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

Abstract

The echocardiographic assessment of mitral valve regurgitation (MR) by characterizing specific morphological features and grading its severity is still challenging. Analysis of MR etiology is necessary to clarify the underlying pathological mechanism of the valvular defect. Severity of mitral regurgitation is often quantified based on semi-quantitative parameters. However, incongruent findings and/or interpretations of regurgitation severity are frequently observed. This proposal seeks to offer practical support to overcome these obstacles by offering a standardized workflow, an easy means to identify non-severe mitral regurgitation, and by focusing on the quantitative approach with calculation of the individual regurgitant fraction. This work also indicates main methodological problems of semi-quantitative parameters when evaluating MR severity and offers appropriateness criteria for their use. It addresses the diagnostic importance of left-ventricular wall thickness, left-ventricular and left atrial volumes in relation to disease progression, and disease-related complaints to improve interpretation of echocardiographic findings. Finally, it highlights the conditions influencing the MR dynamics during echocardiographic examination. These considerations allow a reproducible, verifiable, and transparent in-depth echocardiographic evaluation of MR patients ensuring consistent haemodynamic plausibility of echocardiographic results.

Keywords: Echocardiography; Mitral regurgitant orifice area; Mitral regurgitation; PISA method; Quantification; Regurgitant fraction.

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 (MV_RegVol) assessment using different 2D-PISA radii with equal velocity time integrals of regurgitant velocities (r = 8 mm, MV_RegVol = 19 ml; r = 11 mm, MV_RegVol = 39 ml; r = 15 mm, MV_RegVol = 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 LVSV_tot, LVSV_eff, MV_RegVol, 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, LVSV_eff effective LV stroke volume, LVSV_tot total LV stroke volume, MR mitral regurgitation, MV mitral valve, MV_RegVol regurgitant MV volume, PISA proximal isovelocity surface area, PMR primary MR, RF regurgitant fraction, RWT relative wall thickness, SMR secondary MR, VTI velocity time integral

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 (LVSV_tot). The normal LVSV_tot 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 (MV_RegVol) is about 0.25 ml. The normal LVSV_tot of an elephant heart is about 20 l [62] resulting in a RF of about zero, if MV_RegVol is about 0.25 ml. An RF of about 50% needs an MV_RegVol of about 5 l

Fig. 7

Illustration of practical aspects of LVSV_eff or RVSV_eff determination. Labeling of the D_LVOT 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 D_RVOT 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 (LVSV_eff) and of transmitral regurgitant volume (MV_RegVol) 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 (LVSV_tot) is the summation of LVSV_eff and MV_RegVol. LVSV_eff 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 MV_RegVol at the level of the effective regurgitant orifice area (EROA) is equal to MV_RegVol at the level of mitral valve (MV) annulus. Thus, both LVSV_eff and MV_RegVol exhibit proportionality between respective cross-section areas (CSA) and velocity time integrals (VTI). CSA_AV CSA of the AV orifice, CSA_EROA CSA of the MV regurgitant orifice, CSA_LVOT CSA of the LVOT, CSA_MV CSA at the level of the MV annulus, D_AV diameter of the AV orifice, D_EROA diameter of the MV regurgitant orifice, D_LVOT diameter of the LVOT, D_MV  diameter at the level of the MV annulus, VTI_AV VTI of the systolic forward blood flow through the AV orifice, VTI_EROA VTI of the diastolic backward blood flow through the MV regurgitant orifice, VTI_LVOT VTI of the systolic forward blood flow through the LVOT, VTI_MV VTI of the diastolic forward mitral flow at the level of the MV annulus, VTI-MV_RegVol VTI of the systolic regurgitant transmitral blood flow at the level of the MV annulus

Fig. 9

The relation between LVSV_tot, which is equal to LVSV_eff 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 ( LVSV_tot = LVSV_eff, = 60 ml indicating a cardiac index > 2.2 l/min m² at a normal heart rate of 65/min), LVSV_tot must be equal to LVSV_eff, 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 LVSV_eff of 60 ml and MV_RegVol of 60 ml, LVSV_tot 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