Thermodynamic properties of atrial fibrillation cryoablation: a model-based approach to improve knowledge on energy delivery

Abstract

<jats:p> The objective of this study is to describe a suitable model of atrial fibrillation cryoablation thermodynamic properties. Three different thermal loads were applied to a cylindrical copper element simulating the cryoprobe, thermally coupled with a Peltier stack producing the freezing effect, and in contact with a bovine liver sample. Thermal events occurring inside the samples were measured using mirror image technique. Heat subtracted flux during ice formation and minimum temperature measured at probe–tissue interface were, respectively, 1.33 W cm <jats:sup>−2</jats:sup> and −27.8°C for Sample#0, 1.88 W cm <jats:sup>−2</jats:sup> and −35.6°C for Sample#1 and 1.82 W cm <jats:sup>−2</jats:sup> and 1.44 W cm <jats:sup>−2</jats:sup> before and after the ice trigger, respectively, and −29.3°C for Sample#2. Ice trigger temperature was around −8.5°C for Sample#0 and Sample#2, and −10.4°C for Sample#1. In all the investigated samples, ice front penetration was proportional to the square root of time and its velocity depended on the heat flux subtracted. The fraction of the useful energy spent for ice formation was less than 60% for Sample#0, and about 80% for Sample#1 and for Sample#2, before the reduction of the removed heat flux. Freezing time exceeding a cut-off, according to the heat subtracted flux, does not improve the procedure effectiveness and is detrimental to the surrounding tissues. </jats:p>

Experimental Investigation on Thermal Conductivity and Thermal Diffusivity of Water-Agar Gel from Room Temperature to –60℃

“…For this reason, agar can be a good substitute for ex vivo animal tissues, for example bovine tissues (e.g. liver and heart), commonly used in experimental investigations [5,6]. Based on what just written, the agar gel could be used to better understand the behavior of the biological tissues when the latter undergo a process of cryoablation.…”

Recent progress in cryoablation cancer therapy and nanoparticles mediated cryoablation

“…Several factors besides low temperature promote complete ablation, such as the number and position of the cryoprobes, the shape of ice ball optimal for covering the entire tumor 10 , depth of ice penetration, number of freeze-thaw cycles, and freezing time. According to the thermodynamic properties of cryoablation modelled in atrial fibrillation, the ice front penetration is proportional to the square root of time while its velocity depends on the heat subtracted flux during the ice formation, and prolonged freezing time kills surrounding tissues 11 . Although there is no agreed standard duration of cryoablation among physicians, typically longer freeze and thaw durations result in greater cell death.…”

Experimental Investigation on Thermal Conductivity and Thermal Diffusivity of Ex-Vivo Bovine Liver from Room Temperature down to −60 °C

“…It is commonly believed that water-agar gel is able to mimic the thermal behavior of exvivo biological soft tissues and is therefore widely used for in-vitro investigations [22,23]. Since in a previous work the authors presented the temperature dependence of the properties for water-agar gel (2% agar) [24], it is essential to understand whether this material really mimics the thermal behavior of an ex-vivo biological tissue in the temperature range of interest.…”