Flow Appearance
The baseline is placed in the middle of the spectral image. Filling of the left atrium and auricle during ventricular systole is displayed above the baseline (Figure 3.64). An electrocardiogram (ECG) helps identify this systolic flow. Negative flow is displayed during atrial emptying late in diastole. Sometimes there are other positive and negative flows on this spectral image so an ECG identifies the correct flow profiles to use.
Figure 3.64 Filling of the left atrium and auricle during ventricular systole is seen above the baseline (2) and coincides with the QRS complex of the electrocardiogram. Negative flow (1) is displayed during atrial emptying late in diastole coinciding with the P wave of the electrocardiogram.
Tissue Doppler Imaging
Introduction
Returning echoes are constantly bombarding the computer in the ultrasound machine. Until recently filters were in place to eliminate low frequency high amplitude information received from myocardial reflection of sound. Reflection of sound from blood is high frequency and low amplitude. Normal blood flow is typically less than 200 cm/sec while myocardial velocity of motion is usually less than 20 cm/sec. Tissue Doppler imaging (TDI) utilizes this low frequency high amplitude sound to record myocardial velocity during systole and diastole. Pulsed-wave TDI can be obtained in real time by placing a gate over a portion of myocardium and recording positive and negative frequency shifts (65– 74).
Color TDI is obtained by placing a sector of color over the myocardium and saving a video loop of information for off line analysis. After retrieving the color TDI study from computer memory, a gate is placed anywhere color was superimposed over the myocardium, and its corresponding systolic and diastolic movements are displayed. The advantage of color TDI is that the myocardial motion from the entire area of myocardium under the color sector color can be analyzed from one stored loop of video. Gates simply need to be placed over different areas of myocardium under the color sector, and motion information is displayed (Figure 3.65). Information can be displayed simultaneously from
different parts of the ventricle at the same point in the cardiac cycle.
Figure 3.65 (A) Color TDI is obtained by placing a sector of color over the myocardium and saving a video loop of information for off line analysis. This is a systolic frame with red color indicating upward movement. (B) After retrieving the color TDI study from computer memory a gate is placed anywhere color was superimposed over the myocardium and its corresponding systolic and diastolic movements are displayed. Here two gates are placed over the lateral wall of the left ventricle, and myocardial motion is displayed simultaneously from both locations on the right side of the image. (C) Two gates are placed over the lateral wall of the left ventricle on a transverse view, and myocardial motion is displayed simultaneously from both locations on the right side of the image. LV = left ventricle, RV = right ventricle, RA = right atrium, LA = left atrium, S′ = systolic motion, E′ = early diastolic motion, A′ = late diastolic motion.
Pulsed-wave TDI provides information only from one gate location in real time, and the gate must be moved to another location to interrogate any other area of the myocardium (Figure 3.66). Myocardial velocity obtained from PW TDI is usually higher than the velocities obtained off line with color TDI. This is because of better temporal resolution resulting in higher quality velocity
information.
Figure 3.66 Pulsed-wave TDI provides information from one gate location only in real time, and the gate must be moved to another location to interrogate any other area of the myocardium. Here the PW TDI gate is placed at the mitral annulus on an apical four-chamber view. Myocardial motion is displayed to the right. LV = left ventricle, LA = left atrium, S′ = systole, E′ = early diastolic motion, A′ = late diastolic motion.
Imaging Plane Used
Tissue Doppler information can be obtained from a variety of imaging planes. Longitudinal myocardial velocity is obtained from apical four-chamber views of the heart. The lateral walls of the left and right ventricular chamber or the interventricular septum are positioned on the image so that the color sector or Doppler cursor line up parallel with the length of the wall or septum (Figures 3.65, 3.66, 3.67). The loop is stored if using color TDI, and the gate can be place anywhere under the color sector at a later time. PW TDI is immediately obtained by placing the Doppler gate at any point along the wall or septum. Circumferential radial myocardial velocity can be obtained from right parasternal transverse or sagittal imaging planes (Figure 3.67).
Figure 3.67 The lateral walls of the left and right ventricular chamber or the interventricular septum are positioned on the sector so that the color sector or Doppler cursor line up parallel with the length of the wall or septum. Here the color sector is aligned with the right ventricular wall, and a PW TDI display is obtained. RV = right ventricle, RA = right atrium, LA = left atrium, S′ = systolic motion, E′ = early diastolic motion, A′ = late diastolic motion.
Tissue Doppler imaging is an option that can be added to ultrasound equipment. Theoretically, however, by manipulating the filters and changing the pulse repetition frequency, PW tissue velocity information can be obtained from equipment with-out the added option. Turn down the filter settings while in spectral Doppler mode and change the PRF (velocity range) to display low velocity flow of 20 to 30 cm/sec. Place the pulsed-wave gate over the myocardium and press the spectral display button to see the spectral image of myocardial motion under the gate.
Spectral Appearance
Place the baseline in the middle of the spectral display. Systolic contraction (S′ or Sm) (sometimes labeled Sa if the gate is placed at the annulus of an AV valve) results in a positive frequency shift. Diastolic motion of the myocardium is negative and has two phases: early diastolic motion (E′ or Em) (sometimes labeled Ea if the gate is placed at the AV annulus) and late diastolic motion secondary to the atrial contraction (A′ or Am) (sometimes labeled Aa if the gate is placed at the AV annulus) (Figures 3.65, 3.66, 3.67). Between the diastolic and systolic waves, isovolumic contraction and relaxation times can be identified. These systolic and diastolic waves are similar in appearance with slight changes in velocity whether the motion is recorded from longitudinal or circumferential fibers. Fast heart rates, just as with transmitral and trans tricuspid flows will result in superimposed E′ and A′ (Figure 3.68).
Figure 3.68 Fast heart rates, just as with transmitral and trans tricuspid flows, will result in superimposed E′ and A′ myocardial motion. S′ = systolic motion, EA′ = summated early diastolic and late diastolic motion.
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