Magnetic Resonance Imaging in Pacemaker Patients: Hot Topics

for the Implanting Physician

PanelistJ. Rod Gimbel, MDClinical Cardiac ElectrophysiologistEast Tennessee Heart ConsultantsKnoxville, Tennessee

PanelistProf. Torsten Sommer, MDProfessor of RadiologyAcademic Institution of the University of BonnDirector, Department of Diagnostic and Interventional Radiology and Nuclear MedicineGerman Red Cross Hospital Neuwied, Germany

ChairProf. Massimo Santini, MDHead, Cardiovascular DepartmentSan Filippo Neri HospitalRome, Italy

Background: MRI and Pacemakers

> 650,000 new pacemaker implantations per year worldwide

MRI exams performed each year:• > 22 million in the United States• > 35 million worldwide

1. Roguin A, et al. Europace. 2008;10:336-346.

Number of annual MRI scans and of newly implanted ICDs in US[1]

The Clinician’s Dilemma

MRI is contraindicated in patients with implantable cardiac devices.

50% to 75% of patients will develop an indication for MRI over the lifetime of their device…[1,2]

… Suggesting that each year, an estimated 200,000 patients with cardiac devices are denied MRI.[1,2]

1. Kalin R, et al. Pacing Clin Electrophysiol. 2005;28:326-328.

2. Kanal E, et al. AJR AM J Roentgenol. 2004;182:1111-1114.

Why Is MRI Contraindicated in Pacemaker Patients?

1. Roguin A, et al. Europace. 2008;10:336-346.

Potential effects of MRI on pacemaker, CRT devices, ICDs, implantable cardiovascular monitors, and implantable loop recorders

(1) Static magnetic field • Mechanical forces on ferromagnetic components• Unpredictable magnetic sensor activation, reed-switching closure• Changes in electrocardiograms

(2) Modulated radio frequency (RF) field• Heating of cardiac tissue adjacent to lead electrodes• Possible induction of life-threatening arrhythmias (very rare)• Pacemaker reprogramming or reset• RF interactions with the device (over- and under-sensing)

(3) Gradient magnetic field• Possible induction of life-threatening arrhythmias (unlikely in bipolar mode)• Induced voltages on leads cause over- and under-sensing

(4) Combined field effects• Alteration of device function because of EMI• Mechanical forces (vibration)• Electronic reset of device• Damage to pacemaker/ICD and/or leads

Pacemakers are switched either to asynchronous magnet or interference mode, ICD therapy is switched off, and interference mode does not exist.

When to Perform MRI in a Pacemaker Patient: Guideline RecommendationsScanning device patients is now considered a relative contraindication (vs absolute).

Decision should be weighed principally on risk-benefit ratio and the urgency of the clinical indication for MRI.[1,2]

If risk-benefit ratio favors MRI and there is no imaging alternative, then one should proceed, but with precautions including:[1,2]

• Performing it only at “extremely-experienced” centers• Collaboration between cardiologist and radiologist• Monitoring• Reprogramming the device• Careful follow-up of the patient after MRI

1. Roguin A, et al. Europace. 2008;10:336-346. 2. Levine GN, et al. Circulation. 2007;116:2878-2891.

MRI-Safe

M = Monitoring (ECG and pulse oximetry)

R = Reprogramming

I = Make the device Invisible or Invulnerable:

• Invisible for nondependent PM patients -- turn off device features (OOO)

• Invulnerable for PM-dependent patients -- asynchronous mode should be programmed (VOO or DOO)

S = Keep SAR as low as possible

Be mindful that even if one applies these recommended strategies, there is no guarantee that the outcome is going to be safe.

Requirements During and After MRI Scanning: Guideline Recommendations

Procedure Requirements ACR[1] AHA[2] ESC[3]

ACLS-certified personnel

Direct supervision with cardiologist

Pacemaker/ICD programmer

Personnel to ensure safe practice guidelines (scanning parameters)

Crash cart, including defibrillator onsite

Uninterrupted monitoring of heart rhythm and vital signs

Interrogation of device post examination

1. Kanal E, et al. AJR AM J Roentgenol. 2007;188:1-27. 2. Levine GN, et al. Circulation. 2007;116:2878-2891.3. Roguin A, et al. Europace. 2008;10:336-346

MRI Scanning in ICD Patients[1]

ICDs may falsely detect the MR RF field as VF, charge capacitors, and deliver ATP, cardioversion, or defibrillation therapies

• Can still occur if therapy delivery has been deactivated because of electrical reset with subsequent therapy activation

Devices may not be able to deliver ICD therapy in the static magnetic field (needs further investigation)

• ICD transformer will be magnetically saturated and may not have the voltage necessary to charge the capacitor

• Can lead to permanent device failure • Magnetic fields may prevent detection of VT or VF

Limited number of clinical reports on the use of MRI in ICD patients

1. Roguin A, et al. Europace. 2008;10:336-346.

Issue of RF-Induced Heating of Leads?

Heating of ICD leads comparable with that of pacemaker leads

Temperature increase in vitro at lead tips can result in loss of capture or myocardial perforation

Can result from:• Energy of RF pulse• Position of electrodes

w/in RF field• Specific lead model

Unknowns:• Thermal injury in vivo?• Deterioration of capture

thresholds?• Risk for perforation?• Role for specific geometric

configurations

Evidence for RF-Related Alterations at the Lead Tip/Endocardium Interface[1]

1. Sommer T, et al. Circulation. 2006;114:1285-1292.

Results suggest that there is some heating at the interface of the lead tip and the endocardium, but that it is clinically insignificant.

The increase in PCT did not have clinically relevant effects in any patients (ie, increase of the pacemaker output was not necessary in any patient to ensure stimulation with a sufficient safety margin).

Inhibition of pacemaker output or induction of arrhythmias was not observed.

Significant pacing capture threshold (PCT) increase (P = .017) pre/post MRI.

PCT increase (≥ 1.0 V at 0.4 ms) pre/post MRI in:• 6/115 MRI exams• 6/195 PM leads

Troponin I increases (> 0.1 ng/mL) pre/post MRI in:• 4/116 MRI exams (1 increase associated with PCT increase)

Significant lead impedance decrease (P = .025) pre/post MRI.

Safety:System-related, complication-free rate: 91.7% (P < .001)• No clinical (bradycardia or tachycardia), subclinical

(pacemaker performance), or technical (pacemaker or lead damage, or interference) adverse events

Efficacy:No significant differences between MRI and control groups at 1 month in atrial pacing and ventricular pacing capture thresholds

Overcoming Limitations? Initial Data on an MR-Conditional Pacemaker System†[1]

1. Wilkoff BL, et al. Presented at Heart Rhythm; May 2009; Boston, Massachusetts.

Initial data suggest that the technology is safe and may allow patients to undergo MRI to multiple parts of the body (with the exception of the chest).

†CE mark approval Nov 2008, US investigational only (FDA approval pending)

The Future

More MR-conditional systems will be developed

Medical/legal implications: • Problem with legacy leads• Need to develop recommendations for the

implanting physician:• How to manage medical/legal implications • Patient selection for device implantation

Develop international registries to determine long-term reliability

Effects from 3.0 T MR scanners?

ConclusionFor patients with current generation devices:

• MRI should not be considered an absolute contraindication• Physicians should weigh risk-benefit ratio• Institute special protocol, technique (ie, programming of the

device, etc)

If indications for MR-conditional pacemaker system are not expanded to all patients, system should be used in:

• Patients indicated for a PM who had undergone prior MRI (with future MRIs anticipated)

• Patients with long life expectancy (ie, those of young age) should at least receive a lead that is MR-conditional

Hopefully, in the future, MRI will become more compatible with all devices, allowing patients access to this useful diagnostic technique