Dual-frequency setting for urinary stone fragmentation during shock wave lithotripsy: an in vitro study

Extracorporeal shock wave lithotripsy (SWL) is less invasive compared to the other invasive modalities of stone treatment that are gaining popularity. Hence, methods to improve the efficacy of SWL are desirable. We studied the effectiveness of dual frequency on the efficacy of stone fragmentation, but minimizing treatment time. A phantom 10 mm spherical BegoStone was fragmented in vitro in a kidney model using an electromagnetic lithotripter (Storz MODULITH^®SLX-F2). A total of 78 stones were fragmented each with 3000 shocks at 60 Hz or 120 Hz or a dual frequency (DF) of 60–120 Hz. For the DF setting, the first 1000 shocks were delivered at 60 Hz and the next 2000 at 120 Hz. Total weight and number of significant fragments of > 3 mm (TWSF and TNSF, respectively) and also > 2 mm was measured. Results: The mean TWSF was 0.1, 0.16, and 0.08 g for 60 Hz, 120 Hz, and DF 60–120 Hz, respectively. The TWSF of DF 60–120 Hz was significantly lower than that of 120 Hz (p = 0.02), but same as the 60 Hz (p = 0.32). The mean TNSF of > 3 mm was 2.6, 3.0, and 2.0 for 60 Hz, 120 Hz, and DF 60–120 Hz, respectively, without significant differences between each setting. However, increasing trend of TWSF, TW2 mm and TN2 mm was seen in the order of DF, 60 Hz and 120 Hz (p = 0.019, p = 0.004 and 0.017, respectively). Treatment time for 60 Hz, 120 Hz, and DF 60–120 Hz was 50, 25, and 34 min, respectively. Dual-frequency setting produced effective stone fragmentation compared to the recommended 60 Hz, while decreasing treatment time. DF variation is one other factor that may be tailored for effective stone comminution and needs clinical evaluation.