Troy Rhodes, MD, PhD, FHRS, CCDS
A 67-year-old woman with a history of sick sinus syndrome underwent dual chamber pacemaker implantation in 1997. She developed persistent atrial fibrillation (AF) and underwent two left atrial ablations, but with recurrent AF had difficulty controlling ventricular rates leading to AV junction ablation. With chronic right ventricular pacing, she developed a nonischemic cardiomyopathy (LVEF 35%) and underwent upgrade to a biventricular pacemaker (Boston Scientific Contak Renewal) with the addition of St Jude Medical 1058T QuickSite XL in November 2008. Her existing right atrial and right ventricular leads (SJM 1188T Tendril, SJM 1246T Passive Plus TiN) had stable lead performance at upgrade. She is device-dependent with underlying sinus rhythm and complete AV block with ventricular asystole.
In 2010, she presented with retro-orbital headaches with head CT demonstrating a pituitary mass, followed by trans-sphenoidal resection with pathology showing an arachnoid cyst. Her headaches resolved following surgery, but she recently had recurrent headaches, and repeat CT imaging showed a residual mass in the left aspect of the sella turcica. Neurosurgery recommended brain magnetic resonance imaging (MRI) to further evaluate the residual mass and the association between arachnoid cysts and type 1 Chiari malformation.
Prior to MRI, device interrogation showed normal device and lead function. Unfortunately, an asynchronous mode (DOO) was not an available mode; therefore, her device was programmed DDI, magnet response was disabled, and the ventricular sensitivity was increased to 10 mV. Due to magnetic interference with ECG telemetry, the pulse oximetry waveform was monitored (Figure 57-1) with no ectopy, inhibition, or tracking noted. Following completion of her MRI, device interrogation showed stable sensing, capture thresholds, and impedances, and her initial device programming (DDDR) was restored.
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.
In February 2011, the U.S. Food and Drug Administration (FDA) approved an MRI-conditional pacemaker for marketing in the United States (EnRhythm MRI SureScan Pacing System, Medtronic, Inc.) which utilizes a special lead system. The first- and second-generation devices are currently limited to 1.5 Tesla scanners. The MRI Surescan pacing system utilizes the Medtronic CapSureFix MRI Surescan (Model 5086) leads which were designed to minimize lead tip heating during MRI and impacts lead handling and patient complications. The materials, proximal and distal ends of the MRI-conditional 5086 leads are similar to the conventional bipolar Medtronic model 5076 leads; however, the 5086 leads use 2 filars (number of wires used in the conductor) instead of 4 (5076) to increase inductance and reduce lead tip heating during MRI.
The lead tip of the MRI-conditional 5086 leads are also stiffer (2.0 psi) than the 5076 lead (1.58 psi),19,20 and this stiffness has been reported to be associated with increased risk of procedural complications.21 A retrospective analysis of lead-related complications following implantation of 434 Surescan leads in 217 patients, reported an acute complication rate of 4.8% and an increased rate in women. Women accounted for 64 (64%) of cases requiring lead revision with all RV lead perforations occurring in women with apical lead placement. The higher complication rate was felt to be related in part to the stiffer design of the lead and the unique features of deploying the screw.
The 5086 lead requires special handling to minimize complications. The active fixation helix should be “exercised” (extended and retracted) on the surgical table prior to implant. The proximal lead segment should be straightened while extending the helix. During lead positioning, the stylet should be withdrawn 2 cm to reduce stiffness. After six to eight rotations, the lead tip should be monitored by fluoroscopy, since the helix may fully extend as built up torque is transferred to the lead tip. More rotations may be required for leads with tortuous path and atrial lead placement. RV septal lead placement should be considered, especially in women.19
Boston Scientific and St Jude Medical MRI-conditional pacemaker systems are currently in research trials.
The Centers for Medicare and Medicaid Services have approved reimbursement for MRI in patients with the MRI-conditional pacemaker system but does not reimburse MRIs performed in patients with other CIEDs.22
MRI AND IMPLANTABLE LOOP RECORDER
The Medtronic Reveal Plus Implantable Loop Recorder (ILR) is labeled “MR conditional,” and patients may undergo MRI anytime following implantation.13 Since the device contains ferromagnetic components, patients may feel slight movement of the device during scanning.3 The electromagnetic field may adversely affect data stored on the device so interrogation should be performed prior to MRI; postscanning interrogation may reveal “arrhythmias” (Figure 57-2) recorded during the MRI due to artifact from the electromagnetic field.12
FIGURE 57-2 Interval plot (A) and stored EGM (B) recorded from a patient with a Medtronic Reveal ILR during a brain MRI. Noise recorded by the device was interpreted as VT.
• Magnetic resonance imaging is considered a relative contraindication for patients with conventional pacemakers and implantable cardioverter defibrillators (ICDs) due to the potential for multiple adverse interactions between a strong magnetic field and cardiac implantable electronic devices (CIEDs).
• MR scanning should be performed at experienced centers with expertise in MRI and electrophysiology.
• A physician with device expertise and a crash cart with external defibrillator and programmer should be present during scanning.
• The device should be interrogated prior to and after the MRI. Pacemaker-dependent patients should be programmed in an asynchronous mode (DOO, VOO) while a nonpacing mode (ODO, DDI, VVI) should be used for nondependent patients. Magnet, rate response, PVC, noise, ventricular sense, conducted atrial fibrillation (AF) response, and tachyarrhythmia therapies should be disabled.
• In February 2011, the FDA approved an MRI-conditional pacemaker for marketing in the U.S. (EnRhythm MRI SureScan Pacing System, Medtronic, Inc.) which utilizes a special lead system and requires special handling.
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18. http://www.mayoclinic.org/medicalprofs/protocols-for-MRI-in-pacemaker-patients-cvuv9n3.html. Accessed June 30, 2013.
19. MRI SureScan Leads. http://www.medtronic.com/surescan/capsurefix.html. Accessed June 20, 2013.
20. Forleo GB, Santini L, Della Rocca DG, et al. Safety and efficacy of a new magnetic resonance imaging-compatible pacing system: early results of a prospective comparison with conventional dual-chamber implant outcomes. Heart Rhythm. 2010;7(6):750-754.
21. Rhodes T, McComb B, Augostini R, et al. Acute complications with MRI Surescan Leads. Heart Rhythm. 2013;10:S159.
22. MLN Matters. http://www.cms.gov/outreach-and-education/medicare-learning-network-MLN/MLNMattersArticles/downloads/MM7296.pdf. Updated August 14, 2012. Accessed June 30, 2013.