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MRI Conditional Pacemaker MRI Conditional Pacemaker SystemSystem

高雄醫學大學附設醫院 心臟血管科 陳偉華醫師

ContentsContents What kind of activity that pacemaker patient could What kind of activity that pacemaker patient could

not do ?not do ? What is MRI and why we need this kind of What is MRI and why we need this kind of

examination ?examination ? What is the possible complication of MRI examination What is the possible complication of MRI examination

in pacemaker patient ?in pacemaker patient ? How the CIED company solve this problems?How the CIED company solve this problems? Recent available MRI conditional pacemaker in Recent available MRI conditional pacemaker in

Taiwan Taiwan

What does the What does the pacemaker afraid of ?pacemaker afraid of ?

Source of EMI Source of EMI

www.thrs.com.tw

Why we need MRI Why we need MRI examination ?examination ?

Fastest Growing Standard of Care in Diagnostic ImagingFastest Growing Standard of Care in Diagnostic Imaging11

Superior Soft Tissue ImagingSuperior Soft Tissue Imaging22

Primary method to evaluate:Primary method to evaluate: Central Nervous SystemCentral Nervous System Musculoskeletal SystemMusculoskeletal System Oncological ConditionsOncological Conditions Some Cardiovascular DisordersSome Cardiovascular Disorders

MRI complements CT (which excels when imaging bony structures)MRI complements CT (which excels when imaging bony structures)

No radiation risk to patient or healthcare providerNo radiation risk to patient or healthcare provider

Since the absence of x-ray radiation, MRI is optimal for follow-up of chronic Since the absence of x-ray radiation, MRI is optimal for follow-up of chronic diseases that require repeat imaging and for diagnostic imaging in young diseases that require repeat imaging and for diagnostic imaging in young patients and women of childbearing age. patients and women of childbearing age.

Why MRI Scans are Important Why MRI Scans are Important to Clinical Medicine to Clinical Medicine

1. Kaiser CP. Soaring MRI use draws scrutiny. Diagnostic Imaging Online January 4, 2002. CMP United Business Media: A CMP Healthcare Media Web Site. Available at: http://www.diagnosticimaging.com/dinews/2002010401.shtml. Accessed October 19, 2004.

2. Duru F, Luechinger R, Scheidegger MB, et al. Pacing in magnetic resonance imaging environment: Clinical and technical considerations on compatibility. Eur Heart J. January 2001;22(2):113-124.

Cervical spine computed tomography (CT) vs MRI in a patient with neck pain and fever.

Nazarian S et al. Circ Arrhythm Electrophysiol 2013;6:419-428

Copyright © American Heart Association

Brain computed tomography (CT) vs MRI in a patient with weakness.

Nazarian S et al. Circ Arrhythm Electrophysiol 2013;6:419-428Copyright © American Heart Association

Cardiac computed tomography (CT) vs MRI in a patient with facial swelling.

Nazarian S et al. Circ Arrhythm Electrophysiol 2013;6:419-428Copyright © American Heart Association

Clinical Need: MRI Scanning Capabilities of Clinical Need: MRI Scanning Capabilities of the Thoracic Regionthe Thoracic Region

• 60 million MRI scans performed worldwide 60 million MRI scans performed worldwide annuallyannually11, with prevalence growing for MRI as a , with prevalence growing for MRI as a preferred diagnostic modalitypreferred diagnostic modality

• Over 30% of all MRI scans are done in the Over 30% of all MRI scans are done in the thoracic regionthoracic region22

32%thoracic

1. www.browsemedic.com/MRI2. 2007 MRI Market Summary Report – Commissioned by St. Jude Medical, Inc. June 20083

What is MRI and what What is MRI and what could it do with our could it do with our device ?device ?

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Anatomy of an MRI Anatomy of an MRI ScannerScanner

Three basic components:Three basic components:

Static magnetStatic magnet Gradient magnetsGradient magnets RF coilRF coil

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Determines magnetic strength of scanner:

1.5 or 3.0 tesla 1 tesla (T) = 10,000

gauss. The earth’s magnetic

field = 0.5 gauss. Magnet response in SJM

pacemakers occurs in response to 8-10 gauss directly over the pacemaker.

Length/position of pacing leads Length/position of pacing leads Patient and device position within machinePatient and device position within machine Patient factors / medical historyPatient factors / medical history MRI scan durationMRI scan duration Blood flow at lead/tissue interfaceBlood flow at lead/tissue interface Strength of RF fieldStrength of RF field Target anatomy of scanTarget anatomy of scan Type of imaging MRI sequence Type of imaging MRI sequence Pacemaker and Lead Design Pacemaker and Lead Design

Variables Affecting Magnitude of Variables Affecting Magnitude of RisksRisks

The most intuitive potential interaction of The most intuitive potential interaction of implanted devices with an external magnetic implanted devices with an external magnetic field is the possibility for movement and field is the possibility for movement and dislocation of the device because of magnetic dislocation of the device because of magnetic force.force.  

Current lead designs contain little or no Current lead designs contain little or no ferromagnetic components and are not likely ferromagnetic components and are not likely to experience force and torque. to experience force and torque.

The potential for movement of a pacemaker The potential for movement of a pacemaker or ICD generator in the MRI environment or ICD generator in the MRI environment depends on the depends on the magnetic field strength magnetic field strength ferromagnetic properties of the device componentsferromagnetic properties of the device components the implant distance from the magnet bore and the the implant distance from the magnet bore and the

stability of the implant.stability of the implant.

Force , torque and vibration Force , torque and vibration

The RF and pulsed gradient magnetic fields of The RF and pulsed gradient magnetic fields of the MRI scanner may induce electric currents the MRI scanner may induce electric currents in leads within the field, if the lead is part of in leads within the field, if the lead is part of a current loop that is completed through the a current loop that is completed through the body. body.

The ratio of lead length versus RF wavelength The ratio of lead length versus RF wavelength and lead conformations, such as loops, are and lead conformations, such as loops, are strongly associated with the extent of current strongly associated with the extent of current induction.induction.

Current/ voltage inductionCurrent/ voltage induction

Metallic devices and leads can act as an antenna thus Metallic devices and leads can act as an antenna thus amplifying local radiofrequency energy deposition.amplifying local radiofrequency energy deposition.

Fractured leads or lead loop configurations may Fractured leads or lead loop configurations may increase the potential for heating. increase the potential for heating.

Epicardial leads that are not cooled by blood flow and Epicardial leads that are not cooled by blood flow and abandoned leads may also be prone to increased abandoned leads may also be prone to increased heating.heating.

Essentially the lead acts as an antenna and picks up Essentially the lead acts as an antenna and picks up RF currents that can generate heating upon reaching RF currents that can generate heating upon reaching the tissues at the lead electrodes.the tissues at the lead electrodes.

Resistance of cardiac tissue to current flow generates Resistance of cardiac tissue to current flow generates heat near the lead tip.heat near the lead tip.

Heating at the lead tip can result in threshold Heating at the lead tip can result in threshold changes.changes.

Heating and Tissue Damage Heating and Tissue Damage

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–

Lead Heating Clinical ImpactLead Heating Clinical Impact

• PCT = Pacing Capture Threshold

• PCT is lowest at implant

• Healing produces scar

• Increased distance increases PCT

• Significant heating causes tissue damage

• Increased scar volume increases PCT

CIED may provide unnecessary therapies or CIED may provide unnecessary therapies or fail to provide necessary therapies when fail to provide necessary therapies when placed in the MRI scanner. placed in the MRI scanner.

Pacemakers and ICDs have the potential for Pacemakers and ICDs have the potential for receiving electromagnetic interference (EMI) receiving electromagnetic interference (EMI) in the MRI environment, resulting in: in the MRI environment, resulting in: radiofrequency noise trackingradiofrequency noise tracking asynchronous pacingasynchronous pacing inhibition of demand pacinginhibition of demand pacing delivery of ICD therapiesdelivery of ICD therapies programming changesprogramming changes loss of function.loss of function.  

Malfunction of devicesMalfunction of devices

The static magnetic field of the MRI The static magnetic field of the MRI scanner can also alter device function by scanner can also alter device function by inducing unexpected inducing unexpected reed switch opening reed switch opening or closure. or closure.

In addition, temporary programming In addition, temporary programming changes made to avoid device interaction changes made to avoid device interaction with the MRI scanner (such as disabling with the MRI scanner (such as disabling of tachycardia therapies) may lead to of tachycardia therapies) may lead to catastrophic results if a spontaneous catastrophic results if a spontaneous arrhythmia occurs and is not recognized. arrhythmia occurs and is not recognized.

Malfunction of devicesMalfunction of devices

Tachycardia induction due to Tachycardia induction due to gradients gradients

Gradient Waveform

Am

pli

tud

e

0.4 ms

500 ms – 750 ms

Pacing Pulse

Time

~ 0.005 msGradient Induced Pulse

Gradient Induced Pulse

Gradient MechanismGradient Mechanism

Unintended Cardiac Stimulation Unintended Cardiac Stimulation (Gradient Pulses)(Gradient Pulses)

Lead provides path for gradient magnetic fields to Lead provides path for gradient magnetic fields to induce voltages and give rise to electrical currentsinduce voltages and give rise to electrical currents

If these currents are generated outside of refractory If these currents are generated outside of refractory periods they may result in arrhythmiasperiods they may result in arrhythmias

Induced arrhythmiasInduced arrhythmias 6 non-pacemaker-dependent patients died during 6 non-pacemaker-dependent patients died during

an MRI conducted without cardiac monitoringan MRI conducted without cardiac monitoring11

3 cases showed evidence of induced ventricular 3 cases showed evidence of induced ventricular fibrillation.fibrillation.

Stimulation hazard gradient-induced high rate pacingStimulation hazard gradient-induced high rate pacing

Unintended Stimulation Clinical Unintended Stimulation Clinical ImpactImpact

Start of Scan

EKG

Pulse Ox

Canine Test

!!!!!!! The MRI scanner is pacing the heart !!!!!!!!

MRI-conditional pacemakerMRI-conditional pacemaker

What CIED company have What CIED company have to do ?to do ?

no inhibition of pacemaker output or cardiac no inhibition of pacemaker output or cardiac arrestarrest

no sustained ventricular arrhythmiasno sustained ventricular arrhythmias no unexpected changes of heart rateno unexpected changes of heart rate no electrical resetsno electrical resets no pacemaker system disturbances andno pacemaker system disturbances and no sensation of torque or painno sensation of torque or pain

MRI Safety TerminologyMRI Safety TerminologyMR Safe

MR Conditional

MR Unsafe

*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.

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MRI Conditional (MR MRI Conditional (MR Conditional)Conditional)

A device or implant that may contain magnetic, electrically A device or implant that may contain magnetic, electrically conductive or RF reactive components that is safe for conductive or RF reactive components that is safe for operations to the MRI, provided the conditions for safe operations to the MRI, provided the conditions for safe operation are defined and observedoperation are defined and observed

FDA limits 4 W/kg averaged over the whole body for a 15-minute period

(reflects our labeling) 3 W/kg averaged over the head for any 10-minute period 8 W/kg in any gram of tissue in the extremities for any period of 5

minutes

Device Design Device Design SolutionsSolutions

Minimize ferromagnetic contentMinimize ferromagnetic content

Hybrid-case connection

Hall sensor

Optimize input circuitry

Lead Reliability and Filters Lead Reliability and Filters An MRI conditional pacing lead must be able to withstand the magnetic forces, gradients, and RF energy present during An MRI conditional pacing lead must be able to withstand the magnetic forces, gradients, and RF energy present during scanning and the harsh environment of the human body.scanning and the harsh environment of the human body.

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Filter board added to pacemaker hardware.2 filters are incorporated into the pacing lead to reduce the risk of heating from RF signals.

PATIENT MANAGEMENTPATIENT MANAGEMENT

1.1. Identity cardIdentity card

2.2. Radiopaque identification Radiopaque identification

For patients who require pacing support, program the device to an asynchronous pacing For patients who require pacing support, program the device to an asynchronous pacing mode (DOO, AOO, VOO). mode (DOO, AOO, VOO).

For patients who do not require pacing support, program the device to the non-pacing For patients who do not require pacing support, program the device to the non-pacing mode (ODO). mode (ODO).

Recent MRI Conditional Recent MRI Conditional Pacemaker , CRT and Pacemaker , CRT and ICD in the Market ICD in the Market

St Jude MedicalSt Jude MedicalAccent MRI RF Pacemaker Accent MRI RF Pacemaker

MedtronicMedtronic

Ensura MRI SureScan Pacing System ( DDDR) Ensura MRI SureScan Pacing System ( DDDR)

Advisa MRI SureScan Pacing System ( DDDRP)Advisa MRI SureScan Pacing System ( DDDRP)

Biotronik Biotronik

Many Thanks and Good Bye……..Many Thanks and Good Bye……..