JACC: Cardiac MR may be ideal for mitral regurgitation assessment
Cardiac MR (CMR) can help determine the progression of mitral regurgitation (MR) in patients with mitral valve prolapse (MVP), according to a study published Oct. 20 in the Journal of the American College of Cardiology, while an editorial questioned the validity of the approach.

"Controversy exists regarding the prognosis of MVP," Francesca N. Delling, MD, of Beth Israel Deaconess Medical Center and Harvard Medical School in Boston, and colleagues wrote. "Compared with echocardiaography, CMR predictors of MVP-related MR are yet to be defined."

While echocardiography is commonly used to follow patients with chronic MR, the authors pointed to the technique's poor image quality, significant variability in flow diameter measurements and geometric assumptions of flow orifice as motivating the present CMR study. "We sought to investigate the correlation between mitral valve characteristics and MR in the MVP population," Delling and co-authors wrote.

Seventy-one patients with MVP identified by echocardiography underwent CMR, where evidence for MVP was defined using similar standards to those of echocardiography: 2 mm displacement of the mitral leaflets into the left atrium. The researchers used several statistical models to assess the relationships of the following variables to MR: annular dimensions; maximum systolic anterior and posterior leaflet displacement; papillary muscle distance to coaptation point and prolapsed leaflets; diastolic anterior and posterior leaflet thickness and length; and left ventricle volume and mass.

The study also measured inter- and intraobserver variability with two readers, each reading all studies twice (with at least five days between rereads).

Left ventricle mass, anterior leaflet length and posterior displacement were the best determinants of MR volume, with a tranverse relaxation rate (R2) of .6. For valvular characteristics alone, anterior mitral leaflet length, posterior mitral leaflet displacement, posterior leaflet thickness and the presence of flail showed the strongest correlations to MR volume, with an R2 of .5.

"In this CMR study of 71 subjects with MVP and MR, we found that anterior leaflet length, posterior leaflet displacement, posterior leaflet thickness, and the presence of flail are the best CMR valve determinants of MVP-related MR," the authors noted.

Left ventricle mass, which had not been measured in other studies, was found to be a strong predictor of mitral regurgitation in the present study, reflecting the effects of regurgitation on development of compensatory hypertrophy, according to the authors.

Inter- and intraobserver variability were low and consistent across all variables. "Our study showed acceptable intraobserver and interobserver variability with low percentage variability achievable in a trained observer, further confirming the ideal role of CMR as an imaging modality for the assessment of MVP patients with significant MR," the researchers argued.

"In an era when interventions for mitral valve disease improve and are recommended earlier in the disease course, it becomes particularly important to assess MVP patients with a precise and accurate modality such as CMR," Delling and colleagues wrote.

Questions remain
In an editorial commentary in JACC, Maurice Enriquez-Sarano, MD, of Mayo Clinic in Rochester, Minn., listed six sharp criticisms of Delling and co-authors' article, applauding their research but calling their conclusion "unproven."

Enriquez-Sarano argued that the authors' small sample size gave the study "limited power in providing a full analysis of the determinants of MR severity." Echoing the authors' own comments, Enriquez-Sarano mentioned the importance of a longitudinal study for understanding MR.

"The picture that we obtain from the present series is skewed by the distribution of the patients that it examined ... [I]t would be preferable to separate the analysis into specific morphologic subsets, such as bileaflet MVP, to minimize the bias introduced by the combination of heterogeneous subgroups.

"The limitations of this population leads to the presentation, as the main result of the study, of a truism already well known, which states that patients with flail leaflets have generally more severe MR than patients with MVP without flail leaflet. We do not learn much here."

Enriquez-Sarano did applaud the researchers for quantitating MR. While expressing his regret that regurgitant volumes as measured by CMR were not included in the study, he noted that the research does contribute to physicians' incomplete knowledge about the mitral valve, normal or diseased. Enriquez-Sarano said the development of 3D echocardiography is essential for understanding the valve.

Delling and co-authors concluded that the relationships discovered between valvular characteristics and MR in patients with MVP were "reproducible and represent an important step towards the development of prospective CMR studies to define MR progression." Enriquez-Sarano, on the other hand, called Delling and colleagues' findings into sharp question, writing that "the conclusions about CMR as an ideal tool to image MVP and MR are unproven."