Systems and methods are provided for reducing heating within pacing/sensing leads of a pacemaker or implantable cardioverter-defibrillator that occurs due to induced loop currents during a magnetic resonance imaging (MRI) procedure, or in the presence of other sources of strong radio frequency (RF) fields. For example, bipolar coaxial leads are described herein wherein the ring conductor of the lead is disconnected from the ring electrode in response to detection of MRI fields so as to convert the ring conductor into an RF shield for shielding the inner tip conductor of the lead so as to reduce the strength of loop currents induced therein and hence reduce tip heating. Techniques are also described herein for selectively disconnecting the tip electrode of the lead during an MRI procedure, except during actual delivery of pacing pulses, so as to permit delivery of individual pacing pulses to pacemaker dependent patients during the MRI. Still other techniques describe the use of both RF shielding and tip switching.