#  Lithotripsy literature database Reviewer's Choice

##  Rassweiler J. et al., 2021: In-vitro comparison of two electromagnetic shock-wave generators: low-pressure-wide focus versus high-pressure small focus - the impact on initial stone fragmentation and final stone comminution.

Rassweiler J, Rieker P, Pecha R, Dressel M, Rassweiler-Seyfried MC.
J Endourol. 2021 Jul 27. [doi: 10.1089/end.2021.0416](https://pubmed.ncbi.nlm.nih.gov/34314251/)

## Abstract

Context: Recently developed concepts for higher efficacy ESWL with low-pressure wide focus systems resulting in finer fragmentation of the calculi.

Objective: To compare two different electromagnetic shock wave sources (low-pressure wide focus (XL) versus high-pressure small focus (SL)) by sound-field measurements and in-vitro fragmentation.

Evidence acquisition: The CS-2012A XX-ES lithotripter (self-focusing electromagnetic shock-wave generator with concave spherical curved electrical coil; Xinin Lithotripter = XL) was compared to the Siemens Lithoskop (= SL) (electromagnetic generator with a flat electric coil with an acoustical lens). Different sound-field measurements were performed using a fiber-optic hydrophone. Measurements at three different power settings (XL: 8.0kV, 9.3kV and 10.3kV; SL: Level 1, 5 and 8). 10 ATS-stones and 15 BegoStones (9.3 kV, Level 3) with a frequency of 90/minute (SL) and 20/minute (XL). Number of impulses to the first crack and for complete stone comminution (residual fragments <2mm) were documented.

Results: The median number of shock waves for the first crack in ATS-stones with the XL was 12 (10-14), with the SL 7 (6-9). Complete disintegration was accomplished after 815 (782-824) shock waves with XL, 702 (688-712) with SL. The difference was not statistically significant. The median number of shock waves to produce the first crack in BegoStones was 524 (504-542) with XL and only 151 (137-161) with SL. Numbers of shock waves for complete disintegration did not differ significantly (XL:2518 vs SL:2287). Using a wide focus with low pressure shows more homogeneous disintegration.

Conclusion: Two stone models showed significant differences regarding form and time of the initial fragmentation. Impulses for stone comminution did not differ significantly. The advantages of a low-pressure wide focus-system include minimal trauma and a homogeneous fragment size but is more time consuming. High-pressure small-focus systems are clinically effective.

## Comment Hans-Göran Tiselius

This is one of the most interesting articles regarding SWL that I have seen during the past years. It was early noted that there was a difference in results obtained with the original unmodified HM3-lithotripter and several or all modern late generations of lithotripters. Authorities in the field of stone treatments have claimed that the outstanding results obtained with the HM3 device so far not have been attained \[1\]. Although personally I am very satisfied with the accomplishments with modern shockwave technology these achievements are based on experience with Storz lithotripters (SLX, SLXF2). Having said that I need to add that some occasional achievements recorded with the Dornier HM3 lithotripter would be, if not impossible, so at least very difficult to attain with the small focus and high-pressure devices that most commonly are used today. This is of course of minor importance, but more remarkable is it that 40 years after introduction of SWL we still do not know which geometry and focus energy that is optimal. One basic question remains: Should we use a large focus with low energy density or a small focus with high energy density (like that in Storz Modulith lithotripters).

Irrespective of what the answer to that question might be, it is important to know that despite complains about the lack of progress in SWL, several technical achievements have been incorporated in modern lithotripters. Thus, it was possible to replace the water tub with a “dry” shock wave transmission and nevertheless maintain acceptable energy levels. The electrohydraulic technology was replaced by electromagnetic sources. It was clearly demonstrated that SWL can be completed with only analgesics and sedatives. However, contrary to what urologists in general believe this kind of pain treatment was possible also with the unmodified Dornier HM3 lithotripter \[2\].
In this report the authors have compared the in-vitro properties between the Xi lithotripter with large focal volume, low energy density and slow shockwave generation and those obtained with small focal volume and high energy and shockwaves delivered at a frequency of 1.5 Hz.

The authors claim that it now is necessary to consider that in the competition between endoscopic procedures (URS, RIRS and PCNL) and SWL, the latter method seems to come out as a looser. An increasing number of urologists favour endourological methods. Why is this so? There are some factors that might explain this strategy. Endoscopy can result in stone removal usually without re-treatments and this technology certainly satisfies the surgical mind of most urologists, or expressed differently, endourology is considered less boring than SWL.

Is it true that the achievements with the HM3 device is superior to those obtained with modern lithotripters? This question is difficult to answer today because in modern guidelines, and accordingly in the current clinical use of SWL there is an increasingly narrow range of indications for SWL. Whereas stones of 30 mm or more 30 years ago were considered as candidates for SWL, the limits subsequently have decreased to 25, 20 or 10- 15 mm and there are some recent studies that have suggested a limit at 5 mm \[3\]. The fundamental question that seeks an answer seems to be if there is anything that we have missed during 40 years of development of SWL technology?

One factor that recently has been put forward is that stones with modern laser technology can be turned into dust rather than fragments. The conclusion drawn by the authors of the current report is that if SWL should survive in competition with modern endourology, it is necessary to improve SWL in direction of dusting rather than disintegration. Solutions presented so far have been burst-wave lithotripsy of which there still is very limited clinical experience. Moreover, it was presented at the recent German Urology meeting that high-frequency generation of shockwaves successfully disintegrated stones to ts subsequently should be eliminated with an efficient non-invasive method.

During all years that I spent with SWL, stone disintegration, pain treatment and the need of repeated sessions were not the major clinical problems. The most annoying shortcoming was the presence of residuals at follow-up whether occurring as dust or fragments. In my mind elimination of residuals was the greatest concern encountered in most patients.

References
1\. Zehnder P, Roth B, Birkhäuser F, Schneider S, Schmutz R, Thalmann GN, Studer U
A prospective randomised trial comparing the modified HM3 with the MODULITH® SLX-F2 lithotripter. E.Eur Urol. 2011 Apr;59(4):637-44. doi: 10.1016/j.eururo.2011.01.026. Epub 2011 Jan 25.PMID: 21296481 Clinical Trial.
2\. Tiselius HG.
Anesthesia-free in situ extracorporeal shock wave lithotripsy of ureteral stones.
J Urol. 1991 Jul;146(1):8-12. doi: 10.1016/s0022-5347(17)37701-7.PMID: 2056608
3\. Al-Zubi M, Al Sleibi A, Elayan BM, Al-Issawi SZ, Bani-Hani M, Alsharei A, AlSmadi J,
Abualhaj S, Ibrahim AY.The effect of stone and patient characteristics in predicting extra-corporal shock wave lithotripsy success rate: A cross sectional study. Ann Med Surg (Lond). 2021 Sep 10;70:102829. doi: 10.1016/j.amsu.2021.102829. eCollection 2021 Oct.PMID: 34540217
4\. Rassweiler-Seyfried MC, Mayer J, Goldenstedt C, Storz R, Marlhaus E, Heine G, Alken P.
Elektrohydraulische Hochfrequenz ESWL – Evaluation der Niernenschäden. Urologe A 2020; 59; Sippl (Abstract 77)
Hans-Göran Tiselius

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