First of all, the device is not "leadless." Rather, there are no leads placed inside blood vessels with this defibrillator, produced by Cameron Health, Inc. The device does have a lead that is tunneled beneath the skin from the upper left chest
53 patients were studied the the information provided. The average defibrillation threshold without any internal lead was 36 joules. No inappropriate shocks occurred, even when there was an aggressive attempt to induce sensing of muscular potentials with vigorous arm movement.
It's only drawback: there was no backup pacing provided by the device, so if the rhythm is converted from ventricular fibrillation to asystole (no heart beats... and this CAN happen), then the patient still might not survive. Nonetheless, the implications for decreasing physician reimbursement for electrophysiologists (since now any surgeon could implant these) and what this will do to pressure existing device companies to drop their prices once the device reaches the mainstream US market for primary prevention of life-threatening arrhythmias, remains to be seen.