Clinical Predictors of Stone Fragmentation Using Slow-Rate Shock Wave Lithotripsy

Abstract

Aim: To determine efficacy and clinical predictors of stone fragmentation when using slow-rate shock wave lithotripsy (SWL). Patients and Methods: In total, 116 patients with radiopaque urinary tract stones were randomized into two groups: 57 patients were treated with SWL at 90 shocks/min, and 59 patients were treated with SWL at 120 shocks/min. The efficacy of SWL was evaluated within 1 month after treatment. Patient characteristics, features of stones, and SWL conditions were reviewed. Success rates relating to individual parameters were assessed by using chi-square and Student t tests. All factors were further entered into multivariate logistic regression analysis. Results: There were no statistically significant differences between the two groups with regard to age, sex, site and size of the stones, renal function, and total number of shock waves. In univariate analysis, the success rate was significantly related to shock wave frequency (p = 0.023), length and width of the stones (p < 0.001), total number of shock waves (p = 0.047), and age (p = 0.049). In multivariate analysis, however, only shock wave rate and stone length remained statistically significant (p = 0.021 and p = 0.046, respectively). The overall success rate was significantly higher in the group treated with 90 shocks/min (p = 0.02). However, this higher success rate was statistically significant only in patients with a stone length ≧10 mm (50.0 vs. 18.5%, p = 0.019). Conclusion: SWL at 90 shocks/min yielded better outcomes than SWL at 120 shocks/min, particularly in patients with stone lengths ≧10 mm.