Impact of wall thickness on tissue cooling effect of cryoballoon ablation: Investigation using an experimental heart model

Abstract

Abstract Background Understanding of the tissue cooling properties of cryoballoon ablation during pulmonary vein isolation is lacking. Purpose To delineate the depth of the tissue cooling effect during cryoballoon freezing at the pulmonary venous ostium. Methods A left atrial-pulmonary vein model, produced by a 3-dimensional printer using CT data from a patient, was constructed so that porcine thigh muscles of various thicknesses could be fixed and thermocouples could be fixed at locations corresponding to the epicardial side of the pulmonary vein ostium. The model was placed in a 37-degree water bath with a pulmonary vein water flow at a rate that mimicked biological blood flow, and the cryoballoon was advanced into the left superior vein until the vein was completely occluded. Cryofreezing was performed 5 times each for a porcine thigh muscle of 2-, 4-, and 6-mm thickness, and epicardial tissue cooling was monitored as assessed by the mean temperature of 12 evenly distributed thermocouples covering the roof region of the left superior vein. Results Epicardial tissue cooling effects were more in the order of 2-mm, 4-mm, and 6-mm thickness (Figure) with a mean temperature of -41.4 ± 4.2 for 2 mm, -33.0 ± 4.0 for 4 mm, and 8.0 ± 8.7 °C for 6 mm at 180 sec (p for trend < 0.0001). In addition, tissue temperature drops were steeper in thin muscle (maximum temperature drop per 5 s: 5.2 ± 0.9, 3.9 ± 0.7, 1.3 ± 0.7 °C, p for trend < 0.0001). Conclusion The cooling effect is weaker in the deeper layers during cryobaloon freezing, and longer freezing duration would be recommended in case of thick myocardium.