Implantable cardioverter-defibrillators (ICDs) and magnetic resonance imaging (MRI) were previously contraindicated, but that is no longer the case thanks to a study (NCT02117414) led by Michael Gold, M.D., Ph.D., Director of the Division of Adult Cardiology at MUSC, the results of which were published in the June 23, 2015 issue of the Journal of the American College of Cardiology. Gold is one of the worldwide principal investigators for the study.
ICDs are used in patients at risk of cardiac arrest (sudden cardiac death); the device is placed underneath the patient’s skin in the upper chest to monitor and stabilize their heartbeat. If the heart beats uncontrollably quickly or abnormally slowly, the device will send a small electrical signal to pace or a larger electrical shock to the heart to normalize the beat.
In the past, physicians were unable to use the most popular method of imaging on patients with ICDs. The magnetic field caused by the MRI could either decrease the overall efficacy of the heart-pacing device, or it could overheat the wires, causing the heart to enter tachyarrhythmia — meaning it was beating too quickly.
The study led by Gold tested the efficacy and safety of an ICD that has a “sleep mode” and that has been modified to protect its internal circuits. This sleep mode is referred to as SureScan (Medtronic; Minneapolis, MN) and disables tachyarrhythmia sensing and defibrillation therapies within the device. It can still monitor the patient’s heartbeat, but the device is temporarily incapable of sending an electric shock to the heart. After placing these novel ICDs under the skin of 275 study participants, researchers conducted either a full-body MRI scan with 1.5T of the chest, cervical, and head regions to ensure maximum radiofrequency exposure up to 2W/kg specific absorption rate (SAR) and gradient field exposure to 200 T/m/s per axis or kept the patient waiting for an hour with no MRI. Researchers then monitored the study participants for adverse changes in their ICD over the next 30 days. The device showed no change in its ability to pace or accurately sense ventricular fibrillation following the scan. The novel ICD was thus deemed to be compatible with MRI.