Vein wall thickness (VWT) and catheter size are more important than vein diameter in optimising endovenous thermal ablation (EVTA) – results of a mathematical model of how VWT changes when veins constrict under tumescence.

Abstract

Background: Catheter-based endovenous thermal ablation (EVTA) under tumescent anaesthesia is the standard treatment for truncal venous reflux. Doctors often use vein diameter alone to select treatment settings and protocols. Adequate venous ablation requires thermal energy to penetrate the vein wall deeply and probably transmurally. Hence the thicker the vein wall when constricted during treatment, the deeper the required thermal penetration. We constructed a mathematical model to predict vein wall thickness (VWT) during EVTA of veins of different diameters, initial wall thicknesses and device diameters. Methods:A mathematical model was constructed under the simplifying assumptions that the vein is a perfect circle, that the wall has a constant volume and that it constricts uniformly without folding. A set of representative vein diameters and thicknesses, and common device diameters were applied to the model to study the variables. Results:Numerical analysis predicted that vein walls would thicken when constricted compared to their initial state. Veins that initially had thicker walls and larger diameters, had thicker walls when constricted than thin walled or small diameter veins, using the same size EVTA devices. For each vein, as the diameter of the device decreased, the constricted VWT increased. Sensitivity analysis of the variables affecting the constricted VWT revealed that the initial VWT was most important, followed by device diameter and finally initial diameter of the vein. Conclusion:Our model shows that for a range of vein sizes and wall thicknesses, the constricted VWT increases markedly with decreasing device size. Although doctors often use vein diameter to select treatment parameters, this model suggests that initial VWT followed by the size of EVTA device are more important variables. Furthermore, the current trend to make EVTA devices thinner may be disadvantageous, as this increases the constricted VWT at treatment, making adequate thermal penetration harder to achieve.