Background: Transcatheter microwave ablation is a novel technique for treating cardiac arrhythmias.
Methods: We investigated the effects of catheter temperature, application duration, and antenna length on lesion dimensions during catheter-based microwave ablation. In a swine thigh muscle preparation, microwave was delivered at targeted temperatures of 60 degrees C (n = 18), 70 degrees C (n = 27), 80 degrees C (n = 43), or 90 degrees C (n = 18) for 120 seconds with 10-mm antenna; and at targeted temperatures of 80 degrees C for 120 seconds (n = 22), 150 seconds (n = 18), 180 seconds (n = 18), 210 seconds (n = 18), and 240 seconds (n = 17) with 20-mm antenna using 10 F catheter (MedWaves, San Diego, CA, USA) during parallel orientation. Conventional radiofrequency ablation (RF) using a 4-mm tip electrode was performed as control.
Results: With 120-second energy applications, lesion length and depth were significantly larger with targeted temperatures of 80 degrees C and 90 degrees C than 60 degrees C (P< 0.05). Furthermore, lesion depth and width, but not length, were significantly increased by prolonging energy application duration from 120 to 240 seconds at targeted temperature of 80 degrees C (P< 0.05). Compared to RF, microwave lesions were significantly longer but had comparable depth and width. A 20-mm microwave antenna produced longer lesions than either a 10-mm antenna or RF ablation catheter. Multivariate analysis demonstrated that targeted temperature >or=80 degrees C, application duration >or=150 seconds, and use of 20-mm antenna were independent predictors for lesion depth and width (P< 0.05). Surface dessication was observed in 4/18 (22%) lesions at 90 degrees C, as compared with 1/136 (0.7%) at 80 degrees C targeted tip temperature (P < 0.05).
Conclusions: This study demonstrated that lesions size with transcatheter microwave ablation can be controlled by adjusting targeted temperature, energy application duration, and antenna length. A targeted temperature of 80 degrees C for more than 150 seconds should provide optimal lesion dimensions and lower risk of surface dessication or charring.