What is your approach to persistently low INR despite escalating doses of warfarin in a patient with bioprosthetic mitral valve replacement who is unable to be on DOACs?

The assumption here is that the mitral valve is mechanical, or there are presumably other reasons that a DOAC cannot be used. If this is, in fact, a mechanical mitral valve, it would make sense to start with low molecular weight heparin injections as soon as feasible while awaiting a therapeutic INR...

Depends on whether it is mechanical vs. bio prosthetic.