to the inferior vena cava. We then compared tissue temperatures during 50W-HPSD guided by AI 400 or LSI 5.0, and 90 W/4 s-vHPSD ablation using THERMOCOOL SMARTTOUCH SF (STSF), TactiCath ablation catheter, sensor enabled (TacthCath), and QDOT MICRO (Qmode and Qmode+ settings) catheters. STSF produced the highest maximum tissue temperature (Tmax ), followed by TactiCath, and QDOT MICRO in Qmode and Qmode+ (62.7 ± 12.5°C, 58.0 ± 10.1°C, 50.0 ± 12.1°C, and 49.2 ± 8.4°C, respectively; p = .005), achieving effective transmural lesions. Time to lethal tissue temperature ≥50°C (t-T ≥ 50°C) was fastest in Qmode+, followed by TacthCath, STSF, and Qmode (4.3 ± 2.5, 6.4 ± 1.9, 7.1 ± 2.8, and 7.7 ± 3.1 s, respectively; p < .001). The catheter tip-to-thermocouple distance for lethal temperature (indicating lesion depth) from receiver operating characteristic curve analysis was deepest in STSF at 5.2 mm, followed by Qmode at 4.3 mm, Qmode+ at 3.1 mm, and TactiCath at 2.8 mm. Ablation at the SVC near the phrenic nerve led to sudden injury at t-T ≥ 50°C in all four settings. The esophageal adventitia injury was least deep with Qmode+ ablation (0.4 ± 0.1 vs. 0.8 ± 0.4 mm for Qmode, 0.9 ± 0.3 mm for TactiCath, and 1.1 ± 0.5 mm for STSF, respectively; p = .005), correlating with Tmax . This study revealed distinct tissue temperature patterns during HSPD and vHPSD ablations with the three catheters, affecting lesion effectiveness and collateral damage based on Tmax and/or t-T ≥ 50°C. These findings provide key insights into the safety and efficacy of AF ablation with these four settings.

Tissue poromechanical deformation effects on steam pop likelihood in 3-D radiofrequency cardiac ablation

Radiofrequency Cardiac Ablation (RFCA) is a common procedure that heats cardiac tissue to destroy abnormal signal pathways to eliminate arrhythmias. The complex multiphysics phenomena during this procedure need to be better understood to improve both procedure and device design. A deformable poromechanical model of cardiac tissue was developed that coupled joule heating from the electrode, heat transfer, and blood flow from normal perfusion and thermally driven natural convection, which mimics the real tissue structure more closely and provides more realistic results compared to previous models. The expansion of tissue from temperature rise reduces blood velocity, leading to increased tissue temperature, thus affecting steam pop occurrence. Detailed temperature velocity, and thermal expansion of the tissue provided a comprehensive picture of the process. Poromechanical expansion of the tissue from temperature rise reduces blood velocity, increasing tissue temperature. Tissue properties influence temperatures, with lower porosity increasing the temperatures slightly, due to lower velocities. Deeper electrode insertion raises temperature due to increased current flow. The results demonstrate that a 5% increase in porosity leads to a considerable 10% increase in maximum tissue temperature. These insights should greatly help in avoiding undesirable heating effects that can lead to steam pop and in designing improved electrodes.

In-silico investigation of intratumoural magnetic hyperthermia for breast cancer therapy using FePt or FeCrNbB magnetic nanoparticles

In this work, we conduct a numerical study on magnetic nanoparticle hyperthermia for the treatment of a breast tumour. The geometry of the problem is comprised of a deformed ellipsoidal tumour region, a healthy glandular tissue region, a fat tissue layer and a skin tissue layer. An aqueous suspension of magnetic nanoparticles (FeCrNbB or FePt) is directly injected into the breast tumour using a syringe. The perfusion of blood through the tissue regions is modelled using the Darcy-Brinkman-Forchheimer equation, and the shear-thinning behaviour of blood is described by the Carreau–Yasuda model. The transport and deposition of nanoparticles within the tissues, the temperature distribution during therapy, and the survival rates of healthy cells and cancer cells are also considered. The governing equations with their associated initial and boundary conditions are solved using the finite element method, and the solution algorithm developed in FreeFEM++ was validated against results from the existing literature. Subsequently, the influence of the nanoparticle solid volume fraction, injection time, and magnetic field amplitude and oscillation frequency on the velocity, temperature, nanoparticle concentration distribution, duration required for effective hyperthermia, and thermal damage to healthy tissues was examined. The numerical results reveal that the cell damage is greater in skin tissue than the healthy gland and fat tissues. For small injection time (tinj=0.4), the healthy gland tissue damage is greater for FePt nanoparticles than FeCrNbB nanoparticles. However, this trend is reversed for larger injection times (tinj=0.5, 0.6). For small magnetic field frequency (ω=5×104, 105), the maximum tissue temperature is higher with FePt nanoparticles than FeCrNbB nanoparticles, but a reversal in trend occurs for larger values of ω (ω=2×105). The findings show that the time duration required for effective magnetic hyperthermia and thermal damage to the healthy tissue regions is reduced with increased injected nanoparticle volume fraction, duration of nanoparticle injection, and the amplitude and frequency of the alternating magnetic field. Moreover, the effective hyperthermia duration and the healthy tissue damage are less for FePt nanoparticles than FeCrNbB nanoparticles.

Preclinical Assessment of Tissue Effects by Gastrointestinal Endoscope Tip Temperature

Endoscope tips are heated by their electrical and illuminating components. During the procedure, they might get in close or even direct contact with intestinal tissues. To assess endoscope tip and tissue temperature as well as histopathologic changes of gastrointestinal (GI) tissues when exposed to the heated tip of GI endoscopes. The endoscope tip temperatures of four GI endoscopes were measured for 30 minutes in a temperature-controlled chamber. The temperature of ex vivo porcine GI tissues was measured for 5-, 15-, and 120-minute exposure to endoscope tips within a climate chamber to control environmental factors (simulation of fever as worst-case). Exposed tissues were histopathologically examined afterward. Control samples included untreated mucosa, tissue samples exposed to endoscope tips for 120 minutes, as well as tissue samples thermally coagulated with a bipolar high-frequency probe. Actual endoscope tip temperatures of 59 to 86°C, dependent on the endoscope type, were measured. After 10 to 15 minutes, the maximum temperatures were reached. Maximum tissue temperatures of 44 to 46°C for 5 and 15 minutes, as well as up to 50°C for 120 minutes, were recorded dependent on tissue and endoscope type. No direct heat-induced histopathologic tissue alterations were observed in the 5- and 15-minute samples. Both clinically relevant and a worst-case control were tested. Even though elevated temperatures were recorded, no heat-related tissue alterations were detected. This overall supports the safety profile of GI endoscopy; however, the study findings are limited by the ex vivo setting (no metabolic tissue alterations accessible, no blood flow) and small sample number.

In vivo tissue temperatures during 90 W/4 sec-very high power-short-duration (vHPSD) ablation versus ablation index-guided 50 W-HPSD ablation: A porcine study.

Neither the actual in vivo tissue temperatures reached with 90 W/4 s-very high-power short-duration (vHPSD) ablation for atrial fibrillation nor the safety and efficacy profile have been fully elucidated. We conducted a porcine study (n = 15) in which, after right thoracotomy, we implanted 6-8thermocouples epicardially in the superior vena cava, right pulmonary vein, and esophagus close to the inferior vena cava. We compared tissue temperatures close to a QDOT MICRO catheter, between during 90 W/4 s-vHPSD ablation during ablation index (AI: target 400)-guided 50 W-HPSD ablation, both targeting a contact force of 8-15 g. Maximum tissue temperature reached during 90 W/4 s-vHPSD ablation did not differ significantly from that during 50 W-HPSD ablation (49.2 ± 8.4°C vs. 50.0 ± 12.1°C; p = .69) and correlated inversely with distance between the catheter tip and the thermocouple, regardless of the power settings (r = -0.52 and r = -0.37). Lethal temperature (≥50°C) was best predicted at a catheter tip-to-thermocouple distance cut-point of 3.13 and 4.27 mm, respectively. All lesions produced by 90 W/4 s-vHPSD or 50 W-HPSD ablation were transmural. Although there was no difference in the esophageal injury rate (50% vs. 66%, p = .80), the thermal lesion was significantly shallower with 90 W/4 s-vHPSD ablation than with 50W-HPSD ablation (381.3 ± 127.3 vs. 820.0 ± 426.1 μm from the esophageal adventitia; p = .039). Actual tissue temperatures reached with 90 W/4 s-vHPSD ablation appear similar to those with AI-guided 50 W-HPSD ablation, with the distance between the catheter tip and target tissue being shorter for the former. Although both ablation settings may create transmural lesions in thin atrial tissues, any resulting esophageal thermal lesions appear shallower with 90 W/4 s-vHPSD ablation.

Analytical and numerical analysis of the dual-pulse lag heat transfer in a three-dimensional tissue subjected to a moving multi-point laser beam

An extensive algorithm based on both analytical and numerical solution methodologies is proposed to obtain transient temperature distributions in a three-dimensional living tissue subjected to a moving single-point and multi-point laser beam by considering metabolic heat generation and blood perfusion rate. Here, the dual-phase lag/Pennes equation is analytically solved by using the method of Fourier series and the Laplace transform. The ability to model single-point or multi-point laser beams as an arbitrary function of place and time is a significant advantage of the proposed analytical approach, which can be used to solve similar heat transfer problems in other living tissues. Besides, the related heat conduction problem is numerically solved based on the finite element method. The effects of laser beam transitional speed, laser power, and the number of laser points on the temperature distribution within the skin tissue are investigated. Moreover, the temperature distribution predicted by the dual-phase lag model is compared with that of the Pennes model under different working conditions. For the studied cases, it is observed that the maximum tissue temperature decreased about 63% by an increase of 6mm/s in the speed of the laser beam. An increase in the laser power from 0.8W/cm3 to 1.2W/cm3 results in a 28 °C increase in the maximum temperature of the skin tissue. It is observed that the maximum temperature predicted by the dual-phase lag model is always lower than that of the Pennes model and the temperature variations over time are sharper, while their results are entirely consistent over the simulation time. The obtained numerical results indicated that the dual-phase lag model is preferred in heating processes occurring at short intervals. Among the investigated parameters, the laser beam speed has the most considerable effect on the difference between the results of the Pennes and the dual-phase lag models.

In vivo tissue temperatureduring lesion size index-guided 50W ablation versus 30W ablation: A porcine study.

Neither the actual in vivo tissue temperatures reached with lesion size index (LSI)-guided high-power short-duration (HPSD) ablation for atrial fibrillation nor the safety profile has been elucidated. We conducted a porcine study (n = 7) in which, after right thoracotomy, we implanted 6-8 thermocouples epicardially in the superior vena cava, right pulmonary vein, and esophagus close to the inferior vena cava. We compared tissue temperatures reached during 50 W-HPSD ablation with those reached during standard (30 W) ablation, both targeting anLSIof 5.0 (5-15 g contact force). Tmax (maximum tissue temperaturewhen the thermocouple was located ≤5 mm from the catheter tip)reached during HPSD ablation was modestly higher than that reached during standard ablation (58.0 ± 10.1°C vs. 53.6 ± 9.2°C; p = .14) and peak tissue temperature correlated inversely with the distance between the catheter tip and the thermocouple, regardless of the power settings (HPSD: r = -0.63; standard: r = -0.66). Lethal temperature (≥50°C) reached 6.3 ± 1.8 s and 16.9 ± 16.1 s after the start of HPSD and standard ablation, respectively (p = .002), and it was best predicted at a catheter tip-to-thermocouple distance cut point of 2.8 and 5.3 mm, respectively. All lesions produced by HPSD ablation and by standard ablation were transmural. There was no difference between HPSD ablation and standard ablation in the esophageal injury rate (70% vs. 75%, p = .81), but the maximum distance from the esophageal adventitia to the injury site tended to be shorter (0.94 ± 0.29 mm vs. 1.40 ± 0.57 mm, respectively; p = .09). Actual tissue temperatures reached with LSI-guided HPSD ablation appear to be modestly higher, with a shorter distance between the catheter tip and thermocouple achieving lethal temperature, than those reached with standard ablation. HPSD ablation lasting <6 s may help minimize lethal thermal injury to the esophagus lying at a close distance.

Computer simulations of consecutive radiofrequency pulses applied at the same point during cardiac catheter ablation: Implications for lesion size and risk of overheating

Background and objectivesTo 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). MethodsAn 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. ResultsINT 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 to 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. ConclusionsApplying 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.

Evaluation of linear lesion formation and thermodynamics by dragging ablation with the third-generation laser balloon.

BackgroundThe lesion formation properties of a motorized rotational delivery (RAPID) mode, third-generation laser balloon (LB3) ablation compared to point-by-point laser ablation in patients with atrial fibrillation remain unclear.ObjectiveThe purpose of this study was to assess lesion characteristics and thermodynamics in LB3 ablation with a RAPID mode in vitro model.MethodsChicken muscles were cauterized using LB3 in RAPID mode with 13 W and 15 W and 50% overlapped point-by-point fashion with 7 W/30 seconds, 8.5 W/20 seconds, 10 W/20 seconds, and 12 W/20 seconds. Lesion depth, width, and continuity were compared. Lesion continuity was classified by the visible gap degree categorized from 1 (perfect) to 3 (poor). Thermodynamics and maximum tissue temperatures were assessed under infrared thermographic monitoring. Fifteen and 5 lesions were evaluated per ablation protocol for measurement of lesion size and continuity and for thermographic assessment, respectively.ResultsLesion depth and width were smaller in RAPID mode laser ablation than point-by-point laser ablation (P <.001). However, RAPID mode laser ablation revealed sufficient mean lesion depth of 5 mm or more. Lesion continuity was 1 (perfect) in all samples in RAPID mode laser ablation and point-by-point laser ablation (P = 1). Infrared thermographic observation demonstrated fast and gapless linear lesion formation with thermal stacking in RAPID mode laser ablation. Maximum tissue temperature was lower in RAPID mode laser ablation than point-by-point laser ablation (P <.001).ConclusionRAPID mode LB3 ablation could provide fast, gapless, and acceptable lesion formation with thermal stacking and moderate tissue temperature rise.

Improved Oxygenation of Human Skin, Subcutis and Superficial Cancers Upon Mild Hyperthermia Delivered by WIRA-Irradiation.

Clinical trials have shown that mild hyperthermia (HT) serves as an adjunct to cancer treatments such as chemo- and radiotherapy. Recently, a high efficacy of mild HT immediately followed by hypofractionated radiotherapy (RT) in treatment of recurrent breast cancer has been documented if temperatures of 39-43°C are achieved for 40-60 min. In the present study, temperature and oxygenation profiles were measured in superficial tissues of healthy volunteers exposed to water-filtered infrared-A- (wIRA)- irradiation, to verify that adequate thermal doses together with the improved tumor oxygenation necessary for radiosensitisation are obtained. Experiments were performed using a wIRA-system equipped with two wIRA-radiators, each with a thermography camera for real-time monitoring of the skin surface temperature. Temperatures within the abdominal wall were measured with fibre optic sensors at defined tissue depths (subepidermal, and 1-20 mm inside the tissue). The corresponding tissue pO2 values were assessed with fluorometric microsensors. In selected situations, hyperspectral tissue imaging was used to visualise the oxygenation status of normal skin and superficial tumours in patients. Pre-treatment skin surface temperature was 34.6°C. Upon wIRA exposure, average skin surface temperatures reached 41.6°C within 5-12 min. Maximum tissue temperatures of 41.8°C were found at a tissue depth of 1mm, with a steady decline in deeper tissue layers (41.6°C @ 5mm, 40.8°C @ 10mm, 40.6°C @ 15mm, and 40.1°C @ 20mm). Effective HT levels ≥39°C were established in tissue depths up to 25 mm. Tissue heating was accompanied by a significant increase in tissue pO2 values [e.g., at a tissue depth of 13 mm mean pO2 rose from 46mmHg to 81mmHg (@ T=40.5°C). In the post-heating phase (+ 5min), pO2 was 79mmHg (@ T=38°C) and 15 min post-heat pO2 was 72mmHg (@ T=36.8°C)]. pO2 values remained elevated for 30-60 min post-heat. Non-invasive monitoring of normal skin and of recurrent breast cancers confirmed the improved O2 status by wIRA-HT. In conclusion, wIRA-irradiation enables effective tissue heating (T=39-43°C) associated with distinct increases in blood flow and pO2. These adjustments unequivocally meet the requirement for effective radiosensitisation.

Actual tissue temperature during ablation index-guided high-power short-duration ablation versus standard ablation: Implications in terms of the efficacy and safety of atrial fibrillation ablation.

Actual in vivo tissue temperatures and the safety profile during high-power short-duration (HPSD) ablation of atrial fibrillation have not been clarified. We conducted an animal study in which, after a right thoracotomy, we implanted 6-8 thermocouples epicardially in the superior vena cava, right pulmonary vein, and esophagus close to the inferior vena cava. We recorded tissue temperatures during a 50 W-HPSD ablation and 30 W-standard ablation targeting an ablation index (AI) of 400 (5-15 g contact force). Maximum tissue temperatures reached with HSPD ablation were significantly higher than that reached with standard ablation (62.7 ± 12.5 vs. 52.7 ± 11.4°C, p = 0.033) and correlated inversely with the distance between the catheter tip and thermocouple, regardless of the power settings (HPSD: r = -0.71; standard: r = -0.64). Achievement of lethal temperatures (≥50°C) was within 7.6 ± 3.6 and 12.1 ± 4.1 s after HPSD and standard ablation, respectively (p = 0.003), and was best predicted at cutoff points of 5.2 and 4.4 mm, respectively. All HPSD ablation lesions were transmural, but 19.2% of the standard ablation lesions were not (p = 0.011). There was no difference between HPSD and standard ablation regarding the esophageal injury rate (30% vs. 33.3%, p > 0.99), with the injury appearing to be related to the short distance from the catheter tip. Actual tissue temperatures reached with AI-guided HPSD ablation appeared to be higher with a greater distance between the catheter tip and target tissue than those with standard ablation. HPSD ablation for <7 s may help prevent collateral tissue injury when ablating within a close distance.

B-PO04-014 ACTUAL HEATING PATTERN IN THE ESOPHAGUS INJURY DURING HIGH-POWER SHORT-DURATION ABLATION USING A NOVEL PORCINE ESOPHAGEAL MODEL

The safety during High-power short-duration (HP-SD) ablation to the pulmonary vein (PV) close to esophagus has not been clarified. To clarify the tissue heating in esophageal injury during HPSD ablation. Because the porcine esophagus is located away from the PVs, we created a novel model in which a gauze was inserted underneath the esophagus to locate it close to the inferior vena cava (IVC) for esophageal temperature recording (Figure A). In 7 pigs, after right thoracotomy, 3∼4 thermocouples were implanted on the surface of esophagus close to the IVC. The time-vs-tissue temperatures were obtained during the 50W-HPSD ablation to the endocardial IVC (8-20g contact force, target ablation index 400). The maximum temperature, time to achieve 50°C, distance of thermocouples from the catheter tip were assessed. We assess pathological findings of esophageal ablation points. In pathological finding, all IVC lesions were transmural, but esophageal injury occurred in 5/16 ablation points (Figure B). Maximum esophageal tissue temperature was significantly higher (78.3±5.6 vs. 45.3±2.7°C), time to 50°C (5.8±1.3 vs. at least 12.4±1.1 sec), and distance from the catheter tip were shorter in the injury group (1.28±0.6 vs. 11.6±2.1 mm) (p<0.05 for all) (Figure C). HPSD ablation setting is effective in the generating temperatures needed for transmural lesions, however, esophagus injury sometimes occurs, which depends on the maximum tissue temperatures. The time to tissue temperature≥50°C was 5.8 sec in the injury group, and thus, ablation time of < 6 sec may help to prevent esophageal injury while achieving transmural PV lesions in the HPSD ablation.

Randomized comparative study of the effectiveness and safety of various bipolar devices during electrosurgical vaginal hysterectomy

AIM: The aim of this study was to investigate the morphometric features of tissues after exposure to bipolar energy of various electrosurgical generators and surgical hemostatic instruments used in vaginal hysterectomy.&#x0D; MATERIALS AND METHODS: The study included 48 individuals who underwent a vaginal hysterectomy. The patients were divided in three groups based on the instrument used for sealing blood vessels: a BiClamp was applied in Group 1 (n = 16), a TissueSeal PLUS COMFORT in Group 2 (n = 16), and a Thunderbeat in Group 3 (n = 16). The maximum temperature of tissue measured using a Fluke FLK TIS 40 9HZ thermal imaging infrared camera was compared within the groups.&#x0D; RESULTS: The maximum tissue temperature between the branches on electroligation, the minimum tissue temperature, and the tissue temperature at the coagulation boundary were significantly lower when using a TissueSeal PLUS COMFORT clamp than when using BiClamp and Thunderbeat clamps (H value = 41.8, p 0.01). Morphometric parameters (prevalence, coagulation depth and area) were the smallest with a TissueSeal PLUS COMFORT clamp compared to other clamps.&#x0D; CONCLUSIONS: Using a TissueSeal PLUS COMFORT clamp during vaginal hysterectomy is effective and safe and has the best thermometric and morphometric characteristics when applied to the tissue, thereby reducing the risk of lateral thermal damage. The possibility of perifocal heat transfer varies with the type of tool and with the temperature at the coagulation boundary.

Assessing temperature increase during photodynamic therapy: a simulation model

Photodynamic therapy (PDT) is a non-invasive procedure mainly used for treatment of malignancies. It is based on cytotoxic products generation after the excitation of absorbed photosensitizing drugs by non-ionizing radiation. The wavelength chosen is usually in the 620 - 700 nm region, resulting in limited tissue penetration depth. The relatively low irradiance values and the treatment time that, in most cases, lasts for a few minutes result in limited photothermal effects, which are usually overlooked. Therefore, in this study we computationally assess the temperature distribution during PDT in a cancer bearing mouse model. A user-friendly application is created that could be used in the treatment planning step of PDT. It receives as input various parameters, such as laser power, beam radius, irradiation time, body temperature and returns the maximum tissue temperature and irradiance values. Furthermore, it offers visualization of the generated effects through the spatial distribution of temperature, irradiance, acute necrosis and damaged tissue percentage that are presented in the form of interactive 3D plots. The conducted simulations reveal that 43 °C, which are in the hyperthermia range, are difficult to be excessed in PDT clinical practice, although topical thermal effects are observed.

A porcine study of the area of heated tissue during hot-balloon ablation: Implications for the clinical efficacy and safety.

Hot-balloon ablation depends solely on thermal conduction, and myocardial tissue is ablated by only conductive heating from the balloon surface. Despite growing clinical evidence of the efficacy and safety of hot-balloon ablation for atrial fibrillation (AF), the actual tissue temperature and the mechanism of heating during such ablation has not been clarified. To determine, by means of a porcine study, the temperatures of tissues targeted during hot-balloon ablation of AF performed with hot-balloon set temperatures of 73°C or 70°C, in accordance with the temperatures now used clinically. After a right thoracotomy, thermocouples with markers were implanted epicardially on the superior vena cava (SVC) and pulmonary veins (PVs) in six pigs. The tissue temperatures during hot-balloon ablation (balloon set temperatures of 73°C and 70°C, 180 s/PV) were recorded, and the maximum tissue temperatures and fluoroscopically measured distance from the balloon surface to the target tissues were assessed. Sixteen SVC- and 18 PV-targeted energy deliveries were performed. Full-thickness circumferential PV lesions were created with all hot-balloon applications. A significant inverse relation was found between the recorded tissue temperatures and distance (r = -.67; p < .001) from the balloon surface. No tissue temperature exceeded either of the balloon set temperatures. The best distance cutoff value for achieving lethal tissue temperatures more than 50°C was 3.6 mm. The hot-balloon set temperature, energy delivery time, and tissue temperature data obtained in this porcine study supported the clinical efficacy and safety of the hot-balloon ablation as currently practiced in patients with AF.

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.

Study of laparoscopic monopolar devices and its thermal effects

Objective: Energy devices are frequently used in minimally invasive surgeries (MIS). For MIS involving gynecologic malignancies, energy devices should be used cautiously to prevent thermal injuries to nearby organs. We evaluated monopolar electrosurgery devices and measured increases in temperature in the tissue and device. Methods: Briefly, the surface of a porcine tissue was incised using short and long activation times. Subsequently, the maximum temperature at the tip of the monopolar device, the cooling time required to reach a temperature of 60 ∘C, and the maximum tissue temperature were recorded. Results: Longer activation time was correlated with a higher tip temperature. With all activation times, there was an increase in the tip temperature that exceeded 100 ∘C. The cooling time to reach 60 ∘C was faster with the short activation times than with the long activation times. Even with the same output, the temperature decreased faster in the coagulation mode, suggesting that the cooling times were shorter with lower outputs. The tissue temperature dropped to 60 ∘C or less within 1 s in the cut mode but required approximately 2 s in the coagulation mode at 40 W. The temperature of the dissected tissue increased to 60 ∘C or higher; the cooling time was longer with high output and in the coagulation mode. Conclusions: We revealed that the activation of the monopolar device under routine use conditions exceeded a temperature of 100 ∘C. Additionally, the temperatures of the tip and tissue were significantly higher in proportion to the output and time. For MIS involving gynecologic malignancies, careful attention is necessary to avoid thermal injury.

Computer simulations of an irrigated radiofrequency cardiac ablation catheter and experimental validation by infrared imaging

Purpose To develop and validate a three-dimensional (3-D) computer model based on accurate geometry of an irrigated cardiac radiofrequency (RF) ablation catheter with microwave radiometry capability, and to test catheter performance. Methods A computer model was developed based on CAD geometry of a RF cardiac ablation catheter prototype to simulate electromagnetic heating, heat transfer, and computational fluid dynamics (blood flow, open irrigation, and natural convection). Parametric studies were performed; blood flow velocity (0–25 cm/s) and irrigation flow (0–40 ml/min) varied, both with perpendicular (PE) and parallel (PA) catheter orientations relative to tissue. Tissue Agar phantom studies were performed under similar conditions, and temperature maps were recorded via infrared camera. Computer model simulations were performed with constant voltage and with voltage adjusted to achieve maximum tissue temperatures of 95–105 °C. Results Model predicted thermal lesion width at 5 W power was 5.8–6.4 mm (PE)/6.5–6.6 mm (PA), and lesion depth was 4.0–4.3 mm (PE)/4.0–4.1 mm (PA). Compared to phantom studies, the mean errors of the computer model were as follows: 6.2 °C(PE)/4.3 °C (PA) for maximum gel temperature, 0.7 mm (10.9%) (PE)/0.1 mm (0.8%) (PA) for lesion width, and 0.3 mm (7.7%)(PE)/0.7 mm (19.1%) (PA) for lesion depth. For temperature-controlled ablation, model predicted thermal lesion width was 7–9.2 mm (PE)/8.6–9.2 mm (PA), and lesion depth was 4.3–5.5 mm (PE)/3.4–5.4 mm (PA). Conclusions Computer models were able to reproduce device performance and to enable device evaluation under varying conditions. Temperature controlled ablation of irrigated catheters enables optimal tissue temperatures independent of patient-specific conditions such as blood flow.

Contrast therapy: Tissue heating and cooling properties within the equine distal limb.

Rehabilitation of tendon injuries in horses often involves cryotherapy to reduce inflammation and occasionally tissue heating to increase collagen extensibility. The application of alternating cold and hot (ie contrast therapy) is widely used in human physical therapy; however, its utility in equine rehabilitation is largely unknown. The objectives of this study were to (a) assess if the equipment could achieve therapeutic tissue temperatures (<15 and >40°C) at different tissue depths relative to the digital flexor tendons and (b) evaluate the time-temperature profiles during serial heating and cooling cycles using a contrast therapy device. In vivo experiment. In 4 adult horses with normal forelimb digital flexor tendons, fine-wire temperature probes were placed superficially on the skin and implanted subcutaneously, deep to the superficial digital flexor tendon (SDFT) and deep to the deep digital flexor tendon (DDFT). Temperatures were recorded over three complete thermal (hot-cold) cycles. Minimum and maximum temperatures were recorded and the rate of temperature changes and the areas underneath the time-temperature curves (ie thermal load) were calculated. Minimum and maximum tissue temperatures (°C) included: superficial skin [12.6±1.0; 42.4±2.4], subcutaneous tissues [14.1±0.8; 42.3±2.2], deep to the SDFT [15.6±0.8; 41.7±2.6] and deep to DDFT [25.1±2.0; 38.0±3.5]. An initial rapid rate of tissue temperature change between 3.2 and 4.3°C/min occurred within tissues to the depth of the DDFT. Tissue thermal loads during heating ranged from 255 to 607°C*second and from 309 to 780°C*second during tissue cooling, with the lower values noted deep to the DDFT. Unknown clinical efficacy in diseased tissues. The applied contrast therapy was consistently able to induce cooling and heating of tissues to the depth of the DDFT.