Extracorporeal shock-wave lithotripsy: A comparative study of electrohydraulic and electromagnetic units

Purpose: We determined the results of shock wave lithotripsy with a newer electromagnetic lithotriptor and compared them with those in a contemporary series of cases managed by an electrohydraulic lithotriptor using identical treatment and followup criteria at a single center. Materials and Methods: Between 1995 and 1999, 356 patients (375 renal units, 483 upper urinary tract stones) meeting study inclusion criteria were treated with an MFL 5000 electrohydraulic shock wave lithotripsy unit (Dornier Medical Systems, Inc., Marietta, Georgia). From 1999 to 2000, 173 patients (175 renal units; 218 upper urinary tract stones) meeting identical study inclusion criteria were treated using an electromagnetic Modulith SLX shock wave lithotripsy unit (Karl Storz Lithotripsy, Atlanta, Georgia). In each group stone-free results were determined by plain abdominal x-ray and renal ultrasound 1 month after lithotripsy and efficiency quotients were developed. Baseline patient and stone characteristics were compared by the Wilcoxon rank sum and Fisher exact tests. All variables significant at p <0.05 were included in subsequent outcome analysis using multivariate logistic regression. Results: Baseline characteristics were equivalent, including patient age, gender, stone number and location, although patients treated with the electrohydraulic unit had a significantly larger median stone burden (103 versus 71 mm.2, p = 0.015). Multivariate regression analysis demonstrated a higher stone-free rate in the electrohydraulic group (77% versus 67%, p = 0.01) but also a higher rate of total adjunctive measures (56% versus 47%, p = 0.04). Consequently the efficiency quotients were comparable for the electrohydraulic and electromagnetic lithotripsy units (0.45 and 0.42, respectively, p = 0.43). Conclusions: Electrohydraulic lithotripsy resulted in a higher stone-free rate at 1 month, although it was associated with a higher rate of auxiliary measures. Ultimately the efficiency quotients were equivalent, implying that these 2 contemporary energy sources are acceptable. According to single center treatment and followup criteria they are equally efficacious.