On Myocarditis and a New Era for Cardiac Magnetic Resonance Imaging

Things have not always looked this promising for cardiac magnetic resonance imaging (MRI). The late 1990s and early 2000swere a period of great innovation in cardiacMRI, including an impressive global refinement of image quality, balanced steady-state free precession cine techniques supplanting legacy gradient echo sequences, multichannel systems with parallel imaging and accelerated scansfinally allowing for realtime cine imaging. Radiologists were excited about the promise of themodality but as the 2000s progressed, utilization did not increase at the rate hoped for. There was concern that turf battles between radiology and cardiology, reimbursement issues in the United States, and ‘competition’ from the new upstart – cardiac computed tomography (CT) – would relegate MRI to largely a research imaging modality. How could an examination that takes an hour compete effectively with echocardiography or CT? The answer, of course, was that cardiac MRI needed to better establish its niche. The past decade has seen two important developments which have boosted the awareness and clinical footprint of cardiac MRI. First, ongoing technological improvements have been made which allow us to do more in a shorter period of time. Progressively accelerated sequences can significantly reduce overall scan time, and tissue characterization has been improved with the advent of myocardial T1 and T2 mapping techniques as well as high-quality cardiac diffusion-weighted imaging. Second, radiologists have utilized these new techniques to provide value to clinicians and patients in ways that they could not before. CardiacMR exams initially were heavily focussed on cardiac masses, congenital heart disease and viability imaging, but in the last decade, MR has become an essential modality for evaluating the patient with a nonischemic cardiomyopathy or with suspected cardiac chest pain without evidence of coronary artery disease to explain it. The tools we have now allow radiologists to assess for myocardial infiltration and inflammation in ways that were not possible in the year 2000. The workup of myocarditis has radically altered the typical clinical cardiac MRI workflow in recent years. Cardiac MRI now has become a key part of the evaluation of acute inpatients. Patients with a clinical presentation of acute coronary syndrome and elevated troponin who then go on to have cardiac catheterization that does not explain the presentation routinely go to MRI next. Increasingly, low pretest probability patients in this situation may undergo CT coronary angiography instead of catheterization, followed by MRI if negative. Imaging departments in cardiac centres now will deal with multiple urgent inpatient requests for cardiac MR service in a week, many of which are for this scenario. This transition greatly accelerated in 2020 due to SARSCoV-2. Initially, radiologists noticed that myocarditis was being seen as a consequence of the viral infection. Once the novel mRNA vaccines were introduced, it was then identified that myocarditis can be temporally related to vaccination, with a predisposition for adolescents and young adults. A study by Truong et al published this year showed that of 139 adolescents and young adults presenting with symptoms suspicious for myocarditis (chest pain and elevated troponin) within 30 days of COVID-19 vaccination, 75 (77.3%) had findings on cardiac MR consistent with myocarditis, including late gadolinium enhancement or myocardial oedema. This comes as little surprise to those of us who were performing cardiac MRI throughout the pandemic and saw many of these cases. With media attention, anyonewith chest discomfort in proximity to vaccination seemed to present to an emergency department and in 2021 cardiac MRI was used as an essential acute clinical tool to both triage and risk stratify these patients, as late gadolinium enhancement or functional abnormalities are associated with worse outcomes. The strain on the health care system meant that hospitals needed to be judicious about admissions and monitoring, and radiologists stepped up and assisted our clinical colleagues in making many of these difficult decisions during the pandemic. The use of cardiac MRI in this manner has improved the visibility of the modality across multiple clinical specialities and cemented its role in the acute inpatient system. Departments across the country are seeing more requests for inpatient cardiac MR than ever before, in large part because of this pivotal role it played in diagnosing myocarditis over the last 2 years. In this issue, Dr Fresno and their team provide a broad overview of myocarditis and both the current and future role of MRI in its assessment, along with that of other modalities such as echocardiography and positron emission tomography. A true highlight of the paper is the quality of the figures which


On Myocarditis and a New Era for Cardiac Magnetic Resonance Imaging
Iain D. C. Kirkpatrick, MD, FRCPC, FCAR, FSAR, FACR 1  Things have not always looked this promising for cardiac magnetic resonance imaging (MRI).
The late 1990s and early 2000s were a period of great innovation in cardiac MRI, including an impressive global refinement of image quality, balanced steady-state free precession cine techniques supplanting legacy gradient echo sequences, multichannel systems with parallel imaging and accelerated scans finally allowing for realtime cine imaging. Radiologists were excited about the promise of the modality but as the 2000s progressed, utilization did not increase at the rate hoped for. There was concern that turf battles between radiology and cardiology, reimbursement issues in the United States, and 'competition' from the new upstartcardiac computed tomography (CT)would relegate MRI to largely a research imaging modality. 1 How could an examination that takes an hour compete effectively with echocardiography or CT?
The answer, of course, was that cardiac MRI needed to better establish its niche. The past decade has seen two important developments which have boosted the awareness and clinical footprint of cardiac MRI. First, ongoing technological improvements have been made which allow us to do more in a shorter period of time. Progressively accelerated sequences can significantly reduce overall scan time, and tissue characterization has been improved with the advent of myocardial T1 and T2 mapping techniques as well as high-quality cardiac diffusion-weighted imaging. 2 Second, radiologists have utilized these new techniques to provide value to clinicians and patients in ways that they could not before. Cardiac MR exams initially were heavily focussed on cardiac masses, congenital heart disease and viability imaging, but in the last decade, MR has become an essential modality for evaluating the patient with a nonischemic cardiomyopathy or with suspected cardiac chest pain without evidence of coronary artery disease to explain it. The tools we have now allow radiologists to assess for myocardial infiltration and inflammation in ways that were not possible in the year 2000.
The workup of myocarditis has radically altered the typical clinical cardiac MRI workflow in recent years. Cardiac MRI now has become a key part of the evaluation of acute inpatients. Patients with a clinical presentation of acute coronary syndrome and elevated troponin who then go on to have cardiac catheterization that does not explain the presentation routinely go to MRI next. Increasingly, low pretest probability patients in this situation may undergo CT coronary angiography instead of catheterization, followed by MRI if negative. Imaging departments in cardiac centres now will deal with multiple urgent inpatient requests for cardiac MR service in a week, many of which are for this scenario.
This transition greatly accelerated in 2020 due to SARS-CoV-2. Initially, radiologists noticed that myocarditis was being seen as a consequence of the viral infection. 3 Once the novel mRNA vaccines were introduced, it was then identified that myocarditis can be temporally related to vaccination, with a predisposition for adolescents and young adults. A study by Truong et al published this year showed that of 139 adolescents and young adults presenting with symptoms suspicious for myocarditis (chest pain and elevated troponin) within 30 days of COVID-19 vaccination, 75 (77.3%) had findings on cardiac MR consistent with myocarditis, including late gadolinium enhancement or myocardial oedema. This comes as little surprise to those of us who were performing cardiac MRI throughout the pandemic and saw many of these cases. With media attention, anyone with chest discomfort in proximity to vaccination seemed to present to an emergency department and in 2021 cardiac MRI was used as an essential acute clinical tool to both triage and risk stratify these patients, as late gadolinium enhancement or functional abnormalities are associated with worse outcomes. 4,5 The strain on the health care system meant that hospitals needed to be judicious about admissions and monitoring, and radiologists stepped up and assisted our clinical colleagues in making many of these difficult decisions during the pandemic.
The use of cardiac MRI in this manner has improved the visibility of the modality across multiple clinical specialities and cemented its role in the acute inpatient system. Departments across the country are seeing more requests for inpatient cardiac MR than ever before, in large part because of this pivotal role it played in diagnosing myocarditis over the last 2 years.
In this issue, Dr Fresno and their team provide a broad overview of myocarditis and both the current and future role of MRI in its assessment, along with that of other modalities such as echocardiography and positron emission tomography. 5 A true highlight of the paper is the quality of the figures which show the spectrum of imaging findings across multiple MR techniques, illustrating the varied ways in which MRI can evaluate the myocardium and ventricular function in order to provide a diagnosis and estimation of future risk to guide patient management. When clinicians see images of this quality while reviewing cases with us in the department or in multidisciplinary rounds, the information we can provide and the value radiology can offer is made clear. These same techniques can give us insight into many other pathologies, including infiltrative processes such as cardiac amyloid and sarcoid, and provide data that is unattainable with other noninvasive methods.
There is every indication that SARS-CoV-2 and its various strains will be with us for a while, and this paper is particularly timely as radiologists on the front lines must be fully aware of both the condition and the role each imaging modality plays in its assessment. The evolving techniques described in this review have helped make cardiac MRI more relevant than ever before. We are in a new era for cardiac MRI where it has become a routinely ordered test on an acute inpatient basis. Credit for that must be given to research teams such as the authors of this important paper for bringing us to this point.

Declaration of Conflicting Interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding
The author(s) received no financial support for the research, authorship, and/or publication of this article.