Shockwave frequency affects fragmentation in a kidney stone model

PURPOSE: To study the effect of altering shockwave frequency on the efficiency of stone fragmentation using the MFL 5000 spark-gap lithotripter. MATERIALS AND METHODS: Standardized solid plaster stones, 12.0 +/- 0.5 mm in diameter, were fragmented at an energy setting of 20 kV. The shockwave frequencies tested were 60, 80, and 117 per minute. Stones were fragmented throughout the entire lifespan of the electrode, from 0 to >100% consumption, at each frequency tested. Electrode pressure output was studied for each frequency. RESULTS: A greater number of shocks was required to fragment the plaster balls at higher frequencies (regression coefficient 1.93; p < 0.003). An inverse relation was found between the number of shocks necessary to break the stones and electrode consumption (regression coefficient -2.16; p < 0.001). The analysis of delivered pressure from the electrode failed to demonstrate a linear relation with frequency (regression coefficient -0.40; p < 0.728) or consumption (regression coefficient -1.11; p < 0.158). CONCLUSIONS: The number of shocks required to fragment a stone is influenced in part by the frequency at which the shockwaves are delivered. Increasing the shockwave frequency from 60 to 117 per minute in this study caused a significant rise in the number of shocks required to break the stone. The pressure output of the electrode was similar at the frequencies tested, thus making the difference in stone fragmentation secondary to the mechanism of stone disintegration and not the function of the electrode.     

Dual-head lithotripsy in synchronous mode: acute effect on renal function and morphology in the pig

OBJECTIVE: To assess the effect of dual-head lithotripsy on renal function and morphology in a pig model of shockwave (SW) injury, as lithotripters with two shock heads are now available for treating patients, but little information is available with which to judge the safety of treatment with dual pulses. MATERIALS AND METHODS: A dual-head electrohydraulic lithotripter (Duet, Direx Corp., Natick, MA, USA) was used to treat the lower renal pole of anaesthetized pigs with a clinical dose of SWs (2400 dual SWs; 10 kidneys) delivered in synchronous mode, i.e. both heads fired simultaneously. For comparison, pigs were treated with either 2400 SWs (12 kidneys) or 4800 SWs (eight) with a conventional electrohydraulic lithotripter (HM3, Dornier, Wessling, Germany). RESULTS: Dual-pulse SW treatment with the Duet lithotripter caused a decline in the mean (sd) glomerular filtration rate (GFR) of 4.1 (1.9) mL/min, with a trend for the effective renal plasma flow (RPF), at 31 (19) mL/min, to also decrease. These changes in renal haemodynamics were similar to the decreases in GFR and RPF in response to treatment with the HM3 lithotripter with 2400 SWs, at 4.8 (0.8) and 32 (10) mL/min, respectively, or 4800 SWs, at 5.4 (1.0) and 68 (14) mL/min, respectively. Linear association analysis showed that the functional response to dual-pulse SWs was more variable than with conventional SWs. Morphological quantification of kidney damage (expressed as a percentage of functional renal volume, FRV) showed that tissue injury with 2400 paired SWs with the Duet, at 0.96 (0.39)% FRV, was similar to injury produced by either 2400 single SWs, at 1.08 (0.38)% FRV, or 4800 single SWs, at 2.71 (1.02)% FRV, with the HM3. However, morphological damage was less consistent with the Duet (measurable in only five of eight kidneys) than that with the HM3 (measurable in all 12 kidneys). Acoustic output and the timing of dual SWs in synchronous mode increased in variability as the electrodes aged, affecting the amplitude and targeting of focal pressures. CONCLUSION: With the caveat that variability in the timing of dual SWs will unpredictably alter the distribution of SW energy within the kidney, this study shows that a clinical dose of dual-head SWs delivered in synchronous mode elicits a renal response similar to, but more variable than, that with a clinical dose of SWs from a conventional electrohydraulic lithotripter.     

Why stones break better at slow shockwave rates than at fast rates: in vitro study with a research electrohydraulic lithotripter

BACKGROUND AND PURPOSE: Stones break better when the rate of shockwave (SW) delivery is slowed. It has been hypothesized that the greater cavitation accompanying a fast rate shields pulse propagation, thus interfering with the delivery of SW energy to the stone. We tested this idea by correlating waveforms measured at the SW focus with cavitation viewed using high-speed imaging. MATERIALS AND METHODS: A series of U30 gypsum stones held in a 2-mm mesh basket were exposed to 200 SWs at 30 or 120 SW/min from a research electrohydraulic lithotripter (HM3 clone). Waveforms were collected using a fiberoptic probe hydrophone. High-speed imaging was used to observe cavitation bubbles in the water and at the stone surface. Results: Stone breakage was significantly better at 30 SW/min than at 120 SW/min. The rate had little effect on SW parameters in the water free field. In the presence of particulates released from stones, the positive pressure of the SW remained unaffected, but the trailing tensile phase of the pulse was significantly reduced at 120 SW/min. CONCLUSIONS: Cavitation bubbles do not persist between SWs. Thus, mature bubbles from one pulse do not interfere with the next pulse, even at 120 SW/min. However, cavitation nuclei carried by fine particles released from stones can persist between pulses. These nuclei have little effect on the compressive wave but seed cavitation under the influence of the tensile wave. Bubble growth draws energy from the negative-pressure phase of the SW, reducing its amplitude. This likely affects the dynamics of cavitation bubble clusters at the stone surface, reducing the effectiveness of bubble action in stone comminution.     

CT attenuation value and shockwave fragmentation

PURPOSE: To evaluate whether, in principle, the mean CT attenuation values of kidney stones could predict fragmentation by shockwaves. MATERIALS AND METHODS: Four types of artificial kidney stones having different CT attenuation values were tested. Artificial stones were weighed and exposed to 700 shockwaves at 21 kV at the focus of an electrohydraulic lithotripter. Fragments were strained through meshes with 2x2-mm and 3.1x3.1-mm openings. The material left on the meshes after shockwave exposure was dried and weighed on a precision scale. Half of all artificial stones were saturated by immersing them in water several days before fragmentation. Fragmentation coefficients (i.e., percent weight loss) were associated with CT attenuation values using a statistical model. RESULTS: Higher CT numbers resulted in lower fragmentation coefficients. Artificial stone weight was inversely proportional to the percent weight loss. Larger fragments were obtained at lower fragmentation coefficients. Statistical analysis revealed that fragmentation can be predicted knowing the weight and the CT number of a stone before shockwave application. CONCLUSION: Prediction of the number of shockwaves necessary for successful SWL could be possible. Our statistical model proved to fit in vitro fragmentation of artificial stones; however, clinical application requires further research.     

Variability of protein content in calcium oxalate monohydrate stones

BACKGROUND AND PURPOSE: Urinary stones are heterogeneous in their fragility to lithotripter shockwaves. As a first step in gaining a better understanding of the role of matrix in stone fragility, we measured extractible protein in calcium oxalate monohydrate (COM) stones that were extensively characterized by micro-computed tomography (micro CT). MATERIALS AND METHODS: Stones were scanned using micro CT (Scanco mCT20, 34 microm). They were ground, and the protein extracted using four methods: 0.25M EDTA, 2% SDS reducing buffer, 9M urea buffer, and 10% acetic acid. Protein was measured using NanoOrange. The SDS extracts were also examined using polyacrylamide electrophoresis (PAGE). RESULTs: Extracted protein was highest with the SDS or urea methods (0.28% +/- 0.13% and 0.24% +/- 0.11%, respectively) and lower using the EDTA method (0.17% +/- 0.05%; P < 0.02). Acetic acid extracted little protein (0.006 +/- 0.002%; P < 0.001). Individual stones were significantly different in extractability of protein by the different methods, and SDS-PAGE revealed different protein patterns for individual stones. Extracted protein did not correlate with X-ray-lucent void percentage, which ranged from 0.06% to 2.8% of stone volume, or with apatite content. CONCLUSIONS: Extractible stone-matrix protein differs for individual COM stones, and yield is dependent on the extraction method. The presence of X-ray-lucent voids or minor amounts of apatite in stones did not correlate with protein content. The amounts of protein recovered were much lower than reported by Boyce, showing that these methods extracted only a fraction of the protein bound up in the stones. The results suggest that none of the methods tested will be useful for helping to answer the question of whether matrix content differs among stones of differing fragility to lithotripter shockwaves.     

Optimizing results of lithotripsy using robust electromagnetic probe.

BACKGROUND AND OBJECTIVE: A significant impediment to the measurement of the pressures and forces created by lithotripter shockwaves has been their destructive properties, which have rendered most measuring devices impractical. We have developed and tested a robust electromagnetic probe to measure cavitational forces in vitro in the focal zones of extracorporeal lithotripters. The probe responds to the pressure gradient generated by the radial motion of cavitation bubbles. MATERIALS AND METHODS: The effects of shockwaves from the Dornier MPL 9000 electrohydraulic lithotripter were measured over the lifetime of multiple electrodes. RESULTS: The pulse energy from the electrodes dropped off rapidly after approximately 50% of the lifetime quoted by the manufacturer. The electrodes were more efficient at higher power settings. As a result, we altered our protocol for the treatment of ureteral stones to use a higher kilovoltage and a second electrode whenever necessary. Stone-free rates after shockwave lithotripsy (SWL) in situ for stones < 11 mm have increased from 68.2% to 83.3%, and the retreatment rate has dropped from 23% to 15%. Despite significantly higher power settings (23.7 kV v 18.7 kV; P < 0.0001), the need for sedoanalgesia has remained relatively constant (26% v 31%). CONCLUSIONS: Measurement of cavitational forces from lithotripters using a robust electromagnetic probe is useful in planning treatment strategy. We have demonstrated a clinically measurable improvement since implementing our new treatment protocol. Because the probe responds directly to cavitational forces, it should also prove useful for the objective comparison of different SWL machines.     

Extracorporeal shock wave lithotripsy with a transportable electrohydraulic lithotripter: experience with >300 patients

OBJECTIVE: To review a multicentre experience of using a transportable lithotripter (STS-T, Medstone, Inc, Aliso Viejo, CA. USA) for treating patients with urolithiasis in all parts of the urinary tract. PATIENTS AND METHODS: In all, 326 patients with a total of 370 stones were treated as outpatients with the STS-T lithotripter. All patients received a single shock wave lithotripsy treatment and were followed after 4-6 weeks in the outpatient clinic, the primary endpoint being to determine the efficacy (as defined by the stone-free rate). Secondary objectives included establishing a database of patient demographic information, stone characteristics, stone location, procedural endpoints, and complication rates. RESULTS: In all there were 370 procedures, with a mean of 2394 shocks administered at an energy level of 24 kV. The mean treatment time was 51 min, excluding anaesthesia-induction time. The mean stone aggregate size was 8.2 mm; 62% of the stones were in the kidney while 38% were in various locations in the ureter. Of the treated stones, 90% had definite or probable evidence of fragmentation. The overall stone-free rate after one treatment with the STS-T was 52.8%. Of patients with residual fragments, most (61%) had fragments of <4 mm in aggregate diameter. The overall complication rate was 3.8%, the most common complication being postoperative pain. CONCLUSION: The Medstone STS-T lithotripter was an effective device for treating urolithiasis in all parts of the urinary tract. This system had a high margin of safety, as shown by the low complication rate. With no apparent sacrifice of efficacy compared to first-generation or fixed (not transportable) second-generation devices, the Medstone STS-T represents an important advance in the development of a truly transportable lithotripter.     

Extracorporeal shockwave lithotripsy in the pediatric population.

BACKGROUND: Shockwave lithotripsy (SWL) is being used increasingly as a therapeutic modality for childhood urolithiasis. We reported our experience and results of SWL in the pediatric population. METHODS: The 59 renal units (RU) of 54 patients were retrospectively reviewed. The mean patient age was 10+/-3.5 years. All patients were treated with the Lithostar lithotripter in outpatient settings. Those with positive culture results were treated under appropriate antibiotic coverage. Seven patients were treated under general anesthesia and the rest under sedoanalgesia. Shielding of the lung fields or gonads was not used. For the upper pole stones, protection of the lungs was accomplished by elevating the upper half of the body with supportive pillows, thus moving the kidney away from the lung fields. Six RUs were catheterized via double-pigtail ureteral catheters or by percutaneous nephrostomy tube prior to treatment. The average stone load was 1.8+/-2.5 cm2. RESULTS: Patients were treated with an average of 2.5 sessions. A total of 1000 to 2500 shockwaves were delivered between 14.5 and 17.8 kV. Routine spasmolytic treatment was not initiated. The stone-free rate was 64%, and clinically insignificant residual fragments (CIRF) were present in 29% of RUs; thus, the success rate was 93%. Fever that necessitated hospitalization occurred in one patient. No other complications were seen except skin bruising and early hematuria. CONCLUSION: Shockwave lithotripsy is a safe and effective treatment modality for childhood stones of appropriate size and radiologic characteristics.     

Percutaneous stone implantation in the pig kidney: a new animal model for lithotripsy research

PURPOSE: This report describes a new animal model for research on the parameters of shockwave delivery and the mechanisms of shockwave action in SWL. MATERIALS AND METHODS: Female pigs (approximately 45 kg) were anesthetized for creation of an upper pole peripheral caliceal access. The tract was dilated with a 30F Nephromax balloon and Amplatz sheath, and a 24F rigid nephroscope was used to guide a gypsum artificial stone into a lower pole calix. An internal ureteral stent was then placed. After a 2-hour recovery period, lithotripsy was performed using an unmodified Dornier HM3 lithotripter. Following SWL, en bloc excision of the urinary tract was performed, and the stone fragments were collected. RESULTS: As observed by nephroscopy, most stones were surrounded by urine that was free of clot or debris. Urine output was >1 mL/kg per minute by the time the animal was positioned for SWL after a 2-hour observation period. When the conditions of shockwave (SW) exposure were 400 SWs, 20 kV, and 120 SW/min, the efficiency of stone fragment recovery was 85% +/- 2% (N = 6 stones). CONCLUSIONS: This procedure provides a minimally invasive method for placement of model stones of clinically relevant size within the pig kidney. Stone implantation is efficient and permits experiments to be conducted in 1 day. Stone fragmentation can be quantitated, and the animal can serve as its own control. Long-term experiments are also feasible. Overall, this new animal model is appropriate for experimentation on the parameters of SW delivery in SWL.     

Independent assessment of a wide-focus, low-pressure electromagnetic lithotripter: absence of renal bioeffects in the pig

OBJECTIVE

To assess the renal injury response in a pig model treated with a clinical dose of shock waves (SWs) delivered at a slow rate (27 SW/min) using a novel wide focal zone (18 mm), low acoustic pressure (<20 MPa) electromagnetic lithotripter (Xi Xin‐Eisenmenger, XX‐ES; Xi Xin Medical Instruments Co. Ltd., Suzhou, PRC).

MATERIALS AND METHODS

The left kidneys of anaesthetized female pigs were treated with 1500 SWs from either an unmodified electrohydraulic lithotripter (HM3, Dornier MedTech America, Inc., Kennesaw, GA, USA; 18 kV, 30 SW/min) or the XX‐ES (9.3 kV, 27 SW/min). Measures of renal function (glomerular filtration rate, GFR, and renal plasma flow) were collected before and after SW lithotripsy, and kidneys were harvested for histological quantification of vascular haemorrhage, expressed as a percentage of the functional renal volume (FRV). A fibre‐optic probe hydrophone was used to characterize the acoustic field, and the breakage of gypsum model stones was used to compare the function of the two lithotripters.

RESULTS

Kidneys treated with the XX‐ES showed no significant change in renal haemodynamic function and no detectable tissue injury. Pigs treated with the HM3 had a modest decline from baseline (≈ 20%) in both GFR (P > 0.05) and renal plasma flow (P = 0.064) in the treated kidney, but that was not significantly different from the control group. Although most HM3‐treated pigs showed no evidence of renal tissue injury, two had focal injury measuring 0.1% FRV, localized to the renal papillae. The width of the focal zone for the XX‐ES was ≈ 18 mm and that of the HM3 ≈ 8 mm. Peak positive pressures at settings used to treat pigs and break model stones were considerably lower for the XX‐ES (17 MPa at 9.3 kV) than for the HM3 (37 MPa at 18 kV). The XX‐ES required fewer SWs to break stones to completion than did the HM3, with a mean (sd ) of 634 (42) and 831 (43) SWs, respectively (P < 0.01). However, conditions were different for these tests because of differences in physical configuration of the two machines.

CONCLUSION

The absence of renal injury with the wide focal zone XX‐ES lithotripter operated at low shock pressure and a slow SW rate suggests that this lithotripter would be safe when used at the settings recommended for patient treatment. That the injury was also minimal using the Dornier HM3 lithotripter at a slow SW rate implies that the reduced tissue injury seen with these two machines was because they were operated at a slow SW rate. As recent studies have shown stone breakage to be improved when the focal zone is wider than the stone, a wide focal zone lithotripter operated at low pressure and slow rate has the features necessary to provide better stone breakage with less tissue injury.     

Impact of shockwave coupling on efficacy of extracorporeal shockwave lithotripsy

PURPOSE: To evaluate the impact of a slow gated treatment rate on the efficacy of extracorporeal shockwave lithotripsy (SWL). PATIENTS AND METHODS: From August 1990 to July 2002, 40,462 SWL procedures were performed using the slow frequency electrocardiography (ECG)-gated lithotripter (82.5%) and fast frequency ECG-ungated (17.5%) modes for the Medstone STS lithotripter. Treatment characteristics, including the mode of SWL, location and size of the stone, re-treatment status, auxiliary procedures required, perioperative complications, and treatment outcomes, were recorded. The stone-free rate was reported by the treating physician on the basis of the finding of no residual stone fragments on a plain radiographic image. RESULTS: The treatment rate for the slow mode was a mean of 79.6 shocks/min, while the rate for the fast mode was 120/min. The total procedure time was 47.0 minutes for the slow mode and 40.6 minutes for the fast. The overall stone-free rate was higher for slow (66.9%) than fast (63.6%) procedures (P < 0.001). The stone-free rate for 1- to 10-mm stones was higher for the slow procedures (75.7%) than the fast procedures (70.7%; P < 0.001). Upper-ureteral stones responded better to slow treatment in terms of stone-free rate (79.5% v 72.6%; P < 0.001), re-treatment rate (6.5% v 8.0%, P = 0.05), auxiliary-procedure rate (6.1% v 8.9%; P = 0.01), and efficiency quotient (71 and 62). There was no significant difference in complication rates overall between slow and fast treatment. CONCLUSIONS: With a minimal increase in procedure time, greater efficacy can be obtained for the treatment of radiopaque stones with a slower shock-delivery rate. In particular, upper-ureteral calculi and calculi <10 mm benefit from a slower treatment rate.     

Experience with percutaneous nephrostomy, extracorporeal shock wave lithotripsy and chemolysis in the treatment of obstructive uric acid stones.

Intravenous pyelography (IVP), retrograde ureteral catheterization and percutaneous nephrostomy (PCN) have been used to locate radiolucent stones during ESWL in an X-ray localization system lithotripter. We also used an alternative method combining PCN, ESWL and chemolysis to treat 8 obstructive uric acid stones. The average number of shock wave pulses was 1,725 (range 1,000-2,000), the generator voltage of the HM-3 Dornier lithotripter was 20-22 kV, and the local chemolysis lasted 4 days (range 2-7). All radiolucent uric acid stones were successfully disintegrated. Of the 8 patients treated, 5 were completely free of stones and the other 3 had insignificant residual stones after 3 months. Three patients who developed fever during local chemolysis with 0.1 M sodium bicarbonate solution were managed conservatively without severe sequelae. Only 1 patient retained a PCN tube after discharge. Because PCN can provide a path for local chemolysis and better localization, it is especially helpful in treating obstructive uric acid stones.     

Shock wave lithotripsy for uric acid stones

OBJECTIVE: To report our experience of extracorporeal shock wave lithotripsy (SWL) for patients with uric acid stones. METHODS: From December 1987 to December 2003, a total of 443 patients with uric acid stones in the kidney or ureter accepted SWL using ultrasound-guided lithotripters together with alkali therapy. Among them, 168 patients with an average stone burden of 9.1 mm were treated using an EDAP LT-01 piezoelectric lithotripter. The other patients, with an average stone burden of 9.6 mm, were treated using a Dornier Compact S electromagnetic lithotripter. RESULTS: The average duration of treatment using the EDAP LT-01 device was 52.1 minutes with a pulse frequency of 1.25-2.5 shocks per second at 100% power. The average treatment parameters on the Dornier Compact S device were 3,196 shocks at 14.8 kV. For the EDAP LT-01, the 3-month stone-free rate was 86.4%, with a retreatment rate of 24.2%. For the Dornier Compact S, the 3-month stone-free rate was 90.3%, with a retreatment rate of 29.0%. Auxiliary therapy with the push-back technique was needed in 0.45% of patients with upper ureteral stones that could not be localized using ultrasound. The treatment results were best for stones smaller than 20 mm. No anaesthesia was required for any patient. CONCLUSION: SWL with ultrasound localization for uric acid stones is safe and effective. The combination of SWL with urine alkalization may further improve the stone-free rate.     

Recent developments in SWL physics research

Two projects in our laboratory highlight some recent developments in shockwave lithotripsy (SWL) physics research. In the first project, we developed a prototype of a piezoelectric annular array (PEAA) shockwave generator that can be retrofitted on a Dornier HM-3 lithotripter for active control of cavitation during SWL. The PEAA generator, operating at 15 kV, produces a peak positive pressure of approximately 8 MPa with a -6-dB beam diameter of 5 mm. The shockwave generated by the PEAA was used to control and force the collapse of cavitation bubbles induced by a laboratory electrohydraulic shockwave lithotripter with a truncated HM-3 reflector. With optimal time delay between the lithotripter pulse and the PEAA-generated shockwave, the collapse of cavitation bubbles near the stone surface could be intensified, and the resultant stone fragmentation in vitro could be significantly improved. In the second project, high-speed shadowgraph imaging was used to visualize the dynamics of lithotripter-induced bubble oscillation in a vascular phantom. Compared with the free bubble oscillation in water, the expansion of cavitation bubble(s) produced in silicone tubes and a 200-microm cellulose hollow fiber by either a Nortech EHL or a Dornier XL-1 lithotripter was found to be significantly constrained. Rupture of the cellulose hollow fiber was observed consistently after about 20 shocks from the XL-1 lithotripter at an output voltage of 20 kV. These results confirm experimentally that SWL-induced cavitation in vivo can be significantly constrained by the surrounding tissue, and large intraluminal bubble expansions could cause rupture of capillaries and small blood vessels.     

In vitro gallstone fragmentation by three piezoelectric lithotripters

Several different piezoelectric lithotripters have been under clinical investigation for gallstones in the USA. Design differences in the different shock wave generators result in different characteristics for the three devices and different peak pressures at the focus of the lithotripters. Using gallstone families, we sought to study fragmentation in the three lithotripters. A total of 56 gallstones from eight gallstone families were studied. Forty-eight stones were fragmented in three lithotripters (16 in each), Diasonics (Therasonic), EDAP (LT01), and Wolf lithotripter (Piezolith 2300), at maximum power and a rate of 2-2.5 Hz. A total of 500 shocks was applied to each stone in each of the three lithotripters. Gallstone composition was determined by infrared spectroscopy on one stone of each family (8 x 1). Initial stone weight and size were similar in all the three groups. All families consisted of cholesterol stones ( greater than 70% cholesterol). The fraction of the initial stone mass reduced to fragments less than or equal to 2 mm was not significantly different in the three lithotripters (Diasonics [n = 16] = 60 +/- 4%, EDAP [n = 16] = 53 +/- 6%, Wolf [n = 16] = 50 +/- 7%; p = 0.068).(ABSTRACT TRUNCATED AT 250 WORDS)     

First experience with the Lithoring in the management of urinary stones

The Lithoring Multi-One is a lithotripter recently developed in Italy. Its main features are (1) spark gap generator with large ellipsoid, with tunable power for treatments with or without analgesia; (2) localization by fluoroscopy and ultrasounds without moving the patient; (3) isocentric variation of shock wave window, and (4) multifunctional table. It can treat both urinary and biliary stones. The first 50 patients were treated without anesthesia with an average of 1,700 shock waves at 19.2 kV. 37 patients had stones larger than 1 cm. 13 patients had ureteral stones. Two patients had complete staghorn stones. The disintegration rate was 97.9%, the overall stone-free rate at 3 months' follow-up was 83.3%, and the retreatment rate was 1.29 treatments for patients. No complication occurred.     

New-generation lithotripters for treatment of patients with implantable cardioverter defibrillator: experimental approach and review of literature

PURPOSE: The influence of shockwaves applied during extracorporeal shockwave lithotripsy on the function of implantable cardioverter defibrillators was evaluated. Mechanical influences as well as proper electrical function were tested in an experimental approach. MATERIALS AND METHODS: Two implantable defibrillators (Ventak Mini 1743 and AVII 1821) were exposed to the shockwaves of a new-generation lithotripter. Each of the antidysrhythmic devices was tested at several distances from and within the focus of the lithotripter. All studies were performed with maximum energy and the number of shockwaves used for stone treatment. The devices were connected to an ECG simulator, and continuous recording of a surface ECG, a shock ECG, and marker channel was performed. RESULTS: No macroscopic and microscopic mechanical damage was observed. The detection function of the implantable defibrillators was not altered by any electromagnetic artifacts even when brought into the focus of the shockwaves. All induced ventricular dysrhythmias were terminated properly regarding artifact sensing. However, after defibrillation, the pacing function of the Ventak Mini cardioverter defibrillator, which was programmed into the demand mode, failed. In this case, there was no post-shock pacing in the period of post-defibrillation asystole. The failure was caused by artifact oversensing. CONCLUSION: In patients with implanted cardiac devices undergoing treatment with a new-generation lithotripter, deactivation of the defibrillator is not mandatory. For safety reasons, continuous ECG recording is recommended. To avoid pacing failure by artifact oversensing, the shockwaves should be applied in a R-wave synchronous mode.     

Efficacy and safety of the Healthtronics LithoTron lithotripter

PURPOSE: To evaluate our experience with the LithoTron lithotripter (Healthtronics, Atlanta, GA), a dry portable system that utilizes a spark-gap electrode as an energy source. PATIENTS AND METHODS: We prospectively evaluated the first 312 treatments performed on 199 men and 99 women with an average age of 43.5 years (range 4 months-80 years), over a 25-month period between May 1999 and June 2001. Of the 468 stones treated, 136 were located in the ureter, 52 in the renal pelvis or ureteropelvic junction, and 230 in the kidney; the sites of 50 were not specified in our database. The average stone size was 8.0 mm (range 1-40 mm). Follow-up included a plain (KUB) film, CT scan, or intravenous urogram (IVU) and was available for 256 patients. "Stone free" was defined as no fragments visible on postoperative images. The mean radiographic follow-up was 74 days (range 0-866 days). Data collection was initially done manually by data sheets, but a Web-based medical database application was developed in order to enter, store, retrieve, and analyze the data more efficiently. RESULTS: The average number of shocks delivered per renal unit was 2689 at 25.8 kV. Seventy-five percent of the procedures were performed with intravenous sedation. Two thirds (169/256) of the patients were rendered stone free with one treatment. According to size, 71% (209/294) of stones <1 cm, 57% (39/68) of stones between 1.0 and 1.5 cm, and 22% (8/36) of stones >1.5 cm were eliminated. There were 23 patients who required further treatment; from the available data, 18 of them are currently stone free. Perioperative complications occurred in 6 patients (2%). No patient had worsening renal function or new-onset hypertension. The effectiveness quotient was 59.3%. CONCLUSION: The LithoTron lithotripter is satisfactory for stones <1 cm.     

Improvement of stone comminution by slow delivery rate of shock waves in extracorporeal lithotripsy

AIM: The aim of this study was to investigate the effect of delivery rate of shockwaves (SW) on stone comminution and treatment outcomes in patients with renal and ureteral stones. METHODS: Patients with radio-opaque stones in the upper urinary tract that were treated by extracorporeal shock wave lithotripsy (ESWL) were divided into two groups according to delivery rate (120 or 60 SW/min). The effective fragmentation after one ESWL session and treatment success at 3 months after ESWL was compared between the two groups. RESULTS: Of 134 patients (84 men and 50 women), 68 patients were treated at a fast rate and 66 were treated at a slow rate. Thirty and 38 patients in the fast rate group and 28 and 38 in the slow rate group had renal and ureteral stones, respectively. After one ESWL session, effective fragmentation was noted more often in the slow group (65.2%) than the fast group (47.1%) (P = 0.035), particularly for smaller stones (stone area <100 mm(2)) (P = 0.005) and renal stones (p = 0.005). However, there was no significant difference in treatment success at 3 months after ESWL between the two groups. In univariate logistic regression analysis, slow SW rate and smaller stones were significant factors for effective fragmentation after one ESWL session. In multivariate analysis, slow SW rate and smaller stones were also independent factors. CONCLUSIONS: Slow SW rate contributed to better stone comminution than fast rate, particularly for small stones and renal stones. ESWL treatment at a slow SW rate is recommended to obtain efficient stone fragmentation.     

The effect of treatment strategy on stone comminution efficiency in shock wave lithotripsy

PURPOSE: The comminution of kidney stones in shock wave lithotripsy (SWL) is a dose dependent process caused primarily by the combination of 2 fundamental mechanisms, namely stress waves and cavitation. The effect of treatment strategy with emphasis on enhancing the effect of stress waves or cavitation on stone comminution in SWL was investigated. Because vascular injury in SWL is also dose dependent, optimization of the treatment strategy may produce improved stone comminution with decreased tissue injury in SWL. MATERIALS AND METHODS: Using an in vitro experiment system that mimics stone fragmentation in the renal pelvis spherical BegoStone (Bego USA, Smithfield, Rhode Island) phantoms (diameter 10 mm) were exposed to 1,500 shocks at a pulse repetition rate of 1 Hz in an unmodified HM-3 lithotripter (Dornier Medical Systems, Kennesaw, Georgia). The 3 treatment strategies used were increasing output voltage from 18 to 20 and then to 22 kV every 500 shocks with emphasis on enhancing the effect of cavitation on medium fragments (2 to 4 mm) at the final treatment stage, decreasing output voltage from 22 to 20 and then to 18 kV every 500 shocks with emphasis on enhancing the effect of stress waves on large fragments (greater than 4 mm) at the initial treatment stage and maintaining a constant output voltage at 20 kV, as typically used in SWL procedures. Following shock wave exposure the size distribution of fragments was determined by the sequential sieving method. In addition, pressure waveforms at lithotripter focus (F2) produced at different output settings were measured using a fiber optic probe hydrophone. RESULTS: The rate of stone comminution in SWL varied significantly in a dose dependent manner depending on the treatment strategies used. Specifically the comminution efficiencies produced by the 3 strategies after the initial 500 shocks were 30.7%, 59% and 41.9%, respectively. After 1,000 shocks the corresponding comminution efficiencies became similar (60.2%, 68.1% and 66.4%, respectively) with no statistically significant differences (p = 0.08). After 1,500 shocks the final comminution efficiency produced by the first strategy was 88.7%, which was better than the corresponding values of 81.2% and 83.5%, respectively, for the other 2 strategies. The difference between the final comminution efficiency of the first and second strategies was statistically significant (p = 0.005). CONCLUSIONS: Progressive increase in lithotripter output voltage can produce the best overall stone comminution in vitro.