Releasable retaining mechanisms for an actuator assembly of a delivery apparatus for an expandable prosthetic heart valve are disclosed. As one example, an actuator assembly can include an outer sleeve comprising a tube portion and an extension that extends distally from the tube portion and includes a first aperture in its distal end, an actuation member extending through the tube portion of the outer sleeve, and a retaining element configured to extend through the first aperture and hold the outer sleeve against an end portion of a frame of a prosthetic device. The retaining element is biased into a first position that holds the outer sleeve in engagement with the frame and is configured to flex in response to a pulling force into a second position that enables the retaining element to be released from the first aperture to disengage the outer sleeve from the end portion of the frame.