EBR Systems (ASX:EBR) said the US Food and Drug Administration (FDA) is reviewing an incident where, during post-implant echocardiograms, two patients at one site, implanted with the Wireless Stimulation Endocardially (WiSE) system, separately developed ventricular fibrillation, and one patient went into cardiac arrest, could not be resuscitated, and died, according to a Friday Australian bourse filing.

Noting online speculation, the firm said the complications suffered by the two patients were not related to the procedure or the effective functioning of the system and were a result of the use of external echocardiography for imaging. It will provide a detailed risk assessment with its conclusion as part of the US FDA process.

Its internal assessment is that this is an isolated event related to a disclosed risk that is mitigated when following the recommended echocardiography procedures. It added that it provides clear echocardiography guidelines and imaging procedures for patients implanted with the system.

Its shares plunged past 9% in recent trading on Friday, reaching their lowest point in over four years.