In an implantable medical device having an electrical lead coupled to tissue of a user and a circuit for measuring the impedance of the lead, a method and apparatus for responding to impedance variations in the lead which includes measuring the impedance of the lead while monitoring physiologic parameters of the user, detecting the presence or absence of electromagnetic interference, and if the impedance of the lead is out-of-range, determining whether the electromagnetic interference exceeds a predetermined value, and if the electromagnetic interference exceeds a predetermined value, administering a therapy to the tissue of the user.