Microwave ablation using a spiral antenna design in a porcine thigh musclepreparation: In vivo assessment of temperature profile and lesion geometry

Microwave Ablation with Spiral Antenna Design. Introduction: Theoretical st udies have suggested that microwave energy can increase the depth of heatin g compared with radiofrequency energy. A spiral microwave antenna design ma y have advantages over previous designs using smaller designs because the r esulting power deposition pattern is considerably larger than the catheter diameter. We tested the efficacy of a spiral antenna using microwave energy in a porcine thigh muscle preparation. Methods and Results: In five anesthetized pigs, the thigh muscle was expose d and bathed in heparinized bovine blood (36 degrees to 37 degrees C), A he lical microwave catheter with a fiberoptic thermometer attached to the dist al end was positioned perpendicular to the thigh muscle, The antenna-tissue interface and tissue temperatures at depths of 3.0 and 6.0 mm were measure d. A 915-MHz microwave generator delivered energy at one of three power out puts (50, 100, or 150 W) for 60 seconds. Seventy lesions were created: 50 W (n = 23), 100 W (n = 24), and 150 W (n = 23), The mean depths at 50, 100, and 150 W were 4.3 +/- 1.8 mm, 7.2 +/- 1.7 mm, and 9.4 +/- 0.9 mm, respecti vely. Lesion depth (R = 0.96, P = 0.05), maximum surface dimension (R = 0.9 9, P = 0.06), and volume (R = 0.99, P = 0.04) were closely correlated to th e power applied. Conclusion: Power is an important determinant of lesion size using a spiral microwave antenna. A novel, spiral microwave antenna design can create les ions of significant depth that may be applicable for the ablative therapy o f ventricular tachycardia.