Effect of vessel diameter on the creation of ovine lung radiofrequency lesions in vivo: preliminary results.

OBJECTIVE: We sought to evaluate the effect of radiofrequency ablation (RFA) on pulmonary vessels with respect to potential of injury of these structures, to assess perfusion-mediated "heat sink" effect, and to consider acute and chronic complications.
MATERIAL AND METHODS: RFAs targeted to perihilar, middle third, and peripheral lung regions were created in vivo in the lung of 10 crossbred sheep. The RITA generator and the Starburst XLi electrode with deployable hooks were used. The approach was open, performed under general anesthesia. Lesions 4 cm in diameter at a target temperature of 80 degrees C were created. Acute (immediate postinterventional euthanasia), subacute (96 h), and chronic (28 days) lesions were evaluated macroscopically, and histologic analysis of the vessels was performed. Patency of the vessels, both arteries and veins, was macroscopically assessed by presence or absence of thrombus and the degree of vascular injury and the viability of perivascular pneumocytes as well as endobronchial injury were histologically assessed.
RESULTS: In the acute, subacute, and chronic setting, heat sink effect, indicated by invagination of the tissue between vessel and ablated region, was only observed in vessels greater than 3 mm in diameter. Thrombus was seen in 20% of the vessels smaller than 3 mm. On histopathology, vessels smaller than 3 mm showed at least partial vessel wall injury, characterized by endothelial cell necrosis and luminal thrombus. In the vessels greater than 3 mm the extent of vessel wall injury decreased with increasing vessel diameter. No acute complications were noted. For the chronic complications a bronchopleural fistula and a lung abscess were found.
CONCLUSION: There seems to be a narrow transition zone for pulmonary vessels around 3 mm, beyond which the heat sink effect was seen consistently and substantial vascular injury was rare.