• Can patients with metallic prostheses or stents perform Cardio-MR?

Yes. Patients with metallic, biological prostheses, annuloplasty rings, percutaneously implanted prostheses (TAVR) can safely perform Cardio-RM. Similarly, patients with coronary stents can safely perform cardio-RM, regardless of their type, number or location.

  • How long from the implant of the stent / valve prosthesis can MRI be performed safely?

Immediately after implantation of stents / prostheses. Their “endothelization” is not necessary. The stents or prostheses will not be “ripped” and will function normally in the magnet. [1]

  • Is Gadolinium nephrotoxic?

No. Gadolinium is not nephrotoxic. However, it is not given for creatinine clearance lower then <30 mL/min/1.73 m2, dbecause it can induce a very rare but severe condition called nephrogenic systemic fibrosis in this category of patients. On the other hand, dialysis patients may receive Gadolinium. [2]

  • What is the most common indication for Cardio-MR?

Ischemic coronary artery disease. In these patients, MR is performed both for the assessment of myocardial viability after a myocardial infarction and for the non-invasive diagnosis of myocardial ischemia. In our clinic, about 30% of all cardio-RM exams are stress cardio-MR.

  • Can stress Cardio-MR be performed in patients with atrial fibrillation?

Yes. Stress perfusion images have good quality even in patients with atrial fibrillation. In this category of patients, stress cardio-MR is a good alternative to coronary angio-CT, where images acquired in patients with atrial fibrillation are suboptimal. It is preferred, however, that the frequency of fibrillation to be controlled, so it wont exceed 100 / min.

  • Stress Cardio-MR or coronary angio-CT?

The 2 investigations offer different information. Angio-CT provides anatomical data on the location and stage of coronary stenosis with very good spatial resolution. However, coronary angio-CT does not provide information on the functional significance of the identified coronary stenoses.

Stress Cardio-MR provides information on the functional significance of possible coronary stenoses, but it does not have a spatial resolution good enough to visualize the coronary arteries until they are distal. At the most, Cardio-MR can visualize the proximal segments of the coronary arteries.

Thus, the ideal investigation would be a hybrid , which provides information on both the anatomy of coronary stenosis and their functional significance .

  • How is myocardial viability assessed by the MR?

Assessing myocardial viability does not necessarily require a stress test. Most simply, the viability is assessed based on the transmurality of the myocardial scar, respectively the percentage of the thickness of the myocardium that is occupied by fibrotic tissue. It is necessary to administer gadolinium, which is an exclusively extracellular contrast agent, and which, therefore, attaches to fibrotic areas, lacking myocardiocytes.

The higher the percentage of fibrosis in the thickness of the myocardial wall, the more non-viable myocardium, and therefore it will not recover its contractility after revascularization. In contrast, if the scar occupies less than 25% of the thickness of the myocardium, then that area of ​​myocardium is most likely viable, and has higher chances of recovery after revascularization.

  • How is the ventricular volume and ejection fraction measured by the MR?

Images are recorded cine (dynamic-agoing)in short axis sections covering the entire left ventricle from the mitral ring to the apex. We record these sections with a thickness of 8mm, with a space between sections of 2mm.
Then, for each section, the endocard is shaped both in the telediastole and in the telesistol, obtaining the respective volumes and the ejection fraction.

  • How can we verify the correctness of the measurements?

The stroke volume of the LV should be approximately equal to the stroke volume of the RV, in the absence of shunts. (up to 10ml difference is accepted between the beating volumes of the 2 ventricles).

  • What additional information do the T1, T2, T2 * maps bring to cardiomyopathy assessment?

With these maps, a number of specific etiologies of cardiomyopathies can be differentiated, some of them treatable, such as Fabry’s disease, hemochromatosis or cardiac amyloidosis (in the case of amyloidosis, MR can even differentiate between AL and ATTR forms).In addition, with the help of T1 maps, the percentage of myocardial fibrosis can be quantified, with a prognostic role.

  • Where can I read practical information about Cardio-MR for a beginner level?

The European Magnetic Resonance ESC / EACVI Guide provides beginner information for the clinician. The guide can be downloaded from the ESC website- Cardiovascular Magnetic Resonance Pocket Guide – Authors: Bernhard Herzog, John Greenwood, Sven Plein, Pankaj Garg, Philip Haaf, Sebastian Onciul.

  • How is the stress Cardio-MR performed?

In our clinic we use the technique of first-pass perfusion during maximal coronary vasodilation with Adenosine. The protocol is as follows:

Adenosine is administered at a dose of 140 mcg / kg / min for 3 minutes while the patient is in the device. The heart rate is expected to increase by > 10 beats per minute or blood pressure to decrease> 10mmHg from the initial values.

During maximal vasodilation, the contrast bolus is injected, and images are acquired during each cardiac cycle (for 60-100 cardiac cycles). Usually 3 sections are purchased at each cardiac cycle, so that all 17 segments of the left ventricle are covered.

Once the images have been acquired, it is possible to analyze how the contrast agent initially arrives in the right cavities, later in the pulmonary circulation, and then in the left cavities and then enters the myocardium. Normally perfused areas will become an increasingly light gray due to contrast, while hypoperfused areas will remain black.

Stress Cardio-MR: On the bottom row you can see infusion defect in the inferior and inferior-lateral walls from the base to the apex (arrows). This infusion defect no longer appears on the infusion images at rest (top row). Examination is positive for stress-induced ischemia in the territory of the right coronary artery.

REFERENCES

[1]             T. D. Karamitsos and H. Karvounis, “Magnetic resonance is a safe imaging technique in patients with prosthetic heart valves and coronary stents,” Hell. J. Cardiol., 2017.

[2]             S. P. Bernhard Herzog, John Greenwood and S. Onciul. Pankaj Garg, Philip Haaf, ESC/EACVI Cardiovascular Magnetic Resonance Pocket Guide, Second Edi. 2017.

[3]             S. Onciul and S. Plein, “Cardiovascular magnetic resonance for detection of coronary artery disease – a practical approach,” Rom. J. Cardiol., vol. 27, no. 4, pp. 490–498, 2017.

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