Wrong detection of ventricular fibrillation in an implantable cardioverter defibrillator caused by the movement near the MRI scanner bore.

Abstract

The static magnetic field generated by MRI systems is highly non-homogenous and rapidly decreases when moving away from the bore of the scanner. Consequently, the movement around the MRI scanner is equivalent to an exposure to a time-varying magnetic field at very low frequency (few Hz). For patients with an implanted cardiac stimulators, such as an implantable cardioverter/defibrillator (ICD), the movements inside the MRI environment may thus induce voltages on the loop formed by the leads of the device, with the potential to affect the behavior of the stimulator. In particular, the ICD's detection algorithms may be affected by the induced voltage and may cause inappropriate sensing, arrhythmia detections, and eventually inappropriate ICD therapy.We performed in-vitro measurements on a saline-filled humanshaped phantom (male, 170 cm height), equipped with an MRconditional ICD able to transmit in real-time the detected cardiac activity (electrograms). A biventricular implant was reproduced and the ICD was programmed in standard operating conditions, but with the shock delivery disabled. The electrograms recorded in the atrial, left and right ventricle channels were monitored during rotational movements along the vertical axis, in close proximity of the bore. The phantom was also equipped with an accelerometer and a magnetic field probe to measure the angular velocity and the magnetic field variation during the experiment. Pacing inhibition, inappropriate detection of tachyarrhythmias and of ventricular fibrillation were observed. Pacing inhibition began at an angular velocity of about 7 rad/s, (dB/dt of about 2 T/s). Inappropriate detection of ventricular fibrillation occurred at about 8 rad/s (dB/dt of about 3 T/s). These findings highlight the need for a specific risk assessment of workers with MR-conditional ICDs, which takes into account also effects that are generally not considered relevant for patients, such as the movement around the scanner bore.