Break Wave lithotripsy meets both co-primary end points in SOUND trial

The SOUND pivotal trial (NCT05701098) of Break Wave ultrasonic lithotripsy, a noninvasive, anesthesia-free device for the treatment of upper urinary tract stones, met both of its coprimary end points, demonstrating noninferiority to extracorporeal shock wave lithotripsy (ESWL) for safety and efficacy.

Results were presented by Ben H. Chew, MD, MSc, FRCSC, an endourologist at the University of British Columbia in Vancouver, at the 2026 American Urological Association (AUA) Annual Meeting.¹

How Break Wave works

Break Wave is a noninvasive lithotripsy platform developed by SonoMotion that uses ultrasonic burst waves to fragment urinary calculi without requiring anesthesia, sedation, or radiation exposure. The device is similar in external appearance to a standard diagnostic ultrasound machine, consisting of an imaging system with a dedicated probe; an internal generator creates the therapeutic waveform. The outer portion of the probe delivers focused ultrasonic energy in small packets that generate standing stress waves within the stone, producing a grid of high-stress points that lead to fragmentation.

"The secret sauce is just below the control panel…in this generator. This generator is actually what generates the Break Waves," Chew said. He distinguished Break Wave from conventional ESWL by the energy levels involved: ESWL delivers a single large shock of up to approximately 45 megapascals, whereas Break Wave operates at pressures up to 8 megapascals—analogous, he said, to the difference between a boxer striking a heavy bag vs a speed bag. The lower pressure amplitude inside the stone is approximately 10 times higher than in the surrounding tissue, a property that enables effective stone fragmentation while maintaining a low and safe pressure level in adjacent renal parenchyma.

According to Chew, because no sedation or anesthesia is required, Break Wave can be delivered in any clinical setting. The device can also be combined with the same platform's Stone Clear function, which uses ultrasound propulsion to reposition and expel stone fragments following lithotripsy—without additional anesthesia, x-ray exposure, or ionizing radiation.

SOUND trial design and patient population

The SOUND pivotal trial was a prospective, single-arm, open-label study conducted at 10 sites across the United States and Canada. The planned sample size was 64 eligible subjects. Study success was defined as noninferiority to ESWL for both coprimary end points, based on an objective performance criterion established in agreement with the FDA. One retreatment was permitted per protocol. The study timeline included a 2-week follow-up visit, 10-week imaging with kidney-ureter-bladder x-ray or CT, and a 90-day chart review.

Key inclusion criteria required subjects to be at least 18 years old with an upper urinary tract stone measuring greater than 4 mm and 10 mm or less on CT that was indicated for shock wave lithotripsy per AUA criteria and individually visualizable and separable on ultrasound. Exclusion criteria included untreated urinary tract infection or urosepsis, uncorrected bleeding disorder, anticoagulant use with inability to stop for the procedure, pregnancy, calcified aortic or renal artery aneurysm, distal urinary obstruction, stones not visible on ultrasound, and anatomy or acoustic window limitations precluding Break Wave delivery.

A total of 139 patients were consented; 75 were screen failures, and 64 were enrolled, comprising the modified intent-to-treat population. Of the 64 enrolled patients, 45 were from the United States and 19 from Canada. All 64 patients completed end-of-follow-up chart review (100% retention). Seventeen patients (27%) underwent Break Wave retreatment per protocol. Two imaging results were missing and were imputed under a missing-at-random assumption.

Mean patient age was 50.2 plus or minus 13.2 years; 39.1% were female, and 25% were of non-White race. Mean body mass index was 27.5 ± 4.0 kg/m². Mean stone size was 7.8 plus or minus 1.5 mm overall, with renal stones averaging 8.3 plus or minus 1.5 mm and ureteral stones 7.3 plus or minus 1.4 mm. (Four renal stones and one ureteral stone exceeded 10 mm per retrospective independent radiology assessment.) Mean stone density was 891 plus or minus 305 HU; 24 stones had a density of at least 1000 HU (mean 1195 ± 164 HU), and 40 had a density lower than 1000 HU (mean 709 ± 209 HU). Mean skin-to-stone distance on CT was 10.6 plus or minus 1.8 cm. A total of 57.8% of patients had a prior stone history. Stone locations were evenly split between renal (32 stones, 50%) and ureteral (32 stones, 50%), with the most common individual locations being the ureterovesical junction (UVJ; 32.8%), lower pole (29.7%), and distal ureter (14.1%).¹

Coprimary safety and effectiveness end points met

The primary safety co-end point assessed the rate of clinically significant or symptomatic perirenal or intrarenal hematoma, urinary tract sepsis, and serious cardiac arrhythmia. Zero events of any of these 3 types occurred in the 64-patient cohort (0.0%; 2-sided 95% CI, 0.0%-5.6%; P=.001). The upper bound of the 95% CI (5.6%) was below the prespecified noninferiority safety performance goal of 11.0%, established with the FDA to reflect ESWL's historical safety profile, thus meeting the primary safety end point.

The primary effectiveness co-end point was the proportion of subjects who were stone-free or had residual fragments of 4 mm or smaller on independent radiologist assessment at 10 plus or minus 2 weeks postfinal Break Wave procedure. The radiographic success rate was 70.0% (N=64; 2-sided 95% CI, 57.6%-80.0%; P = .0016). The lower bound of the 95% CI (57.6%) exceeded the prespecified noninferiority effectiveness performance goal of 50.9%, thereby meeting the primary effectiveness end point.

Fragmentation evidence and efficacy by stone location

Evidence of stone fragmentation—defined as stone passage or imaging confirmation—was observed in 98% of all stones, including 97% of renal stones, 100% of ureteral stones, 95% of lower pole stones, and 100% of UVJ stones.¹

Radiographic success rates varied by stone location. For renal stones overall, the success rate was 52%, with a stone-free rate of 26%, fragments 0 mm to 2 mm in 10%, and fragments 2 mm to 4 mm in 16%. For ureteral stones, the success rate was 87%, with a stone-free rate of 71%, fragments 0 mm to 2 mm in 16%. Lower pole stones achieved a 47% success rate (stone free, 21%; 0-2 mm, 11%; 2-4 mm, 16%). UVJ stones achieved a 90% success rate, with 80% stone free and 10% in the 0-2 mm range.¹

"About a third of them were in the lower pole, and a third of them were at the UV edge," Chew noted. "Forty-seven percent in the lower pole, which we know are harder—these are ones that have to go up and against the level of gravity in order to get out—and 90% success in the ureter."

Procedure characteristics and patient tolerability

Across all index and retreatment procedures (N=81), mean therapy delivery time was 29.7 plus or minus 1.2 minutes, and mean procedure-to-discharge time was 14.0 plus or minus 15.6 minutes, indicating patients were typically in and out of the office in approximately 45 to 60 minutes. The mean intraprocedural pain score was 2.0 plus or minus 1.4 on a 0 to 10 scale. No postprocedure ureteral stents were placed (0%). The onetime retreatment rate was 27%. Most procedures (94%) were performed in a clinic or office setting, with 6% in a surgical suite.

Adverse events (AEs) of any type occurred in 60 of 64 patients (93.8%). The most common were mild, with transient hematuria occurring in 87.5% of patients; this resolved spontaneously within a mean of 1.7 days across all hematuria events. Pain or renal colic occurred as a mild AE in 26.6% of patients and as a moderate AE in 12.5%. Moderate adverse events overall were reported in 18.8%, including 2 infections (3.1%), 1 episode of fever (1.6%), and 1 case each of moderate voiding changes and other findings. Severe adverse events occurred in 4.7% (3 patients), consisting of urinary obstruction (3 patients, 4.7%), voiding changes (1 patient, 1.6%), and pain or renal colic (1 patient, 1.6%). No patients required immediate unplanned intervention.¹

Chew emphasized that the AE profile was consistent with what is observed with ESWL, and that none of the 3 clinically significant AE types comprising the primary safety end point occurred in any patient.¹

Patient-reported treatment preference

Patient-reported preference data showed strong acceptance of Break Wave. Of 63 evaluable patients, 97% (61 of 63) stated they would choose the Break Wave procedure again for a future stone. Among patients with prior ureteroscopy (URS) experience (n=12), 92% (11 of 12) indicated they would prefer Break Wave over URS. Among patients with prior ESWL experience (n=13), 92% (12 of 13) stated they would prefer Break Wave over ESWL. Chew attributed the high preference rates primarily to the absence of anesthesia, the absence of bowel preparation requirements, and the ability to drive oneself to and from the procedure.

Screen failures and updated commercial probe

Among the 75 screen failures, the most common reason was lack of a viable acoustic window (41%), defined as insufficient space between the iliac crest and the 12th rib to accommodate the probe. Other screen failure reasons included stones not visible on ultrasound (19%), stone passage prior to treatment (15%), stone size outside protocol parameters (8%), multiple stones (8%), and other reasons (9%).

To address the acoustic window limitation, SonoMotion developed a smaller commercial probe with a footprint up to 31% smaller than the probe used in the SOUND trial, which has received FDA clearance and delivers the same clinical therapeutic dose. Preliminary results from 11 patients treated with the new commercial probe suggest improvements in stone-free rates: The overall stone-free rate increased from 48% (SOUND trial) to 64% with the new probe; renal stone-free rate increased from 26% to 50%; and ureteral stone-free rate increased from 71% to 100%. For lower pole stones, the success rate increased from 47% to 71% (n=6); for UVJ and distal ureter stones, success reached 100% (n=3).¹

Chew cautioned that the commercial probe data are based on a small number of cases and should be interpreted with appropriate caution pending further data. He suggested the improvements may reflect both expanded patient access due to the smaller probe footprint and potentially greater depth of energy penetration from a smaller probe surface area.

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