By Michael H. Crawford, MD, Editor
SYNOPSIS: Using cardiac MRI as a gold standard, the presence of a flail mitral leaflet or a wall-impinging mitral regurgitant jet on transthoracic echocardiography were associated with severe mitral regurgitation, but not diagnostic of it.
SOURCE: Uretsky S, Morales KCV, Aldaia L, et al. Characterization of primary mitral regurgitation with flail leaflet and/or wall-impinging flow. J Am Coll Cardiol 2021;78:2537-2546.
Uretsky et al studied 193 patients with mitral regurgitation (MR) by transthoracic echocardiography (TTE) and by cardiac MRI to determine the severity of MR. After excluding patients with other significant valve disease, shunts, hypertrophic cardiomyopathy, pregnancy, or secondary MR, the final study population consisted of 158 patients (mean age = 63 years; 61% men). TTE and CMR were performed a median difference of two days apart, and the patient’s heart rate and systolic blood pressure were not different between the study days. Independent investigators blinded to the CMR results graded the severity of MR by the American Society of Echocardiography criteria and noted the presence of flail leaflet or regurgitant flow wall impingement (WI).
By TTE, 69% of the patients exhibited at least moderate MR (grade 3 or more), 33% showed WI, 35% showed flail, and 14% exhibited both. Severe MR was present by TTE in 44% with WI, 65% of those with flail, and 77% of those with both. Also, severe MR was more frequent if WI or flail was present (P < 0.001). Compared to cardiac MRI-determined regurgitant volume (RV), where more than 60 mL is severe, WI carried a positive predictive value (PPV) of 34% for detecting severe MR and a 82% negative predictive value (NPV). For flail, the PPV was 45% and the NPV was 88%. For both, the PPV was 63% and the NPV was 83%. When cardiac MRI-regurgitant fraction (RF) was used, the PPVs were lower (all < 45%) and the NPVs were slightly higher. The authors concluded the detection of a WI jet or a flail leaflet by TTE in patients with MR was associated with the presence of severe MR by CMR vs. those without these features — but they do not establish the diagnosis of severe MR.
COMMENTARY
The TTE assessment of the severity of MR is challenging because it is a decision based on multiple criteria involving complex measurements. Most labs for routine TTE interpretations just estimate the severity, which works fairly well in experienced hands, but should not be relied on for deciding in whom to intervene on their mitral valve. Such decisions should be made based on the full qualitative and quantitative assessment of the severity of regurgitation. It appears flail leaflet has become an automatic criterion for severe MR. However, a flail in a small part of the valve leaflet, perhaps supplied by one chorda, does not create severe MR. Also, although WI is an important observation that can result in the visual underestimation of MR severity, this is not always the case. Thus, this systematic study using cardiac MRI as the gold standard is of interest. Uretsky et al showed 80% of TTEs that revealed a flail leaflet were graded as severe, but less than half were graded as severe by cardiac MRI. Similarly, of those with WI by TTE, 77% were graded severe, but one-third were severe by cardiac MRI. These results appear to indicate that flail and WI are important findings, but do not automatically signify severe MR.
Still, there were some weaknesses to the Uretsky et al study. The population studied was small, and transesophageal and 3D echocardiography were not employed. Both techniques can add important information about the size of the regurgitant orifice. Also, cardiac MRI is a tarnished gold standard and has not been verified independently.
Two measurements of MR severity were considered: RV and RF. The authors did not agree on who had severe MR; more subjects were severe by RV than RF. In primary MR, where left ventricular enlargement is moderate and ejection fraction is high, normal, or hyperdynamic, the RV criterion for severe often is reached before the RF criterion. The opposite could hold in dilated, lower ejection fraction secondary MR. However, left ventricular volumes and ejection fraction were not provided in this paper. In addition, cardiac MRI was not compared to the TTE assessment of MR severity by using the complete set of measurements recommended rather than just flail and WI. It is likely that a complete TTE evaluation would be superior to just considering flail or WI. In the final analysis, the diagnosis of severe MR is important since it is required to intervene mechanically. Thus, when in doubt, TTE, 3D echo, or cardiac MRI would be appropriate to help establish the severity of MR.
Using cardiac MRI as a gold standard, the presence of a flail mitral leaflet or a wall-impinging mitral regurgitant jet on transthoracic echocardiography were associated with severe mitral regurgitation, but not diagnostic of it.
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