Upload
sanjoy-sanyal
View
3.129
Download
2
Embed Size (px)
DESCRIPTION
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,
Citation preview
Staff seminar on 29 Feb 2008
Safety of MRI in patients with CV devices
By Dr S. Sanyal
MBBS, MS, MSc (UK), ADPHA, ADHRD
Consultant Surgeon & Associate Professor
Seychelles
Study highlights
• CV devices• MRI mechanisms• MRI risk determinants• FDA classification of CV devices• Recommendations• Conclusions• Reference • Addendum
Examples of CV devices
• Coronary stents
• Peripheral stents
• Aortic stent grafts
• Embolization coils
• IVC filters
Examples of CV devices
• Prosthetic heart valves
• Annuloplasty rings
• Cardiac closure / occluder devices
• Loop recorders
• Retained fractured intravenous leads
Examples of CV devices
• Pacemakers
• Implantable cardioverter defibrillators (ICD)
• Hemodynamic support devices
– Intra-aortic balloon pumps (IBP)
– Right ventricular (RV) assist devices
– Left ventricular (LV) assist devices
Recommendations for CV devices in general
• Screening: Patients with CV device requiring MRI should undergo screening to accurately identify the implanted device
• Temporary devices: Inpatients should be examined for temporary devices
MRI safety
• No ionizing radiation
• Non-invasive procedure
• No iodinated contrast agents
MRI risk mechanisms
• Static magnetic field
• Radiofrequency (RF) energy
• Gradient magnetic fields
Static magnetic field
• 1.5 to 3 Tesla, which corresponds to 30,000 - 60,000 times the strength of earth's magnetic field
• Scanners are typically superconducting
• Thus, they are always ‘on’.“
• Attraction of a ferromagnetic object into the scanner
Recommendation for static
• Devices should be non-ferromagnetic or weakly ferromagnetic (most are)
• Lowest field strength available to minimize ferromagnetic risk
RF energy
• RF energy pulsed into body to generate the MR image → ohmic heating.
• Metallic devices (e.g. lead) act as antennae → concentrate RF energy → excessive local heating at device tip
• Electrical currents created in wires / leads → arrhythmias.
Gradient magnetic field
• Rapidly changing magnetic fields
• Excite peripheral nerves
• Induce electrical currents in conductive devices.
• Flow of electricity in conductive blood produce ECG changes / arrhythmias
Risk determinants
• MRI emergency / elective
• Material of CV device
– ferromagnetic / weakly ferromagnetic / non-ferromagnetic
• Specific type of device
MRI elective vs. emergency
• Knee pain for 5 years and needs an MRI but has just had a device implanted 2 days ago
Vs.
• Admitted to hospital after being hit by a car; acute knee pain; surgeons want urgent MRI
Material of CV device
• Non-metallic safer than metallic
• Among metallic
– Non-ferromagnetic < weak ferromagnetic < strong ferromagnetic
Recommendations based on material
• Non-ferromagnetic ‘passive’ implant (e.g. titanium, titanium alloy, nitinol)
– MRI immediately after implantation
• Weakly ferromagnetic devices – MRI 6 weeks after implantation
Specific type of device
• Obsolete FDA definitions –
– ‘MR safe’ / ‘MR compatible’
• Current FDA definitions –
– ‘MR safe’
– ‘MR conditional’
– ‘MR unsafe’
MR safe
• Non-metallic
• Non-conducting
• Nonmagnetic
MR conditional
• No known hazards in a specified MR environment with specific conditions
MR unsafe
• Known to pose hazards in all MR environments
Specific recommendations
• Those pacemakers that have been tested have been labelled “MR unsafe”
• Pacemaker / ICD – strong relative contraindication to MR examination
– Scan only at experienced centres
– Written informed consent.
– Clinician with pacemaker / ICD expertise– Crash cart including defibrillator
Specific recommendations
Known retained fractured intravenous leads Poses a high risk for thermal injury. MR examination should not be
performed
Specific recommendations
• Hemodynamic support devices (IBP, RV / LV assist devices) with variable ferromagnetic / electrical components – Absolute contraindications to MR
examination
Specific recommendations
Coronary / peripheral vascular stents, cardiac occluder devices, embolization coils Most considered ‘MR safe’ Some considered ‘MR conditional’ MRI can be conducted with non-
ferromagnetic stents
Specific recommendations
Most aortic stent grafts that have been tested are labelled ‘MR safe’
Only Zenith AAA endovascular graft (Cook Vascular, Inc) is labelled ‘MR unsafe’.
Specific recommendations
Most prosthetic heart valves / annuloplasty rings that have been tested are labelled ‘MR safe’
Some are ‘MR conditional’
Specific recommendations
Loop recorders that are considered ‘MR conditional
May experience slight movement of the device during MRI
Should be warned to avoid undue concern
Conclusion
• MRI risks arise from 3 mechanisms
– Static magnetic field
– RF energy
– Gradient magnetic fields
Conclusion
• Hemodynamic support devices (IBP, RV / LV assist devices)
– Absolute contraindications to MR examination
Conclusion
ICDs and pacemakers
Relative contraindications to MRI
Conclusion• For most devices, if there is good clinical
indication for MRI scan, then benefits probably outweigh the risks
– American Heart Association
– American College of Cardiology
– North American Society for Cardiac Imaging
– Society for Cardiovascular Magnetic Resonance
Journal source• 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
• New Statement on Safety of MRI With CV Devices. URL: http://www.medscape.com/viewarticle/566881
Addendum
• Next 15 slides give some examples of cardiovascular devices that are implanted in patients.
• The images have been culled from various sources, which are obvious from the caption, where relevant.
• This is meant as an APPENDIX to the main presentation.
Coronary stent
Coronary stent – Drug eluting
PTCA stent – Enlarged view
Peripheral stent
Aortic stent-graft
Tornado® Embolization coil
Gunther-Tulip IVC filter
IVC Filter – University of Texas Health Science Centre
Heart valve – TTK Chitra
Annuloplasty ring
Septal occluder
Loop recorder
Implantable Cardioverter Defibrillator
Intra-aortic balloon catheter
Ventricular assist device