Determination of cryothermal injury thresholds in tissues impacted by cardiac cryoablation

Investigation of Lung Cancer Cell Response to Cryoablation and Adjunctive Gemcitabine-Based Cryo-Chemotherapy Using the A549 Cell Line

Due to the rising annual incidence of lung cancer (LC), new treatment strategies are needed. While various options exist, many, if not all, remain suboptimal. Several studies have shown cryoablation to be a promising approach. Yet, a lack of basic information pertaining to LC response to freezing and requirement for percutaneous access has limited clinical use. In this study, we investigated the A549 lung carcinoma cell line response to freezing. The data show that a single 5 min freeze to -15 °C did not affect cell viability, whereas -20 °C and -25 °C result in a significant reduction in viability 1 day post freeze to <10%. These populations, however, were able to recover in culture. Application of a repeat (double) freeze resulted in complete cell death at -25 °C. Studies investigating the impact of adjunctive gemcitabine (75 nM) pretreatment in combination with freezing were then conducted. Exposure to gemcitabine alone resulted in minimal cell death. The combination of gemcitabine pretreatment and a -20 °C single freeze as well as combination treatment with a -15 °C repeat freeze both resulted in complete cell death. This suggests that gemcitabine pretreatment may be synergistically effective when combined with freezing. Studies into the modes of cell death associated with the increased cell death revealed the increased involvement of necroptosis in combination treatment. In summary, these results suggest that repeat freezing to -20 °C to -25 °C results in a high degree of LC destruction. Further, the data suggest that the combination of gemcitabine pretreatment and freezing resulted in a shift of the minimum lethal temperature for LC from -25 °C to -15 °C. These findings, in combination with previous reports, suggest that cryoablation alone or in combination with chemotherapy may provide an improved path for the treatment of LC.

One hundred percent utilization of a modified CryoMaze III procedure for atrial fibrillation with mitral surgery

OBJECTIVES

Concomitant atrial fibrillation often goes untreated because of surgeon concerns regarding lesion set complexity and pump times. We describe a new cryoablation procedure to address this.

METHODS

From June 2013 to March 2021, a modified CryoMaze III procedure was used using 3 left atrial ± 3 right atrial cryo-applications creating the key lesions of the Cox Maze III procedure. Since 2018, 3-minute cryo-lesions were used for the left atrial box lesion for total cryoablation times of 8 minutes for the left atrium ± 6 minutes for the right atrium. By using propensity matching, patients undergoing mitral valve surgery with no atrial fibrillation history were compared with CryoMaze III-treated patients.

RESULTS

A total of 100% of the 277 patients with atrial fibrillation requiring mitral valve surgery ± other procedures received the modified CryoMaze III procedure. After propensity score matching (n = 161 each group), the modified CryoMaze III group had mean crossclamp and bypass times 10.5 and 13.4 minutes longer than the control group, respectively. There were no significant differences in 30-day mortality, morbidity, pacemaker use, renal dysfunction, or late survival between groups, but there were less postoperative strokes in the CryoMaze III group. Freedom from atrial fibrillation off antiarrhythmics was 77% (mean follow-up of 3.0 ± 2.1 years). At 12 months, freedom from atrial fibrillation off antiarrhythmics was 90% for the 3-minute ablation group. Late survival was similar to age- and sex-matched Centers for Disease Control and Prevention controls.

CONCLUSIONS

The modified CryoMaze III technique is efficient, safe, and effective. Education of the surgical community regarding the late benefits of ablation and the simplicity of this new technique should improve adoption of the Class I Guidelines to treat concomitant atrial fibrillation.

CPA toxicity screening of cryoprotective solutions in rat hearts

In clinical practice, donor hearts are transported on ice prior to transplant and discarded if cold ischemia time exceeds ∼5 h. Methods to extend these preservation times are critically needed, and ideally, this storage time would extend indefinitely, enabling improved donor-to-patient matching, organ utilization, and immune tolerance induction protocols. Previously, we demonstrated successful vitrification and rewarming of whole rat hearts without ice formation by perfusion-loading a cryoprotective agent (CPA) solution prior to vitrification. However, these hearts did not recover any beating even in controls with CPA loading/unloading alone, which points to the chemical toxicity of the cryoprotective solution (VS55 in Euro-Collins carrier solution) as the likely culprit. To address this, we compared the toxicity of another established CPA cocktail (VEG) to VS55 using ex situ rat heart perfusion. The CPA exposure time was 150 min, and the normothermic assessment time was 60 min. Using Celsior as the carrier, we observed partial recovery of function (atria-only beating) for both VS55 and VEG. Upon further analysis, we found that the VEG CPA cocktail resulted in 50 % lower LDH release than VS55 (N = 4, p = 0.017), suggesting VEG has lower toxicity than VS55. Celsior was a better carrier solution than alternatives such as UW, as CPA + Celsior-treated hearts spent less time in cardiac arrest (N = 4, p = 0.029). While we showed substantial improvement in cardiac function after exposure to vitrifiable concentrations of CPA by improving both the CPA and carrier solution formulation, further improvements will be required before we achieve healthy cryopreserved organs for transplant.

Feasibility and safety of trans-biliary cryoablation: Preclinical evaluation of a novel flexible cryoprobe

Cryoablation, as a well-characterized technology, has multifarious clinical applications in solid malignancy. However, trans-biliary cryoablation for malignant biliary obstruction has not been reported yet. Thus, this study aimed to determine the efficacy and safety of trans-biliary cryoablation with a novel CO₂ gas-based flexible cryoprobe in standardized preclinical settings. For fresh porcine liver ex vivo, the freezing efficacy of cryoablation was evaluated by using fresh porcine liver. The real-time CO2 flow rate, freezing temperature and freezing range were examined and the frozen appearance was visualized. In vivo study, acute and chronical effects were investigated by using the models of canine bile duct. Histopathology and laboratory examination were performed. The lowest temperature that the electrode could deliver to the tissue was -60.7 °C. At 60s after freezing, the tissue temperature dropped to -22.6 °C and -4.3 °C at 0.1 and 0.2 cm from the electrode center, respectively. The frozen size was greater in liver tissue ex vivo than that in bile duct tissue in vivo. No biliary hemorrhage, perforation, stricture, obstruction, and adjacent organ injury were observed. With histopathologic examination, acute intercellular vacuoles were observed in the lamina propria adjacent to the lumen. Chronic changes, including uneven coagulative necrosis, fibro-proliferation, inflammatory infiltration and connective tissue thickening were observed in the lamina propria of the all biliary samples. The results demonstrated CO₂ gas-based trans-biliary cryoablation is safe and efficacious. These findings may provide a potential new modality for primary malignant biliary obstruction and malignant obstruction within a biliary stent and contribute to cryoablation of clinical practice.

Recent advances in cryoballoon ablation for atrial fibrillation

Introduction: Pulmonary vein isolation (PVI), by catheter ablation, represents the current treatment for drug-resistant atrial fibrillation (AF). Nowadays cryoballoon (CB) is a recognized ablation method in patients with atrial fibrillation, mainly due to its ease of use, leading to reproducible and fast procedures. This novel single shot technology literally revolutionized the approach to AF ablation. Areas covered: The historical development of the cryoballoon, ablation techniques and new approaches beyond the ordinary PVI and complications are summarized here. Expert opinion: Although cryoballoon ablation has greatly standardized the approach to PVI a few critical points still need to be clarified scientifically in order to further uniform this procedure in cath labs worldwide. Duration and dosage of the cryoapplication is undoubtedly a topic of great interest.

Reporting of thermography parameters in biology: a systematic review of thermal imaging literature

Infrared (IR) thermography, where temperature measurements are made with IR cameras, has proven to be a very useful and widely used tool in biological science. Several thermography parameters are critical to the proper operation of thermal cameras and the accuracy of measurements, and these must usually be provided to the camera. Failure to account for these parameters may lead to less accurate measurements. Furthermore, the failure to provide information of parameter choices in reports may compromise appraisal of accuracy and replicate studies. In this review, we investigate how well biologists report thermography parameters. This is done through a systematic review of biological thermography literature that included articles published between years 2007 and 2017. We found that in primary biological thermography papers, which make some kind of quantitative temperature measurement, 48% fail to report values used for emissivity (an object's capacity to emit thermal radiation relative to a black body radiator), which is the minimum level of reporting that should take place. This finding highlights the need for life scientists to take into account and report key parameter information when carrying out thermography, in the future.

Towards a tailored cryo-pulmonary vein isolation. Lessons learned from second-generation cryoballoon ablation

Second-generation cryoballoon ablation has emerged as an effective and practical approach for the treatment of atrial fibrillation. It gained the overall interest of the electrophysiology community due to its excellent success rates, and reproducible clinical outcomes comparable to the point-by-point radiofrequency technique. This technology offers several advantages including a fast learning curve and shorter procedure times making this device widely adopted in many EP-laboratories as an alternative strategy to conventional point-by-point radiofrequency ablation. As compared to its predecessor, the improved technical performances of the second-generation cryoballoon translated into favorable clinical outcomes, which are maintained in long-term follow-up. However, the ideal cryo-application duration and the adequate number of freeze-thaw cycles are not well established and predictors of durable electrical isolation are poorly known. This review provides some practical advices for a successful ablation using the second-generation cryoballoon.

Mirror image technique for the thermal analysis in cryoablation: Experimental setup and validation

The paper presents a set of experiments that were performed to characterize the freezing front propagation in water first, and in an agar-gel solution afterwards. The experimental setup made of Peltier devices, to emulate the cryogenic effect, and a copper cold finger, to mimic the cold probe interface, are described. We claim that by monitoring some temperatures at the generating cryodevice, several pieces of information can be derived through the cold interface to assess the outside thermodynamic changes. The employed technique, known as mirror image, allows determining the occurrence of the initial ice formation outside the cryo-probe and in the surrounding material, also with different magnitudes of the thermal contact resistance at the cold interface. For both water and agar the ice penetration was found to be non linear versus time, and proportional to the square root of time in the performed experiments. The ice drift velocity decreases according to its penetration inside the tested materials. At the beginning of ice formation, the measured drift velocities are approximately 0.11 mm/s and 0.06 mm/s for water and agar, respectively, and after the ice penetrates 2 mm, they become approximately 0.03 mm/s for both materials.