Increasing the pulse delivery rate of extracorporeal shock wave lithotripsy (ESWL) can provide excellent results in the management of ureteral stones, according to investigators.

Daniel P. Nguyen, MD, and colleagues at the University of Bern in Bern, Switzerland randomly assigned 254 patients with ureteral stones to receive a shock wave (SW) delivery rate of either 60 or 90 pulses per minute (130 and 124 patients, respectively).

The stone-free rate at 3 months—the study’s primary endpoint—was 91% in the group that received 90 pulses per minute compared with 80% in the group that received 60 pulses per minute, a significant difference between treatment arms, investigators reported in The Journal of Urology (2015;194:418-423). The significantly better stone-free rate observed with the 90 versus 60 pulses per minutes was observed in patients with proximal and mid-ureteral stones (100% vs. 83% and 96% vs. 73%, respectively), but not in those with distal ureteral stones.

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“These findings are relevant in the context of the decreasing popularity of ESWL for ureteral stones, indicating that optimizing the SW delivery rate can achieve excellent outcomes even for mid and proximal ureteral stones,” the authors wrote.

The researchers noted that favorable cavitation bubble dynamics may explain the superior ESWL efficacy at 90 pulses per minute. “Shock waves create pressure changes that lead to bubble formation,” they wrote. “When these bubbles collapse at the stone surface, they release high energy waves that induce stone fragmentation. An increased SW delivery rate leads to increased production of cavitation bubbles at the stone surface, potentially leading to enhanced fragmentation.”

The main study limitation was that all patients were treated with the modified HM-3 lithotripter, so it is unknown whether their results can be generalized to the current generation of electromagnetic or piezoelectric lithotripters, the researchers stated.