Jet Area To Left Atrial Area In Mitral Regurgitation

1.4-2,1

Values from cardiac ultrasound laboratory, Massachusetts General Hospiiall

Fig. 14. Left ventricle dimensions in mitral regurgitation. Values from cardiac ultrasound laboratory, Massachusetts General Hospital.

Values from cardiac ultrasound laboratory, Massachusetts General Hospiiall

Fig. 14. Left ventricle dimensions in mitral regurgitation. Values from cardiac ultrasound laboratory, Massachusetts General Hospital.

mitral valve surgery (Tables 6 and 7). In chronic compensated MR, cardiac output is maintained via an increase in the LVEF, and such patients typically have LVEFs greater than 65%. LV hypertrophy is not a feature of isolated MR as the regurgitant chamber—the left atrium (LA)— usually adapts and dilates to accommodate increases in preload (end-diastolic volume [EDV]; Fig. 13C). Even in the acute setting, LV contractility and LVEF increase in response to an increase in preload (Fig. 13B). However, LV contractility can decrease silently and irreversibly in chronic MR. For this reason, increasingly earlier surgical interventions for less severe degrees of MR are being recommended (Fig. 13D).

LA Size

The LA will dilate in response to chronic volume and pressure overload. Its dimensions may help to assess MR severity and chronicity (Figs. 15 and 16). Acute-onset severe MR, as occurs with papillary muscle rupture, does not cause LA dilatation. The excess regurgitant blood entering the small noncompliant atrium causes acute increase in LA pressures and can precipitate acute pulmonary hypertension and right heart pressure overload. Increased LA pressures and systolic flow into reversal pulmonary veins may be the only echocardiographic findings that document the severity of acute-onset MR. LA size may predict the onset of atrial fibrillation, but is otherwise of little prognostic value in MR itself, in the absence of heart failure. Measurements should be adjusted for age and body surface area.

doppler methods for grading mr severity

Color Flow Doppler Parameters

Color flow Doppler imaging is perhaps the most intuitive of all measures, is useful for detecting the jet origin, direction, and spatial relationships and has excellent sensitivity and specificity. Each of the three components

Doppler Mapping Jet
Fig. 15. (A) Measuring left atrial size. (B) Left atrial measurements. Values from cardiac ultrasound laboratory, Massachusetts General Hospital.

of the MR jet—flow convergence zone, vena contracta, and jet profile—can provide a semiquantitative or quantitative measure of MR severity (Fig. 17).

MR jets are best assessed using multiple windows to obtain a three-dimensional (3D) perspective. Qualitative estimates of MR jets are categorized on a scale of 0-4: grade 0 = none or trace MR, grade 1 = mild MR through to grade 4 = severe MR (Fig. 18). The notation

1+, 2+, and so on, to denote increasing grades of MR severity is also popular (Table 8).

Color Jet Area

The same color jet profiles can be measured within the LA. Color jet areas are influenced by jet velocity, momentum, and direction. Mild MR jets cover less than 20% of total LA area (or a maximal jet area < 4.0 cm2),

Task Force 118

Fig. 16. Left atrial volume. (Reproduced with permission from Roberto M. Lang et al. Recommendations for chamber quantification. A report from the American Society of Echocardiography's Nomenclature and Standards Committee and the Task Force on Chamber Quantification American Society of Echocardiography, 2005.)

Fig. 16. Left atrial volume. (Reproduced with permission from Roberto M. Lang et al. Recommendations for chamber quantification. A report from the American Society of Echocardiography's Nomenclature and Standards Committee and the Task Force on Chamber Quantification American Society of Echocardiography, 2005.)

Task Force 118
Fig. 17. Mitral regurgitation: color jet profile.

Table 8

Eyeball Estimation of Color Jet Area in MR

Advantages

1. Ease of use

2. Good screening test for mild versus severe regurgitation

3. Evaluate in at least 2 views (PLAX, A4C, A3, or A2C)

4. Best "estimate" using scale of 1+ (mild) to 4+ (severe)

Disadvantages

1. Can be unreliable for estimation of regurgitation severity

2. Not good at distinguishing moderate MR from mild or severe MR

3. Influenced by transducer frequency and other instrument settings, especially pulse repetition frequency and color gain

4. Size of color jet may be misleading, especially with eccentric jets

Color Doppler

Fig. 18. Schema illustration of jet profile of mitral regurgitation as viewed from the apical four-chamber window. Color Doppler mapping allows visualization of the spatial distribution of blood flow within the heart by displaying the blood flow velocities in terms of ranges of color. Visual estimation of the jet profile is a simple method of estimating mitral regurgitation severity. Color Doppler mapping, however, is very sensitive to instrument settings, hemodynamic status, regurgitant orifice geometry (affects jet eccentricity), and atrial dynamics—e.g., wall constraint, wall impingement, and the presence of secondary flow.

Fig. 18. Schema illustration of jet profile of mitral regurgitation as viewed from the apical four-chamber window. Color Doppler mapping allows visualization of the spatial distribution of blood flow within the heart by displaying the blood flow velocities in terms of ranges of color. Visual estimation of the jet profile is a simple method of estimating mitral regurgitation severity. Color Doppler mapping, however, is very sensitive to instrument settings, hemodynamic status, regurgitant orifice geometry (affects jet eccentricity), and atrial dynamics—e.g., wall constraint, wall impingement, and the presence of secondary flow.

with severe MR jets more than 40% of total LA area (or a maximal jet area > 10 cm2). At least two orthogonal views should be used with the Nyquist limit set at 50-60 cm/s (Fig. 19; please see companion DVD for corresponding video).

Larger color jet areas indicate more severe MR when the jet is centrally directed, but can be misleading with eccentrically directed jets. Hugging or entrainment (Coanda effect) of the eccentric jet to the LA wall results in smaller jet areas even when MR is severe. A thorough evaluation of eccentrically directed jets should include evaluation for etiologies, such as a flail leaflet, prolapse or perforation. Severe MR with eccentrically directed jets sometimes exhibit a "wrap around" effect in the LA (Fig. 20).

In acute MR, even centrally directed jets may be misleadingly small. A small nondilated atrium in the setting of acute regurgitation constrains the regurgitant jet momentum and hence the visible color jet area.

Vena Contracta Width

The vena contracta is the narrow neck of the MR jet as it traverses the regurgitant orifice (Fig. 21). The vena contracta measured from the parasternal long-axis view is best optimized by using a narrow sector scan, optimal color gain, and Nyquist limit between 40-70 cm/s. The vena contracta appears as the well-defined light blue or light yellow high-velocity core on the red-blue color Doppler scale. This portion of the regurgitant jet, unlike the flow convergence zone and the distal turbulent jet profile, most closely mirrors that of the actual regurgitant orifice. It is, therefore, a more reliable marker of MR severity with significant advantages over other methods provided that the recommended technique is used (Table 9).

A single vena contracta width (VCW) measurement, however, is a 2D snapshot across an elongate regurgitant orifice area that extends to a variable degree along the crescenticleaflet coaptation line (Fig. 1B). A closer approximation of the actual regurgitant orifice area is best obtained by scanning through multiple planes and selecting the greatest VCW. Such considerations are better appreciated and measured on 3D echocardiogra-phy. Averaging VCW measurements over at least three beats and using two orthogonal planes is recommended. A VCW less than 0.3 cm indicates mild MR; a VCW more than 0.7 cm indicates severe regurgitation (Fig. 21; Table 5).

The effective regurgitant orifice area (EROA)—a marker of MR severity that is less affected by loading conditions—can be calculated from the VCW using the formula:

Good agreement exists between this EROA formula and other validated measures of MR severity. VCW measurements are not valid for assessing MR severity with multiple MR jets (Fig. 22).

Proximal Flow Convergence and Proximal Isovelocity Surface Area

According to fluid dynamics, fluids within an enclosure stream symmetrically toward a narrowed outlet or orifice in near concentric isovelocity zones. This is akin to water being drained from a kitchen sink, or when water from a lake flows into a narrowed estuary (Fig. 23). The same principle applies when blood in the LV stream converges toward a narrowed (stenosed or regurgitant) orifice. This method can be used for estimating the area of the regurgitant orifice—which is hard to measure directly because actual regurgitant orifice is dynamic, functional, and 3D. As regurgitant blood converges toward the regurgitant orifice at the proximal convergence zone, the size and velocity of the innermost shell or hemisphere can be measured (Fig. 24).

Furthermore, according to the continuity principle (see Chapter 11, Fig. 11), the amount of fluid that passes through the regurgitant orifice is the same

Pisa Measurement

amount that flows in the regurgitant jet (the law of conservation of mass). Therefore, total flow at the proximal isovelocity surface area (PISA) will equal total flow in the distal MR jet.

The apical four-chamber view is recommended for optimal visualization of the MR jet PISA measurement.

The area of interest is optimized by lowering imaging depth and lowering the Nyquist limit (on the color Doppler scale) to approx 40 cm/s. The velocity at which the blue-red color shift occurs identifies the PISA shell. The PISA radius (r) is then measured and multiplied by the PISA velocity, i.e., the aliasing velocity

Vena Contracta

Flow

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Responses

  • sari
    What does jet area mean in echo?
    10 months ago

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