Anna J Sharp et al., 2024: Matched pair analysis of wide versus narrow focus during shockwave lithotripsy for urolithiasis

Anna J Sharp, Catherine E Lovegrove, Roshan Sreekumar, Mandy Spencer, Benjamin W Turney Urolithiasis. 2024 Dec 21;53(1):11. doi: 10.1007/s00240-024-01682-0

Abstract

Purpose: To compare stone clearance and complications between a 'wide' (9 × 50 mm) and 'narrow' shockwave focus (6 × 28 mm) when undertaking shockwave lithotripsy (SWL) in patients with renal or ureteric stones.

Methods: Data from patients undergoing SWL using the dual focus Storz Modulith SLX-F2 lithotripter at a single centre were prospectively collected between February 2018 and September 2020. Patients were matched by stone size, location, and number of treatments. Stone clearance, re-presentation within 31 days, symptoms, complications, and need for post SWL-interventions were compared using McNemar's test.

Results: Patients receiving wide focus SWL (WF-SWL, n = 152) were matched with patients receiving narrow focus SWL (NF-SWL, n = 152). Median stone size was 6 mm; energy delivered to WF-SWL and NF-SWL groups was comparable. Complete stone clearance was achieved in 55% of WF-SWL patients (n = 84) and 41% (n = 63) of NF-SWL patients (p = 0.04). Treatment was considered successful in 74% (n = 113) of WF-SWL cases and 66% (n = 100) of NF-SWL (p = 0.20). No difference in rates of readmission, post-procedural pain, haematuria, urinary tract infections, analgesia or antibiotic requirements were identified.

Conclusion: This service evaluation demonstrates no differences in rates of overall treatment success nor complications on comparing WF-SWL and NF-SWL.

Comment Hans-Göran Tiselius

The importance of the SWL focus size is considered fundamental for the outcome of the treatment. The Storz SLX-F2 lithotripter is equipped with a reflector offering two focus sizes: 9 x 50 mm and 6 x 28 mm. In this report the outcome of the lithotripsy was not significantly different with these two machine settings despite matched comparisons. These results were about the same as those recorded for ureteral stones treated with the SLX-F2 device in my own department [1].
The most effective geometry and energy delivered during SWL has remained a matter of discussion ever since SWL was first introduced. There has been no definite explanation for why the original Dornier HM3 lithotripter was so effective and had a superior capacity to disintegrate large stones compared with modern lithotripters.
The importance of a large focus for Dornier HM3 has been explained by combining this geometry with low energy density and relatively slow administration of shockwaves. The Dornier HM3 lithotripter had a focus size of 15 x 60 mm and it was concluded that the large diameter supported stone disintegration by taking advantage of the squeezing forces enabled in the large focus.
Little attention subsequently has been paid to the geometry of the reflector and the energy density in that lithotripter. Only Eisenmenger used a lithotripter with large focus and low energy density [2] and reported interesting results. Similarly interesting findings were reported in an animal experiment in 2008 [3]. After that there are no reports emphasising these lithotripter properties.
The reason for a lack of interest in these aspects can certainly be explained by the fading interest in SWL in the shadow of the endourological enthusiasm that has characterized stone removal during recent years. With less successful results of SWL the indications of non-invasive lithotripsy also were changed. Accordingly, there has been little interest for manufacturers of lithotripters to deal with these lithotripter properties. Nevertheless, it is the reviewer’s opinion that further interest in the aspects discussed above would be beneficial for SWL and re-establish SWL as a basic treatment of stones in the kidney and ureters also above the size limits applied today in all guidelines and to a much lower cost than is caused by endourological surgery.
References
1. Tiselius HG.How efficient is extracorporeal shockwave lithotripsy with modern lithotripters for removal of ureteral stones? J Endourol. 2008 Feb;22(2):249-55. doi: 10.1089/end.2007.0225.
2. Eisenmenger W, Du XX, Tang C, Zhao S, Wang Y, Rong F, Dai D, Guan M, Qi A.The first clinical results of "wide-focus and low-pressure" ESWL.Ultrasound Med Biol. 2002 Jun;28(6):769-74. doi: 10.1016/s0301-5629(02)00507-0.
3. Evan AP, McAteer JA, Connors BA, Pishchalnikov YA, Handa RK, Blomgren P, Willis LR, Williams JC Jr, Lingeman JE, Gao S.Independent assessment of a wide-focus, low-pressure electromagnetic lithotripter: absence of renal bioeffects in the pig. BJU Int. 2008 Feb;101(3):382-8. doi: 10.1111/j.1464-410X.2007.07231.x. Epub 2007 Oct 8.PMID: 17922871

Hans-Göran Tiselius