Why Some Patients with Mitral Regurgitation Should be Assessed by Cardiac MRI
Echocardiography and, to a lesser extent, cardiac catheterization are most commonly used to evaluate mitral regurgitation. However, because MRI is a 3D volumetric technique, it can better quantify the severity of the regurgitation, as well as quantify its effect on LV size and function. In patients with isolated mitral regurgitation, MRI can quantify the leak using three different methods. The regurgitant volume can be calculated as (1) the difference between LV stroke volume and the aortic flow, (2) the difference between LV stroke volume and pulmonary artery flow, and (3) the difference between the LV and RV stroke volumes. Having multiple volumetric methods of quantifying the regurgitant volume often further increases diagnostic confidence in the MRI results. Furthermore, because MRI does not rely on direct assessment of the regurgitant jet, quantifying eccentric or mutiple regurgitant jets is not problematic, as it can be with echocardiography. Finally, the assessment of mitral regurgitation with MRI is completely noninvasive. It does not require intravenous contrast and it does not use ionizing radiation.
Are the differences between echocardiography and MRI significant? In many patients we have found large, clinically important discrepancies between MRI and echocardiography. For example, we have seen a number of patients where echocardiography described the mitral regurgitation as severe when in fact the MRI showed it to be mild.
When should a patient with mitral regurgitation get a cardiac MRI? The initial evaluation should be with echocardiography. If the echocardiogram clearly shows the regurgitation is mild, no MRI is warranted. However,if the echocardiogram suggests the mitral regurgitation is moderate or severe, an MRI may be warranted. . MRI is helpful to quantify the leak, quantify left ventricular size and function, and serve as a baseline for subsequent follow-up studies. Finally, if surgery is being considered in a patient with "severe" mitral regurgitation based on echocardiography, a cardiac MRI should be strongly considered to avoid or delay a potentially unnecessary surgery.
If the patient has had multiple echocardiographic studies that show severe mitral regurgitation, should cardiac MRI still be considered? Definitely, yes. Multiple studies performed the same way and using the same criteria only prove reproducibility, not accuracy.
Can any center that does cardiac MRI reliably quantify mitral regurgitation? No. Unfortunately, cardiac MRI expertise varies greatly among imaging centers, both with regard to image acquisition and interpretation. Before referring a patient, a physician should inquire as to how comfortable the imaging center is in performing and interpreting cardiac MRI studies in general, and whether they routinely quantify valve disease. As cardiac MRI becomes more widely utilized for quantifying valve disease, it will become more widely available..
Isn't cardiac MRI too expensive a test to order routinely? No. While costs vary by payer and geographic location, cardiac MRI is comparable to other cardiac imaging tests. In general, cardiac MRI is slightly more costly than echocardiography, and less costly than nuclear perfusion (SPECT) studies. Considering the cost of a potentially unnecessary open heart surgery, cardiac MRI is inexpensive.