History: A 57 year-old woman with increasing shortness of breath had a transthoracic echocardiogram that showed severe mitral regurgitation and posterior leaflet prolapse. A cardiac MRI was requested to quantify the severity of the regurgitation, and to evaluate its physiologic effect on the left ventricle.
Technique: ECG-gated short- and long-axis SSFP images were acquired. ECG-gated gradient echo images were acquired parallel and perpendicular to the mitral valve annulus. Phase-contrast (PC) images (not shown) were acquired through the ascending aorta and main pulmonary artery.
Findings: The upper left panel shows a midventricular short-axis SSFP cine with normal LV function. The upper right panel shows a 3-chamber SSFP cine. The still frame below shows prolapse of the posterior leaflet of the mitral valve (red arrow), which results in the regurgitant jet being directed anteriorly (yellow arrow).
The lower left panel is a fast gradient echo cine parallel to the plane of the mitral valve annulus. It shows the mitral valve opening and closing. When the mitral valve is closed, one can see two regurgitant jets in cross-section: a tiny central jet, and a much larger jet which is closer to the anterior commissure.
The lower right panel shows a fast gradient echo 3 chamber cine. In contrast to the SSFP cine above, it shows the regurgitant jet as dark. The jet is larger than in the cine above because the gradient echo sequence has a longer TE (6 ms vs. 2 ms), which allows for more intravoxel dephasing. In MRI the size of the jet depends on the acquisition parameters, so it can sometimes be misleading to use the size of the jet to grade the severity of mitral regurgitation.
A dark eccentric jet can sometimes simulate an abnormally thickened valve leaflet. However, a truly thickened leaflet is thick throughout the entire cardiac cycle. In the cine above, the anterior leaflet looks thick during systole. If the leaflet were truly thick, it should appear so during the entire cardiac cycle. The 3-chamber view is also useful for assessing the size of the left atrium, which is slightly enlarged in this patient.
Analysis of all the short axis cine images showed the LV SV to be 111 ml. Analysis of the phase contrast images (not shown) reveal a forward flow of 72 ml. The difference between these two values is 39 ml and is the regurgitant volume. A regurgitant volume of 39 ml corresponds to moderate mitral regurgitation.
It is not uncommon for echocardiography to overestimate the severity of mitral regurgitation. Many echocardiographic methods (color flow jet size, vena contracta, PISA) assess the regurgitant jet at a single timepoint, when the jet is most severe. Yet, it is well known that mitral regurgitation severity changes substanitally during systole. When mitral regurgitation severity varies greatly during systole, there is increased risk that it will be overestimated by echocardiography. The upper right panel illustrates this phenomenon, as the jet is larger in late systole as compared to early systole.
The patient’s left ventricular end-diastolic volume index is normal. Studies have shown a tight coupling between regurgitant volume and left ventricular end-diastolic volume. Patients with isolated mitral regurgitant have LV enlargement, even when the mitral regurgitation is mild. This patient had diastolic dysfunction in addition to mitral regurgitation. Diastolic dysfunction causes a decrease in end-diastolic volume. In this patient, because both diseases are present and have opposite effects of LV size, the left ventricular size is normal. Yet, both diseases work cooperatively to contribute to the patient’s shortness of breath.
Comment: This case demonstrates how MRI can define mitral valve anatomy, quantify mitral regurgitation severity, and assess its physiologic effect on the left ventricle. In this case the mitral regurgitation was moderate, even though it was thought to be severe on echocardiography.
Patients with mitral regurgitation can be treated either medically or surgically. The aim of medical therapy is often to decrease afterload so as to reduce regurgitant severity. In the past, surgery has been reserved for symptomatic patients. More recently, guidelines recommend surgery even when patients are asymptomatic.
Surgical options include mitral valve repair and replacement. Most physicians believe mitral valve repair is preferable to replacement. Unfortunately, sometimes the decision to replace the valve can only be made during the surgery itself. Patients that receive a mechanical valve require anticoagulation and monitoring for the rest of their life. Patients that receive a bioprosthesis are at risk of needing a second surgery to replace the original valve, which typically has a lifetime of 10-15 years.
MRI has been shown to be more accurate than echocardiography in determining MR severity. When used appropriately, it can spare patients like this one, unnecessary surgery. Even if MRI only delays the surgery, sometime this could lead to patients receiving a bioprosthetic valve rather than a mechanical one.
- Recommendations for Evaluation of the Severity of Native Valvular Regurgitation with Two-dimensional and Doppler Echocardiography
- Hundley, et al. Magnetic Resonance Imaging assessment of the severity of mitral regurgitation. Comparison with invasive techniques. Circulation 1995;92:1151-1158.