MRI Conditional Pacemaker

核磁共振相容節律器

Sep 07, 2013

振興醫院 張鴻猷醫師

2013 Taiwan Heart Rhythm Society –

Allied Professional Education Program

MR Conditional Labeling*

MR 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.

MRI 基本步驟

•1. 把人放進去MRI裡

•2. 給能量去激發人體內的氫原子

•3. 把能量關掉

•4. 接收氫原子激發後回傳的能量波

•5. 轉換此能量波訊號成為影像

設備圖

Magnet Gradient Coil RF Coil

RF Coil

4T magnet

gradient coil

(inside)

B0

Main Components of a MRI

Scanner

• Static Magnetic Field Coils

• Gradient Magnetic Field Coils

• Magnetic shim coils

• Radiofrequency Coil

• Control computer

1.5 or 3.0 telsa

1 telsa (T) = 10000 gauss

地球磁場 = 0.5 gauss

Transmit Receive

RF

coil

RF

coil

Main

magnet Main

magnet

Gradient Shimming

Control

Computer

質子 (Proton)

•帶正電

•會自旋

The Effect of Irradiation to the Spin System

Lower

Higher

Spin System After Irradiation

MRI 原理

•利用磁場原理，把人體置於強大且均勻的靜磁場 (static magnet) 中，再利用特定的射頻無線電波脈衝，激發人體組織內的氫原子核

•由於人體內的水分子和脂肪都含有氫原子核，這些氫原子核本身又具有磁場特性，如同一個小小的磁鐵

•若使儀器改變體內氫原子核的旋轉排列方向，原子核就會釋放吸收的能量，能量激發後放出電磁波信號，再經由電腦分析組合成影像，這就是一般所看到的 MRI 影像

•由於不同的組織受到刺激後，釋出不同的回波，因此在影像上便會產生非常良好的對比

MRI 優點

•非侵入性、無傷害的診斷系統，沒有使用 X 光及放射線物質

•安全、無痛苦，能呈現具體的多方向切面影像

•可以很精細的提供腦部、脊椎、軟組織的狀況

•所測量的不僅是組織的解剖影像，更重要的是組織的各種功能性影像，具備對各種組織器官功能性與新陳代謝性障礙的診斷能力

•檢查前病患不需要特別做什麼準備，例如在檢查前不需要空腹、可以進食

MRI 缺點

•設備費用昂貴，檢查費用較高

•掃描時間需時較長

•對肺部的檢查不優於X射線或CT檢查

•對身體移動非常敏感，若移動易產生偽影，故不適合急診病患及危急病人，也容易引發禁閉恐懼症

•心律調節器、金屬性人工心臟瓣膜、各類電子傳導器、腦動脈瘤手術夾等裝置會受到磁場干擾，患者不適合 MRI 檢查

•無法鑑別鈣化點

裝置節律器的病人常需要MRI檢查

It is estimated that 50 to 75% of pacemaker patients will have a medical need for an MRI over the lifetime of their device

Average Age of Pacemaker Patient

13% Ages 25-64

86% Age 65+

The Prevalence of Common

Comorbidities Increases Rapidly

Over Age 65

慢性病多、需要多專科同時照護

Number of Comorbidities in

Pacemaker Patients

85% of all pacemaker patients have one or more comorbidities

15% 0 comorbidities

30% 1 comorbidity

28% 2 comorbidities

27% 3 or more

comorbidities

Opthalmology

Otolaryngology

Neurosurgery

Neurology

Cardiothoracic Surgery

Surgical Oncology

Nephrology

Gynecologic Oncology

Urology

Rheumatology

Oncology

Radiation Oncology

Interventional Radiology

Gastrointestinal Surgery

Orthopedic Surgery

Vascular Surgery

85%1 1 or more

comorbidities

1 Kalin R, Stanton MS. PACE. 2005;28:326-328.

MRI: Three Powerful Fields

Static Field

Gradient Field

RF Field

MP – 14

背景磁力永遠存在

Static Gradient RF

Device Interactions

Stimulation (UCS)

Lead Heating

UCS = unintended cardiac stimulation - Inhibitor pacemaker function

- Trigger rapid pacing

- Deliver inappropriate shocks

Lead 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

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

Device Interactions Clinical

Impact

Failures can be temporary or permanent

MP – 53

Pacemaker System Design

Solutions

Device Design Solutions

• Minimize ferromagnetic content

Unintended cardiac stimulation Device interactions Force and Torque

• Hybrid-case connection

• Hall sensor

• Optimize input circuitry

Lead Heating Design Solution • Lead inner conductor coil design mitigates lead heating

• 4 filar to 2 filar increases inductance and reduces

heating

• 5086 provides 3:1 reduction in lead tip heating

0

10

20

30

40

50

60

70

80

90

100

0 5 10 15 20 25 30 35 40 45 50

Perc

en

t o

f M

axim

um

Lead Path

5076 vs. 5086MRI Comparison

5076 - 52

5086 - 52

Clinical Confirmation of

Safety

Clinical Study Experience (EnRhythm MRI)

• Prospective, randomized, multi-center – Implantation: 464 subjects

– 41 international centers • 21 Europe, 13 U.S., 6 Canada, 1 Middle East

• Enrollment: – February 2007 through July 2008

• Primary End Points: – Consistent Capture Thresholds

– Consistent Sensed Amplitudes

MRI Group

MRI Scans

9-12 Week Visit

Post-MRI

Pre-MRI

Control Group

No MRI

1-Week Post-MRI

Visit

1-Month Post-MRI

Visit

Enrollment

2 Month

Visit

Implant

and Randomization

Clinical Visit Schedule

6-Month

Post-Implant Visit

and Every Six

Months Thereafter

Primary Effectiveness Endpoint

No measurable difference between MRI and control groups

Atrial & Ventricular Capture Threshold: Pre-visit to 1-month post-visit

0

20

40

60

80

-1 -0.5 0 0.5 1

Change in Atrial

Threshold (V)

% o

f P

ati

en

ts

MRI

(n=165)

Control

(n=164)

0

20

40

60

80

-1 -0.5 0 0.5 1

Change in Ventricular

Threshold (V)%

of

Pati

en

ts

MRI

(n=190)

Control

(n=184)

Clinical Confirmed Safety and

Effectiveness

• Safety demonstrated – No MRI-related complications

– No sustained ventricular arrhythmias or

asystole

• Effectiveness demonstrated – Consistent capture thresholds

– Consistent sensed amplitudes

• Complete system: MRI compatible

pacemaker with two MRI compatible leads

• Implanted for at least 6 weeks

• No abandoned leads

• Pacing capture threshold ≤ 2.0 V at 0.4 ms

• Lead impedance of 200 Ω to 1500 Ω

• SureScan programming

US Conditions of Use – Cardiology

• 1.5 Tesla Scanner

• Gradient field:

– Maximum Gradient Slew Rate ≤ 200 T/m/s (per axis)

• RF field: Normal Operating Mode

– Whole body SAR ≤ 2.0 W/kg

– Head SAR < 3.2 W/kg

• Patient monitoring

US Conditions of Use – Radiology

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

1

PRESCREENING

2 PRE-SCAN

3 SCAN

4 POST SCAN

X-Ray

Radiopaque identifies the system via unique radiopaque visible under x-ray

1 PRE-

SCREENING

2 PRE-SCAN

3 SCAN

4 POST SCAN

1 Location of the device radiopaque symbol 2 Device radiopaque MRI symbol 3 Lead radiopaque MRI symbol

Programmer print out

Programmer

Printout

Provides

confirmation that

the system is MR-

Conditional, model

number and

checklist for

relevant conditions

1 PRE-

SCREENING

2 PRE-SCAN

3 SCAN

4 POST SCAN

SureScan Programming Steps

1 PRE-

SCREENING

2 PRE-SCAN

3 SCAN

4 POST SCAN

During the Scan – Monitoring

• Patient must be monitored during the MRI

scan:

– Visual and verbal contact

– Pulse oximetry

– Blood pressure

– Electrocardiography (rate only)

• There is no requirement for the monitoring

person to be from cardiology.

1 PRE-

SCREENING

2 PRE-SCAN

3 SCAN

4 POST SCAN

Post-Scan

1 PRE-

SCREENING

2 PRE-SCAN

3 SCAN

4 POST SCAN

Thank you!!