Ungated Medstone outpatient lithotripsy.

Ungated lithotripsy has raised the specter of possible cardiac arrhythmias. We reviewed ungated outpatient lithotripsy performed on 82 patients to evaluate the incidence of arrhythmias encountered and time saved. All patients were chosen in a random nonselected, prospective fashion. All treatments were performed on a mobile Medstone 1050 STS lithotriptor. The incidence of arrhythmias was 21%. All but 2 arryhthmias were benign and all reversed with gating. No arrhythmias occurred during treatment of right ureteral stones. In the left ureter only 1 patient had benign premature ventricular contractions during treatment. Arrhythmias occurred at 20 to 24 kv. in 20% of patients with right renal stones and 31% with left renal stones. All arrhythmias resolved with gating. No arrhythmias were encountered at an energy level of less than 20 kv. There was no evidence of electrocardiographic changes up to 1 hour after treatment. Pharmacological manipulation to maintain a heart rate of 100 may allow a treatment time of approximately 24 minutes. With ungating the rate may reach 120, allowing for a treatment time of approximately 20 minutes. In this series average ungated lithotripsy time was 36 minutes. In comparison, the average treatment time in 20 patients undergoing gated lithotripsy was 38.7 minutes. It is not clear from this study whether persistent ungated lithotripsy would have precipitated any life threatening arrhythmias since our practice has been to terminate the procedure and re-gate the shocks at the first sign of any persistent change in cardiac rhythm. Our data indicate that ungated lithotripsy with the Medstone device is safe when simple monitoring rules are followed.