The efficacy of gated versus nongated shockwave lithotripsy using the Medstone STS lithotriptor

To determine the efficacy of a gated and slower shockwave lithotripsy (SWL) vs a nongated and faster SWL delivery with regard to stone fragmentation and clearance using the Medstone STS lithotriptor.

We performed a retrospective chart review of 300 consecutive patients who underwent SWL for renal stones at our institution from 2001 to 2007. One hundred and five patients underwent SWL with shocks gated to the electrocardiographic signal and 195 patients underwent nongated SWL with an externally fixed signal. Subset analysis was performed between stones <1 cm and > or =1 cm. Main outcome was stone-free rates.

The gated procedure was performed 35% of the time. Gated and nongated patients underwent treatment at average rates of 76 shocks/minute and 120 shocks/minute, respectively. Operative time for the gated group was significantly longer at 50 minutes vs 34 minutes. A significantly higher percentage of men underwent a gated procedure. Other variables for age, body mass index, American Society of Anesthesiologists class, percent lower pole, percent stented, preoperative stone burden, and mean follow-up were comparable between groups. Overall stone-free rates were comparable for gated and nongated at 33.3% and 35.4%, respectively (P = 0.819). For stones <1 cm, stone-free rates were 41.2% vs 39.7% (P = 0.957) for gated and nongated groups, respectively. For stones > or =1 cm, stone-free rates were 18.9% vs 26% (P = 0.520) for gated and nongated groups, respectively.

Gated SWL requires a significantly longer time to perform and does not appear to have an affect on stone-free rates, regardless of stone size.