A medical device assembly may include an elongated guidewire, an elongated flexible tubular membrane disposed about the guidewire, and a percutaneous medical device, wherein the membrane is configured to permit the percutaneous medical device to pass through the lumen. A method of advancing a medical device through a vessel may include advancing an elongated flexible tubular membrane through the vessel to a treatment site, inserting the medical device into the membrane, and advancing the medical device through the membrane while maintaining the membrane in an axially stationary position relative to the vessel.