Cardiac Magnetic Resonance Imaging and Valvular Heart Disease

Educational Objectives

After completing the activity, the clinician will be better able to describe specific situations in which cardiac magnetic resonance imaging may be of use in patients with valvular heart disease.

Summary

Interviewer: Christopher M. Kramer, MD, FACC

Take-home Messages:

• In the last few years, a growing body of evidence has established specific situations in which cardiac magnetic resonance (CMR) imaging can be a useful tool for assessing valvular heart disease.
• Echocardiography (echo) remains the first choice of imaging for most patients with valvular heart disease. Often, however, it is not enough, as when there is discordance between echo and patient symptoms, or discordance between echo and the clinical examination.
• CMR may be useful when there remains uncertainty as to the severity of the lesion, the related remodeling, or the mechanism. It provides important information on the severity of regurgitation and stenosis, as well as the mechanism of the abnormality and the consequences of the lesion on the heart.

For most patients with valvular heart disease, echocardiography is the standard imaging modality. Most guidelines, like those published by the American Society of Echocardiography (ASE), make recommendations in this setting based largely on the consensus of experts. When there are data available, the results with echo are not often compared against hose with cardiac magnetic resonance imaging.

In one current set of ASE guidelines, for the noninvasive evaluation of native valvular regurgitation, the document acknowledges that while echo remains the first-line modality, “in some situations, it may be suboptimal.”¹

The guidelines note, “In these instances, CMR can play a useful role because of a number of unique advantages: it provides a view of the entire heart without limitations of imaging windows or body habitus, allows free choice of imaging planes as prescribed by the scan operator, is free of ionizing radiation, and does not require contrast administration. In addition

to assessing the severity of the regurgitant lesion, a comprehensive CMR study is able to quantitate cardiac remodeling and provide insight into the mechanism of regurgitation.”

One of the primary advantages to CMR is the ability to visualize the morphology and motion of each valve from any desired image orientation. CMR methodology is not affected by regurgitant orifice shape; moreover, blood flow velocities can be measured from the entire region of interest without assuming a flat flow profile.

In the last few years there has been a greater appreciation for CMR measurements of mitral regurgitation (MR) volume, which successfully identifies patients with severe MR and adverse outcomes. Indeed, assessment of MR by CMR is more accurate than 2-dimensional transthoracic echo and should be strongly considered before referring a patient to mitral valve (MV) surgery. Also, there is evidence that CMR is better able to predict reverse remodeling that occurs after MV surgery than echocardiography is.

In an important study, transthoracic or transesophageal Doppler echo was associated with misclassification of the severity of organic MR in about 25% of patients. Investigators specifically looked at the patients in who echo did worse than CMR. Misclassification tended to be more likely in those with late systolic, eccentric, or multiple jets.² In these cases, more liberal use of CMR-derived quantification of MR severity to guide clinical management may be helpful.

Specifically, CMR-derived regurgitant volume showed the highest discriminative power among all the imaging parameters to predict all-cause mortality or its combination with the development of indication for MV surgery. The Doppler echo-derived parameters showed lower discriminative power.

CMR provides important information on the severity of regurgitation and stenosis, as well as on the mechanism of the abnormality; for example, is it a bicuspid valve? Is it MV prolapse due to a specific leaflet that is prolapsing or flail?

CMR also can reveal important information regarding the consequences of the lesion on the heart itself in terms of remodeling. Decisions on when to intervene can be based on not just the action of the valve itself but also its impact on the heart: how the heart is managing the load and any resulting remodeling. CMR is uniquely suited to answer these questions because it can provide comprehensive information on left or right ventricular volumes, left atrial sizes and volumes, as well as function and mass.

However, CMR is not always the best approach. If the point of the study is to rule out endocarditis, both 2- and 3-dimensional transesophageal echocardiography have proven utility — and improve the diagnostic accuracy of transthoracic echocardiography — whether for infectious or inflammatory endocarditis. With CMR, visualization of vegetation is limited by the low spatial and temporal resolution of small, highly mobile structures with images that are taken over several cardiac cycles. As a result, it can be difficult to identify a small vegetation.

Similarly, determining the extent of stenosis in a bioprosthetic valve or mechanical dysfunction of the prosthesis can also be challenging using CMR. Finally, while not a contraindication for CMR, if a patient has a lot of heart rate variability — such as atrial fibrillation or a lot of premature ventricular contractions (PVCs) — it poses additional challenges and may require medications to control the heart rate or suppress the PVCs.

Tricuspid regurgitation (TR) is another situation in which echo may have a role not previously appreciated. Dipan Shah, MD, and colleagues report in JACC Imaging that several individual echo parameters of the severity of TR have satisfactory accuracy compared to TR regurgitant volume determined by CMR.³ There was a 68% agreement with CMR — but 100% agreement when a 1-grade difference in TR severity was considered acceptable. The 2017 ASE guidelines note that echo classifies TR in 90% of patients.

Shah and his team noted that a hierarchal approach, based on routinely acquired signals, was effective enough that no patients with severe TR by CMR were classified as having mild TR by echocardiography. This suggests that echo might be an appealing method to grade TR, although its performance in prospective patient groups with a wide range of TR severity still needs to be evaluated against that of CMR. Plus, the utility of echo to judge response to treatment is of interest, too, and needs to be studied.

Finally, there are times where CMR can reveal important information about risk that was not previously clear. This was demonstrated in another paper by Dr. Shah and colleagues in patients with primary MR. They reported that left ventricular fibrosis is more prevalent in patients with MV prolapse than patients without prolapse.⁴ This suggests a unique pathophysiology beyond volume overload in the setting of MV prolapse. Moreover, left ventricular fibrosis in primary MR seemed to represent a risk marker of arrhythmic events.

As Dr. Shah explains, CMR is often not going to be the first-line imaging choice. Instead, patients will have undergone echo, but some uncertainty remains as to the severity of the lesion, the related remodeling, or the mechanism. In these patients, echocardiography can give some idea about what is going on and what the clinical dilemma is; then CMR can be used to obtain “cine” images of cardiac structure and function. Flow quantification is then done using phased-contrast CMR. Think of it as the magnetic resonance imaging equivalent of echo Doppler. Velocity of flow can be encoded for in each individual pixel in any slice of interest.

Based on the data, Dr. Shah expects to see more use of CMR in patients with valvular disease, especially given that the technology is becoming more widely available.

References:

1. Zoghbi WA, Adams D, Bonow RO, et al. Recommendations for Noninvasive Evaluation of Native Valvular Regurgitation: A Report from the American Society of Echocardiography Developed in Collaboration with the Society for Cardiovascular Magnetic Resonance. J Am Soc Echocardiogr 2017;30:303-71.
2. Penicka M, Vecera J, Mirica DC, Kotrc M, Kockova R, Van Camp G. Prognostic Implications of Magnetic Resonance-Derived Quantification in Asymptomatic Patients With Organic Mitral Regurgitation: Comparison with Doppler Echocardiography-Derived Integrative Approach. Circulation 2018;137:1349-60.
3. Zhan Y, Senapati A, Vejpongsa P, Xu J, Shah DJ, Nagueh SF. Comparison of Echocardiographic Assessment of Tricuspid Regurgitation Against Cardiovascular Magnetic Resonance. JACC Cardiovasc Imaging 2020;13:1461-71. https://imaging.onlinejacc.org/content/early/2020/06/16/j.jcmg.2020.01.008
4. Kitkungvan D, Nabi F, Kim RJ, et al. Myocardial Fibrosis in Patients with Primary Mitral Regurgitation with and Without Prolapse. J Am Coll Cardiol 2018;72:823-34. https://www.onlinejacc.org/content/72/8/823

Readings

Disclosures

Dipan J. Shah, MD, FACC, Houston, TX

This author has nothing to disclose.

Interviewer: Christopher M. Kramer, MD, FACC

This author has nothing to disclose.

Acknowledgements

CME/CE INFO

Accreditation:

The Audio- Digest Foundation is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education for physicians.

The Audio- Digest Foundation designates this enduring material for a maximum of 0 AMA PRA Category 1 Credits™. Physicians should claim only the credit commensurate with the extent of their participation in the activity.

Audio Digest Foundation is accredited as a provider of continuing nursing education by the American Nurses Credentialing Center's (ANCC's) Commission on Accreditation. Audio Digest Foundation designates this activity for 0 CE contact hours.

Lecture ID:

AC520907

Expiration:

This CME course qualifies for AMA PRA Category 1 Credits™ for 3 years from the date of publication.

Instructions:

To earn CME/CE credit for this course, you must complete all the following components in the order recommended: (1) Review introductory course content, including Educational Objectives and Faculty/Planner Disclosures; (2) Listen to the audio program and review accompanying learning materials; (3) Complete posttest (only after completing Step 2) and earn a passing score of at least 80%. Taking the course Pretest and completing the Evaluation Survey are strongly recommended (but not mandatory) components of completing this CME/CE course.

Estimated time to complete this CME/CE course:

Approximately 2x the length of the recorded lecture to account for time spent studying accompanying learning materials and completing tests.

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