Had A Mechanical Heart Valve Replacement In May 2015. On

had a mechanical heart valve replacement in may 2015. on warfarin my inr levels were very " up and down" so my gp changed my drug to riveroxiban, ive been now changed back to warfarin as the cardiologist says riveroxiban hasn't been lisenced for my condition, I get irregular heart beats which ive been told is first degree block but didn't get it as often on riveroxiban. what is your advice please