Novel lithotriptor shortens stone penetration time

Indianapolis-For urologists who are less than happy with the current options for performing intracorporeal lithotripsy, researchers from one of the country's highest-volume stone centers have some good news. A novel, dual-probe lithotriptor appears to offer the best features of both pneumatic and ultrasonic devices, and provides a significantly shorter penetration time than a combination pneumatic-ultrasonic device, in vitro research data show.

In a presentation at the AUA annual meeting, urologists from the Methodist Hospital Institute for Kidney Stone Disease at Indiana University, Indianapolis, provided results of an in vitro study comparing the new, still-investigational device known as Cyberwand (Cybersonics, Erie PA), with the pneumatic-ultrasonic device, Lithoclast Ultra (Boston Scientific, Natick, MA). With this and other studies, the researchers have hoped to find a lithotrite that provided efficient stone penetration as well as stone removal capability.

"The question is, can we get something that's as good as a pneumatic device at breaking a stone and as good as an ultrasonic device at removing a stone, and that's where the Cyberwand falls in," said lead author Samuel C. Kim, MD, voluntary clinical assistant professor of urology at Indiana University School of Medicine. "Hopefully, it's the best of both worlds."

The Cyberwand has two concentric probes located inside its handpiece that vibrate at different frequencies. The inner probe, which is fixed to the handpiece, vibrates at 21,000 Hz. The "free-floating" outer probe vibrates at about 1,000 Hz. Excursion of the outer probe, which is driven by free mass, acts as a frequency coupler. Excursion of the outer probe is further restricted by a coil spring.

"The synergistic effect of combining the ballistic action of the outer probe and the ultrasonic effect of the inner probe is designed to perform more efficient stone comminution," Dr. Kim explained.

In vitro testing model

The Indiana group had previously developed an operator-independent in vitro testing system to assess ultrasonic lithotriptors (J Urol 2003; 170:1101-4), and the system was used in the current study to compare the Cyberwand and the Lithoclast Ultra. The Lithoclast Ultra was chosen for comparison because studies have found it to be the most efficient commercially available intracorporeal lithotriptor (Urology 2002; 60:28-32 and J Endourol 2004; 18:153-6).

In the "hands-free" testing model, the lithotrite is secured upright, and an artificial gypsum stone is placed at the tip of the probe. A 63.4-gram weight provides constant force. Each lithotrite was tested at the maximal settings with 10 stones, and stone penetration times were recorded.

Mean stone penetration time for the Cyberwand was 4.8 seconds, compared with 8.1 seconds for the Lithoclast Ultra, a statistically significant difference (p<.0001). Neither device exhibited malfunctioning, overheating, or occlusion.

"As the Cyberwand is a variant of the ultrasonic devices and the safety profile of these ultrasonic devices is well established, the Cyberwand is now ready to be tested in vivo," Dr. Kim concluded.

Session moderator Joseph Segura, MD, of the Mayo Clinic, asked Dr. Kim if the differences seen in lithotriptors were clinically relevant.

"Right now, the question is, which one is the most efficient?" Dr. Kim responded. "In our testing, the Lithoclast Ultra was the quickest commercially available intracorporeal lithotriptor we tested to date, but I think there are some ergonomic issues with it. The hope with [the Cyberwand] is that it will not only be more efficient, but last longer than the currently available lithotrites."