M-Mode, color flow Doppler, pulse wave Doppler and Continuous wave Doppler are utilized to assess chamber dimensions, flow dynamics, valve area and device placement. Advanced TEE includes more input into surgical and interventional decision-making such that functioning at this expert level requires a keen knowledge of this aspect of ultrasound.
M-Mode refers to "motion over time" such that the image is displayed along a chosen time line. In this video M-Mode demonstrates motion over time for poor ventricular function with EF 15%. The change in diameter is used to calculate EF, here listed as around 15-16%.
The Doppler Effect states that when a sonic source is moving towards or away from a stationary listening device/probe the relative frequency of the ultrasound wave will be shifted according to the velocity of the source. As the ultrasound wave returns the frequency will be altered in our case based on the speed and direction of the travelling red blood cell. The ultrasound machine can use the frequency shift to calculate changes in velocity and direction which are displayed as different colors and degrees/shades of color. The pneumonic is "Blue Away Red Towards" (BART). In this midesophageal four chamber view, normal blood flow from the atria into the ventricles is blue (away from the transducer) while blood flow through the LVOT is red (towards the transducer).
Color doppler overlays information about the velocity of moving objects (e.g., red blood cells) over a B-mode or 2-D image. In this case a sample volume is placed over an area of interest, the mitral valve. The ultrasound machine then uses the frequency and amplitude of returning echoes to display information regarding flow (direction and velocity) in that region. The shade is generally lighter for lower flows and more intense for higher velocity flows. The velocity is very high in this regurgitant jet from a prolapsed P2 mitral valve leaflet.
Color doppler is useful to interrogate chambers for the presence or absence of blood flow (e,g., left atrial appendage) and quickly investigate other areas for turbulent flow (e.g., LVOT, aortic valve). Although some quantitative information may be gained by use of color Doppler, it is usually more qualitative as pulse wave Doppler and Continuous wave Doppler offer specific velocities and flows. Here you have some insane velocities and bidirectional flow in this midesophageal four chamber view with tricuspid regurgitation, mitral regurgitation and HOCM with high velocity LVOT flow.
Pulse wave Doppler is used to determine frequency shifts within a specific area of interest. B-mode imaging (2-D echo) is used to set the location of a sample volume or "gate" for interrogation with pulsed wave Doppler. The probe then transmits short sound pulses and waits for the returning echo. Since the speed in soft tissues (e.g., mitral valve) is known the probe can isolate the returning echoes from the sample volume or gate. In this manner velocity and direction and can be "carved out" and a narrow band of velocities displayed within a narrow range. A major limitation of pulse wave Doppler involves the number of pulses that can be sent over time (pulse repetition frequency). Thus aliasing occurs at velocities greater than 1 meter/second and PW Doppler may not be used with higher gradients such as encountered with aortic stenosis and mitral stenosis. In these cases continuous wave Doppler is required, which is more complex and a discrete sample gate/volume is unavailable.
In this example, color and pulse wave Doppler are used to determine direction and velocity of blood flow across an atrial septal defect, in this case mostly left to right shunt.
Pulse wave Doppler has high utility in assessing diastolic compliance, seen here in a normal left ventricle with a normal E:A ratio.
Diastolic relaxation and early filling is impaired in noncompliant ventricles such as this patient with aortic stenosis. Here the filling is greater with atrial systole such that the velocity is higher during atrial systole ("E to A" is reversed), designating diastolic dysfunction.
Continuous wave Doppler is used to determine frequency shifts/velocities along an entire path of interrogation instead of a discrete sample volume/gate. As there are separate transmission and reception transducers, sound can be transmitted and received continuously. Because all velocities along a given path are obtained the waveform appears "filled in" instead of empty as with PW Doppler. While CW Doppler can measure very high velocities it is unable to pinpoint exactly where these velocities occur, and the beam of insnation (origin) must be lined up with the path of blood flow. This requires a specific ultrasound view, such as the deep transgastric long axis view for measuring aortic valve stenosis. In this normal LV, the velocity across the valve is one meter/second, with a minimal gradient across the valve (referring to the difference between LV systolic and aorta systolic pressure).
Velocities across the aortic valve typically are less than 2 meters/second, such that gradients including prosthetic valves are less than 20 mmHg. As velocities across the aortic valve with aortic stenosis exceed 1 meter/second, continuous wave Doppler must be used. In this patient with severe aortic stenosis the velocity is almost 5 meters/second, signifying a high gradient across the valve almost 100 mmHg). This calculation is made using the modified Bernoulli equation, (velocity squared) x 4=gradient, the gradient is 97 mmHg.
Typically gradients across the mitral valve are less than 5 mmHg including prosthetic mitral valves. In this patient with severe mitral stenosis the gradient is much higher than 5 mmHg and signifies clinically significant MS. Using the modified Bernoulli equation again, with a velocity of 1.7 meters/second, this patient has a gradient of 11.5 mmHg.
Differences between 2-D and 3-D TEE involve image acquisition and processing. 2-D TEE involves standard sector planes or narrow "slices" while 3-D TEE involves entire volumes involving multiple 2-D planes. In addition the display and processing for 3-D may be live 3-D (pyramid volume as seen in this 3-D full volume ME 4 here), 3-D zoom of a volume such as the mitral or aortic valve or full volume or zoom with color flow mapping.
Again a 3D zoom of the mitral valve this time in a patient with mitral regurgitation. The outpouching of the P2 scallop of the posterior mitral leaflet demonstrates the mitral regurgitation.
In this 3D zoom of a patient with mitral stenosis a small orifice is demonstrating, typical with mitral valve stenosis.
3D also offers color Doppler (Color Flow Mapping) to further aid in diagnosis and assessing degree of pathology and impact of any intervention
TrueVue is a 3D view that is stunning in detail but typically only useful for en face views of structures with confluent depths such as the mitral valve. Advantages include highly realistic imaging with sophisticated lighting and shadowing.
While only 25% of all aortic valve may be viewed using 3D Zoom, multiplane rendering /3DQ allows exact measurements.
3D TEE is a crucial imaging tool used for providing en face views of the defect, its size, shape and surrounding anatomy.
Along with increasing the accuracy of sizing (instead of measuring at 0,45,90 and 135 degrees), 3D TEE improves the ability to assess for device position, anchoring, size and seal
Tool or Toy? Depends on your skill set and the utility of 3D over 2D datasets.
Long video but you need this skill set to do interventional and practice advanced TEE
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