It is provided an electrode extension assembly comprising: a fastener for releasably fastening the electrode extension assembly to a user; a device holder for releasably holding a portable sensor device configured to capture electrocardiogram signals and audio signals; at least two extenders extending radially outwards from the device holder, wherein each extender comprises: a connector configured to connect to a respective electrode of the portable sensor device; an outer electrode connected at a distal end of the extender, the outer electrode being configured to be applied to a user; a conductor connected on one end to the connector and on the other end to the outer electrode; and an audio signal conveyor for conveying audio signals from the user to an audio sensor of the portable sensor device.