REVIEW ARTICLES International Journal of Arrhythmia 2016;17(3): doi: New Technologies for Magnet

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1 REVIEW ARTICLES International Journal of Arrhythmia 2016;17(3): doi: New Technologies for Magnetic Resonance Imaging Compatible Device of Boston Scientific 정지운 보스턴사이언티픽코리아 Ji Woon Jung Boston Scientific Korea, Seoul, Republic of Korea Received: February 19, 2016 Revision Received: April 18, 2016 Accepted: April 18, 2016 Correspondence: Ji Woon Jung, IBHRE, CCDS Boston Scientific Korea 19F, SEI Tower, 39, Eonjuro 30-gil, Gangnam-gu, Seoul 06292, Republic of Korea Tel: Fax: Copyright 2016 The Official Journal of Korean Heart Rhythm Society Editorial Board & MMK Co., Ltd. ABSTRACT The use of both magnetic resonance imaging (MRI) and pacing devices has vastly increased worldwide in recent years. A significant number of implanted patients will likely need monitoring using magnetic resonance imaging (MRI) over the course of the lifetime of their device. Some studies have demonstrated that with appropriate precautions, MRI can be safely performed in patients with selected implantable pacemakers. However, MRI is still contraindicated in patients with pacemakers. Recently, new pacing systems have been specifically designed for safe use in the MRI environment. The first reported experience suggests that the technology is safe and may allow patients with these new pacemakers to undergo MRI. This review will describe the outstanding issues and controversies surrounding the safety of MRI in patients with pacemakers, and the potential benefits of the new MRI-conditional technology. We will also discuss how to decide whether an MRI-conditional system should be implanted, and highlight key issues that warrant further studies. Key Words: Magnetic Resonance Imaging Pacemaker Safety 서론 자기공명의원리와이식형기기에미치는영향 세계적으로 MRI (magnetic resonance imaging) 장비와부정맥치료용으로사용되는 CIED (cardiovascular implantable electronic device) 제품의사용은지속적으로증가하고있다. 과거에는 MRI 촬영시발생할수있는여러가지위험성때문에 CIED 장치를이식한환자에서촬영이금지되어있었으나, 최근에는조건에따라촬영이가능한 CIED 제품들이출시되어 CIED 이식환자라도특정조건아래에서 MRI 촬영이가능하게되었다. 1 MRI 촬영장비는크게 3가지주요요소로이루어져있다 (Figure 1). 2 MRI 장비의구성을보면 RF (radiofrequency)- coil, gradient coil, magnet으로구성되어있으며, MRI 촬영시에발생되는전압이나전류, RF 등은 CIED 제품작동에치명적인오류나이상을일으킬수있다. MRI 촬영시 MRI 장비를구성하는 3가지주요요소로부터유발될수있는 CIED 에서의위험은아래와같이다양하다. 첫번째로는 static magnetic field로인해유발되는증상으로 CIED의 150

세번째로 gradient coil에서발생되는에너지가전극선과 PG에고전류를흐르게하여회로의이상이나오동작을유발하여치명적인부정맥을발생시키기도한다 (Figure 4). 최근에출시되는보스톤사이언티픽의 CIED 제품들은오랜기간의연구를통해 MRI 촬영시발생할수있는여러위험요소에도 CIED 이식환자가안전할수있도록전극선의디자인변화, PG의주요부품변경및삽입을통해발전해왔다.

2 Magnetic Resonance Imaging Compatible Devices stimulation을억제하거나 PG (pulse generator) 의프로그램을 reversion할수있다 (Figure 2). 2 두번째로는 MRI 촬영시에 RF coil에서 RF B1에해당하는에너지가발생하는데, 이로인해인체에삽입된전극선이가열되면서그기능에영향을주거나전극선주변의조직들에열이가해져 loss of capture의원인이되기도한다 (Figure 3). 세번째로 gradient coil에서발생되는에너지가전극선과 PG에고전류를흐르게하여회로의이상이나오동작을유발하여치명적인부정맥을발생시키기도한다 (Figure 4). 최근에출시되는보스톤사이언티픽의 CIED 제품들은오랜기간의연구를통해 MRI 촬영시발생할수있는여러위험요소에도 CIED 이식환자가안전할수있도록전극선의디자인변화, PG의주요부품변경및삽입을통해발전해왔다. 현재심박동기 (permanent pacemaker) 는 3.0 T, 삽입형제세동기 (implantable cardioverter-defibrillator, ICD) 와심장재동기화치료 (cardiac resynchronization therapy, CRT X4 [4극제품 ]) 는각각 1.5 T의 MRI 장비에서전신촬영이가능하고, 촬영시간의제한도없는제품들이 Figure 1. An magnetic resonance imaging scan generates 3 field: radiofrequency coil, gradient coils, magnet. MRI, magnetic resonance imaging. Figure 2. Static magnetic field (B0) effect on cardiovascular implantable electronic device. Figure 3. The radiofrequency magnetic field (B1) effect on cardiovascular implantable electronic device. Figure 4. The magnetic gradient (Gx, Gy, Gz) effect on cardiovascular implantable electronic device. 151

International Journal of Arrhythmia 2016;17(3):150-155 출시, 사용되고있다. MRI 조건에적합한전극선디자인 앞서 MRI 촬영시생성되는 RF로인해전극선에전류가흐르면서전극선이가열되고, 발생된열로인해서주변심장조직에영향을미치며역치값이높아지는현상이발생한다고언급하였다.

전극선의내부는일반적으로코일이감겨있는형태로이루어져있는데, 코일의지름이크고, 간격이좁고, wire의지름이작을수록 RF에의한열은감소한다. 반면코일의지름이작고, 간격이넓으며, wire의지름이크면 RF에의해발생하는전극선의열은더크게발생한다.

Dual filar 형태나 multi-filar coil의형태로제작된전극선은코일간격이더넓어 MRI 촬영시에 RF가생성되면넓은코일간격으로인해전극선내부와끝부분에온도가높아지기때문에 single filar coil 형태를채택하였다.

3 International Journal of Arrhythmia 2016;17(3): 출시, 사용되고있다. MRI 조건에적합한전극선디자인 앞서 MRI 촬영시생성되는 RF로인해전극선에전류가흐르면서전극선이가열되고, 발생된열로인해서주변심장조직에영향을미치며역치값이높아지는현상이발생한다고언급하였다. 이에보스톤사이언티픽은전극선에강한전류가흐르더라도열의발생을줄이는새로운전극선디자인을고안하였다 (Figure 5). 3 전극선의디자인에따라 MRI 촬영시 RF에의해열이더많이발생하거나더적게발생할수있다. 전극선의내부는일반적으로코일이감겨있는형태로이루어져있는데, 코일의지름이크고, 간격이좁고, wire의지름이작을수록 RF에의한열은감소한다. 반면코일의지름이작고, 간격이넓으며, wire의지름이크면 RF에의해발생하는전극선의열은더크게발생한다. 현재보스톤사이언티픽에서출시된 INGEVITY TM 전극선은코일의지름이크고, 코일의간격은매우촘촘하게좁으며, wire 지름은작고 single filar coil 형태로디자인되어 MRI 촬영시생성되는 RF가전극선에흐르더라도발열을최소화하도록설계되었다 (Figure 6). Dual filar 형태나 multi-filar coil의형태로제작된전극선은코일간격이더넓어 MRI 촬영시에 RF가생성되면넓은코일간격으로인해전극선내부와끝부분에온도가높아지기때문에 single filar coil 형태를채택하였다. MRI 조건에적합한내재성 Pacemaker 디자인요소 MRI 촬영시생성되는 RF로인해열이발생하는부작용은새로운전극선디자인의설계로해결하였으나여전히 gradient coil에서발생하는고전류로인해 pacemaker에문제가발생할수있다. 이를보안하기위해보스톤사이언티픽의 permanent pacemaker 장치에는 surge suppressor라는부품이추가삽입되어 MRI 촬영시고전류가 pacemaker에전달되더라도안정적으로전류를공급하도록유지한다 (Figure 7). Figure 5. Magnetic resonance imaging Lead Design for lower heating. 152

Magnetic Resonance Imaging Compatible Devices Figure 6. Design of Ingevity TM lead for 3 T magnetic resonance imaging condition.

보스톤사이언티픽의 permanent pacemaker는갑작스럽게높은전압이내부회로에흘러도 surge suppressor를통해안정적으로전압을유지한다.

B0 (static magnet field) 으로인해생성되는 자력으로인해발생하는부작용을최소화하였고, MICS (medical implant communication service) 안테나를삽입하여프로그래머와무선통신이가능하다.

4 Magnetic Resonance Imaging Compatible Devices Figure 6. Design of Ingevity TM lead for 3 T magnetic resonance imaging condition. MRI 촬영시 gradient coil 에서발생하는높은전압이 pacemaker에전달되면 surge 현상으로인해 pacemaker가비정상적으로동작하거나회로의고장을유발한다. Surge는갑작스럽게높은전압이유입되는현상을의미하며, 일반적으로 surge 증상이기계장치에발생하면장치의회로가고장난다. 보스톤사이언티픽의 permanent pacemaker는갑작스럽게높은전압이내부회로에흘러도 surge suppressor를통해안정적으로전압을유지한다. Surge suppressor와같이 pacemaker 내부의다른주요부품들도 MRI 촬영이가능하도록구성을변경하였는데, 촬영시미치는영향을최소화하도록배터리재질도기존에사용되던니켈 (nickel) 에서스테인리스스틸 (stainless steel) 로변경하였다. B0 (static magnet field) 으로인해생성되는 자력으로인해발생하는부작용을최소화하였고, MICS (medical implant communication service) 안테나를삽입하여프로그래머와무선통신이가능하다. 또한기기구성의변경을통해 RF가기계내부에흐를때미치는영향을줄이며, EMI (electromagnetic interference) 필터가 pacemaker 안에장착되어 RF로인해발생하는 EMI를감소시키고, PG 헤더부분에위치한전극선고정부위의재질을변경하고, 아날로그 IC (integrated circuit) 전자회로를사용하여 gradient coil로인해발생되는전류의흐름에의한영향을최소화하였다. 4 Permanent pacemaker에는 surge suppressor가삽입되어있으나, ICD와 CRT 제품에는 surge suppressor가삽입되지않았다. 5 그러나나머지부품들은 high voltage의특성에맞추어 MRI의영향을최소화하는부품으로변경하였다 (Table 1). 또한조건적으로 MRI 촬영이가능한 pacemaker는 X-ray ID만으로알수있도록 PG 내에위치한 ID 부분에 tag 를달았다. 응급상황이나환자가이식한기계에대한정보가없더라도단순 X-ray 촬영으로 MRI 촬영이조건에따라가능한 pacemaker인지를판별이가능하다. 보스톤사이언티픽의모든 pacemaker는 X-ray tag가삽입되어있는데, MRI 촬영이가능한제품의경우가장앞쪽에삼각형모양이삽입되어있다 (Figure 9). 6 Figure 7. Surge suppressor in pacemaker. LV, left ventricle; RA, right atrium; RF, radiofrequency; RV, right ventricle. 153

International Journal of Arrhythmia 2016;17(3):150-155 Figure 8. Magnetic resonance imaging pacemaker system. Figure 9.

Inherent cardiovascular implantable electronic device design for magnetic resonance imaging environment (ICD, CRT) Side A Digital integrated circuits ball grid array assembly Radiofrequency module

5 International Journal of Arrhythmia 2016;17(3): Figure 8. Magnetic resonance imaging pacemaker system. Figure 9. A specific triangle that is added on the identifier that can be found in the header of the can. Table 1. Inherent cardiovascular implantable electronic device design for magnetic resonance imaging environment (ICD, CRT) Side A Digital integrated circuits ball grid array assembly Radiofrequency module Accelerometer Discrete electronic components (resistors, diodes, capacitors, crystal oscillator, inductors) Side B Analog integrated circuit Wafer Level Chip Scale Package (WLCSP) Super output module High voltage charge module Discrete electronic components (capacitors, transformer, inductor) CRT, cardiac reorganizations therapy; ICD, implantable cardioverter-defibrillator. MRI 스캔에적합한 CIED 시스템관리 MRI conditional 제품의경우 MRI 를촬영하기위해관련된필요한조건의확인이반드시필요하다. CIED 시술후최소 6주이상경과한환자 Pectoral implantation No abandoned leads, lead extenders or adapters Lead electrically intact, with stable and normal function Lead impedance between 200 and 1,500 ohm Capture threshold <2.0 V/0.4 msec 7 MRI 사용이가능한 CIED 제품이라도상기조건에해당하는환자만 MRI 촬영이가능하며, 각 CIED 제품에따라촬영부위가전신또는신체의일부분만촬영이가능한지, 촬영시간의제한이있는지, MRI의종류에있어 1.5 T 또는 3.0 T에서촬영이가능한 CIED 제품인지확인이필요하다. 그리고촬영전에 MRI mode로변경하여촬영하여야한다. CIED 제품을 MRI mode로변경하는방법은출시된회사마다차이가있다. 보스톤사이언티픽의경우에는 MRI protection time-out 기능이내장되어있어서 MRI mode로변경한이후설정된시간이지나게되면변경전설정으로자동변경된다 (Figure 10). 8 결론 MRI 촬영이보편화되었지만, 불과몇년전까지만하더라도 CIED 이식환자들은 MRI 촬영에대한안전을보장받지못하여 MRI 촬영이불가능했다. 하지만지금은관련회사들의여러노력으로인하여조건부로 MRI 촬영이가능한제품들이등장하였고, 앞으로는이보다더발전된기술의제품이출시되기를기대해본다. 154

Magnetic Resonance Imaging Compatible Devices way to widespread clinical application. Pacing Clin Electrophysiol. 2013;36:270-278. 2) Boston Scientific.

6 Magnetic Resonance Imaging Compatible Devices way to widespread clinical application. Pacing Clin Electrophysiol. 2013;36: ) Boston Scientific. ANZ_PSST_13009_ImageReady technical training_25feb2013 [Data on file]. 3) Boston Scientific. INGEVITY PTM Fineline-ingevity MRI technical guide [Data on file]. 4) Boston Scientific. INGENIO pacemaker system MRI design summary ( ) Rev B [Data on file]. 5) Boston Scientific. CRM AA_AUG2014_ACCOLADE_ (only)_inservice_final_ttt [Data on file]. Figure 10. Magnetic resonance imaging (MRI) protection mode. References 1) Santini L, Forleo GB, Santini M, World Society of Arrhythmias. Evaluating MRI-compatible pacemakers: patient data now paves the 6) Boston Scientific. AEMA MRI Ask the experts ANZ_ PSSP_13037 EMEA MRI ask the experts [Data on file]. 7) Park JW. MRI compatible pacemaker: current perspectives [in Korean]. Korean Heart Rhythm Society Symposium; 2015; Ilsan, Goyang, Republic of Korea. 8) Boston Scientific. CRM AA JUL 2015 Tachy MRI in-service green [Data on file]. 155

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