Real-time cavitation monitoring drives Break Wave's renal hematoma safety advantage

The favorable safety profile of Break Wave lithotripsy in the SOUND pivotal trial (NCT05701098)¹ reflects not just the absence of serious adverse events, but specific physical mechanisms that structurally limit the risk of the complications most associated with conventional shock wave lithotripsy—and the boundaries of patient and stone selection remain an active area of exploration as the technology enters commercial use, according to Ben H. Chew, MD, MSc, FRCSC.

The adverse events observed in the trial were consistent with what clinicians expect from any lithotripsy modality: mild transient hematuria, passage-related pain, and occasional renal colic. No patients required urgent intervention, and no cases of sepsis, renal hematoma, or arrhythmia occurred. Chew attributed the absence of renal hematoma to a specific safety advantage of Break Wave's ultrasound-guided delivery: real-time visualization of cavitation bubbles.

"With regular shock wave lithotripsy, when you're doing fluoroscopy, you actually do not see the cavitation bubbles," Chew said. Cavitation is the same mechanism exploited by ablative therapies such as high-intensity focused ultrasound to destroy tissue. In conventional shock wave lithotripsy, it is a byproduct that progressively reduces the efficacy of subsequent shocks and can cause renal parenchymal damage. Because Break Wave uses continuous ultrasound monitoring, cavitation is visible in real time.

"Because we're able to identify it, we're able to stop, adjust the frequency, adjust our angle, and do something in order to change this so the cavitation settles down and we don't get that," he said.

The absence of arrhythmias is similarly mechanistic. Conventional shock wave lithotripsy delivers energy at pressures of 45 to 100 megapascals — enough to cause cardiac rhythm disturbances, particularly when treating right-sided stones where the energy path traverses toward the heart. Break Wave operates at 8 megapascals, delivered not as a single high-intensity shock but as small packets at resonant frequency.

"Because we're at such a lower intensity energy than regular shock wave lithotripsy, this is why we're not seeing any arrhythmias," Chew said. ECG monitoring during procedures remains an FDA requirement, but no arrhythmias have been recorded across the trial population.

The mechanism by which Break Wave fragments stone also differs fundamentally from shock wave lithotripsy. Rather than applying a single large pressure wave that fractures stone from the inside out, Break Wave vibrates stone at resonant frequency from the outside in—a process Chew likened to dusting rather than fragmenting. This has implications for Hounsfield unit thresholds, which are central to patient selection for conventional shock wave.

"Hounsfield units are still important in Break Wave, but much less so," Chew said, noting that approximately two thirds of SOUND trial patients had stones around 1200 Hounsfield units—above the conventional 1000-unit threshold—yet the trial still achieved its primary efficacy end point.

Questions around patient anatomy, larger stone burdens, and greater skin-to-stone distances represent an exploratory frontier. The pivotal trial confined enrollment to stones 10 mm or smaller and skin-to-stone distances under 10 cm—parameters Chew acknowledged are likely conservative.

"I think we're going to find out where those limits are once this gets commercially available," he said. "We think we can tackle bigger stones and probably deliver more energy than we have in this pivotal trial."

REFERENCE

1. Chew BH, Harper JD, Ahn J, et al. SOUND pivotal trial of Break Wave lithotripsy for upper urinary tract stones. Presented at: 2026 American Urological Association Annual Meeting; May 15-18, 2026; Washington, DC. https://www.auajournals.org/doi/10.1097/01.JU.0001192572.07890.f8.03