MRI Safety In Patients With Implanted CV Devices - Sanjoy Sanyal


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Dr Sanjoy Sanyal (then Associate Professor and Consultant Surgeon in Seychelles) presented this article in a Seychelles medical college on 29 February 2008

Latest MRI safety recommendations in patients with implanted cardiovascular devices are presented herein.

Implanted Cardiovascular Devices pose significant health risks when patients are concurrently subjected to MRI, because of the strong Magnetic Fields involved in MRI.

This article adresses some of these issues and mentions the currently accepted guidelines.

Tags: cardiovascular devices, mri safety, sanjoy sanyal, MRI, Implanted devices, Ferromagnetic substances,

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MRI Safety In Patients With Implanted CV Devices - Sanjoy Sanyal

  1. 1. Safety of MRI in patients with CV devices By Dr S. Sanyal MBBS, MS, MSc (UK), ADPHA, ADHRD Consultant Surgeon & Associate Professor Seychelles
  2. 2. Study highlights <ul><li>CV devices </li></ul><ul><li>MRI mechanisms </li></ul><ul><li>MRI risk determinants </li></ul><ul><li>FDA classification of CV devices </li></ul><ul><li>Recommendations </li></ul><ul><li>Conclusions </li></ul><ul><li>Reference </li></ul><ul><li>Addendum </li></ul>
  3. 3. Examples of CV devices <ul><li>Coronary stents </li></ul><ul><li>Peripheral stents </li></ul><ul><li>Aortic stent grafts </li></ul><ul><li>Embolization coils </li></ul><ul><li>IVC filters </li></ul>
  4. 4. Examples of CV devices <ul><li>Prosthetic heart valves </li></ul><ul><li>Annuloplasty rings </li></ul><ul><li>Cardiac closure / occluder devices </li></ul><ul><li>Loop recorders </li></ul><ul><li>Retained fractured intravenous leads </li></ul>
  5. 5. Examples of CV devices <ul><li>Pacemakers </li></ul><ul><li>Implantable cardioverter defibrillators (ICD) </li></ul><ul><li>Hemodynamic support devices </li></ul><ul><ul><li>Intra-aortic balloon pumps (IBP) </li></ul></ul><ul><ul><li>Right ventricular (RV) assist devices </li></ul></ul><ul><ul><li>Left ventricular (LV) assist devices </li></ul></ul>
  6. 6. Recommendations for CV devices in general <ul><li>Screening : Patients with CV device requiring MRI should undergo screening to accurately identify the implanted device </li></ul><ul><li>Temporary devices : Inpatients should be examined for temporary devices </li></ul>
  7. 7. MRI safety <ul><li>No ionizing radiation </li></ul><ul><li>Non-invasive procedure </li></ul><ul><li>No iodinated contrast agents </li></ul>
  8. 8. MRI risk mechanisms <ul><li>Static magnetic field </li></ul><ul><li>Radiofrequency (RF) energy </li></ul><ul><li>Gradient magnetic fields </li></ul>
  9. 9. Static magnetic field <ul><li>1.5 to 3 Tesla , which corresponds to 30,000 - 60,000 times the strength of earth's magnetic field </li></ul><ul><li>Scanners are typically superconducting </li></ul><ul><li>Thus, they are always ‘on’.“ </li></ul><ul><li>Attraction of a ferromagnetic object into the scanner </li></ul>
  10. 10. Recommendation for static <ul><li>Devices should be non-ferromagnetic or weakly ferromagnetic (most are) </li></ul><ul><li>Lowest field strength available to minimize ferromagnetic risk </li></ul>
  11. 11. RF energy <ul><li>RF energy pulsed into body to generate the MR image -> ohmic heating . </li></ul><ul><li>Metallic devices (e.g. lead) act as antennae -> concentrate RF energy -> excessive local heating at device tip </li></ul><ul><li>Electrical currents created in wires / leads -> arrhythmias. </li></ul>
  12. 12. Gradient magnetic field <ul><li>Rapidly changing magnetic fields </li></ul><ul><li>Excite peripheral nerves </li></ul><ul><li>Induce electrical currents in conductive devices . </li></ul><ul><li>Flow of electricity in conductive blood produce ECG changes / arrhythmias </li></ul>
  13. 13. Risk determinants <ul><li>MRI emergency / elective </li></ul><ul><li>Material of CV device </li></ul><ul><ul><li>ferromagnetic / weakly ferromagnetic / non-ferromagnetic </li></ul></ul><ul><li>Specific type of device </li></ul>
  14. 14. MRI elective vs. emergency <ul><li>Knee pain for 5 years and needs an MRI but has just had a device implanted 2 days ago </li></ul><ul><li>Vs. </li></ul><ul><li>Admitted to hospital after being hit by a car; acute knee pain; surgeons want urgent MRI </li></ul>
  15. 15. Material of CV device <ul><li>Non-metallic safer than metallic </li></ul><ul><li>Among metallic </li></ul><ul><ul><li>Non-ferromagnetic < weak ferromagnetic < strong ferromagnetic </li></ul></ul>
  16. 16. Recommendations based on material <ul><li>Non-ferromagnetic ‘passive’ implant (e.g. titanium, titanium alloy, nitinol) </li></ul><ul><ul><li>MRI immediately after implantation </li></ul></ul><ul><li>Weakly ferromagnetic devices </li></ul><ul><ul><li>MRI 6 weeks after implantation </li></ul></ul>
  17. 17. Specific type of device <ul><li>Obsolete FDA definitions – </li></ul><ul><ul><li>‘ MR safe’ / ‘MR compatible’ </li></ul></ul><ul><li>Current FDA definitions – </li></ul><ul><ul><li>‘ MR safe’ </li></ul></ul><ul><ul><li>‘ MR conditional’ </li></ul></ul><ul><ul><li>‘ MR unsafe’ </li></ul></ul>
  18. 18. MR safe <ul><li>Non-metallic </li></ul><ul><li>Non-conducting </li></ul><ul><li>Nonmagnetic </li></ul>
  19. 19. MR conditional <ul><li>No known hazards in a specified MR environment with specific conditions </li></ul>
  20. 20. MR unsafe <ul><li>Known to pose hazards in all MR environments </li></ul>
  21. 21. Specific recommendations <ul><li>Those pacemakers that have been tested have been labelled “MR unsafe” </li></ul><ul><li>Pacemaker / ICD – strong relative contraindication to MR examination </li></ul><ul><ul><li>Scan only at experienced centres </li></ul></ul><ul><ul><li>Written informed consent. </li></ul></ul><ul><ul><li>Clinician with pacemaker / ICD expertise </li></ul></ul><ul><ul><li>Crash cart including defibrillator </li></ul></ul>
  22. 22. Specific recommendations <ul><li>Known retained fractured intravenous leads </li></ul><ul><ul><li>Poses a high risk for thermal injury . </li></ul></ul><ul><ul><li>MR examination should not be performed </li></ul></ul>
  23. 23. Specific recommendations <ul><li>Hemodynamic support devices (IBP, RV / LV assist devices) with variable ferromagnetic / electrical components </li></ul><ul><ul><li>Absolute contraindications to MR examination </li></ul></ul>
  24. 24. Specific recommendations <ul><li>Coronary / peripheral vascular stents, cardiac occluder devices, embolization coils </li></ul><ul><ul><li>Most considered ‘MR safe’ </li></ul></ul><ul><ul><li>Some considered ‘MR conditional’ </li></ul></ul><ul><ul><li>MRI can be conducted with non-ferromagnetic stents </li></ul></ul>
  25. 25. Specific recommendations <ul><li>Most aortic stent grafts that have been tested are labelled ‘MR safe’ </li></ul><ul><li>Only Zenith AAA endovascular graft (Cook Vascular, Inc) is labelled ‘MR unsafe’. </li></ul>
  26. 26. Specific recommendations <ul><li>Most prosthetic heart valves / annuloplasty rings that have been tested are labelled ‘MR safe’ </li></ul><ul><li>Some are ‘MR conditional’ </li></ul>
  27. 27. Specific recommendations <ul><li>Loop recorders that are considered ‘MR conditional </li></ul><ul><li>May experience slight movement of the device during MRI </li></ul><ul><li>Should be warned to avoid undue concern </li></ul>
  28. 28. Conclusion <ul><li>MRI risks arise from 3 mechanisms </li></ul><ul><ul><li>Static magnetic field </li></ul></ul><ul><ul><li>RF energy </li></ul></ul><ul><ul><li>Gradient magnetic fields </li></ul></ul>
  29. 29. Conclusion <ul><li>Hemodynamic support devices (IBP, RV / LV assist devices) </li></ul><ul><ul><li>Absolute contraindications to MR examination </li></ul></ul>
  30. 30. Conclusion <ul><li>ICDs and pacemakers </li></ul><ul><ul><li>Relative contraindications to MRI </li></ul></ul>
  31. 31. Conclusion <ul><li>For most devices, if there is good clinical indication for MRI scan, then benefits probably outweigh the risks </li></ul><ul><ul><li>American Heart Association </li></ul></ul><ul><ul><li>American College of Cardiology </li></ul></ul><ul><ul><li>North American Society for Cardiac Imaging </li></ul></ul><ul><ul><li>Society for Cardiovascular Magnetic Resonance </li></ul></ul>
  32. 32. Journal source <ul><li>Levine GN, Gomes AS, Arai AE, et al. Safety of magnetic resonance imaging in patients with cardiovascular devices. Circulation 2007 doi: 10.1161 / CIRCULATION AHA.107.187256 </li></ul><ul><li>New Statement on Safety of MRI With CV Devices. URL: </li></ul>
  33. 33. Addendum <ul><li>Next 15 slides give some examples of cardiovascular devices that are implanted in patients. </li></ul><ul><li>The images have been culled from various sources, which are obvious from the caption, where relevant. </li></ul><ul><li>This is meant as an APPENDIX to the main presentation. </li></ul>
  34. 34. Coronary stent
  35. 35. Coronary stent – Drug eluting
  36. 36. PTCA stent – Enlarged view
  37. 37. Peripheral stent
  38. 38. Aortic stent-graft
  39. 39. Tornado ® Embolization coil
  40. 40. Gunther-Tulip IVC filter
  41. 41. IVC Filter – University of Texas Health Science Centre
  42. 42. Heart valve – TTK Chitra
  43. 43. Annuloplasty ring
  44. 44. Septal occluder
  45. 45. Loop recorder
  46. 46. Implantable Cardioverter Defibrillator
  47. 47. Intra-aortic balloon catheter
  48. 48. Ventricular assist device