Harper JD. et al., 2022: Fragmentation of Stones by Burst Wave Lithotripsy in the First 19 Humans.
Harper JD, Lingeman JE, Sweet RM, Metzler IS, Sunaryo P, Williams JC Jr, Maxwell AD, Thiel J, Cunitz BW, Dunmire B, Bailey MR, Sorensen MD.
Department of Urology, University of Washington School of Medicine, Seattle, Washington.
Department of Urology, Indiana University School of Medicine, Indianapolis, Indiana.
Department of Urology, Northwest Permanente, Portland, Oregon.
Department of Anatomy, Cell Biology, and Physiology, Indiana University School of Medicine, Indianapolis, Indiana.
Center for Industrial and Medical Ultrasound, Applied Physics Laboratory, University of Washington,Seattle, Washington.
Division of Urology, Veterans Affairs Puget Sound Health Care System, Seattle, Washington.
Purpose: We report stone comminution in the first 19 human subjects by burst wave lithotripsy (BWL), which is the transcutaneous application of focused, cyclic ultrasound pulses.
Materials and methods: This was a prospective multi-institutional feasibility study recruiting subjects undergoing clinical ureteroscopy (URS) for at least 1 stone ≤12 mm as measured on computerized tomography. During the planned URS, either before or after ureteroscope insertion, BWL was administered with a handheld transducer, and any stone fragmentation and tissue injury were observed. Up to 3 stones per subject were targeted, each for a maximum of 10 minutes. The primary effectiveness outcome was the volume percent comminution of the stone into fragments ≤2 mm. The primary safety outcome was the independent, blinded visual scoring of tissue injury from the URS video.
Results: Overall, median stone comminution was 90% (IQR 20, 100) of stone volume with 21 of 23 (91%) stones fragmented. Complete fragmentation (all fragments ≤2 mm) within 10 minutes of BWL occurred in 9 of 23 stones (39%). Of the 6 least comminuted stones, likely causative factors for decreased effectiveness included stones that were larger than the BWL beamwidth, smaller than the BWL wavelength or the introduction of air bubbles from the ureteroscope. Mild reddening of the papilla and hematuria emanating from the papilla were observed ureteroscopically.
Conclusions: The first study of BWL in human subjects resulted in a median of 90% comminution of the total stone volume into fragments ≤2 mm within 10 minutes of BWL exposure with only mild tissue injury.
J Urol. 2022 Mar 21:101097JU0000000000002446. doi: 10.1097/JU.0000000000002446. Online ahead of print. PMID: 35311351. FREE ARTICLE
Burst Wave Lithotripsy (BWL) is new technique for human stone fragmentation using bursts of ultrasound waves instead of single pulse of shock waves (SWL) for comminution of different kinds of stones. The ambitious goal is to improve the quality of fragmentation to all fragments ≤2 mm keeping tissue injury mild.
After years of development the authors present first clinical results of BWL. Successful first human application is always a milestone and a decisive requirement for later clinical usefulness.
The authors conclude: The first study of BWL in human subjects resulted in a median of 90% comminution of the total stone volume into fragments ≤2 mm within 10 minutes of BWL exposure with only mild tissue injury. Congratulation for that.
This new technique intends to invade the well-established field of SWL, the results of BWL may be compared to SWL.
1. Stone location during treatment is based on in-line sonography. Due to limited flexibility the in-line mounted US transducer, image quality was often not sufficient to visualize known stones with the device. In 19 of 42 of the selected patients, the stones could not be targeted by in-line sonography. (exclusion criterion, not easy to improve). Many stones (e.g ureteral stones) require X-ray localization.
2. Limited penetration depth up to 7cm restricts treatment of obese patients. BMI ≤24 kg m2 Current SWL feature up to 18 cm focal depth. A linear extension up to acceptable values 12-15 cm (minimum for obese patients) would significantly enlarge the device, make it heavier and reduce the hand-held flexibility.
3. Patient were under general anaesthesia, what may facilitate precision of targeting. A wake patient, feeling some pain, may move and reduce accuracy of targeting.
4. The aimed fragmentation ability to ≤2 mm size was limited to 39% of the selected stones ≤12mm. Fig. 3 of the paper shows fragments much larger than 2mm although the initial size was only ~ 6 mm. Current SWL is recommended up to 20mm stones and more. Stone size and composition is a critical feature for success of fragmentation.
5. The idea, simply to increase the power of the bursts, may be not appropriate since side effects and tissue injuries and the disposition to generate excessive cavitation may increase.
The authors state: The results are a step toward an office-based lithotripsy for awake patients.
There is no doubt that this paper shows the capability of BWL in successful human applications.
In spite of the presented achievements, I see more technical and applicational steps to be done before BWL will find its place in routine clinical stone therapy.
My critical view of the paper is motivated by my year’s long experience of developing lithotripter devices, knowing all about hassles and pitfalls. Particularly the development of a reliable and practicable sonographic identification and targeting device for human gallbladder stones required a considerable technical effort before the first human application could be successfully performed in the year 1985. Good Luck.