Echo Mv Area By Pressure Half Time

Echocardiography Images

Fig. 4. Apical four-chamber views of severe longstanding mitral stenosis in a 44-yr-old Vietnamese female. (A) Note marked thickening and calcification of mitral valve leaflets (arrows) and subvalvular apparatus accompanied by marked distortion in left heart chamber architecture. (B) This patient had severe pulmonary hypertension with grossly dilated right heart chambers and severe tricuspid regurgitation (arrow).

Mitral Stenosis Severity

Normal...

,„ 4.0 - 6.0 cm!

Mild

... 1.6 - 2.0 cm2

Moderate

...1.1 -1.5 cm

Severe

<1.0 cm2

Mitral Stenosis Severity

Mitral Velocity Time Integral
Fig. 5. Measurement of pressure gradients in mitral stenosis. Tracing the continuous-wave Doppler velocity time integral (VTI) envelope across stenotic mitral valve gives maximum and mean pressure gradients.

two gradients, the mean gradient is most frequently used clinically. The peak gradient can be calculated from the modified Bernoulli equation: P = 4 V2, where V is the peak velocity as measured by CW Doppler. The mean gradient is calculated from the time velocity integral across the MV as measured by CW Doppler. Although there are no absolute pressure gradient cutoffs demarcating the severity of stenosis, some general categories for the mean gradient are as follows:

Mean gradient

0-5 mmHg (mild stenosis) 5-10 mmHg (moderate stenosis) >10 mmHg (severe stenosis)

Severe Mitral Stenosis

Fig. 6. Mean pressure gradient. Continuous-wave Doppler patterns in a patient with severe mitral stenosis. Atrial fibrillation is present and is reflected in marked variation in the tracings as shown in A and B (mean gradient approx 12 mmHg). In such patients, gradients should be averaged over 5-10 cardiac cycles. Mitral valve area calculated by the pressure half-time method (Figs. 8 and 9) was ~0.8 cm2.

Fig. 6. Mean pressure gradient. Continuous-wave Doppler patterns in a patient with severe mitral stenosis. Atrial fibrillation is present and is reflected in marked variation in the tracings as shown in A and B (mean gradient approx 12 mmHg). In such patients, gradients should be averaged over 5-10 cardiac cycles. Mitral valve area calculated by the pressure half-time method (Figs. 8 and 9) was ~0.8 cm2.

Table 4

Mean Pressure Gradient: Pitfalls

• Flow-rate dependent, e.g., affected by volume depletion or anemia

• Low cardiac output states and bradycardia may lead to low mean pressure gradient calculations in the presence of severe mitral stenosis

• Heart rate dependent, e.g., affected by exercise

• Atrial fibrillation: need to average over 5 to 10 cardiac cycles

• Doppler beam alignment dependent, especially with eccentric jets

A key caveat: pressure gradients are influenced by both the MV area, as previously discussed, and the amount of blood flow across the valve, as an increase in flow will yield a higher gradient for a given valve area. Therefore, using pressure gradients alone to estimate the severity of stenosis can be problematic. For example, it is possible to observe markedly elevated gradients with mild to moderate mitral stenosis in the setting of high flow (e.g., anemia) and to observe lower gradients with severe stenosis in the setting of low flow (although the latter example is more commonly an issue with aortic stenosis than with mitral stenosis) (Table 4).

Table 5

Mitral Valve Area: Quantification

• Two-dimensional planimetry

• Mean pressure gradient

• Pressure half-time

• Continuity equation

• Proximal isovelocity surface area assessment of mitral valve area

There are a number of ways to determine the MV area (Table 5).

Planimetry

The orifice of the MV can be well visualized in the parasternal short-axis view. Consequently, direct measurement of the orifice area via planimetry is possible (Fig. 7). There is reasonable correlation between this echocardiographic technique and the mitral valve area determined at both the time of surgery and during cardiac catheterization. When assessing the MV in this way, it is necessary for the sonographer to slowly scan up and down in the plane of the MV in order to identify the smallest orifice. Otherwise, it is possible to overestimate the valve area. In addition, the imaging plane

Mva Pressure Half Time
Fig. 7. Mitral valve area by two-dimensional planimetry.

should run parallel to the valve orifice, as off-axis views will likely lead to an overestimation of the true valve area (Table 6). Also, image acquisition should occur early in diastole, as the valve orifice is maximally dilated at that time.

Pressure Half-Time (P1/2)

The P1/2 is the time it takes for the pressure gradient across the MV to decrease by half (Fig. 8). The valve area is calculated using the equation, MVA = 220/P1/2 where MVA = MV area and P1/2 = pressure half-time (Figs. 9 and 10). This method correlates well with the invasive measurement of MVA. The concept behind the P1/2 method is as follows: the LV fills when blood from the LA crosses the MV during diastole. As the MV orifice area decreases, blood flow from the LA to the LV becomes increasingly compromised, and the time required for blood to flow from LA to LV becomes longer. This decreasing valve area is reflected in the length of time required for the pressure gradient across the MV to fall during diastole. The smaller the valve orifice, the longer it takes for the pressure gradient to decrease.

In short, MV area is inversely related to the pressure half-time by the formula MVA = 220/P1/2. It is important to remember that what is measured is the time it takes for the pressure to reach one-half of the original pressure. Pressure and velocity are related by the Bernoulli equation (pressure = 4 x velocity2).

Table 6

Two-Dimensional Planimetry: Pitfalls

Poor image quality Gross distortion of leaflet anatomy Improper tomographic plane Inadequate two-dimensional gain settings Heavy annular and leaflet calcification Postmitral commissurotomy

There are a number of important caveats (Table 7) to consider when assessing MV area by P1/2:

1. Atrial fibrillation. Although the P1/2 is largely independent of heart rate, if the heart rate for any given cycle is markedly elevated, a clear image of the pressure gradient fall may not be visible. Therefore, during atrial fibrillation it may be necessary to evaluate many beats (most labs assess at least 5 and often up to 10 beats).

2. Aortic regurgitation or other conditions that increase left ventricular end-diastolic pressure. Aortic regurgitation can shorten the time it takes for the LV to fill during diastole, as the LV is filled with blood from both the LA and the aorta. Therefore, the P1/2 time may be "artificially" decreased leading to an overes-timation of the MV area. This overestimation typically becomes clinically relevant in the setting of moderate to severe aortic regurgitation. In other

Pressure Half Time
Fig. 8. PHT measures how quickly the peak pressure across the mitral valve drops by half. Does the peak transmittal gradient drop quickly or does it take a longer time? The longer the PHT, the worse the stenosis.

Pressure Half Time (PHT)

time . 3bo ssc Empirical Formula

TIME . H30 sac PHT

MVÂ7P«Ï3TË34 MV CEC slope SED. MV P^t max v 3 3 5.

Pressure Half Time Formula

Fig. 9. The PHT is a reflection of the rate at which left atrial and ventricular pressures equilbrate during diastole. Mitral valve area is calculated as 220 divided by the PHT.

conditions in which left ventricular end-diastolic pressure is elevated, such as restrictive cardiomyopa-thy or ischemic heart disease, the rate of equilibration between LA and LV is increased, and the estimation of MV area by P1/2 can also be falsely increased. Post PMV. A key assumption for this equation is that the P1/2 measurement is largely independent of LA and left ventricular compliance. After PMV, this assumption is not valid for approx 72 h as the chambers re-equilibrate. Therefore, during that time following mitral valvuloplasty, the P1/2 method is not considered valid.

Continuity Equation

The MV orifice area can be determined by the continuity principle (Fig. 11). According to this principle,

Pressure Half Time
Fig. 10. Pressure half-time (PHT). Mitral stenosis can then be categorized as mild, moderate, or severe as shown. The PHT in this patient measured 187 ms—indicating moderate mitral stenosis.

Table 7

Pressure Half-Time Method: Pitfalls and Caveats

Flow-rate dependent, e.g., affected by volume depletion or anemia

Heart rate dependent, e.g., affected by exercise Atrial fibrillation: need to average over 5 to 10 cardiac cycles

Doppler beam alignment dependent, especially with eccentric jets

Measure P1/2 from slope with longer duration whenever deceleration slopes differ

P1/2 can be prolonged (i.e., increased) in nonmitral stenotic states, e.g., diastolic dysfunction, but low E

peak velocities may accompany the latter

P1/2 method is unreliable in patients with severe aortic regurgitation or immediately post-balloon valvuloplasty

Atrial septal defects, immediate post-mitral valvotomy, and a noncompliant left atrium shorten P1/2. This leads to overestimation of MVA

Changes that prolong P1/2, e.g., a chronically dilated and overcompliant left atrium leads to underestimation of MVA.

MVA, mitral valve area; P , pressure half-time.

flow at any point along a tube is constant (i.e., flow [Q] = VTI1 • A1 = VTI2 • A2, where VTI = velocity time integral at pointx and A = area at pointx). Therefore, if we know the flow at another point in the "tube" (or heart), e.g., the left ventricular outflow track (LVOT),

Left Ventricular Outflow Track

LVOT, left ventricular out now tract; VTI. velocity time integral; T[ (pi) = 3.14 Fig. 11. Continuity equation in mitral stenosis.

and we know the velocity time integral across the MV as measured by CW Doppler, we can solve for the MV area. Specifically, Q = VTI, VTI

LVOT ' AreaLVOT= VTIMV • AeaMV. Or, lvot/VTImv. This method correlates well with the invasive assessment of MVA.

One key limitation of this method is that if there is regurgitation through the MV or the comparison point (e.g., aortic or pulmonic outflow tract), flow will not be the same at those two points (Table 8). Therefore, the estimation of the MV area may not be accurate.

Flow Towards Transducer

Color Slow Doppler ~~ Scale Slow

Flow

Away from Transducer

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Responses

  • What do you measure in cw doppler in echo?
    3 years ago
  • lorena
    How to calculate pressure half time from slope?
    2 years ago
  • ROSE
    How to measure pressure half time by echo?
    1 year ago
  • Salvatore Pugliesi
    What can cause mitral valve pressure half time to be falsely low?
    11 months ago
  • Sarama
    How to measure mitral valve pressure half time?
    3 months ago
  • Abbi
    How to measure pressure half time mitral stenosis?
    2 months ago
  • theresa
    How to measure mean mitral valve gradient?
    2 months ago
  • gilly
    What is the equation for pressure half time?
    15 days ago

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