1. New Technology:
核磁共振相容節律器
(MRI Conditional Pacemaker System)
林圀宏
心臟內科
中國醫藥大學附設醫院
2013 心臟電生理相關專業人員教育課程

2. 輻射線 警告標誌

3. Why MRI Scans are Important to Clinical Medicine
• Fastest Growing Standard of Care in Diagnostic Imaging1
• Superior Soft Tissue Imaging2
 Primary method to evaluate:
 Central Nervous System
 Musculoskeletal System
 Oncological Conditions
 Some Cardiovascular Disorders
• MRI complements CT (which excels when imaging bony structures)
• No radiation risk to patient or healthcare provider
• 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 patients
and women of childbearing age.
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.

4. 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

5. Brain computed tomography (CT) vs MRI in a patient with weakness.
Nazarian S et al. Circ Arrhythm Electrophysiol 2013;6:419-
428
Copyright © American Heart Association

6. Cardiac computed tomography (CT) vs MRI in a patient with facial swelling.
Nazarian S et al. Circ Arrhythm Electrophysiol 2013;6:419-
428
Copyright © American Heart Association

8. Complication while having MRI

9. 核磁共振 (MRI) 警告標誌

10. 10
Anatomy of an MRI Scanner
Three basic components:
 Static magnet
 Gradient magnets
 RF coil
10
Static
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.

13. Force
• The most intuitive potential interaction of implanted devices
with an external magnetic field is the possibility for
movement and dislocation of the device because of magnetic
force.
• Current lead designs contain little or no ferromagnetic
components and are not likely to experience force and
torque.
• The potential for movement of a pacemaker or ICD
generator in the MRI environment depends on the
 magnetic field strength
 ferromagnetic properties of the device components
 the implant distance from the magnet bore and the
stability of the implant.

14. Current induction
• The RF and pulsed gradient magnetic fields of the MRI
scanner may induce electric currents in leads within the field,
if the lead is part of a current loop that is completed through
the body.
• The ratio of lead length versus RF wavelength and lead
conformations, such as loops, are strongly associated with the
extent of current induction.

15. Gradient Waveform
Amplitude
0.4 ms
500 ms – 750 ms
Pacing Pulse
Time
~ 0.005 ms
Gradient Induced Pulse
Gradient Induced Pulse
Gradient Mechanism

16. Stimulation hazard gradient-induced high rate pacing
Start of Scan
EKG
Pulse Ox
Canine Test
Unintended Stimulation Clinical Impact
The MRI scanner is pacing the heart

17. Heating and tissue damage
• Metallic devices and leads can act as an antenna thus
amplifying local radiofrequency energy deposition.
• Fractured leads or lead loop configurations may increase
the potential for heating.
• Epicardial leads that are not cooled by blood flow and
abandoned leads may also be prone to increased heating.

18. Heating of cardiac tissue
Heating at the lead tip can result in threshold changes.

19. Malfunction of devices
• CIED may provide unnecessary therapies or fail to provide
necessary therapies when placed in the MRI scanner.
• Pacemakers and ICDs have the potential for receiving
electromagnetic interference (EMI) in the MRI environment,
resulting in:
 radiofrequency noise tracking
 asynchronous pacing
 inhibition of demand pacing
 delivery of ICD therapies
 programming changes
 loss of function.

20. Figure 2. EMI noise from different MR scan protocols interpreted by the device as ventricular
fibrillation (VF).
Roguin A et al. Circulation 2004;110:475-482

21. Simultaneous electrocardiography and pulse oximetry while in 3T
bore of magnetic resonance imaging followed by application of
gradient scan leading to inhibition of effective pacing.
Gimbel J R Europace 2009;11:1241-1242

22. Malfunction of devices
• The static magnetic field of the MRI scanner can also
alter device function by inducing unexpected reed switch
opening or closure.
• In addition, temporary programming changes made to
avoid device interaction with the MRI scanner (such as
disabling of tachycardia therapies) may lead to
catastrophic results if a spontaneous arrhythmia occurs
and is not recognized.

23. Simultaneous recording of ECG and pulse oximetry during MRI of the brain in a patient with a
Thera pacemaker reprogrammed to D00 80 bpm.
Sommer T et al. Circulation 2006;114:1285-1292
Copyright © American Heart Association

24. During and/or after the MRI
• no inhibition of pacemaker output or cardiac
arrest
• no sustained ventricular arrhythmias
• no unexpected changes of heart rate
• no electrical resets
• no pacemaker system disturbances and
• no sensation of torque or pain

25. Variables Affecting Magnitude of Risks
 Length/position of pacing leads
 Patient and device position within machine
 Patient factors / medical history
 MRI scan duration
 Blood flow at lead/tissue interface
 Strength of RF field
 Target anatomy of scan
 Type of imaging MRI sequence
 Pacemaker and Lead Design

26. MR Conditional Labeling*
MR Safe
MR Conditional
MR Unsafe
An item that has been
demonstrated to pose no known
hazards in a specified MRI
environment with specified
conditions of use.

27. Device Design Solutions
• Minimize ferromagnetic
content
• Hybrid-case connection
• Hall sensor
• Optimize input circuitry

28. Solutions to Reduce MRI Risk
• Filter board added to pacemaker hardware
• When the filter detects MRI RF signals, it will not allow the
signals to be sent back down the lead (rectification), which
would result in cardiac stimulation.
.
28
X-ray marker
MRI filter assembly

29. Solutions to Reduce MRI Risk
• 2 filters are incorporated into the pacing lead to reduce the
risk of heating from RF signals.

30. PATIENT
MANAGEMENT

31. Patient Care Pathway
1. Pre-Screening and Scheduling
2. Pre-scan
3. Scan
4. Post-Scan

32. Pre-screening
• Ways to ID pacemaker system:
1. Patient ID Card
2. X-Ray
3. Call cardiology

33. Patient ID Card

34. X-Ray
Radiopaque identifies the system via unique
radiopaque visible under x-ray
1 Location of the device radiopaque symbol
2 Device radiopaque MRI symbol
3 Lead radiopaque MRI symbol

35. Radiopaque identification available:
1. pulse generator
2. lead

36. 36
MRI Pacemaker Identification

37. MRI Pacemaker Identification (Con’t)
• To verify that a patient has a MRI pacemaker, you may use X-ray
identification, confirming that the pacemaker and the lead are appropriate.
Radiopaque markers will show if the patient has an appropriate system for an
MRI scan
37
St. Jude Medical
Identifier
Device MRI
Symbol

38. To program MRI SureScan to On, go to Params
-> Additional Features.

39. When programmed to On, MRI SureScan operation disables
• Arrhythmia detection,
• Magnet mode,
• All user-defined diagnostics.
On

41. • For patients who require pacing support, program the device to an
asynchronous pacing mode (DOO, AOO, VOO).
• For patients who do not require pacing support, program the device to the
non-pacing mode (ODO).

43. Patients and their implanted systems must be screened to meet the
following requirements:
•No previously implanted (active or abandoned) medical devices,
leads, lead extenders, or lead adaptors.
•No broken leads or leads with intermittent electrical contact as
confirmed by lead impedance history.
•A SureScan pacing system that has been implanted for a minimum of
6 weeks.
•A SureScan pacing system implanted in the left or right pectoral
region.
•Pace polarity parameters set to Bipolar for programming MRI
SureScan to On (for Advisa DR MRI).
•Pacing capture thresholds of ≤ 2.0 volts (V) at a pulse width of 0.4
milliseconds (ms).
•A lead impedance value of ≥ 200 ohms (Ω) and ≤ 1500 Ω.
•No diaphragmatic stimulation at a pacing output of 5.0 V and at a
pulse width of 1.0 ms in patients whose device will be
programmed to an asynchronous pacing mode when MRI
SureScan is on.
Cardiology requirements:

44. Radiology requirements

45. -45-
Competitive Comparison
SJM Accent MRI™
Static magnet 1.5 T- closed bore
Scan Zones Fully body scan
SAR Restrictions Max SAR 4W/kg
MRI settings
activation without
programmer
Yes- SJM MRI Activator™ device
Wireless Telemetry Yes
Daily Remote
Monitoring
Yes

46. Preparing Accent MRI Patient for an MRI Scan

47.  Seamless workflow when a patient needs an MRI
 No programmer needed at MRI center
 No impact to clinic efficiencies
MR
Pacemaker
Establish
MRI Settings Values
Settings
(Follow-up Appt)
Patient
Needs MRI
Scan
MRI Scan
DeviceClinicMRICenter
MRI Center
Arrival
MR Mode
OFF Button
MR Mode
ON Button
 Simple application of the MRI Activator
pre- and post-scan
No programmer necessary for MRI access
= Additional programming step required by competitive systems
48
Pre-Scan
Follow-up
(optional)

48. Preparing Accent MRI Patient for an MRI Scan
(Con’t)
Traditional MRI patient workflow process

49. Preparing Accent MRI Patient for an MRI Scan
(Con’t)
St. Jude Medical streamlined MRI patient workflow

50. Take Home Message
• Implantable pulse generators and defibrillators have traditionally
been considered contraindications to MRI.
• Patients with newer generation devices (MRI conditional device)
can safely undergo MRI, including cardiac MRI.
• But, the introduction of MRI conditional systems has led to a
conceptual shift in clinical decision making —
‘can this patient undergo MRI safely?’
is being superseded by
‘should this patient be implanted with an MRI conditional
device?’.
• Perform MRI carefully in Pacemaker-dependent patients