Many heart valve prostheses and annuloplasty rings have been evaluated for MR issues, especially with regard to the presence of magnetic field interactions associated with exposure to MR systems operating at field strengths of as high as 4.7-Tesla. Of these, the majority displayed measurable yet relatively minor magnetic field interactions. That is, because the actual attractive forces exerted on the heart valve prostheses and annuloplasty rings were minimal compared to the force exerted by the beating heart (i.e., approximately 7.2-N), an MR procedure is not considered to be hazardous for a patient that has any heart valve prosthesis or annuloplasty ring tested relative to the field strength of the magnet (i.e., MR system) used for the evaluation.
Importantly, this recommendation includes the Starr-Edwards Model Pre-6000 heart valve prosthesis previously suggested to be a potential risk for a patient undergoing an MR examination.
With respect to clinical MR procedures, there has been no report of a patient incident or injury related to the presence of a heart valve prosthesis or annuloplasty ring.
Heart Valve Prostheses and the Lenz's Related Forces. Condon and Hadley (2000) reported the theoretical possibility of a previously unconsidered electromagnetic interaction with prosthetic heart valves that contain metallic disks or leaflets. Basically, any metal (i.e. not just ferromagnetic material) moving through a magnetic field will develop another magnetic field that opposes the primary magnetic field. This phenomenon is referred to as the “Lenz Effect" or Lenz's Law Related Forces. In theory, “resistive pressure” may develop in heart valve prostheses that have metallic disks or leaflets (note, at the present time, mostly tissue valves are used instead of those with metallic leaflets) with the potential to inhibit both the opening and closing aspects of the valve. The Lenz Effect is proportional to the strength of the static magnetic field. Accordingly, it has been suggested that there may be problems for patients with heart valves that have metallic discs or leaflets in association with MRI procedures, especially those performed at very high static magnetic fields.
Edwards, et al. (2015) conducted an in vitro study of the occurrence of Lenz-related forces on various heart valve prostheses at 1.5-Tesla and assessed the risk of the impedance of valve function. The findings provided evidence of the Lenz Effect on certain cardiac valve prostheses exposed to the static magnetic field, which resulted in functional valve impedance and a potentially increased risk of valve regurgitation. While further evaluation of this phenomenon may be warranted, to date, the Lenz Effect has not been observed in association with clinical MR examinations nor has it posed additional risks for patients with certain heart valve prostheses (i.e., those with metallic leaflets or disks) undergoing MRI.
MRI at 3-Tesla and Heart Valve Prostheses and Annuloplasty Rings. Findings obtained at 3-Tesla for various heart valve prostheses and annuloplasty rings that underwent testing indicated that certain implants exhibit relatively minor magnetic field interactions. Similar to heart valve prostheses and annuloplasty rings tested at 1.5-Tesla, because the actual attractive forces exerted on these implants are deemed minimal compared to the force exerted by the beating heart, MR procedures at 3-Tesla are not considered to be hazardous for patients or individuals that have these devices. To date, for the heart valves that have been tested, MRI-related heating has not been shown to reach substantial levels.
Ahmed S, Shellock FG. Magnetic resonance imaging safety: implications for cardiovascular patients. Journal of Cardiovascular Magnetic Resonance 2001;3:171-181.
Condon B, Hadley DM. Potential MR hazard to patients with metallic heart valves: the Lenz effect. J Magn Reson Imag 2000;12:171-176.
Edwards, M-B, Taylor KM, Shellock FG. Prosthetic heart valves: evaluation of magnetic field interactions, heating, and artifacts at 1.5-Tesla. J Magn Reson Imag. 2000;12:363-369.
Edwards MB, et al. Mechanical testing of human cardiac tissue: some implications for MRI safety. J Cardiovasc Magn Reson. 2005;7:835-840.
Edwards MB, et al. In Vitro assessment of the Lenz effect on heart valve prostheses at 1.5 T. J Magn Reson Imaging. 2015 Jan;41(1):74-82.
Frank H, Buxbaum P, Huber L, et al. In vitro behavior of mechanical heart valves in 1.5-T superconducting magnet. Eur J Radiol 1992;2:555-558.
Hassler M, Le Bas JF, Wolf JE, et al. Effects of magnetic fields used in MRI on 15 prosthetic heart valves. J Radiol 1986;67:661-666.
Levine GN, Gomes AS, Arai AE, Bluemke DA, Flamm SD, Kanal E, Manning WJ, Martin ET, Smith JM, Wilke N, Shellock FG. Safety of magnetic resonance imaging in patients with cardiovascular devices: an American Heart Association scientific statement from the Committee on Diagnostic and Interventional Cardiac Catheterization. Circulation 2007;116:2878-2891.
Medtronic Heart Valves, Medtronic, Inc., Minneapolis, MN, Permission to publish 3-Tesla MR testing information for Medtronic Heart Valves provided by Medtronic LifeLine Technical Support, Medtronic Heart Valves, Technical Service. 877-526-7890 or 763-526-7890.
Myers PO, Kalangos A, Panos A. Safety of magnetic resonance imaging in cardiac surgery patients: annuloplasty rings, septal occluders, and transcatheter valves. Ann Thorac Surg. 2012;93:1019;
Pruefer D, et al. In vitro investigation of prosthetic heart valves in magnetic resonance imaging: evaluation of potential hazards. J Heart Valve Disease 2001;10:410-414.
Randall PA, et al. Magnetic resonance imaging of prosthetic cardiac valves in vitro and in vivo. Am J Cardiol 1988;62:973-976.
Shellock FG, Crues JV, Editors. MRI Bioeffects, Safety, and Patient Management. Biomedical Research Publishing Group, Los Angeles, CA, 2014.
Shellock FG. Biomedical implants and devices: assessment of magnetic field interactions with a 3.0-Tesla MR system. J Magn Reson Imag 2002;16:721-732.
Shellock FG. Prosthetic heart valves and annuloplasty rings: assessment of magnetic field interactions, heating, and artifacts at 1.5-Tesla. Journal of Cardiovascular Magnetic Resonance 2001;3:159-169.
Shellock FG, Morisoli SM. Ex vivo evaluation of ferromagnetism, heating, and artifacts for heart valve prostheses exposed to a 1.5-Tesla MR system. J Magn Reson Imag 1994;4:756-758.
Shellock FG, Shellock VJ. MRI Safety of cardiovascular implants: evaluation of ferromagnetism, heating, and artifacts. Radiology 2000;214:P19H.
Soulen RL. Magnetic resonance imaging of prosthetic heart valves Letter. Radiology 1986;158:279.
Soulen RL, Budinger TF, Higgins CB. Magnetic resonance imaging of prosthetic heart valves. Radiology 1985;154:705-707.