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

Introduction: Theoretical studies have suggested that microwave energy can increase the depth of heating compared with radiofrequency energy. A spiral microwave antenna design may have advantages over previous designs using smaller designs because the resulting 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 exposed and bathed in heparinized bovine blood (36°to 37°C). A helical microwave catheter with a fiberoptic thermometer attached to the distal 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 measured. A 915-MHz microwave generator delivered energy at one of three power outputs (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, respectively. Lesion depth (R = 0.96, P = 0.05), maximum surface dimension (R = 0.99, P = 0.06), and volume (R = 0.99, P = 0.04) were closely correlated to the power applied. Conclusion: Power is an important determinant of lesion size using a spiral microwave antenna. A novel, spiral microwave antenna design can create lesions of significant depth that may be applicable for the ablative therapy of ventricular tachycardia.