Potential hazards of using MRI with Older Pacemakers

Potential hazards of using MRI with Older Pacemakers

This discussion is on older generation pacemakers which are not MRI conditional. Magnetic resonance imaging utilises a very strong magnetic field which could be deleterious to the implanted cardiac pacemaker in various ways. Mechanical forces on ferromagnetic components of the pacemaker could occur due to the strong electromagnetic fields. This could lead to unpredictable magnetic sensor activation. Usually magnetic sensor causes closure of a reed switch which makes the pacemaker insensitive to the cardiac signals leading to asynchronous pacing.

Asynchronous pacing can lead on to cardiac arrhythmias including lethal ventricular fibrillation. Heating of cardiac tissue adjacent to lead electrodes could occur due to the currents generated by the alternating magnetic fields. Radiofrequency interactions with the device can cause over- and under-sensing due to the induced voltages on leads. If the pacemaker has been implanted recently it could also lead to physical movement of device within a loose pocket.

Variables affecting the magnitude of risks include the length and position of pacing leads, patient and device position within machine, duration of the MRI scan, blood flow at lead-tissue interface, strength of radiofrequency field and the design of pacemaker and the lead.

To overcome these disadvantages of older generation pacemakers, MRI conditional pacemakers and other cardiac implantable electronic devices are becoming more and more popular. Instead of the reed switch they use Hall sensor. Components have been changed so that MRI can be taken subject to certain conditions.