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2 Key Points ➤ MRI generates static and gradient magnetic fields as well as RF energy. The potential interactions between CIEDs and electromagnetic interference from MRI include the following: • Magnetic field-induced force and torque due to ferromagnetic materials: CIED generator movement is extremely unlikely due to confinement in the subcutaneous tissues. ▶ Leads do not contain any significant ferromagnetic materials to cause movement in a magnetic field. • Gradient magnetic field-induced electrical current: Gradient magnetic fields can induce current in conductive wires within the field that could lead to myocardial capture and potentially lead to atrial or ventricular arrhythmias. • Heating and tissue damage: RF fields can lead to nonconditional CIED component heating and subsequent thermal damage to the surrounding tissue (functional ablation). Changes in sensing or capture thresholds can occur as a result of tissue damage near lead electrodes. • Effects on reed switch activity: The reed switch is a feature that permits programming of the device by placement of a magnet. Magnetic fields might therefore affect the reed switch activity of a nonconditional CIED, leading to asynchronous pacing and inhibition of tachycardia therapies. • Electrical reset: High-energ y electromagnetic interference (EMI) can lead to electrical or power-on-reset, a backup demand mode, wherein pacing might be inhibited and tachyarrhythmia therapy activated. ▶ Power-on-reset parameters vary by vendor and type of CIED (See Tables 1 and 2), and can include reset of pacing polarity to unipolar. ▶ Inhibition of pacing function due to oversensing of MRI-generated signals or pacing at an output below threshold (bipolar or unipolar) in a pacemaker (PM)-dependent patient might occur in the setting of power-on-reset and must be recognized to prevent catastrophic consequences. ▶ Additionally, battery status can be affected, particularly for CIEDs that are near an elective replacement interval (ERI), which could result in unreliable function. • Inappropriate function and therapies: EMI from RF energ y pulses or rapidly changing magnetic field gradients might cause oversensing that can lead to inappropriate inhibition of demand pacing and possibly asystole in a pacing- dependent patient, or induction of therapies such as inappropriate shocks in a patient with an implantable cardioverter defibrillator (ICD). Other inappropriate tracking or programming changes can occur. ➤ These effects are influenced by various factors, including magnet field strength, RF power, position of the patient and the CIED within the MRI bore, CIED characteristics, and the size of the patient. e grading system for indication level of class of evidence was adapted based on that used by the ACC and the AHA. (A. K. Jacobs, Anderson, & Halperin, 2014) (Anderson, 2015) Colors in tables correspond to Class of Recommendation Table on pages 18-19.

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