Magnetic Resonance Imaging and Implantable Devices

Abstract

In recent years, there has been a remarkable increase in the number of patients who benefit from cardiovascular implantable devices. On the other hand, magnetic resonance imaging (MRI) compared with other imaging techniques undoubtedly has many advantages regarding its discrimination ability without radiation exposure. The risks of scanning device patients that have non “MR Safe” or “MRConditional” devices (Table 1), due to field effects, are well known as are the risk mitigation strategies.

 Hazards and safety concerns

 There are three distinct mechanisms associated with MRI that can give rise to potential risks related to cardiovascular devices: (1) the static magnetic field, (2) radiofrequency (RF) energy, (3) gradient magnetic fields or any combination of them. Static main magnetic field exposes ferromagnetic components to mechanical forces and torque and causes unpredictable magnetic sensor activation, reed switch closure and electrocardiograms distortions on electronic implantable pulse generators (IPGs), implantable cardioverter defibrillators (ICDs) and cardiac resynchronization therapy (CRT) devices. Modulated RF field interacts with pacemaker devices and leads causing heating of cardiac tissue adjacent to electrodes, reset and sensing problems of the device. ICDs can falsely detect RF field as ventricular tachycardia (VT) and start the sequence of defibrillation. Gradient magnetic field can induce currents in electrically conductive wires and leads that could cause over-/under-sensing and induce arrhythmias. Combined field effects can cause alteration of device function, vibrations, electronic reset and device or lead damage. Electrical reset is a safety emergency mode that limits pacemaker functionality to minimal in case of battery depletion or dip due to MR field interference. Factory default settings and usually a VVI mode are set while ICD therapies are deactivated. Because ICD’s parts, such as capacitors and batteries, are much larger than those of pacemakers and the technology used is more complicated they tend to pose greater conflicts, electromagnetic and mechanical forces (10 times higher than pacemaker), under MRI conditions. Generally pacemakers are switched to asynchronous magnet or interference mode and ICD therapy is switched off after MR field exposure... (excerpt)