Echocardiographic assessment of mitral regurgitation: discussion of practical and methodologic aspects of severity quantification to improve diagnostic conclusiveness

Fig. 1. The methodological factors influencing color-coded flow phenomena (PISA, VC, jet area)—illustrated by optimal colour Doppler settings with 1.8 MHz Doppler frequency, increased Doppler sample volume, reduced low-velocity reject, increased frame rate, increased Doppler frequency with 3.1 and 3.6 MHz, increased colour pixel smoothing, reduced colour scale, reduced and increased 2D gain, reduced and increased colour gain, reduced and increased 2D priority, and reduced and increased zero line shift

Fig. 2. Limitations of the 2D-PISA method (PISA radius = r)—scheme of the proximal convergence areas and the proximal regurgitant flow phenomenon through the regurgitant orifice illustrating the importance of the accurate definition of the 2D-PISA radius. Example of regurgitant volume (MVRegVol) assessment using different 2D-PISA radii with equal velocity time integrals of regurgitant velocities (r = 8 mm, MVRegVol = 19 ml; r = 11 mm, MVRegVol = 39 ml; r = 15 mm, MVRegVol = 67 ml)

Fig. 3. Scheme to illustrate the diagnostic steps to assess MR by TTE: The first step includes the interpretation of clinical symptoms and the chronicity of the underlying disease in the context of MR with different severity. The second step is the qualitative detection of MR. The third step is the analysis of MV morphology and the differentiation between PMR and SMR. The fourth step is the assessment of LV wall, LA- and LV volumes as well as LV size and LV remodelling to get insights into MR etiology, MR chronicity, and LV geometry. The last step is the grading of MR severity. HOCM hypertrophic cardiomyopathy, LA left atrial, LV left ventricular, LVEDP LV end-diastolic pressure, LVRI LV remodelling index, MR mitral regurgitation, MV mitral valve, PMR primary MR, RWT relative wall thickness, SMR secondary MR, sPAP systolic pulmonary arterial pressure

Fig. 4. Scheme to illustrate the echocardiographic workflow to assess MR severity: After interpretation of symptomatology with respect to the causal relationship to the MR qualitative MR detection results in MR classification due to the MV morphology. Echocardiographic parameters of LA and LV size and LV wall thickness characterize loading conditions and enable to distinguish between pressure or volume overload and between compensated or decompensated conditions. The assessment of MR severity starts with the integrated approach and the analysis of semi-quantitative parameters. The final experts’ task of analysis of MR severity is the quantitative assessment of LVSVtot, LVSVeff, MVRegVol, and RF as a plausibility check. At every level of the assessment of MR severity expert consultation as well as the quantitative analysis of MR severity should be considered with respect to severe symptoms, signs of volume overload and heart failure as well as incongruent results by the grading of MR severity by the semi-quantitative approach. 2D two-dimensional, EROA effective regurgitant orifice area, LA left atrial, LV left ventricular, LVOT LV outflow tract, LVRI LV remodelling index, LVSVeff…

Fig. 5. Proposal for standards of echocardiographic timing in MR patients. The scheme illustrates a potential timeline of echocardiographic investigations during MR treatment. The upper red box presents the therapeutic aspects and strategies, the mid blue box presents the proposed time points of echocardiographic investigations—especially focusing on secondary mitral regurgitation (SMR)-, the bottom green box illustrates the diagnostic targets of the respective echocardiographic investigations. LV left ventricular, MR mitral regurgitation, OMT optimized medical treatment, TOE transoesopageal echocardiography, TTE transthoracic echocardiography

Fig. 6. Illustration of the interspecies differences of regurgitant volume in relation to total stroke volume (LVSVtot). The normal LVSVtot of a rat heart is about 0.5 ml [61] resulting in a regurgitant fraction (RF) of 50% if regurgitant volume at the mitral valve (MVRegVol) is about 0.25 ml. The normal LVSVtot of an elephant heart is about 20 l [62] resulting in a RF of about zero, if MVRegVol is about 0.25 ml. An RF of about 50% needs an MVRegVol of about 5 l

Fig. 7. Illustration of practical aspects of LVSVeff or RVSVeff determination. Labeling of the DLVOT and correct positioning of the pw-sample volume documented by the cusp artefact in the pw-Doppler spectrum with the respective results (a); three-point labeling of diameters at the level of the pulmonic valve (1) documented by the origin of the pulmonary regurgitation, at the level of the proximal pulmonic trunk (2) and at the level of the distal RVOT (3) for the respective position of the pw-Doppler sample volume (b); labeling of the DRVOT and the corresponding pw-Doppler spectrum at the RVOT (c), at the pulmonic valve (d), and at the proximal pulmonic trunk (e) with the respective results. All determined forward stroke volumes are within similar ranges, hence documenting plausible results

Fig. 8. Illustration of the proportionality of forward blood flow volume or effective left-ventricular stroke volume (LVSVeff) and of transmitral regurgitant volume (MVRegVol) between the respective cross-section areas (CSAs) and blood flow velocities in a system of communicating tubes. Considering the volume flow during one heart cycle total left-ventricular stroke volume (LVSVtot) is the summation of LVSVeff and MVRegVol. LVSVeff at the level of the left-ventricular outflow tract (LVOT) is equal to the level of the aortic valve (AV) orifice according to the continuity equation. By analogy MVRegVol at the level of the effective regurgitant orifice area (EROA) is equal to MVRegVol at the level of mitral valve (MV) annulus. Thus, both LVSVeff and MVRegVol exhibit proportionality between respective cross-section areas (CSA) and velocity time integrals (VTI). CSAAV CSA of the AV orifice, CSAEROA CSA of the MV regurgitant orifice, CSALVOT CSA of the LVOT, CSAMV CSA at the level of the MV annulus, DAV diameter of the AV orifice, DEROA diameter of the MV regurgitant orifice, DLVOT diameter of the LVOT, DMV diameter at the level of the MV annulus, VTIAV VTI of the systolic forward blood flow…

Fig. 9. The relation between LVSVtot, which is equal to LVSVeff in the absence of mitral regurgitation (MR) and aortic regurgitation (AR), and left-ventricular end-diastolic volume (LVEDV) with respect to left ejection fraction (LVEF) If LVEDV of 200 ml in the presence of LVEF of 30% is assumed at stable haemodynamic conditions labeled by the blue area ( LVSVtot = LVSVeff, = 60 ml indicating a cardiac index > 2.2 l/min m2 at a normal heart rate of 65/min), LVSVtot must be equal to LVSVeff, indicating the absence of MR and AR to provide the necessary cardiac output or cardiac index. The red arrows display the necessary increase of LVEDV or LVEF assuming severe MR with a regurgitant fraction of 50%. Thus, to provide LVSVeff of 60 ml and MVRegVol of 60 ml, LVSVtot of 120 ml is necessary. Consequently, LVEDV must be 400 ml if LVEF is 30%, and LVEF must be 60% if LVEDV is 200 ml