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Modeling Cryoballoon Ablation Techniques for Enhanced Efficacy in Atrial Fibrillation Management

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Atrial fibrillation is a common form of heart arrhythmia characterized by irregular heartbeat originating in the pulmonary veins (PV) of the heart. The cycle of electrical impulses controlling the beating of the heart is disturbed, leading to poor blood flow to the rest of the heart. In more persistent cases, surgical intervention is needed to isolate the disruptive electrical signals. Cryoballoon ablation (CBA) is a minimally invasive procedure where a catheter with a deflated balloon is inserted into a blood vessel and guided to the heart. Once in the pulmonary vein ostium (region where the pulmonary veins meet the atrium), the balloon is inflated and filled with freezing nitrous oxide to kill the myocardial tissue in contact, preventing the faulty electrical signals originating in the PV from reaching the heart [1].

This study seeks to give greater understanding on the distribution of temperatures within heterogeneous tissue and the effectiveness of the procedure in accordance with biological differences. Currently, there are no technologies that can give data on tissue temperature while the procedure is occurring. This causes a lack of predicting when the procedure is “complete,” that is, complete ablation with low chance of recurrence of atrial fibrillation in the patient [2]. Our model seeks to gain insight into the variation of temperatures in the tissue which is not possible in an in vivo procedure. Additionally, there is wide variety in vein thicknesses and geometries, which can affect efficacy and increase the risk of complications from the procedure. To improve patient outcomes, pre-procedure scans are recommended. Cardiac CT angiography (cCTA) is the most commonly used preoperative scan to get a 3D cardiac visualization for planning catheter placement [2]. With computer simulation software, the effect of various vein thicknesses on a safe and effective duration of pulmonary vein isolation (PVI) can be investigated.

Modeling was done in COMSOL Multiphysics 6.0, a commercially available software, as a transient heat conduction problem with water to ice transitions in blood and myocardial tissue. Simplifications to the CBA procedure were made by adapting real anatomy into 2-D axisymmetric geometry and assuming a constant balloon surface temperature. For our analysis, we considered complete cell death at temperatures below -30°C, which is the critical temperature for myocardium tissue [3].

Our results indicate that the biological variance in thickness in the atrial vein does in fact change the needed length of procedure. Indeed, cryoballoon application times might be reduced in cases where a patient has relatively thin walls constituting the venous ostia. In the future, with improved imaging instruments capable of sub-millimeter resolutions, the preoperative cCTA scan should also include measurements to determine the specific thickness of their venoatrial junctions. Some limitations of our model include not being able to detect damage in surrounding nerves and esophagus and not accounting for differences in bioheat.

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2024-05-17

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cryoballoon ablation; atrial fibrillation; computational modeling; simulation; pulmonary vein; myocardium

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Government Document

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Attribution 4.0 International

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report

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