Cardiovascular magnetic resonance: What clinicians should know about safety and contraindications☆
Introduction
Cardiovascular magnetic resonance (MR) is a multiparametric, highly reproducible, comprehensive imaging technique, with a wide range of clinical applications [[1], [2], [3]]. Overall, it is highly appreciated and prescribed for its safety, feasibility and non-invasiveness, although some conditions or circumstances prevent the acquisition of good-quality images or may pose some hazards to the patient and staff.
In this review we discuss the absolute and relative contraindications to cardiovascular MR, in terms of safety, patient comfort and image quality, which every clinical should be aware of before referring a patient to this type of imaging test. Most of the potential risks for patients undergoing CMR are related to the effects of the physical energies applied to produce images, but employed contrast agents and stressor drugs can also cause some risk and are described separately.
Section snippets
Physical and biological effects of the magnetic fields
The key principle of routine clinical MR imaging is the interaction of magnetic fields with the hydrogen nuclei of biological tissues [4]. To generate images, three different types of magnetic fields are applied, each with different effects on the human body and surrounding objects [5] (Fig. 1):
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The static magnetic field (B0, usually 1.5 T or 3 T), which aligns the proton spins and generates a net magnetization vector (M) in the human body parallel to B0. The static magnetic field is always on,
The importance of the safety questionnaire: how to assess MR-compatibility
Overall, all these three magnetic fields produce no harmful effect on patients and staff, provided that they have no ferromagnetic, conductive or electronic material. The acoustic noise may cause transient hearing loss in patients not protected by headphones or ear plugs, with full recovery after a relatively short period of time; only if the noise is particularly injurious, a permanent threshold shift at specific frequencies may occur [6]. The three magnetic fields are safe even in pregnant
The MR compatibility of cardiac “passive” implants
Currently, nearly all cardiac stents and prosthesis are certified as MR-safe or MR-conditional. Prosthetic heart valves and annuloplasty rings can be safely scanned soon after their implantation, except for very old prosthetic valves (e.g. caged ball valve). Indeed, the attraction to the static magnetic field is trivial when compared to the force exerted by the heart beating; similarly, the induction of electrical currents and tissue heating is negligible. Sternal wires are generally made of
The MR compatibility of cardiac electronic devices
Cardiac implantable electronic device (CIED) is a term that encompasses a heterogeneous group of leads, electrical pulse generator (pacemaker, PM), high energy shock generator (implantable cardioverter defibrillator, ICD), cardiac resynchronization device (CRT) and recording system (implantable loop recorder, ILR). The above mentioned mechanical, electrical and heating effects provide peculiar harmful or even life-threatening risks in patients with CIEDs [21,22]:
- 1.
Theoretically, the static
Cardiovascular MR in patients with claustrophobia, motion artefacts and arrhythmias
Besides safety issues, also patient comfort and image quality should be considered when referring a patient to cardiovascular MR. Indeed, cardiac MR scanning requires patient cooperation in maintaining a supine position during the ≈40 min duration of the study and images are acquired during repeated breath holds of short duration, as respiratory motion may degrade image quality. Some patients may experience anxiety or fear of tight spaces, although current rates of prematurely terminated scans
Gadolinium-based contrast agents
Gadolinium-based contrast agents (GBCAs) are paramagnetic extracellular T1-shortening substances, administered at low dose (0.05–0.2 mmol/Kg) for perfusion, early-enhancement, late enhancement and angiographic sequences [1,34]. GBCAs distribute in the intravascular and in the extracellular space, are eliminated via the kidneys with a plasma half-life of approximately 2 h, and do not pass the intact blood–brain barrier because they are hydrophilic.
While free gadolinium ion is toxic, GBCAs are
Stressor agents
Perfusion stress cardiac MR is commonly performed using vasodilator agents, such as adenosine, dypiridamole and regadenoson [40]. During intense vasodilation, myocardial regions supplied by stenotic coronary arteries show relative hypoperfusion, while wall motion abnormalities appear only when the coronary stenosis is so severe to cause ischaemia (an absolute blood flow reduction due to the “coronary steal” phenomenon) [41]. Vasodilator drugs share a common capability to bind the adenosine
Conclusions
Cardiovascular MR is a versatile imaging technique, with a very high safety profile and very few absolute contraindications. Several strategies are now available to extend its use and optimize image quality even in patients with relative contraindication, including selected foreign bodies/metal objects, devices, arrhythmias and significant renal failure.
Declaration of Competing Interest
All authors report no relationships that could be construed as a conflict of interest.
Acknowledgements
The manuscript has been written by the Authors on behalf of the Working Group on Cardiac Magnetic Resonance of the Italian Society of Cardiology. We would like to thank Alessandra Flori, (PhD, expert in MR physics from the Bioengineering and Clinical Engineering Unit, Fondazione Toscana Gabriele Monasterio, Pisa, Italy) for her support in revising the paragraphs related to the physics and the biological effects of MR.
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