Slow versus fast shock wave lithotripsy rate for urolithiasis: A prospective randomized study

Purpose: We determined the effect of shock wave lithotripsy (SWL) rate on treatment outcome in patients with renal and ureteral stones. Materials and Methods: A total of 156 patients were prospectively randomized to receive SWL using a slow (60 pulses per minute) or fast wave rate (120 pulses per minute). Inclusion criteria were patients with. a single radiopaque renal or ureteral stone not exceeding 30 mm in maximum diameter. Patient characteristics, stone and therapy features were reviewed, and the relation to success rate and total number of shock waves required was assessed using the chi-square, Fisher exact and Mann-Whitney tests. Factors proven to be significant in univariate analysis were entered in a multivariate logistic regression analysis. Results: The study included 114 male (73.1%) and 42 female (26.9%) patients with a mean age +/- SD of 42.1 +/- 13.3 years. Stone length measured in maximum diameter was 13.2 +/- 5.9 min (range 5 to 30). Renal stones were encountered in 94 (60.3%) patients and ureteral stones in 62 (39.7%). The slow SWL rate was used in 76 (48.7%) patients and the fast rate in 80 (51.3%). Baseline variables were comparable in both groups. However, the total number of shock waves required was statistically significantly lower in the slow rate group (p = 0.004) and the treatment time was significantly longer (p = 0.000). The rate of success, defined as being completely stone-free or having clinically insignificant gravel less than 2 mm, was significantly higher with the slow rate (p = 0.034), an increased number of sessions (p = 0.001), decreased stone length (p = 0.000) and greater total number of shock waves (p = 0.011). However, only the slow SWL rate and stone length maintained a statistically significant impact in multivariate analysis. Conclusions: The slow SWL rate is associated with a significantly higher success rate at a lower number of total shock waves compared to the fast SWL rate.