Lead Management for MRI

Transcription

1 Lead Management for MRI Charles J. Love, MD FACC FAHA FHRS CCDS Professor of Medicine Director, Cardiac Rhythm Device Services The Ohio State University Medical Center Columbus, OH USA President, International Board of Heart Rhythm Examiners

2 Disclosures I receive honoraria, research support and/or consult with: Boston Scientific Lake Region Medical LEADEXX Medtronic QRS Systems Spectranetics St. Jude Medical No off label uses of devices or drugs will be part of this presentation.

3 Current Clinical Issues for MRI Scanning of Pacemaker and Defibrillator Patients

4 Computed Tomography vs. MRI CT MRI

5 Why MRI Scans are Important to Clinical Medicine Fastest Growing Standard of Care in Diagnostic Imaging Superior Soft Tissue Imaging 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

6

7 MRI Utilization MRI Procedures by Anatomy IMV Market Research,

8 Prevalence of Common Comorbidities Common Comorbidities, many of which rely on MRI, increase rapidly over age 65

9 Growing Need for Pacemaker Patients Overlapping Demographics > 65y 2x as likely to require MRI * 80% pacemaker patients > 65y * Magnetic Resonance Imaging (MRI) Equipment A Global Strategic Business Report, Global Industry Analysts, Inc., San Jose, CA

10 Safe Access to MRI is a Significant Clinical Need 1.5 million patients with pacemakers in U.S. Approximately 3 of 4 pacemaker patients indicated for MRI * Pacemaker patients subject to risk less sensitive diagnostic evaluations being scanned with pacemakers not designed for MRI use * Roguin A. Europace 2008; 10:

11 Patients Scanned Today Patients and physicians making difficult risk / benefit determinations Persons # with any MRI % per Year No Pacemaker 23,376,000 3,295,000 13% Pacemaker 973,000 25,000 3% Based off 5% sample of the 2007 Medicare Fee-for-Service Population Over Age 65.

12 MRI is not Currently Considered Safe For Device Patients Long standing manufacturer contraindications

13 Magnetic Resonance Imaging Images provided through three applied fields B 0 RF (B 1 ) [f=(42.56mhz/t) B 0 ] G x, G y, G z (Gradient fields) Siemens Avanto 1.5T Scanner B 0 0.5T 1.5T 3.0T 5.0T RF Freq. 21 MHz 64 MHz 128 MHz 213 MHz

14 MRI: Three Powerful Fields Static Field Gradient Field RF Field

15 Source of MRI Electromagnetic Interference 1. Static Magnetic Field: 1.5 & 3.0-Tesla 1-Tesla = 10,000 Gauss 1-Gauss = Earth s Gravitational Pull 2. Modulated Radio Frequency Field (42.57 MHz/Tesla) 3. AC (Gradient) Magnetic Fields (X, Y, and Z directions)

16 How to make Electricity 101 Stator stationary component Contains a set of electrical conductors wound in coils over an iron core. Rotor / Armature moving component Produces a rotating magnetic field By induction These are known as brushless alternators and are usually used in large generators. By permanent magnets This is common in small alternator units

17 How to make Electricity 101 The rotor generates a moving magnetic field around the stator, which induces a voltage difference between the windings of the stator. This produces the alternating current (AC) output of the generator.

18 Hazards of using MRI with Pacemakers and Defibrillators 1. Static Magnetic Field Mechanical forces on ferromagnetic components Unpredictable magnetic sensor activation 2. Modulated Radio Frequency (RF) Field Heating of cardiac tissue adjacent to lead electrodes Possible induction of life-threatening arrhythmias RF interactions with the device (over- and undersensing)

19 Hazards of using MRI with Pacemakers and Defibrillators 3. Gradient Magnetic Field Possible induction of life-threatening arrhythmias Induced voltages on leads cause overand under-sensing 4. Combined Field Effects Alteration of device function due to EMI Mechanical forces (vibration) Electronic reset of device

20 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

21 Why is MRI Safety a Controversial Topic for Device Patients? Multiple papers have been published both supportive and cautioning of routine use of MRI scanning on patients with cardiac implantable electronic devices.

22 MRI and Device Study Summaries Modern Pacemaker and Implantable Cardioverter/ Defibrillator Systems Can Be Magnetic Resonance Imaging Safe Publicized Results: Lead heating in vivo (canine) found to rise < 0.5 C during MRI. Newer ICDs and most pacemakers were not damaged during scans. Authors Conclusions: These data suggest that certain modern pacemaker and ICD systems may indeed be MRI safe. This may have major clinical implications for current imaging practices. Roguin A, Zviman MM, Meininger GR, et al. Modern Pacemaker and Implantable Cardioverter/Defibrillator Systems Can be Magnetic Resonance Imaging Safe. Circulation, 2004; 100(5):

23 MRI and Device Study Summaries However, results that are Cause for Concern Include: 1 animal, after MRI, had pacing capture failure for 12 hours. Small sample size: Only 9 different pacemaker models were tested in a single 1.5-Tesla MR scanner. At deeper (worst case) positioning of the leads in the test gel, substantial heating (increase of 35 C) was noted. Three pacemakers experienced an electrical reset and nine ICD models experienced post scan interrogation problems or battery changes. Notable Quotes from the Authors: Routine imaging of (pacemaker) patients by MR centers would not be appropriate.

24 MRI and Device Study Summaries Magnetic Resonance Imaging and Cardiac Pacemaker Safety at 1.5-Tesla 6 Publicized Results: Fifty-four patients underwent a total of 62 MRI examinations at 1.5-Tesla MRI examinations included cardiac, vascular, and general MRI studies Device interrogations were done before and after MRI. Pacing and sensing thresholds, as well as lead impedances, were measured A total of 107 leads and 61 pulse generators were evaluated No adverse events occurred Authors Conclusions: Safety was demonstrated in this series of patients with pacemakers at 1.5-Tesla. 6 Martin ET, Coman JA, Shellock FG, et al. Magnetic Resonance Imaging and Cardiac Pacemaker Safety at 1.5-Tesla. J Am Col Cardiol. 2004;43:

25 MRI and Device Study Summaries Results that are Cause for Concern: Pacing Thresholds changed in 40 (37%) of the leads Ten (9.4%) leads underwent a significant change in thresholds No intermediate or long-term follow-up of the post- MRI pacing thresholds Especially a concern for those who demonstrated an initial rise in thresholds Pacemaker-dependent patients were excluded from this study All studies were performed using a single 1.5-Tesla MR system

26 MRI-Safety Expert Response Notable Quotes from the Authors: Failing to identify an adverse event is not equivalent to demonstrating safety [with existing products] especially when only a limited number of patients are studied. Patients and the implanting community should expect nothing less than devices that are MR-safe by design, not by chance. MRI scans will not be considered safe until these devices and leads are specifically designed for use with MRI technology and until they receive the necessary approvals from regulatory authorities. 7 Gimbel JR, Kanal E.,Can Patients with Implantable Pacemakers Safely Undergo Magnetic Resonance Imaging? J Am Coll Cardiol. 2004;43:

27 Clear FDA Position the removal of the warnings and contraindications for MRI use with pacemaker or ICD patients will require thorough characterization of the array of safety concerns. This may necessitate bench and animal studies designed to elucidate the underlying mechanisms associated with the potential risks so that they may be better understood and avoided. Device modification may be necessary to mitigate particular concerns, which could result in model-specific MRI recommendations. Faris OP and Shein MJ, PACE April 2005

28 Society Statements Unexpected programming changes, inhibition of pacemaker output, failure to pace, transient asynchronous pacing, rapid cardiac pacing, the induction of ventricular fibrillation, heating of the tissue adjacent to the pacing or ICD system, early battery depletion, and outright device failure requiring replacement may all occur during MRI of patients with pacemakers or ICDs. ACR Guidance Document 2007 Patients who have a pacemaker or ICD should not undergo an MR study if an alternative diagnostic test is available, and MR imaging should only be considered in cases in which the potential benefit to the patient clearly outweighs the risks to the patient. AHA Scientific Statement 2007

29 Hazards and Risks are Real A 2-second pause was noted diminished battery voltage was noted immediately after MRI Significant changes were reported in 9.4% of leads 1.9% required a change in programmed output. increased capture threshold was noted post MRI. Nazarian S. Heart Rhythm, Vol 6, No 1, January 2009

30 Most Likely Risks RF lead tip heating In-vivo Gradient field induced VT In-vivo device inhibition leading to asystole Activation of magnet mode response Pacemakers Defibrillators

31 Unpredictable Device Behavior Europace vol. 11 no. 9 Sept 2009 pp doi: /europac e/eupp162

32 Lead Tip Heating PCT is lowest at implant Healing produces scar Increased distance increases PCT Significant heating causes tissue damage Increased scar volume increases PCT PCT=Pacing Capture Threshold

33 Lead Heating Temperature Profile Temperature Rise [%] Lead Helix 1 mm from lead helix Fibrous Capsule Viable Myocardium High T spatial dependence Rapid decline ~50% at viable tissue Distance from electrode [mm] Helix Lead body

34 PCT Sensitivity to Lead Heating PCT increases within minutes of RF onset PCT decreases after RF is turned off PCT 0.5 ms RF on RF off 32 C, n=31 14 C, n=31 5 C, n= Heat Affected Zone Time (minutes) PCT: excellent tissue temperature/damage indicator Estimated temperature rise 1 mm from helix

35 Measured temperature (heating) 1.5 Tesla MRI gel phantom 52cm AF Lead Heating in Gel Medium Temp (C) Tip 10 Scan initiation 0 9:00:25 PM 9:01:06 PM 9:01:47 PM 9:02:28 PM 9:03:08 PM 9:03:49 PM 9:04:30 PM 9:05:11 PM 9:05:51 PM 9:06:31 PM Time

36 Measured temperature (heating) 3.0 Tesla MRI gel phantom Z Axis Control Lead Temp (C) Note: 96 C was worst-case Time (sec) Tip

37 1.5 T temperature mapping Heating map of off the shelf 52 cm 1688T lead Heating Profile for Distal Tip Delta-T (C) Longitudinal Position (cm) Axial Position (cm)

38 MRI - Thermogenic Damage is Real Normal Healing Response Damage Thermogenic Approximate Outline of Lead Body & Helix

39 Stimulation Clinical Impact MRI Gradient Induced High Rate Pacing EKG Pulse Ox Canine Test Start of Scan The MRI scanner is pacing the heart

40 Unattached Leads Because these leads are not attached to a device that provides filtering, they are particularly capable of heating and current induction! High temps at myocardial interface Rapid stimulation of heart muscle

41 MR Conditional Labeling ASTM Standard F2503 * Defines Three Terms: MR Safe MR Unsafe MR Conditional * ASTM standard F2503: Standard Practice for Marking Medical Devices and Other Items for Safety in the Magnetic Resonance Environment

42 System Design Changes System approach is necessary Pacemaker design Lead design MRI Conditional Programming Coordination with device specialists and MRI scanning service

43 Pacemaker Design Solutions Minimize ferromagnetic content Isolated circuit board Hall sensor Optimize input circuitry Circuit component change Force and Torque Unintended cardiac stimulation Device interactions

44 Greatbatch Band Stop Filter Chip Comparative Temperature Measurements for Tank Leads Temp ( C) T Control 100nH/68pF nH/33pF nH33pF Time (seconds)

45 Variables associated with MR equipment Pacemaker/ICD Lead Wire Heating and Induced Voltage are affected by MRI RF Body Coil Design: Number of capacitive junctions Diameter of coil Length of coil Proximity to patient (isocenter) Diameter of RF shield Capacitance at each junction Cable location Number of drive points Placement of cable baluns E-field distribution Type of scan GRE vs. Spin Echo (software and hardware upgrades) Ref. FDA CRADA Workshop 2006; Dr. Ed. Bosk, GE

46 Lead Heating Design Solution Lead inner conductor coil design mitigates lead heating 4 filar to 2 filar increases inductance and reduces heating MRI Percent of Maximum 5076 vs. 5086MRI Comparison Lead Path

47 Positive System ID: Radiographic Studies X-rays identify the system via unique radiopaque MRI symbol

48 Labeling Implementation Pulse Generator output programmed to 0 ma for the MRI procedure, and afterward, retested by performing the System Diagnostics (Lead Test) and reprogrammed to the original settings Head coil type: transmit and receive only Static magnetic field strength: 2.0 tesla Specific absorption rate (SAR): <1.3 W/kg for a lb (70-kg) Time-varying intensity: <10 tesla/sec

49 Key Conditions of Use Radiology Static magnetic field 1.5 T Maximum gradient slew rate 200 T/m/s Whole body SAR 2.0 W/kg; head SAR < 3.2 W/kg Isocenter (center of bore) superior to C1 or inferior to T12 Patient monitoring (pulse oximetry)

50 Key Conditions of Use Cardiology No unattached, abandoned leads present Pacing capture threshold 2.0 V at 0.4 ms Lead impedance 200 Ω to 1500 Ω Implant 6 weeks MRI Conditional pacemaker, atrial/ventricular MRI compatible leads Appropriate programming

51 Device Inhibition & Asystole Canine Test Initiation of scan Pacemaker was in a sensing mode, reed switch failed to properly detect magnet Unreliable reed switch behavior caused pacemaker inhibition Sedative caused temporary pacemaker dependence in the animal this was not anticipated. Lost pacing function and became asystolic

52 Extraction Consensus Statement Functional Leads IIb/ Non Functional Leads IIa Lead removal may be considered/ is reasonable in patients who require specific imaging techniques (e.g. MRI) that can not be imaged due to the presence of the CIED system for which there is no other available imaging alternative for the diagnosis. Lead removal may be considered/ is reasonable in patients in order to permit the implantation of an MRI conditional CIED system.

53 MRI-Safe M = Monitoring (ECG and pulse oximetry) R = Reprogramming I = Make the device Invisible or Invulnerable: Invisible for nondependent PM patients -- turn off device features (OOO) Invulnerable for PM-dependent patients -- asynchronous mode should be programmed (VOO or DOO) S = Keep SAR as low as possible Be mindful that even if one applies these recommended strategies, there is no guarantee that the outcome is going to be safe for non-mri approved devices.

54 Requirements During and After MRI Scanning: Guideline Recommendations Procedure Requirements ACR [1] AHA [2] ESC [3] ACLS-certified personnel Direct supervision with cardiologist Pacemaker/ICD programmer Personnel to ensure safe practice guidelines (scanning parameters) Crash cart, including defibrillator onsite Uninterrupted monitoring of heart rhythm and vital signs Interrogation of device post examination 1. Kanal E, et al. AJR AM J Roentgenol. 2007;188: Levine GN, et al. Circulation. 2007;116: Roguin A, et al. Europace. 2008;10:

55

56 MRI Scanning in ICD Patients [1] ICDs may falsely detect the MR RF field as VF, charge capacitors, and deliver ATP, cardioversion, or defibrillation therapies Can still occur if therapy delivery has been deactivated because of electrical reset with subsequent therapy activation Devices may not be able to deliver ICD therapy in the static magnetic field (needs further investigation) ICD transformer will be magnetically saturated and may not have the voltage necessary to charge the capacitor Can lead to permanent device failure Magnetic fields may prevent detection of VT or VF Limited number of clinical reports on the use of MRI in ICD patients 1. Roguin A, et al. Europace. 2008;10:

57 The Future More MR-conditional systems will be developed Medical/legal implications: Problem with legacy leads Need to develop recommendations for the implanting physician: How to manage medical/legal implications Patient selection for device implantation Develop international registries to determine longterm reliability Effects from 3.0 T MR scanners?

58 Conclusion For patients with current generation devices: MRI should not be considered an absolute contraindication Physicians should weigh risk-benefit ratio Institute special protocol, technique (ie, programming of the device, etc) If indications for MR-conditional pacemaker system are not expanded to all patients, system should be used in: Patients indicated for a PM who had undergone prior MRI (with future MRIs anticipated) Patients with long life expectancy (ie, those of young age) should at least receive a lead that is MR-conditional Hopefully, in the future, MRI will become more compatible with all devices, allowing patients access to this useful diagnostic technique Leads that are abandoned provide an absolute contraindication to MRI scan at this time

59 a) Stator This is the stationary component. It contains a set of electrical conductors wound in coils over an iron core. (b) Rotor / Armature This is the moving component that produces a rotating magnetic field in any one of the following three ways: (i) By induction These are known as