In vitro and in vivo results of transcatheter microwave ablation using forward-firing tip antenna design.

This study was designed to test a microwave (MW) ablation system using approximately 2,450 MHz of energy and a deflectable catheter with forward-firing tip antenna, an early clinical prototype system. In vitro three-dimensional thermal mapping of single and double helix antenna designs was performed. Quantitative measurements of antenna radiation were recorded on tissue phantoms equipped with temperature sensors distributed radially and outwardly. In vivo testing consisted of closed-chest AV junction ablation in three dogs. Thermal mapping showed hemispherical heat distribution from the tip antenna. For the double helix design, this distribution was measured at 8.4-mm diameter with a maximum temperature of 61.62 degrees C. As expected, the single helix design produced less heating with a measured diameter of 6.4 mm and maximum temperature of 55.90 degrees C. The in vivo study produced lesions of geometry and size concordant with these heating patterns. MW ablation produced bundle branch block in one dog and complete AV nodal block in the remaining two, without transvalvular or other structural damage. The histopathology of the lesions was typical of a thermal burn showing hemorrhage and coagulative necrosis with clearly demarcated borders. We conclude that, using this early clinical prototype system with a deflectable catheter and a forward-firing tip antenna design, MW heating can produce a moderate-size lesion and is safe and effective for cardiac ablation.