Pachaiyappan J. et al., 2025: Ultraslow versus slow-rate shockwave lithotripsy in the management of renal stone: A randomized controlled trial.

Jalaram Pachaiyappan, Santosh Kumar, Santhosh Nagasubramanian, T J Nirmal, Rajiv Paul Mukha 
Indian J Urol. 2025 Oct-Dec;41(4):253-259. doi: 10.4103/iju.iju_229_25. 

Abstract

Introduction: This study aimed to evaluate the efficacy of ultraslow shockwave (SW) lithotripsy compared with slow-rate SW lithotripsy (SWL) in the management of renal stones using a common power ramping protocol.

Methods: This randomized trial enrolled patients with solitary renal calculus ≤2 cms between December 2021 and February 2024. Ultraslow lithotripsy (40 patients) was applied at a rate of 30 shocks per minute and slowrate lithotripsy (40 patients) was applied at a rate of 60 shocks per minute. Common power ramping protocol was followed for both the groups. Up to a maximum of three sessions were carried out with follow-up at 3 months after the last session. The primary outcome was the stone-free rate.

Results: The overall stone-free rate (SFR) was 77.5% in the ultraslow arm and 72.5% in the slow-rate arm (P = 0.60). Ultraslow group attained a higher SFR after the first session (37.5% vs. 20%; P = 0.07) with significantly lesser number of shocks (1300 vs. 1500; P < 0.01). Complications were only mild and similar between both the groups (P = 0.06), with a longer treatment duration in the ultraslow group (100 min vs. 50 min; P < 0.01).

Conclusions: In the setting of an electromagnetic lithotripter with a common ramping protocol and equal energy SWs, both ultraslow and slowrate SWL achieved a comparable overall stone-free rate with a similar safety profile. Higher number of patients in the ultraslow arm, almost double that of the slow arm, attained stone-free status after the first session itself with significantly fewer shocks.

Comment Peter Alken

This is a well described and performed prospective randomized study showing a few similarities and differences between the two study arms. The problem I see is with the case numbers and the statistical power of the results. “The sample size was calculated based on the SFR of a previous study. In a previously published paper on ultraslow-versus slow rate SWL, SFR was 76% versus 39%. With this value, 90% power, 5% alpha, and two sided test, the study required totally 40 subjects in each of two groups.” The previous study they refer to was done by another group with a different lithotripter, a larger patient group of ̴ 80 cases vs 40 per group, on stones of different size of ̴ 18mm vs. ̴ 9mm in the present study, a different treatment protocol and a different outcome showing a 76% vs 38.5 % difference of SFR in favour of the slow frequency group (1) The subsequent small number in the present study probably fails to show significant differences.
The contemporary typical limitation mentioned in both studies is that they do not follow three strong recommendations of the 2025 EAU Urolithiasis guideline:
1. “Consider the stone composition before deciding on the method of removal, based on patient
history, former stone analysis of the patient or Hounsfield unit on unenhanced computed
tomography.
2. Perform stone analysis in first-time formers using a valid procedure (X-ray diffraction or
infrared spectroscopy).
3 .Repeat stone analysis in patients presenting with:
• recurrent stones despite drug therapy;
• early recurrence after complete stone clearance;
• late recurrence after a long stone-free period because stone composition may change.”
This basis neglect of common urological rules is well documented in the limitations mentioned in reference 1: “Another drawback was the absence of data on stone analysis. Most of the analyzed stones were collected from failed cases who were subjected to alternative treatment procedures (i.e. PCNL); thus, mostly non-representable for the stone composition profile in all patients.”
Well, it would have helped to know the stone composition of those failed case to prevent repeating a failure in the next case.

1 Al-Dessoukey AA, Abdallah M, Moussa AS, Sayed O, Abdelbary AM, Abdallah R, Massoud AM, Abdelhamid MH, Elmarakbi AA, Ragheb AM, ElSheemy MS, Ghoneima W. Ultraslow full-power shock wave lithotripsy versus slow power-ramping shock wave lithotripsy in stones with high attenuation value: A randomized comparative study. Int J Urol. 2020 Feb;27(2):165-170. doi: 10.1111/iju.14158. Epub 2019 Dec 2. PMID: 31793084.

Peter Alken