MRI in Patients with

Implanted Electronic

Medical Devices

Dr James FraserDalhousie University

CAR 2016

Objectives

1. Describe the safety concerns and technical challenges

presented by imaging patients with implanted cardiac

electronic medical devices. (CanMEDS role: Health

Advocate)

2. Explain the term MR-conditional device and its

implications.

3. Demonstrate a basic understanding of the CHR/CAR

collaborative Consensus Statement on Magnetic

Resonance Imaging with Cardiac Implantable Electronic

Devices. (CanMEDS roles: Collaborator, Communicator)

Disclosures

No financial interests with any of the companies or

products discussed

The Issue

There is an increasing number of patients with implanted

cardiac devices, many of whom will require an MRI

examination for optimal imaging assessment.

There are serious and potentially fatal risks of performing

MRI in these patients without following appropriate

precautions and protocols.

An increasing number of MR-conditional implanted

cardiac electronic devices (e.g. pacemakers and ICDs)

are becoming available within Canada.

Potential risks of MRI

with conventional pacemakers

Risks associated with MRI due to interaction between Pacemaker system and the static magnetic field, gradient magnetic fields, and radiofrequency energy.

Static magnetic field: movement, torque, dislodgment, magnetic sensor activation and unpredictable reed-switch behavior, magnetohydrodynamic effect.

Gradient magnetic fields: rapidly changing magnetic fields can induce electrical currents in pacemaker leads -> oversensing, undersensing, even life-threatening arrhythmia.

Radiofrequency Energy: Leads can act as “antennae”, concentrate radiofrequency energy, = heat and electrical currents -> reset, battery depletion, effects on sensing, pacingthresholds, lead impedances, causing inappropriate pacingacceleration or inhibition. Abandon or fractured leads more prone to tip heating.

MR Conditional

Labeling for MRI

*ASTM standard F2503: Standard Practice for Marking Medical Devices and Other Items for Safety in the

Magnetic Resonance Environment

*ASTM standard F2503: Standard Practice for Marking Medical Devices and Other Items for Safety in the

Magnetic Resonance Environment

...an item that has been demonstrated to pose

no known hazards in a specified MRI

environment with specified conditions of use.

Minimize ferromagnetic content

Isolated circuit board

Circuit component change

Designed for MRI Environment

Unintended cardiac stimulation

Device interactions

Force and Torque

MR Conditional Pacing Leads

Approved by Health Canada:

Newly developed specific MRI Conditional

Leads

Retroactive MR Conditional Labeling

Health Canada Scanning

ConditionsBiotronik ProMRI

Pre-Scan

Conditions

The following requirements must always be fulfilled in order to perform an MR scan

using BIOTRONIK’s Entovis ProMRI® System:

• The device system consists of a pacemaker with one or two pacing leads in

combination to constitute an MR conditional device system.

• There must be no other implanted medical devices that may interact with MRI, such

as:

-- Abandoned pacemaker/ICD leads

-- Lead extensions

-- Other active medical devices

-- Non-MRI compatible devices

• The absence of phrenic nerve stimulation at 4.8 V at 1.0 ms.

• The leads have been implanted for at least 6 weeks.

• The device system is implanted pectorally.

• The measured pacing threshold is not above 2.0 V at 0.4 ms pulse width.

• The pacing system should be functioning normally prior to an MRI

• The pacemaker is reprogrammed to a special MRI mode immediately prior to the MR

scan.

MRI Scanner

Limitations

The MRI scanner has to meet the following conditions:

• Use of a clinical MRI system with a cylindrical bore or elliptical bore and a static

magnetic field strength of 1.5 Tesla.

• The slew rate of the MRI scanner’s gradient fields should not exceed 200 T/m/s per

axis.

• No additional local transmitting coils are used.

Health Canada Scanning

ConditionsBiotronik ProMRI

Restrictions During

the MRI Scan

The following conditions must be met during the MR scan:

• The mean specific absorption rate (SAR) for the whole body displayed by the MR

scanner must not exceed 2.0 W/kg.

• The head absorption rate displayed by the MRI scanner must not exceed 3.2 W/kg.

• Emergency equipment for resuscitation must be kept at hand and properly certified

staff must be readily available.

• The patient should be continuously monitored in an appropriate manner during the

entire MR scan. Among others, the following parameters can be observed for this

purpose:

-- Blood oxygen saturation

-- Blood pressure

-- ECG

• Adherence to the permissible positioning ranges. The isocenter of the high-frequency

coil should not be below eye level or above the hip bone. In practice, this means that

the marker line of the laser light localizer, which is used for subsequent positioning of

the patient within the MRI scanner, should not be set below eye level (lower edge of eye

socket) and not above the hip bone (two fingers above the symphysis). These areas

have to be adhered to during the MR scan.

Permissible

Positioning Zone

and Scan

Exclusion Zone

The first permissible positioning zone starts at the top of the skull and ends at eye level.

The second permissible positioning zone starts at the hip bone level and ends at the

patient’s feet. The eyes and hip bone serve as the maximum allowed positioning marks

for the isocenter of the MR scanner. These visible marks can be marked with a laser

during MR scanner positioning. Figure 1 below illustrates the permissible positioning

zone and scan exclusion zone of the Entovis MR Conditional system.

Must be programmed into the appropriate

mode by a cardiologist / electrophysiologist or

designate prior to scanning.

Printed Documentation for MRI Record

Confirms pacers required

settings and functionality

Key Conditions: MRI

Patient monitoring

Verbal and Visual

Pulse Ox and/or

EKG

RV

LV

Can artifact

Lead

Signal alteration

Short axis Long axis

T2 DE

MR Conditional Systems

Manuals

Facility requirements for performing MR

imaging in patients with MR-conditional CIEDs

The imaging facility must have a protocol for MR scanning

of patients with CIEDs, developed via a collaborative effort

of MR and CIED specialists. Ideally, it should consist of an

onsite CIED clinic to interrogate and program the CIED

systems. In some cases, it might be possible for a

radiology suite to establish close collaboration with an

offsite CIED clinic where patients are assessed before and

after MR. However, on the day of MR scan, a member of

the CIED team (technician, nurse, or physician) should be

readily accessible for device troubleshooting or

reprogramming, if required.

MRI in patients with conventional

pacemakers

The MagnaSafe Registry 1500 exams, no deaths or poor patient outcomes.

Insufficient data to determine safety, and possible long-term effects are unknown.

Performing MRI in patients with conventional pacemakers cannot be considered a routine procedure. Appropriate multidiscipline risk Vs benefit discussion is paramount.

Special precautions must be taken including: careful patient selection and device programming, rigorous monitoring, reanimation readiness during the procedure, and exclusion of thoracic MRI.

Summary

Multiple MR Conditional Pacemaker systems available for 1.5T MRI systems in Canada.

Very specific Pre-scanning, Scanning and Post-scanning conditions and procedures are necessary.

Present systems require the system to be programmed into MRI mode by Cardiologist/electrophysiologist prior to scanning and reprogrammed after scanning. Collaborative “team approach” protocol should be in place.

Canadian Heart Rhythm Society (CHRS) and CanadianAssociation of Radiologists (CAR) Joint Consensus Statement on Magnetic Resonance Imaging with Cardiac Implantable Electronic Devices.

http://www.carjonline.org/article/S0846-5371%2814%2900074-6/pdf.

Thank You

Questions?