FIGURE 57-1 Patient monitor showing ECG lead artifact during MRI while pulse oximetry (SpO2) is not affected. (Used with permission of Charles J. Love, MD.)
MAGNETIC RESONANCE IMAGING FOLLOWING DEVICE IMPLANTATION
MRI is considered a relative contraindication for patients with conventional pacemakers and implantable cardioverter defibrillators (ICDs). As with this patient, it is anticipated that 50% to 75% of patients will have the need for a clinically indicated MRI during the lifetime of their device.1
There are multiple potential adverse interactions between a strong magnetic field and cardiac implantable electronic devices (CIEDs) including device movement, lead tip heating with thermal injury or changes in lead performance (sensing, capture thresholds, impedance), unpredictable magnetic sensor activation, reed-switch closure, rapid or asynchronous pacing, inhibition of pacing, inappropriate tachyarrhythmia therapies, programming alterations, battery consumption, damage to device circuitry, and arrhythmias.2–10 Deaths associated with MRIs have been reported; all occurred during scans not supervised by a physician.10–12 Hence the exact mechanism of death was not determined, although in one report, ventricular fibrillation was believed to the mechanism.10
The 2007 American Heart Association Guidelines outlined recommendations for device settings and safety monitoring during MRI but did not endorse MRI in patients with CIEDs.13 MRI of patients with CIEDs should only be considered with compelling circumstances, and the risks and benefits for the patient should be established and documented. Several centers have offered MRI to patients with CIEDs but have excluded patients with abandoned or epicardial leads. Some centers have excluded device pacemaker-dependent patients due to the concern for power-on reset, in which the battery voltage decreases below a critical preset level, leading to unpredictable device operation. After the battery voltage recovers, the device typically resets to the manufacturer’s nominal settings. The following recommendations are a compilation of the AHA Guidelines13 and published protocols from academic centers.14–18
1. Patients with non-MR conditional pacemakers and ICDs (“legacy devices”) with mature lead systems (>6 weeks) can be considered for MRI.
2. Prior to MRI, device interrogation should be performed to evaluate battery status, sensing, capture threshold, and lead impedances. Patients with devices that show abnormal or inadequate performance (ie, elevated capture threshold, pacing impedance, or depleted battery voltage) are not recommended to undergo scanning.
3. In patients who are not dependent upon pacing, some centers reprogram the device to an asynchronous mode (DOO, VOO) while others program a nonpacing mode (ODO, DDI, VVI). Reed switch activation by the magnetic field can result in magnet mode pacing; programming the device to an asynchronous mode should theoretically prevent this but it has still been seen in some patients.
4. Magnet, rate response, PVC, noise, ventricular sense, conducted atrial fibrillation (AF) response, and tachyarrhythmia therapies are disabled.
5. MR scanning should be performed at experienced centers with expertise in MRI and electrophysiology. A physician with MRI expertise should be involved optimally to plan the scan and minimize patient risk. MRI has been performed with a 1.5 Tesla magnet and the absorption rate is limited to 1.5 w/kg for a maximum of 30 minutes.
6. Informed consent should be obtained from the patient and should specifically list the risks including device dysfunction and/or damage, arrhythmia, and death.
7. The patient’s vitals and heart rhythm should be monitored, and visual and voice contact should be maintained throughout the MRI. The patient should be instructed to report any concerns or unusual sensations. A physician with device expertise and a crash cart with external defibrillator and programmer should be present during scanning.
8. The device should be interrogated immediately after the MRI to evaluate lead and device performance and restore baseline programming.
MRI-CONDITIONAL PACEMAKER
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