signal as is seen in this right parasternal transverse view of the artery in a dog. PA = pulmonary artery, RV = right ventricle, RA = right atrium, LA = left atrium, AO = aorta, RMPA = right main pulmonary artery.
Figure 3.37 Trivial to mild pulmonary insufficiency is common in all animals. Here a trivial amount of pulmonary insufficiency (arrow) is seen on the right parasternal oblique view of the pulmonary artery in a horse. RV = right ventricle, LV = left ventricle, PV = pulmonic valve, PA = pulmonary artery.
Spectral Doppler
Introduction
Spectral Doppler examination of the heart uses imaging planes that align the sound beam as parallel
with the direction of flow as possible. This is the opposite of sound beam alignment, which will produce the best two-dimensional images. Remember that sound is reflected directly back to the transducer if it strikes the structure with a 90° angle of incidence. Doppler however is dependent upon the angle of incidence in a different manner. The farther away from parallel to flow the sound beam is, the greater the error introduced into defining the maximum velocity. Apical views are therefore the appropriate views for obtaining flow information for mitral and aortic valves. Parasternal long-axis planes are useful when interrogating the pulmonary artery or at times the tricuspid valve. Valvular insufficiencies are recorded in whatever plane aligns the color-flow jet direction with the spectral Doppler cursor.
When simply determining the presence or absence of a regurgitant jet or stenotic lesion is important, then parasternal images may provide that information. It is possible to interrogate the left atrium for instance from parasternal long-axis images and determine the extent of a regurgitant jet into the atrium. Measurement of regurgitant fractions, cardiac outputs, or pressure gradients however, requires parallel alignment with flow, and these are the planes described in the following section (41– 43,45–47,49–53,59).
Controls
Cursor
A cursor is placed along the predicted direction of flow to record velocities (Figure 3.38). The direction of flow can usually be determined with color-flow Doppler (Figure 3.39). Without color guidance however, the flow direction must be determined by interrogating the area carefully.
Figure 3.38 Spectral Doppler interrogation involves placing a cursor representing the Doppler sound beam over the area of interest (thin arrow). A gate placed anywhere along the interrogating Doppler sound beam indicates where blood flow is to be sampled (thick arrow). Angle correction may be used in order to align flow with the Doppler beam (curved arrow).
Figure 3.39 A cursor is placed along the predicted direction of flow to record velocities. The direction of flow can usually be determined with color-flow Doppler. Here a left cranial transverse view shows a color jet of tricuspid regurgitation, which aligns nicely with the Doppler beam (dotted line). Other imaging planes might have shown the regurgitant jet but not aligned it as well. RV = right ventricle, RA = right atrium, AO = aorta, LA = left atrium, TR = tricuspid regurgitant flow.
Gate
The gate is represented by a mark on the cursor line and corresponds to the sampling site (Figure 3.38). Its depth can be adjusted along the cursor with a track ball.
Gate Size
The sample volume size can be adjusted to include more or less area. Increasing the gate size too much will lead to some ambiguity as to exact location of flow information and can introduce too much noise into the signal, but may allow small regurgitant jets to be recorded with greater ease.
Angle Correction
Most machines have a separate line originating from the Doppler cursor (Figure 3.38). This is used to correct for angle when the Doppler cursor cannot be placed parallel to flow. The equipment will take the angle into account when calculating flow velocity and display the pressure gradient accordingly. It is always better to try to align the cursor as parallel to flow as possible instead of using the angle correction since flow velocity alignment errors in the third dimension can be magnified with angle correction.
Baseline
The baseline corresponds to zero velocity. The gate in pulsed-wave Doppler is represented by the baseline and flow moves up or down away from zero velocity. The baseline can be shifted up or down to unwrap mildly aliased signals (Figure 3.40). A baseline positioned at the top of the Doppler spectrum will only display flow away from the gate or transducer but at twice the velocity before
aliasing occurs. The baseline may also be moved down on the spectrum.
Figure 3.40 The baseline may be adjusted up or down in order to reduce the amount of aliasing. (A) Flow exceeding the velocity limit of −104 cm/sec (thin arrow) aliases or “wraps around” the image (thick arrow). (B) When the baseline is moved up, higher flow velocities of 210 cm/sec away from the gate may be recorded (arrow) before aliasing or “wrap around” occurs. The baseline may also be moved down in order to increase maximum positive flow velocities.
Scale
The range of velocities may be changed in both pulsed-wave and continuous-wave displays. Increasing the scale (pulse repetition frequency [PRF]) setting will increase the velocity limits on each side of the baseline and decreasing the scale will decrease the velocity limits (Figure 3.41). The maximum velocity limit (Nyquist limit) in PW Doppler increases with lower frequency transducers or less sampling depth (refer to Chapter 1).
Figure 3.41 Increasing the scale (pulse repetition frequency –[PRF]) setting increases the velocity limits on each side of the baseline, and decreasing the scale decreases the velocity limits. (A) The velocity range is set at −192 cm/sec on this PW display. (B) Flow in this image exceeded the PW Nyquist limit and the velocity range is 8 m/sec using CW Doppler.
Doppler Gain
Similar to other gain controls, this increases or decreases image intensity. Increasing Doppler gain will increase the strength of the returning signal. Turn the gain on high enough to be sure a complete envelope is recorded, and then turn it down until associated noise and mirror image artifacts are minimized.
Wall Filters
Doppler wall filters decrease the amount of low frequency noise that is recorded from moving structures such as cardiac walls and valves. Turning the wall filter up too high however eliminates the start and end of flow information, which is important in some applications (Figure 3.42).
Figure 3.42 (A) This Doppler image of flow has the wall filters turned up high, and low velocities
near the baseline are not recorded (arrow). (B) Decreasing the filter allows low velocity flow signals at the beginning and end of systole to be displayed.
Sweep Speed
This control is the same as the one used for M-mode displays of the heart. Doppler signals can sweep across the display monitor at a rate of 25, 50, or 100 mm/sec. Higher sweep speeds are used to measure time intervals with greater accuracy.
Normal Doppler Flow Profiles and Technique
Introduction
Accurate quantitative information regarding the severity of regurgitation or measurement of left ventricular or systemic pressure is not possible without specifically lining the Doppler beam as parallel with flow as possible. Reports describing imaging planes for Doppler interrogation are available (41–53). Often several planes are available for recording flow, and each should be interrogated to assure the most accurate Doppler recordings. Image quality is sometimes poor when good alignment is achieved, especially in apical five-chamber views, but if alignment with flow is correct then obtaining a good spectral trace is usually still possible.
As already discussed, the presence or absence of abnormal flow can be recorded from many realtime imaging planes. This information is useful, and Doppler interrogation should be attempted in as many planes as possible.
These instructions assume the use of an imaging pulsed-wave or continuous-wave probe. If a nonimaging CW probe is used, the transducer should be placed in the same position as the imaging probe is placed. Often it helps if the two-dimensional image is recorded first in order to localize and orient in your mind the direction necessary for recording the desired flow. The Doppler signal should be
optimized for the crispest sound and the highest velocity.
The decision to use pulsed-wave versus continuous-wave Doppler depends upon the reason for flow interrogation and sometimes on the patient. Recording the highest flow velocity in an aorta or pulmonary artery can be obtained by placing a pulsed-wave gate in the vessel distal to the valve. If a patient is uncooperative or there is a lot of cardiac motion then CW Doppler cursor placed in line with flow in the artery will record the highest velocity without having to place a gate accurately. With PW Doppler if the animal moves and the gate is inadvertently no longer where you think it is, other flow information will be erroneously displayed. If there is outflow tract obstruction a CW gate will automatically record the highest flow. A PW gate placed in the outflow tract will define the aliasing point (where obstruction starts) but will not provide maximum velocity information if the Nyquist limit is exceeded. Pulsed-wave Doppler is always necessary if location is important. This is true of most assessment of diastolic flow and tissue Doppler studies. Always pay attention to where the Doppler cursor is placed. For instance, sometimes CW cursors placed in the aorta will inadvertently also cross over into the left atrium and record mitral regurgitant flow leading to misleading and confusing information about what you think is aortic flow.
Doppler Interrogation
For quantitative information:
Use images that align the Doppler beam parallel with flow.
For nonquantitative information:
Parallel alignment with flow is not necessary.
PW Doppler
Use when site specificity is necessary.
Use when flow is confusing.
Use with low velocity flow.
CW Doppler
Use with high velocity flow.
Use when the animal is moving and the gate does not remain in place.
Aortic Flow
Imaging Plane Used
The optimal plane for recording accurate aortic flow is the apical five-chamber view or the subcostal five-chamber view. The PW Doppler gate is positioned just distal to the aortic valve (Figures 3.43, 3.44). Fan the transducer in and out of the imaging plane in order to satisfy yourself that the highest velocity is being recorded. Remember the image seen on the monitor is two-dimensional, and the Doppler sound beam must interrogate the third dimension by moving side to side and up and down as you scan the aorta. A foreshortened left ventricular chamber appears to have cursor alignment with flow, but the cursor is actually diagonal to the walls of the aorta. Obtain an apical image that shows an LV length about twice as long as width (not possible in severely dilated hearts).
Spectral Doppler
Aortic Flow
Imaging Plane
Left parasternal apical five-chamber view.
Place the gate distal to the aortic valve.
Appearance
Rapid acceleration
Slower deceleration
Asymmetric appearance
Flow starts toward the end of the QRS complex.
Figure 3.43 The optimal recording plane for aortic flow in the small animal is the left parasternal apical five-chamber view. The gate is placed just distal to the aortic valve (arrow). AO = aorta, LV = left ventricle, RV = right ventricle, LA = left atrium, IVS = interventricular septum.
Figure 3.44 Aortic flow in the horse is interrogated from the left parasternal apical five-chamber view. The gate is placed just distal to the aortic valve (arrow). LV = left ventricle, IVS = interventricular septum, AOV = aortic valve, AO = aorta, LA = left atrium, RV = right ventricle.
Flow Appearance
Flow in the aorta is away from the transducer so flow profiles are negative. Flow starts toward the end of the QRS complex and ends just after the T wave (Figure 3.45). There is rapid acceleration, and peak velocity is reached within the first third of systole. There is very little spectral broadening with pulsed-wave Doppler until just after peak velocity is reached. Flow decelerates slower than it accelerated, giving the aortic flow profile an asymmetric appearance. Sometimes diastolic upward flow is seen and this is probably mitral flow as the annulus moves toward the gate during contraction.
Figure 3.45 Aortic flow is negative; it starts just after the QRS complex and continues until after the T wave. Its acceleration phase is rapid, and an asymmetrical appearance is created since deceleration is slower. Shown here are (A) PW aortic flow profiles in a dog, (B) CW aortic flow profiles in a horse, and (C) CW flow profiles in a dog. CW Doppler was used in the horse in order to obtain a stronger spectral signal and in the dog to eliminate an aliased signal.
Left Ventricular Outflow Tract Flow
Imaging Plane Used
Flow within the left ventricular outflow tract also uses the apical five-chamber plane. The gate is positioned just proximal to the aortic valve between the ventricular septum and the open anterior mitral valve leaflet. If a discrete or dynamic subvalvular obstruction is suspected, move the gate up and down the outflow tract in order to record and localize any aliased signals.
Flow Appearance
Outflow tract flow profiles are negative and similar in appearance to aortic flow except that velocities are lower. Negative and positive flow can be seen during diastole depending upon the gate position with respect to mitral inflow. The further the gate moves away from the aortic valve the more upward mitral flow is seen.
Pulmonary Artery Flow
Imaging Plane Used
Pulmonary flow may be recorded from the right parasternal left ventricle with pulmonary artery view, the left parasternal short-axis plane with aorta and pulmonary artery, or the left parasternal long-axis right ventricular outflow view (Figure 3.46). The PW gate is placed distal to the valve within the pulmonary artery.
Figure 3.46 Pulmonary artery flow in the small animal is recorded from one of three possible views. (A) The right parasternal modified long-axis inflow outflow view of the left ventricle with pulmonary artery, (B) the left parasternal short-axis view with aorta and pulmonary artery, or (C) the left parasternal long-axis right ventricular outflow view. The gate is placed distal to the pulmonary valve (arrows). RV = right ventricle, PA = pulmonary artery, PV = pulmonary valve, LV = left ventricle, IVS = interventricular septum, RMPA = right main pulmonary artery, AO = aorta, AOV = aortic valve, LA = left atrium, MV = mitral valve, TV = tricuspid valve, RA = right atrium.
There is good alignment with the Doppler beam on the right parasternal angled view with the left ventricle and pulmonary artery in the horse (Figure 3.47). Although the angle for interrogation is good, depth is often a factor in preventing adequate flow recordings. Try CW Doppler if PW signals are not strong enough.
Spectral Doppler
Pulmonary Flow
Imaging Planes
Right parasternal oblique left ventricle with PA
Left parasternal cranial long-axis with right ventricular outflow
Left parasternal long axis
Place the gate distal to the valve.
Appearance
Symmetrical profile
Peak velocity about midway during ejection
Figure 3.47 Pulmonary flow in the horse is obtained from the right parasternal oblique view of the left ventricle with pulmonary artery. RV = right ventricle, PA = pulmonary artery, PV = pulmonic valve, LV = left ventricle, IVS = interventricular septum.
Flow Appearance
Blood flows away from the transducer in these planes and is negative. Flow starts toward the end of the QRS complex and continues through the T wave (Figure 3.48). Acceleration time is slower than in the aorta, and peak velocity is reached about midway through ejection. This typically gives the flow profile a very symmetrical and rounded appearance and is a good way to distinguish normal aortic from normal pulmonary flow on still images. Reduced vascular resistance is thought to be the reason for decreased acceleration time in the pulmonary artery. As with aortic flow, spectral broadening does not occur until after peak velocity has been reached and flow begins to decelerate.
Figure 3.48 Pulmonary flow is negative on the Doppler display. It starts toward the end of the QRS complex and continues through the T wave. The flow profile is fairly symmetrical since acceleration and deceleration times are similar and peak velocity is reached approximately half way through
ejection.
Right Ventricular Outflow Tract Flow
Imaging Plane Used
Right ventricular outflow velocities are recorded from any of the three views used to interrogate pulmonary artery flow. The gate is positioned proximal to the pulmonic valve with the outflow tract between the right ventricular wall and septum.
The Doppler beam aligns with the outflow tract on the right parasternal angled view with the left ventricle and pulmonary artery. The right parasternal angled view from the right side of the thorax is also used for the outflow tract interrogation in horses (Figure 3.47).
Flow Appearance
Right ventricular outflow Doppler recordings are similar to pulmonary artery flow except velocities are lower.
Transmitral Flow
Imaging Plane Used
Left parasternal apical fourand five-chamber planes are used to record left ventricular inflow (Figure 3.49). The best flow profiles with highest velocities, least spectral broadening, and good definition to the E and A peaks should be looked for when deciding which imaging plane to use. The sample gate is placed at the tips of the leaflets when they are wide open (Figures 3.50, 3.51). Fan the transducer in and out of the imaging plane using color-flow imaging if necessary until alignment is as good as possible. A mitral valve opening click should be clearly heard and a closing click should be barely heard. Lack of an opening sound suggests that the gate is too far into the left ventricle while a loud closing sound is usually heard when the gate is placed too close to the mitral annulus. Incorrect placement of the sample gate will alter the mitral flow profile dramatically and create the appearance of diastolic dysfunction. Samples placed too close to the mitral annulus will typically decrease E velocities and deceleration times.
Spectral Doppler
Mitral Inflow
Imaging Planes
Left parasternal apical four chamber
Left parasternal apical five chamber
Place the gate at the tips of the mitral valve when open.
Appearance
E is higher than A.
Separation of E and A depends upon heart rate.
Positive flow after A is secondary to annular movement.
Figure 3.49 Transmitral flow in the small animal is recorded from either (A) the left parasternal apical five-chamber view or (B) apical four-chamber view. LV = left ventricle, MV = mitral valve, LA
=left atrium, IVS = interventricular septum, RV = right ventricle, RA = right atrium, AO = aorta, IAS
=interatrial septum, TV = tricuspid valve, RA = right atrium, RV = right ventricle, IVS = interventricular septum.
Figure 3.50 (A) The sample gate for transmitral flow is placed at the tips of the mitral leaflets when they are open. (B) Samples placed too close to the mitral annulus will typically decrease E velocities and deceleration times. MV = mitral valve, LA = left atrium, LV = left ventricle, E = early diastolic flow, A = late diastolic flow.
Figure 3.51 The left parasternal apical five-chamber view of the heart is used to record left ventricular inflow in the horse. The gate is placed at the tips of the mitral leaflets when they are wide open. LV = left ventricle, AO = aorta, MV = mitral valve, LA = left atrium.
Pulsed-wave Doppler should be used to assess mitral inflow profiles. CW Doppler summates the velocities along the beam, and flow profiles do not differentiate between that found at the mitral leaflet tips or at the annulus.
Flow Appearance
Mitral valve flow profiles are positive and resemble the letter M similar to M-mode images of mitral valve motion. The two phases of inflow are recorded (Figure 3.52). Rapid ventricular filling is the E peak and corresponds to peak early diastolic velocity. The second peak of the “M” occurs secondary to atrial contraction and upward motion occurs just after the P wave on the electrocardiogram. Left ventricular inflow stops with the onset of systole just after the beginning of the QRS complex.
Figure 3.52 Transmitral flow is positive and resembles the letter M. The E point corresponds to rapid ventricular filling, while the A peak represents flow associated with atrial contraction. Normally the E:A ratio is greater than 1. d = diastole, s = systole.
Closeness of the E and A peaks is dependent upon heart rate. Rapid heart rates will create more compact “Ms” and may even cause the two filling phases to overlap, and waveforms will be
superimposed (Figure 3.53). This overlap generally will start to appear at heart rates approaching 125 beats per minute, and complete loss of separation will always be present when heart rates exceed 200 beats per minute. It is common for transmitral flow profiles in a cat to show summated E and A peaks. Slow heart rates separate the two peaks dramatically (Figure 3.54).
Figure 3.53 Rapid heart rates result in a loss of separation between the two diastolic filling phases. Transmitral flow in this cat with a heart rate of 193 shows only one peak during diastole. d = diastole, s = systole.
Figure 3.54 Slow heart rates separate the E and A peaks of ventricular filling dramatically. d = diastole.
The E peak is usually higher than the A peak in normal hearts. This creates an E:A ratio greater than one. Positive flow may be seen after the A wave and is thought to be secondary to movement of the mitral annulus toward the sternum after the valve closes. This motion pushes blood toward the transducer and is recorded after diastole is concluded.
Trans Tricuspid Flow
Imaging Plane Used
Standard right parasternal apical fourand five-chamber views of the heart usually do not align flow parallel to the Doppler sound beam. This is rectified by moving the transducer cranial and dorsal on the thorax until the tricuspid valve is seen opening in an upward direction. Correct alignment can
therefore be seen in a left parasternal plane found between the apical four-chamber and the transverse view, or on the heart base right atrium and auricle view, or the left parasternal transverse plane through the heart base (Figure 3.55). In the horse right parasternal four-chamber long-axis and left ventricular outflow long-axis views are used to record tricuspid flow profiles in the horse (Figure 3.56). Sometimes the more oblique view through the right atrium is used. To obtain this view, rotate the transducer partially toward the transverse view and tilt the transducer dorsally and cranially until the longest right atrium is seen. Search for the best alignment with flow and the clearest spectral tracings with the least spectral broadening.
Spectral Doppler
Tricuspid Inflow
Imaging Plane
Left parasternal cranial right atrium and auricle
Left parasternal transverse
View between the apical four-chamber and the transverse view
Place the gate at the tips of the valve leaflets when they are open.
Appearance
E is usually higher than A but may be reversed.
Beat to beat changes in velocity due to respiration.
Figure 3.55 Tricuspid flow in the small animal may be recorded from several views including: (A) the left parasternal long-axis view with right atrium and auricle, (B) the left parasternal transverse view of the heart base, or (C) a plane somewhere between the apical four-chamber and the transverse plane.
The sample site is located at the tips of the leaflets when they are wide open (arrow). TV = tricuspid valve, IVS = interventricular septum, RV = right ventricle, LV = left ventricle, RA = right atrium, RAU = right auricle, AO = aorta, LA = left atrium, PV = pulmonic valve.
Figure 3.56 Several views are used to record right ventricular inflow in the horse. (A) The right parasternal tipped four-chamber view, (B) the right parasternal tipped left ventricular outflow view, or an (C) oblique view of the right atrium obtained from the right parasternum. IVS = interventricular septum, RV = right ventricle, RA = right atrium, TV = tricuspid valve, LV = left ventricle, LVW = left
ventricular wall, MV = mitral valve, AO = aorta, AOV = aortic valve, LA = left atrium, PV = pulmonic valve, PA = pulmonary artery.
Place the gate at the tips of the tricuspid valve leaflets when they are wide open (Figure 3.57). Try to
obtain flow profiles in all planes and search for the flow profile showing the highest velocities for both phases of inflow with the least spectral broadening.
Figure 3.57 Place the gate at the tips of the tricuspid valve leaflets when they are wide open in order to record trans tricuspid flow. RV = right ventricle. RA = right atrium, AO = aorta, E = early diastolic flow, A = late diastolic flow.
Flow Appearance
Right ventricular inflow appears similar to mitral inflow profiles. There is both a rapid ventricular filling phase resulting in an E peak and an A peak associated with atrial contraction as in mitral flow recordings (Figure 3.58). Inspiration increases peak flow velocities especially the E wave, so the E:A ratio increases with inspiration and decreases with expiration. E:A ratios can be less than one for trans tricuspid flow and positive systolic flow after the tricuspid valve closes may be greater than those seen in transmitral flow tracings.
Figure 3.58 Trans tricuspid flow is positive and similar to transmitral flow. Rapid right ventricular filling is represented by the E peak, and flow associated with atrial contraction is represented by the A peak. RV = right ventricle, RA = right atrium, AO = aorta.
Pulmonary Vein Flow
Imaging Plane Used
Right parasternal transverse images at the level of the left atrium and aorta, right parasternal long-axis images, left parasternal transverse images with the left atrium and auricle, or modified apical fourchamber views can be used to evaluate this flow (Figure 3.59). Right parasternal transverse imaging planes should have a clear interatrial septum and then using color-flow imaging, the venous flow is identified entering the left atrium from the far field of the image. It is important to keep the interatrial septum in view since it helps identify caudal vena cava flow on the right atrial side of the septum, which looks very similar to pulmonary venous flow. Low tissue priority and low filter settings and low PRF will enhance visualization of this flow. Tip the crystals up and down and sideways very slightly while on this transverse plane until color evidence of this flow is seen. On left parasternal cranial transverse imaging planes, fan the transducer cranial and caudal until the left auricle is seen. The veins will enter the left atrium from the bottom and to the left side of the chamber. Fan the crystals slightly in every direction while keeping the atrial chamber in view and use color-flow imaging to display the veins. Apical four-chamber imaging planes especially when the left atrium is dilated show the veins well. Color flow helps identify the veins while fanning the transducer in multiple directions (60,61).
Pulmonary Vein Flow
Right or left parasternal views
Lower PRF to appreciate color flow in the vein.
Place PW gate entirely in the vein.
Figure 3.59 (A) Right parasternal long-axis images, (B) right parasternal transverse images at the level of the left atrium and aorta, or (C) modified apical four-chamber views can be used to evaluate pulmonary vein flow.
Use whichever plane aligns flow best along the Doppler cursor. This is always obtained using pulsed-wave Doppler. The gate is placed entirely in the vein. It should not extend into the left atrial chamber (Figure 3.59).
Flow Appearance
Pulmonary venous flow is pulsatile and continuous. Most of left atrial filling occurs during ventricular systole when the mitral valve is closed. This creates a positive deflection on the spectral image, the “S” wave (Figure 3.60). Systolic pulmonary venous flow can be biphasic. If it is the early phase, it is labeled SE while the second later phase is called SL. During early diastole while blood is flowing into the left ventricular chamber, there is a drop in left atrial pressure and blood is passively pulled into the left atrium as blood moves through the mitral valve into the left ventricular chamber. This phase of left atrial filling is the “D” wave and is also positive on the spectral image (Figure 3.60). Atrial contraction during the latter part of diastole causes flow to move backward into the veins because there are no valves to prevent this. This wave is referred to as the Ar wave and is negative on the spectral display (Figure 3.60).
Figure 3.60 Pulmonary venous flow is pulsatile and continuous. Systolic flow is positive (S), diastolic flow is positive (D), while flow during atrial contraction is negative (A).
Isovolumic Relaxation Time
Imaging Plane Used
The time that elapses from the end of ventricular ejection to the time the mitral valves open and diastolic flow into the left ventricle begins is the isovolumic relaxation period. No change in volume occurs, and all valves are closed but pressures decrease and the myocardium relaxes.
The isovolumic relaxation time (IVRT) is recorded by placing a PW gate or a CW cursor in the left ventricular outflow tract near the mitral valves and recording a portion of both aortic ejection flow and left ventricular inflow (transmitral flow) (Figure 3.61). Oblique modified left apical fouror fivechamber views that allow the cursor to cross over portions of the mitral valve and the left ventricular outflow tract are ideal (62,63).
Isovolumic Relaxation Time
Apical or modified apical views
Place PW or CW gate in LVOT.
Figure 3.61 The isovolumic relaxation time period (IVRT) (arrow) is recorded by placing a PW gate or a CW cursor in the left ventricular outflow tract near the mitral valve and recording a portion of both aortic ejection flow and left ventricular inflow (transmitral flow). LV = left ventricle, AO = aorta, MV = mitral valve, LA = left atrium.
Flow Appearance
The time interval from cessation of aortic flow to the beginning of mitral inflow corresponds to isovolumic relaxation period (Figure 3.62). Left ventricular inflow cannot begin until left ventricular pressure drops below left atrial pressure and the mitral valve can open. With the spectral baseline in the middle of the spectral image, downward aortic flow and upward transmitral flow should be seen. Ideally the end of systolic downward flow should show the line (click) that corresponds to aortic valve closure. Upward mitral flow should have a clear starting point or can also have a click representing mitral valve opening. The time period between these two points represents IVRT.
Figure 3.62 The time interval from cessation of aortic flow to the beginning of mitral inflow (vertical lines) corresponds to isovolumic relaxation period.
Left Auricular Flow
Imaging Plane Used
The left cranial transverse view of the left auricle or modified (foreshortened) apical four-chamber views, which are twisted and tipped slightly until the auricle is seen, are used to record left auricular filling and emptying. The gate is placed at the junction of the left auricular appendage and the left atrial chamber (Figure 3.63) (64).
Left Auricular Flow
Left cranial or modified apical four-chamber view
Place PW gate at junction of auricle and atrium.
Figure 3.63 The pulsed-wave gate is placed at the junction of the left auricular appendage and the left atrial chamber to record auricular filling and emptying. Auricular flow is displayed to the right. LAA = left auricular appendage, LA = left atrium, AO = aorta.