Proximal Isovelocity Surface Area Method

Fig. 21. Vena contracta width measurement. Table 9

Vena Contracta Width Measurements in MR

Advantages

Disadvantages

1. Relatively quick and easy to assesses using standard windows

2. Good for extremes of MR (mild and severe MR)

3. Assesses basic size of defect

4. Relatively independent of flow rate, driving pressure, or entrainment (Coanda effect)

5. Not influenced by the presence of another regurgitant leak, for example, aortic regurgitation

6. No need for correction for convergence angle as with proximal isovelocity suface area measurement

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

2. Small values; small measurement errors are multiplied

3. True cross-sectional area may be difficult to obtain—use two apical diameteres

4. VCW measurement—a single temporal measurement

5. Overestimates true regurgitant orifice area—a problem of resolution

6. Not valid for multiple MR jets

MR, mitral regurgitation.

(Nyquist limit)—VALIAS —to give the regurgitant flow rate (Fig. 24). If the base of the PISA hemisphere is not horizontal, it should be corrected to 180°.

Reguritant flow rate = 2nr2 x VALIAS (mL/s)

From this, the EROA can be quantified using the continuity principle equation (Figs. 25 and 26; see Chapter 11, Fig. 11) for flow rate: Area1 x Velocity1 = Area2 x Velocity2; and VMAX is the peak velocity of the MR jet on CW Doppler:

EROA = 2nr2 x Valias/v MAX

Regurgitant volume and the regurgitant fraction can then be calculated (Fig. 27).

The PISA method can also be assessed by trans-esophageal echocardiography when indicated (Fig. 28).

The PISA method makes several assumptions (Table 10)—many of which are violated in the clinical setting. 3D echocardiography may ultimately assist in overcoming some of these limitations.

Other Doppler Methods

Systolic Flow Reversal in the Pulmonary Veins

The presence and the degree of reversal of blood flow from the LA into the pulmonary veins can indicate the hemodynamic impact of the MR jet. Visualization of flow reversal into one or more pulmonary veins on i

Systole

Mitral Regurgitation Jet Area

I Apical long axis

Fig. 22. Narrow sector scan (color flow Doppler) showing two separate mitral regurgitant (MR) jets viewed from the apical long axis view. This was confirmed when viewed from multiple windows. When assessing multiple MR jets, each jet should be analyzed and reported separately. Vena contract widths (VCW) measurements are invalid when multiple MR jets are present.

color flow Doppler, or more reliably—pulsed Doppler evidence of flow reversal into the pulmonary veins are measures of MR severity (Fig. 29). In normal individuals, a positive systolic (S) wave followed by a smaller positive diastolic (D) wave is seen, but with moderate or severe MR, blunting or reversal of this pattern may be seen (see Chapter 6). Systolic flow reversal may be indicative of severe MR even if the color jet area suggests milder disease.

Atrial fibrillation and elevated LA pressures from any cause can blunt forward systolic pulmonary vein flow. Blunting of pulmonary forward flow may lack specificity, but is nonetheless a useful parameter that provides information independent from color Doppler methods used to assess MR severity.

Mitral E-Point Velocity

The progressive increase in trans-mitral flow that occurs with increasing MR severity can be detected as higher flow velocities during early diastolic filling. A dominant E-wave more than 1.2 m/s may indicate more severe MR, providing there is no concomitant mitral stenosis (Fig. 30).

Continuous-Wave Jet Intensity and Morphology

Peak MR jet velocities by continuous-wave (CW) Doppler typically range between 4 and 6 m/s—a reflection of the systolic pressure gradient between LV and LA. If the blood pressure at the time of the study is low, the peak velocities and gradients will also be low. Peak MR jet velocities alone, therefore, are not reliable measures of MR severity.

The signal intensity (jet density) of the CW envelope of the MR jet can be a guide to MR severity, but this should be assessed relative to the density of antegrade flow signal (mitral inflow). A dense mitral regurgitant signal with a full envelope of equal in intensity to the antegrade flow signal indicates more severe regurgitation than a faint signal (Fig. 31).

The CW Doppler envelope may show blunting or notching of the CW envelope. This results from the rapid surge in LA pressures in severe MR—the atrial V-wave (Fig. 32). This may reflect an LA that has not yet dilated and show discordance with color Doppler severity.

LV Systolic Performance

The rate of rise of LV systolic pressure over time (dP/dT) may be a useful index of the LV systolic function in MR (Fig. 33). In patients with preserved systolic function, the MR jet velocity shows a rapidly early in systole. A lower dP/dT can unmask patients with declining systolic function, and therefore serve as a guide to more aggressive intervention, especially when supported by other indicators of severity.

Integrating Indices of Severity

Integrated scores have been devised to improve the diagnostic validity of parameters of MR severity. The MR index is a composite score comprising six echocar-diographic parameters—jet length, PISA, CW jet density, pulmonary artery systolic pressure, pulsed wave Doppler, pulmonary vein flow pattern, and LA size. Such scores provide a better overall assessment of MR

Proximal Isovelocity Surface Area
Fig. 23. The proximal isovelocity surface area method. Fluids within a confined space accelerate toward an outlet or orifice in concentric isovelocities. A familiar example of this occurs when water is released from a kitchen sink.

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Responses

  • pierino
    Does the machine sets up the nyquist limit when measuring proximal isovelocity surface area?
    6 months ago

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