I understood that for TAVR procedures, tissue, not mechanical valves, are used so they can be collapsed for insertion through a catheter and then expanded for implantation at the valve site. Have you read that they are implanting mechanical valves via TAVR now?
I'm not sure that they CAN do TAVR on mechanical valves. I can apparently benefit from ablation of a node above my St. Jude aortic valve -- the doctors don't want to go anywhere near the mechanical valve because this will stop it from working and would kill me. I suspect that trying to put a bioprosthetic valve below the mechanical could also risk causing the mechanical to fail. (Further, since mechanicals can last DECADES, why would you need a TAVR in this position anyway?