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Synopsis: The semi-quantitative color flow jet characteristic method for estimating the severity of MR could separate more severe from less severe regurgitation but could not determine the actual hemodynamic load in the more severe grades of MR.
Source: Pu M, et al. Am J Cardiol 2001;87:66-70.
Semi-quantification of the severity of mitral regurgitation (MR) by color flow Doppler echocardiography is routinely used in most echocardiography laboratories because of its simplicity and intuitiveness. However, serious disconnects between the color jet characteristics, the patient’s symptoms, or heart chamber sizes frequently occur and make most of us uneasy about the accuracy of using jet characteristics for quantitating MR. On the other hand, measuring regurgitant volume or orifice area by echocardiography is tedious and demanding. Since the relationship between these semiquantitantive and quantitative measures is not well characterized, Pu and colleagues studied 113 patients undergoing clinically indicated intraoperative transesophageal echocardiography (TEE) who had color Doppler evidence of MR. All patients had a right heart catheter from which cardiac output was measured by thermodilution. Mitral annular stroke volume was determined by pulsed Doppler at the mitral annulus (area times velocity integral) and was subtracted from the left ventricular stroke volume by catheter to derive the regurgitant stroke volume. Mitral regurgitant orifice area was determined by dividing the regurgitant stroke volume by the mitral velocity integral. These measurements were compared to the semiquantitation of MR from the color Doppler jet characteristics using a 1-4 scale with 0.5 increments. The results showed that the relationship between the quantitative and semi-quantitative measures was exponential with a steep increase in regurgitant volume or orifice area at 3+ MR or more. At MR grades less than 3+, regurgitant stroke volume was consistently less than 50 mL, but with grades more than 3+ it ranged up to more than 200 mL. Also, there was considerable variability in the regurgitant stroke volume at all grades of MR, but especially in the higher grades: at 2+ MR, it ranged from near zero to 50 mL; at 3.5+, it ranged from 40 to almost 200 mL. Thus, at grades 3-4+, MR regurgitant stroke volume ranged four-fold and regurgitant orifice area ranged six-fold. Pu et al concluded that the semi-quantitative color flow jet characteristic method for estimating the severity of MR could separate more severe from less severe regurgitation but could not determine the actual hemodynamic load in the more severe grades of MR.
Comment by Michael H. Crawford, MD
This study confirms what many of us who read a lot of echoes and see patients with MR have long suspected; the semi-quantitation of MR by color flow Doppler is seriously flawed. It should be pointed out that this is a TEE study; there is no reason to believe that transthoracic echo would be any better and might well be worse. There are two major findings in this study. First, the exponential relationship between the color flow grade and regurgitant volume or orifice area. Grades 0.5-2.5+ are almost indistinguishable with regards to regurgitant volume, which ranges from zero to 60 mL and shows a similar variability at all 0.5 increments in grade. According to these data to say that someone with 1+ MR has less regurgitation than someone with 2+ MR is ridiculous. However, someone with 3-4+ MR probably has a larger regurgitant volume than someone with 1+ MR. Also, the data suggest that two grade differences correlate with real differences in regurgitant volume, but there is too much overlap between adjacent grades to ascribe meaningful differences in regurgitant volumes. The second major finding is that there is a large variation in regurgitant volumes in grade 3-4+ MR (4-fold) such that it is impossible to accurately define the hemodynamic load of regurgitation in these grades. This undoubtedly explains the variability in symptoms, physical findings, and cardiac chamber size and function in patients with grade 3-4+ MR. This finding suggests that other criteria should be used for determining the hemodynamic significance of MR such as left atrial size, left ventricular size and function, pulmonary artery pressure, and symptoms. In fact, this is what research and derived guidelines on the timing of surgery for MR suggest. Among patients with severe MR by echo or angio, surgery should be considered if other clinical or echocardiographic findings are present. The estimation of regurgitation severity by regurgitant jet characteristics alone is not sufficient reason to operate. Thus, color flow grades 1-2 MR are indistinguishable and hemodynamically insignificant. These patients have a good prognosis and need not be followed closely. Grades 3-4+ MR are usually hemodynamically significant. These patients should be followed more closely and measurements of left heart chamber size and function should be performed serially.
The findings in this study suggest that we may want to consider modifying how we grade MR by echo. Some have suggested we use words such as trivial, mild, moderate, severe, but this is not much different from grade 1-4 and would have the same drawbacks. Others have maintained a 1-4 grading system but have added trivial which results in five grades. Perhaps three grades are enough; insignificant (grades 0.5-2); significant (grades 3-4 without chamber enlargement); and hemodynamically significant (grades 3-4 with chamber enlargement). Unfortunately, in this study, no data on chamber sizes and function were presented, so we do not know how such a classification system would mesh with the data in this study. Lacking a universally agreed upon system, I suggest that each laboratory agree on a system that makes sense to them, use it consistently, and educate your physician users on how to translate it to the clinical arena for patient decisions.