Abstract 1787: Characterization of the Distance-Dependent Tissue Temperatures Profiles Created During High Intensity Focused Ultrasound Ablation of the Pulmonary Veins
Background: While the efficacy of AF treatment with high intensity focused ultrasound (HIFU) balloon ablation is known, the actual tissue temperature (temp) around the pulmonary veins (PVs) generated during HIFU balloon ablation and its dependence on distance from the balloon remains unknown.
Methods: To determine the tissue temp profile and gradients during 20 mm HIFU balloon ablation, 8 dogs underwent 59 HIFU energy deliveries (40 sec, 32 watts) around 51 RSPV, 7 LSPV, and 11 LIPV ablations after implantation of thermocouples around the orifice of each PV via thoracotomies.
Results: 288 temp profiles were obtained. Average maximum temp around the PV orifice was 50.0 ± 15.0 °C, with 2 patterns of tissue temps observed. One was consistent with focused zone heating due to the direct effect of HIFU energy (31/288 (11%) temp profiles), whereas the other was consistent with conductive heating (169/288 (59%) temp profiles). Focused zone patterns showed a rapid temp increase ≥ 50 °C within 10 sec, with an average maximum temp of 82.6 ± 8.9 °C (Fig. 1⇓), located 6.4 ± 4.1 mm from the balloon surface. Conductive heating patterns showed a gradual temp increase over 40 °C, resulting in a maximum temp of 50.8 ± 9.1 °C (Fig. 1⇓), located 8.0 ± 4.4 mm (p = 0.05 vs focused zone location) from the balloon surface. The sensitivity and specificity for lethal tissue temps (≥ 50 °C with focused zone patterns), as shown in the inverted trapezoid area (Fig. 2⇓) [23 mmx20 mmx15 mm] were 72% and 74%, and 94% and 63%, respectively.
Conclusions: Actual tissue temps achieved with focused HIFU ablation as high 60–90 °C at the surface of PVs. Subsequent conductive heating is distance -dependent, but also reached lethal levels.