Computational study on the effect of thermal deformation of myocardium on lesion formation during radiofrequency ablation

Radiofrequency (RF) catheter ablation treats cardiac diseases by inducing thermal lesion of cardiac tissues through radiofrequency energy operating at around 500 kHz. The electromagnetic wavelength is significantly longer than the size of the radiofrequency active electrode, the tissue is heated through resistive heating. During thermal ablation, the coupled thermo-mechanical property of cardiac tissue influencing the contact area between the electrode and tissue plays a crucial role in the formation of thermal lesions, yet the literature often overlooks the effect of thermal deformation. This paper proposes a thermo-hyperelastic constitutive model for myocardium that models thermal contraction and expansion during ablation. Furthermore, a finite element model was established to investigate the effect of the electro-thermo-mechanical coupling property of myocardium on lesion formation under different contact forces. To ensure convergence, we solved the fully coupled electro-thermo-mechanical finite element model using the segregated step method. The computational results demonstrate that thermal deformation, which causes an expansion in the tissue-electrode contact area, increases lesion width and volume, while its influence on lesion depth is negligible. Specifically, after a 30-s ablation under contact forces of 0.1, 0.15, and 0.2 N, the lesion volume increased from 4.53, 7.66, and 10.62 mm³ (without thermo-mechanical coupling) to 5.36, 8.33, and 13.34 mm³ (with thermo-mechanical coupling), respectively. Similarly, the lesion width increased from 2.68, 3.12, and 3.44 mm to 2.78, 3.22, and 3.62 mm. Moreover, both thermal deformation and contact force exert a minimal effect on lesion formation time.