new technology: 核磁共振相容節律器 - ”mri standard of care for...

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

輻射線警告標誌

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.

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.



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



Complication while having MRI

核磁共振 (MRI) 警告標誌

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.

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.

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.

Gradient Waveform

Am

pli

tud

e

0.4 ms

500 ms – 750 ms

Pacing Pulse

Time

~ 0.005 ms

Gradient Induced Pulse

Gradient Induced Pulse

Gradient Mechanism

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

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.

Heating of cardiac tissue

Heating at the lead tip can result in threshold changes.

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.

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

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

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.

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


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

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

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.

Device Design Solutions

• Minimize ferromagnetic content

• Hybrid-case connection

• Hall sensor

• Optimize input circuitry

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.

.

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X-ray marker

MRI filter assembly

Solutions to Reduce MRI Risk

• 2 filters are incorporated into the pacing lead to reduce the

risk of heating from RF signals.

PATIENT

MANAGEMENT

Patient Care Pathway

1. Pre-Screening and Scheduling

2. Pre-scan

3. Scan

4. Post-Scan

Pre-screening

• Ways to ID pacemaker system:

1. Patient ID Card

2. X-Ray

3. Call cardiology

Patient ID Card

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

Radiopaque identification available:

1. pulse generator 2. lead

36

MRI Pacemaker Identification

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

To program MRI SureScan to On, go to Params

-> Additional Features.

When programmed to On, MRI SureScan operation disables

• Arrhythmia detection,

• Magnet mode,

• All user-defined diagnostics.

On

• 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).

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:

Radiology requirements

-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

Preparing Accent MRI Patient for an MRI Scan

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

Devic

e C

lin

ic

MR

I C

en

ter

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)

Preparing Accent MRI Patient for an MRI Scan (Con’t)

Traditional MRI patient workflow process

Preparing Accent MRI Patient for an MRI Scan (Con’t)

St. Jude Medical streamlined MRI patient workflow

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

new technology: 核磁共振相容節律器 - ”mri standard of care for...

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