SLOW VERSUS FAST SHOCK WAVE LITHOTRIPSY RATE FOR UROLITHIASIS: A PROSPECTIVE RANDOMIZED STUDY KHALED MADBOULY, ABDEL MONEIM EL-TIRAIFI, MOHAMED SEIDA, SALAH R. EL-FAQIH, RAMIZ ATASSI AND RIYADH F. TALIC* From the Division of Urology, Department of Surgery, College of Medicine, King Khalid University Hospital, King Saud University, Riyadh, Kingdom of Saudi Arabia ABSTRACT 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 mm (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. KEY WORDS: lithotripsy, urinary calculi, ultrasonics, treatment outcome Treatment of patients with urinary calculi has undergone a dramatic change since the introduction of extracorporeal shock wave lithotripsy that proved to be highly effective with little morbidity. 1 Newer lithotriptors with the ungated shock wave technique (nonelectrocardiogram synchronized shock wave generation) allowed more rapid treatments. Cur- rently administration of shock wave lithotripsy (SWL) at rates of 100 to 120 shock waves (sws)/per minute is common- place in contrast to rates of 60 to 80 shock waves per minute in the original Dornier HM3 (Dornier Medical Systems, Mu- nich, Germany). 2 The effect of shock wave (SW) rate on stone comminution has been assessed by many authors using a variety of in vitro and animal models. It has been demonstrated that decreas- ing the SW rate may improve stone fragmentation. 3–5 How- ever, in vitro experiments may not have adequate reproduc- tion of the environment of a stone within the kidney nor the state of shock wave transmission through the body. Our study tested the hypothesis that changing the SW rate alters the success rate after SWL in the clinical setting. PATIENTS AND METHODS Between June 2001 and February 2002, 156 patients were prospectively randomized to receive SWL using either a slow SW (60 pulses per minute) or fast rate (120 pulses per minute) using an electromagnetic Siemens Lithostar Multi- line lithotriptor (Siemens AG, Munich, Germany). Inclusion criteria were patients with a single, radiopaque renal or ureteral stone not greater than 30 mm in maximum diame- ter. A complete pretreatment evaluation and excretory urogra- phy were performed in all patients. Stone length was meas- ured as the maximal stone diameter. Any patient with bleed- ing disorders, obstruction distal to the stone or severe uncontrolled urinary tract infection was excluded from study. Informed consent was obtained from all patients before treat- ment. All patients were treated while under epidural, spinal or general anesthesia. Patients with renal or upper ureteral calculi were treated in the supine position. For lower ure- teral stones patients were turned prone. Patients were dis- charged home the next day after a plain radiograph was obtained. All treatments were supervised by 2 urologists (KM and MS). Followup data were collected and analyzed at the 3-month visit. Success was defined as being completely stone-free or having clinically insignificant gravel smaller than 2 mm. Patient characteristics, stone and therapy features were re- viewed and correlated to success and SWL rates using the chi-square, Fisher exact and Mann-Whitney tests with dif- ferences considered statistically significant if p 0.05 (table 1). Factors proven to be significant in univariate analysis Submitted for publication April 19, 2004. * Correspondence: Department of Surgery (37), P.O. Box 7805, Riyadh 11472, King Khalid University Hospital, Kingdom of Saudi Arabia (telephone: 96614671836; cellular: 966505440016; FAX: 96614679493; e-mail: rftalic@hotmail.com). 0022-5347/05/1731-0127/0 Vol. 173, 127–130, January 2005 THE JOURNAL OF UROLOGY ® Printed in U.S.A. Copyright © 2005 by AMERICAN UROLOGICAL ASSOCIATION DOI: 10.1097/01.ju.0000147820.36996.86 127