Psax Echocardiography

Nonimaging Transducer
Fig. 5. (See legend, facing page)

acquired in the apical five-chamber, right parasternal long axis, or suprasternal views to obtain the highest velocities across the valve. The maximum velocity obtained is highly dependent on accurate transducer positioning, and will be underestimated when Doppler beam angle deviates from that of blood flowing through the stenotic valve (Fig. 8). A nonimaging probe can be used if inadequate envelopes are found with the duplex imaging transducer.

The calculation of transvalvular pressure gradients is based upon the Bernoulli principle. The modified Bernoulli principle relates the transaortic pressure gradient to the square of the maximal velocity found on CW Doppler: P = 4V2, and is used when the velocity of blood proximal to the stenosis is negligible. In significant aortic stenosis, high gradients across the aortic valve can be seen. The relationship is accurate

Aortic Stenosis Systolic Doming

Fig. 5. Bicuspid aortic valve during diastole (A) and systole (B) in parasternal short-axis (PSAX) view. Note horizontal commissure (arrow) in diastole and "fish mouth" appearance during systole. (C,D) Systolic doming of bicuspid aortic valve during systole (parasternal long-axis view [PLAX]). (Please see companion DVD for corresponding video.)

Fig. 5. Bicuspid aortic valve during diastole (A) and systole (B) in parasternal short-axis (PSAX) view. Note horizontal commissure (arrow) in diastole and "fish mouth" appearance during systole. (C,D) Systolic doming of bicuspid aortic valve during systole (parasternal long-axis view [PLAX]). (Please see companion DVD for corresponding video.)

End-Diastole

Echo Aortic Stenosis Gradient

Fig. 6. Aortic stenosis showing restricted leaflet opening (arrow) during systole (parasternal long-axis view [PLAX]). Left ventricular ejection fraction was reduced, hence "low stroke volume-low gradient" aortic stenosis. (Please see companion DVD for corresponding video.)

PLAX I PLAX

Fig. 6. Aortic stenosis showing restricted leaflet opening (arrow) during systole (parasternal long-axis view [PLAX]). Left ventricular ejection fraction was reduced, hence "low stroke volume-low gradient" aortic stenosis. (Please see companion DVD for corresponding video.)

when the velocity proximal to the stenosis is less than 1.5 m/s. Should the velocity in the left ventricular outflow tract (LVOT) exceed 1.5 m/s, then the long version of the Bernoulli equation should be used to calculate the transaortic gradient. Therefore:

Transaortic pressure gradient = 4 (Vmax2 - VLVOT2) when VLVOT > 1.5 m/sec

In most cases, the modified Bernoulli equation is an accurate and simple measure of the peak instantaneous transaortic pressure gradient.

Peak transaortic gradient measured by Doppler should be differentiated from the peak-to-peak gradient obtained at cardiac catheterization. Hemodynamically, the peak-to-peak gradient measures the difference between the peak left ventricular pressure and the peak aortic pressure—which are not measured simultaneously. Therefore, peak-to-peak gradients are not physiological, and no Doppler measurement exactly corresponds to this measurement in the cathetherization laboratory. However, mean gradients across the aortic valve are similar when measured by Doppler and by cardiac catheterization.

The Doppler derived mean gradient is the average gradient over the systolic ejection period. This is usually calculated by tracing the CW envelope obtained across the aortic valve, and the numerical values are automatically calculated by the machine's software

Mode Bicuspid Aortic Valve Eccentric
Fig. 7. M-mode through aortic valve showing characteristic thickening of valve leaflets in aortic stenosis (compare Chapter 3, Fig. 14A).

Table 1

Two-Dimensional Characteristics of Classic Aortic Stenosis According to Disease Etiology

Calcific degenerative Rheumatic Bicuspid

Table 1

Two-Dimensional Characteristics of Classic Aortic Stenosis According to Disease Etiology

Calcific degenerative Rheumatic Bicuspid

Eccentric closure line

No

No

Yes

in the parasternal

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