Sequence of Views (Table 2-2 and Figure 2-3)

• Finally, rotation of the transducer to about 130 to 150 degrees reveals the ME long axis view: If lined up with the center of the valve, the plane of this view should cut through the middle of A2 and P2.

TABLE 2-2 The Systematic Mitral Valve Examination

Figure 2-3 A-H, The systematic MV examination.

Key Points

• Pitfall: As a general rule, angles of rotation are reliable only if the scanning plane is in the center of the valve. In the long axis view, one can ensure that the scan passes through the center of the valve by turning the probe slightly from left to right. Only then can one be certain that one is looking at A2-P2.

• Intentionally “scanning” the valve from lateral to medial is an advanced technique that can be very useful to pinpoint the location of a lesion. This technique can be applied to the commissural view, two-chamber view, and long axis view.

Three-Dimensional Echocardiography

Three-dimensional (3D) TEE provides exceptional images of the heart. Instead of a plane of information, the computer acquires a volume of data, which can then be reconstructed and viewed from any angle (Figure 2-4). Moreover, the data set can be sliced in any desired plane, much like a computed tomography (CT) scan, in order to re-create 2D images sometimes impossible to obtain by standard 2D echocardiography (Figure 2-5).

Figure 2-4 Real-time 3D TEE image of an MV prolapse from the LA perspective. Note the prolapsed area of the posterior leaflet, involving P2 and P3 (arrows).

Figure 2-5 Multiplane reconstruction. This is a 3D data set of the heart, focusing on the MV. Once the data set is acquired, multiple planes can be displayed simultaneously and the scan lines can be adjusted to show any 2D cross section of the heart.

The MV, because of its proximity to the TEE transducer, lends itself particularly well to 3D imaging. At this time, 3D remains an adjunct to 2D, but as more centers gain experience with this technology, 3D imaging will become an integral part of intraoperative MV assessment.

The mechanism of MR is usually readily apparent on 3D imaging. Furthermore, off-line MV analysis software packages allow detailed quantification of MV disease, including dimensions, prolapses, and restriction (Figure 2-6). This is very useful in planning the surgical management of MR and may help to identify patients who require specialized surgical care. Moreover, the development of leaflet stress analysis packages opens the door to the possibility of predicting, in the immediate post-bypass stage, the durability of some MV repairs.

Figure 2-6 3D MV analysis. Off-line analysis software allows detailed quantitative measurements of the MV, like annular dimensions, leaflet area and elevation, and tenting volumes.

Classification of Mitral Regurgitation

Figure 2-7 Carpentier’s classification of MR based on leaflet motion. A and B, In type 1, the leaflet motion is normal and the jet tends to be central. The cause of MR is usually annular dilatation (A) or leaflet perforation (B). C and D, In type 2, there is excessive leaflet motion and the jet is directed away from the diseased leaflet. E and F, In type 3 lesions, the leaflet motion is restricted. Type 3 lesions are further subdivided into 3A and 3B. The jet can be directed toward the affected leaflet or it can be central if both leaflets are equally affected.

Modified from Perrino and Reeves’ The Practice of Perioperative Transesophageal Echocardiography. Philadelphia: Lippincott Williams & Wilkins; 2003; Chapter 8, Fig. 8.7. With permission.

Evaluation of Mitral Regurgitation

Examination of the Mitral Annulus

• As stated previously, the mitral annulus is a saddle-shaped, dynamic structure, intimately involved in MV competence. The systematic 2D evaluation of the valve includes a careful look at the annulus. Its diameter should be measured in both major axes, bicommissural (∼60 degrees) and anteroposterior (ME long axis view at ∼150 degrees). The normal MV measures 28 to 32 mm in diameter.

• The anterior leaflet and the commissural areas are well supported by the fibrous trigones. Conversely, the posterolateral mitral annulus is relatively poorly supported. For that reason, the MV annulus tends to dilate predominantly in the anteroposterior axis, in a posterior direction.

Flow chart of MR severity (Figure 2-8).

Figure 2-8 Flow chart of MR severity.

Severity of Mitral Regurgitation

Step 2: Qualitative Assessment

Color Flow Doppler

Color flow Doppler remains the best screening method to diagnose MR. It also allows a semiquantitative assessment of the severity of regurgitation and can provide clues to the mechanism of MR. Pitfall: The appearance of MR by color Doppler is highly dependent on the gain and Nyquist limit of the transducer. Setting the gain too high or the Nyquist limit too low can make the MR appear more severe.

• Total jet area:

• All else being equal, small jets tend to be mild and large jets tend to be more severe (see Pitfall, earlier).

• A surface area of the aliasing jet of 10 cm² has been associated with severe MR.

• (As stated previously, the size of the MR jet is dependent on gain and Nyquist limit.)

• Jet area/LA area ratio

• When taken as a percentage of the LA area, the specificity of the jet surface area as an index of severity of MR increases.

• Jet surface area/LA surface area greater than 40% is associated with severe MR on cardiac catheterization.

• Eccentricity of the jet

• The term eccentric jet refers to a jet that has a greater than 45-degree angle of incidence from the mitral annular plane.

• Central jets can be structural or functional.

• Eccentric jets tend to be more structural than functional.

• Wall hugging jets

• The term wall hugging jet refers to an eccentric MR jet that hits the LA wall, then follows it for some distance thereafter (Figure 2-9)

• Wall hugging jets should be considered hemodynamically significant until proven otherwise and they always warrant careful examination:

• It takes a high energy jet to follow the LA wall for some distance.

• Owing to a physical phenomenon called the coanda effect, these jets appear smaller on color flow Doppler than they actually are.

• They are almost always due to a structural leaflet problem.

• Direction of the MR jet (see Figure 2-7)

Figure 2-9 Central (left) vs. wall hugging (right) jet. Note how the latter hits the LA wall, then follows it all the way up to the top of the atrium.

The direction of the jet can provide useful clues about the mechanism of MR and the location of regurgitant lesions.

• In type 1 lesions (normal leaflet motion), the origin and the direction of the jet are usually central.

• In type 2 lesions (excessive leaflet motion), the direction of the jet is usually away from the diseased leaflet. If both leaflets are equally prolapsed, the resulting jet may be mostly central.

• In type 3a lesions (restricted leaflet motion), the direction of the jet is usually toward the diseased leaflet. As in type 2 lesions, if both mitral leaflets are equally affected, the resulting regurgitant jet may be central.

• In type 3b lesions (functional MR), because the posterior papillary muscle attaches to both leaflets, the regurgitant jet is typically central or slightly posteriorly directed.

Spectral Doppler

Spectral Doppler provides additional qualitative signs of the severity of MR

• Density of the continuous wave (CW) Doppler signal (Figure 2-10)

• The peak velocity of the MR jet on CW is determined by the LV-to-LA gradient.

• The density of the MR jet is proportional to the number of blood cells crossing the mitral regurgitant orifice in systole.

• A dense signal with a sharp, complete envelope (contour) is associated with more severe MR.

• A faint signal with an indistinct, incomplete envelope is associated with less severe MR.

• Pulmonary venous flow (Figures 2-11 and 2-12)

• Owing to the absence of valve between the pulmonary veins and the LA, blood can freely flow backward into the pulmonary veins under certain circumstances.

• Once the pulmonary veins have been identified, the flow pattern is evaluated by placing the pulsed wave (PW) sample volume about 1 to 2 cm inside the pulmonary vein.

• The normal flow pattern in the pulmonary veins is forward in systole (the S wave) and forward in diastole (the D wave), with a short period of flow reversal after the atrial contraction (the A wave).

• The S wave is often biphasic: the first deflection (called S₁) corresponds to atrial relaxation whereas the second deflection (called S₂) corresponds to the descent of the atrial floor during systole.

• The S, D, and A waves can be affected by many factors, including filling pressures, diastolic LV function, and MV disease.

• In the context of MR, increasing amounts of MR will lead to progressive blunting and eventually reversal of the S wave.

• In the presence of MR, systolic blunting or reversal of pulmonary venous flow suggests hemodynamically significant MR.

• In severe, central MR, the pulmonary systolic flow tends to be reversed in all pulmonary veins. However, when a jet is very eccentric, there can be situations in which there is flow reversal in only one set of pulmonary veins (left or right). That is why it is important to always check the pulmonary venous flow on both sides.

Figure 2-10 CW Doppler in severe and mild MR. Left, The image demonstrates a dense CW signal with a complete envelope (contour), associated with severe MR. Right, The envelope is faint and indistinct. This is seen with mild MR.

Figure 2-11 Imaging the pulmonary veins (PVs): Finding all four PVs can be a challenge owing to anatomic variations between patients. A and B, The easiest PV to image is the left upper (LUPV). It can be found by rotating the transducer to approximately 50 to 90 degrees and slightly withdrawing the probe until it is visible in the upper right region of the echocardiography screen. C, The left lower pulmonary vein (LLPV) can be imaged at an interrogation angle of approximately 90 to 100 degrees, with the probe rotated toward the patient’s left and advanced slightly. Moving the probe in and out slightly will allow one to switch from one PV to the other, which may facilitate identification of those structures. D, With the probe at 0 to 30 degrees and rotated to the patient’s right from the ME four-chamber view, the right upper (RUPV) and right lower (RLPV) PVs may be seen. After rotating to the right, the probe may need to be withdrawn slightly to image the RUPV and advanced slightly to image the RLPV. Alternatively, the RUPV may be reliably imaged by starting from the bicaval view (E) and rotating the probe further to the patient’s right (F). Note that in all those views, color flow Doppler (arrow) can be used to help identify the vein (A and F). Once the desired PV is identified, the PW cursor is positioned about 1 to 2 cm inside the vein to obtain the spectral Doppler signal.

Figure 2-12 Pulmonary venous flow pattern. Left, The normal pattern: forward flow (upright) in systole (S1 atrial relaxation, S2 ventricular systole) and diastole (D), with brief backward flow (inverted) following atrial contraction (A). Right, Systolic reversal of flow can be seen in severe MR.

Key Points

• Pitfall: Systolic pulmonary venous blunting may occur with any cause of elevated LA pressure.

• Pitfall: In the presence of MR, systolic pulmonary venous flow reversal is specific but not necessarily sensitive, especially if the LA is very large. Absence of flow reversal does not rule out severe MR!

Step 3: Quantitative Assessment

There are few true quantitative methods for assessing the severity of MR. They tend to be time-consuming and require various calculations. Because of this, their intraoperative use tends to be limited to research and borderline clinical cases, in which the surgical management depends on the immediate echocardiographic assessment.

Vena Contracta (Figure 2-13)

• This is probably the exception to the previous rule, a quantitative measurement that can be performed relatively quickly in the operating room.

• The term vena contracta refers to the narrowest point of the mitral regurgitant jet.

• Because of the shape and orientation of the mitral coaptation line, this measurement should be made in the ME long axis view.

• The Nyquist limit should be approximately 55 cm.

• The zoom mode should be used to decrease the measurement error.

• The width of the vena contracta correlates with the size of the regurgitant orifice and the severity of the MR.

• A diameter less than 3 mm correlates with mild MR on cardiac catheterization, whereas a diameter greater than 7 mm is generally accepted as severe.

Figure 2-13 Vena contracta. This ME long axis view of the MV demonstrates a severe anterior leaflet prolapse. Left, Severe prolapse with obvious failure of coaptation. Right, The MR jet is seen by color flow Doppler. The narrowest point of the jet, corresponding to the coaptation gap in the MV, is measured. A diameter greater than 7 mm is associated with severe MR.

Key Points

• Pitfall: If the vena contracta is not circular (as is often the case), the various axes in which it can be measured will yield different numbers. This is why the standardized measurement should be performed in the ME long axis view. This is also the reason why the width of the vena contracta alone is not enough to determine the severity of MR.

• In order to measure the vena contracta, the entire color Doppler jet itself must be visible in continuity, from the zone of flow convergence to the vena contracta and the MR jet itself (see Figure 2-13).

• Recent studies suggest that the surface area of the vena contracta, measured using color 3D echocardiography, may be more reliable than the diameter of the 2D color jet.

PISA (Proximal Isovelocity Surface Area) Method (Figure 2-14)

• This technique is based on the physics of flow acceleration and the continuity equation.

• As blood accelerates from a large chamber into a small orifice, the blood cells accelerate along a series of concentric hemispheres within an area of flow acceleration.

• If a jet is severe enough, this area of flow acceleration (also called the flow convergence area or the PISA shell) will be visible by color flow Doppler (see Figure 2-14).

• The aliasing velocity can be adjusted to facilitate visualization of the PISA shell.

Figure 2-14 PISA demonstration. This figure summarizes the calculation of the regurgitant orifice by the PISA method. (1) Identify the flow convergence area and freeze the image. Measure the radius of the PISA shell where the color shifts from red to blue. (2) Identify the Nyquist limit. (3) Measure the peak systolic velocity across the mitral valve by CW. (4) Calculate the regurgitant orifice using the equation.

Key Points

Qualitatively, the presence of a PISA shell suggests significant MR and warrants closer investigation.

Careful! All elements of the PISA equation should have the same units (i.e., cm or cm/s).

A shortened version of the PISA equation can be used, but only when certain hemodynamic conditions are met. These are:

• The peak MR velocity is approximately 5 m/s, meaning that the difference between the systolic blood pressure and the LA pressure is approximately 100 mm Hg

• The Nyquist limit is set at 40 cm/s.

• No angle correction is necessary.

If those conditions are present, the PISA equation simplifies to:

• Within the flow convergence area, the color Doppler displays the acceleration of blood cells toward the mitral orifice as progressive shades of dark red, brighter red, orange, yellow, and eventually blue (according to generally accepted color Doppler mapping conventions, beyond the scope of this discussion).

• When the color changes to blue, the velocity at that point in space is known with certainty: it is the aliasing velocity or Nyquist limit (displayed on the color map on the right side of the echo screen).

• The radius (r) of the PISA shell defined by that point is measured from the mitral regurgitant orifice.

• Because flow = area × velocity, one can calculate the flow at that particular point in space (Flow = 2πr² × Nyquist limit).

• The continuity equation dictates that flow is constant along the regurgitant jet; therefore, one knows the flow at the regurgitant orifice.

• Once the flow is known at the regurgitant orifice, one can then measure the peak velocity (V_max) of the MR jet by CW Doppler and calculate the regurgitant orifice area.

In summary, one can calculate the regurgitant orifice area (ROA) using the following formula:

• ROA greater than 40 mm² is consistent with severe MR.

• Angle correction: When the PISA shell is incomplete (<180 degrees) because it is restricted laterally by a ventricular wall or a mitral leaflet, one must use an angle correction. This means estimating the angle width (α) of the PISA shell and dividing by 180.

• The complete PISA equation then becomes:

Regurgitant Volume

• Using the method described previously, one calculates the ROA.

• Once the ROA is known, the regurgitant volume (RV) is obtained by measuring the velocity time integral (VTI) of the regurgitant jet on the CW Doppler

• RV > 60 mL is consistent with severe MR.

Modern echocardiography machines automatically calculate the RV and regurgitant fraction (RF).

Regurgitant Fraction

• The RF is obtained by dividing the RV by the total volume ejected by the heart in systole (RV plus forward stroke volume, which can be calculated using the surface area and the VTI of the left ventricular outflow tract [LVOT]).

• RF greater than 50% is consistent with severe MR.

Key Points

The limitations of PISA: The PISA method is based on multiple assumptions that, if not met, can invalidate the whole method:

• It assumes that the mitral regurgitant orifice is round, which is rarely the case. If the orifice is not round, then the PISA shell is not a hemisphere and 2πr² does not define its surface area.

• Adjusting the aliasing velocity will affect the shape of the PISA shell, from a cone to a flattened hemisphere. Again 2πr² may or may not apply.

• The technique does not apply if multiple orifices are present.

• The correction angle is always estimated visually and it is a source of significant potential error.

• Finally, the PISA method assumes that all the measurements are made at the exact same point in the cardiac cycle, which may or may not be the case.

A summary of the methods used to quantify is shown in Table 2-4.

TABLE 2-4 QUALITATIVE AND QUANTITATIVE PARAMETERS USEFUL IN GRADING MITRAL REGURGITATION SEVERITY

Functional Mitral Regurgitation

Functional MR describes a situation in which the mitral leaflets are structurally normal, but failure of coaptation still occurs, resulting in MR. It includes a variety of pathologic states, which have in common LV dilatation and decreased systolic function. The term functional MR is often used interchangeably with ischemic MR, because ischemic heart disease is by far the most common cause of functional MR, but strictly speaking, they are not the same: not all functional MR is ischemic in nature (e.g., idiopathic dilated cardiomyopathy), whereas not all ischemic MR is functional (e.g., a ruptured papillary muscle following a myocardial infarct).

Mechanism of Functional Mitral Regurgitation

• Usually multifactorial, but the final mechanism is tethering (or tenting) of the MV leaflets, preventing proper coaptation.

• Pathophysiologically, dilatation and change in geometry of the LV, especially the posterior wall, results in posterior and apical displacement of the papillary muscles. The chordae tendinae then cause tenting of the mitral leaflets, preventing proper coaptation.

• Poor systolic function may also decrease the “closing” forces on the MV and this is believed to play some role in functional MR.

• The tenting of the valve is most pronounced in the anterior leaflet in most patients and it is readily visible on TEE, especially in the ME long axis view. It appears as though the “hinge point” of the MV is somewhere along the leaflet itself, rather than at its insertion point in the annulus (an appearance that has been termed “seagull deformity”).

• Severe papillary muscle displacement (indicative of worse LV remodeling) is a predictor of recurrence after surgical repair of functional MR.

•The extent of papillary dislocation can be determined by measuring the tethering (or tenting) height and the tethering (or tenting) area (Figure 2-15).

• The tethering height is measured by drawing a perpendicular line from the mitral annular plane to the coaptation point in systole. Eleven millimeters or more is considered significant.

• The tethering area is the area defined by the mitral leaflets (in systole) and the annular plane. A value of 2 cm² or more is generally considered to be indicative of significant tethering.

• 3D echocardiography studies have confirmed the tenting deformity of the MV in ischemic/functional MR.

• MV tethering is almost always accompanied by some degree of mitral annular dilatation and flattening, which compound the problem.

Figure 2-15 Functional MR with tenting of the MV. This ME four-chamber view of the valve in systole demonstrates how to measure the tenting height and tenting area. Left, A perpendicular line is drawn from the annular plane to the coaptation point. Right, One then measures the surface area defined by the annular plane and the mitral leaflets.

Key Points

• Functional MR is a disease of ventricular remodeling, not a problem with the MV leaflets per se. This is important to remember when considering potential surgical treatment of functional MR.

• In the context of ischemic heart disease, the presence of functional MR is a poor prognostic marker. Patients presenting for coronary artery bypass graft (CABG) surgery who have severe functional MR have a significantly worse perioperative mortality and lower survival rates.

Echo Evaluation of Functional Mitral Regurgitation

• Anatomy is paramount!

• Once the screening color images establish the presence of significant MR, the evaluation of MV structure and function is done mostly in 2D.

• A comprehensive MV examination is performed to exclude structural mitral disease (e.g., prolapse or perforation).

• Tethering of the leaflets is noted (especially the anterior leaflet),

• The tenting height and area are measured,

• The mitral annular dimensions are measured in both the anteroposterior and commissural diameters.

• Ventricular function is noted, paying particular attention to dilatation and/or dysfunction of the inferior and posterior walls.

Management of Functional Mitral Regurgitation

• Because MR is only one element of the syndrome of dilated cardiomyopathy, a multimodal approach is recommended, including:

• Revascularization, percutaneous or surgical.

• Aggressive medical therapy (e.g., β-blocker, angiotensin-converting enzyme inhibitors [ACEIs], statins).

• Resynchronization therapy if indicated.

• Treatment of atrial fibrillation.

• Surgical intervention on the MV (see next section).

Left Ventricular Outflow Obstruction, Systolic Anterior Motion, and Mitral Regurgitation

Echocardiographic Signs of Left Ventricular Outflow Tract Obstruction (Figure 2-16)

• 2D: characteristic SAM of the MV.

• Color flow Doppler: systolic aliasing in the LVOT.

• Spectral Doppler: pathognomonic appearance of the CW Doppler signal across the LVOT. The signal has a typical “dagger shape,” with the peak velocity occurring in late systole. This is because the LVOT gradient builds up throughout systole, with increasing obstruction from the MV. The best views to measure the LVOT gradient are the TG mid long axis view of the LV or the deep TG view of the LV, depending on the orientation of the LVOT relative to the probe.

Figure 2-16 Systolic anterior motion of the MV. Left, A four-chamber view of the MV in 2D shows systolic displacement of the valve into the LVOT. Center, The same four-chamber view of the valve with color Doppler demonstrates the flow acceleration in the LVOT and the severe MR resulting from the failure of coaptation. Right, The pathognomonic CW Doppler signal shows the LVOT gradient peaking late in systole.

Etiology

Step 1: Determine the Etiology

Acquired

• Rheumatic disease is by far the most common cause. Rheumatic fever is becoming rare in developed countries but it is still widely prevalent in the developing world. Half the patients do not recall having had rheumatic fever. The rate of progression and time to diagnosis correlate with the number of episodes of rheumatic fever.

• Calcific stenosis is most often seen in elderly or dialysis-dependent patients, who have severe mitral annular calcification encroaching on the leaflets and causing effective stenosis.

• Physical obstructions: tumor (most often myxoma), thrombus, vegetation.

• Carcinoid (rare).

• Radiation-induced stenosis.

• Stenosis after MV repair: see section on “Mitral Regurgitation.”

Congenital

• Congenital MS.

• Parachute MV.

• Double orifice MV.

• Supravalvular ring; cor triatriatum

• Infiltrative disease (e.g., mucopolysaccharidoses)

“Functional” Mitral Stenosis

• Severe aortic insufficiency resulting in apparent poor opening and/or early closure of the MV. This is rarely associated with any significant mitral gradient.

Flow chart on MS severity (Figure 2-17).

Figure 2-17 Flow chart of MS severity.

Evaluation of Mitral Stenosis

Pathophysiologically, chronic inflammation causes leaflet thickening and commissural fusion, leading to the classic “fish mouth” appearance of the valve. Concomitantly, there is fusion and shortening of the subvalvular apparatus results in further decrease in valve mobility. These features are readily visible by echocardiography.

Step 1: 2D Appearance

Because rheumatic MS tends to affect the entire valve, pinpointing the location of disease is often not necessary. Still, a detailed systematic examination of the MV should be performed. Technically, these patients are often difficult to examine: they commonly have severe LA enlargement, which causes rotation of the heart and brings the MV out of alignment with the ultrasound beam. This makes classic TEE cross sections difficult to obtain. The typical 2D echocardiographic findings include

• Thickened, nodular appearance of the leaflets.

• Restricted leaflet motion.

• The leaflet tips are often more affected than the base, leading to the typical “doming” or “hockey stick” appearance in diastole (Figure 2-18).

• There is commissural calcification and/or fusion (readily appreciated on TG basal short axis views and with 3D echocardiography).

• There may be extensive annular calcification.

• The subvalvular apparatus (chordae tendinae ± papillary muscle heads) is often calcified and thickened. This is best viewed in the TG long axis view. (Figure 2-19)

• The LA is usually enlarged (sometimes massively), especially in patients with atrial fibrillation.

• Spontaneous contrast (known in the echocardiography jargon as “smoke”) is visible in the LA. This is due to slow-swirling blood flow causing the formation of red blood cell “rouleaux,” which become visible by echocardiography.

•Patients with slow flow in an enlarged LA are at very high risk of developing LA thrombus, especially in the left atrial appendage (LAA). A careful examination of the LAA is mandatory in every patient with MV stenosis (Figure 2-20).

• The LAA is best visualized in ME views between 60 and 90 degrees of transducer rotation, by pulling out slightly from the mitral position. It appears crescent shaped and contains multiple trabeculations, which may make the diagnosis of LAA thrombus difficult.

Figure 2-18 MS. This ME four-chamber view of the MV in diastole shows typical doming of the anterior mitral leaflet (AML), as well as thickening, shortening, and calcification of the chordae tendinae.

Figure 2-19 Shortened chordae tendinae. Left, The chordae tendinae (arrows) are shortened, thickened, and calcified. Right, This is in contrast to the normal chordae tendinae (arrows).

Figure 2-20 LAA thrombus. Patients with MS are at high risk of developing an LAA thrombus, especially if they have concomitant atrial fibrillation. The LAA appears crescent-shaped and contains trabeculations (short arrows), which can make the detection of clots difficult. The image on the left shows a normal LAA in two planes, whereas the image on the right demonstrates a large LAA thrombus (long arrows).

Key Points

• Pitfall: The presence of pericardial fluid outside the LAA may sometimes create the illusion that the LA wall with its trabeculations is an intra-atrial mass. It is usually possible to distinguish the two by carefully imaging the appendage and by identifying a pericardial effusion on other views.

Step 2: Color Flow Doppler

• Aliasing diastolic flow is seen through the MV (Figure 2-21).

• With significant flow restriction, an area of flow convergence (PISA shell) can be seen on the atrial side of the MV.

Figure 2-21 Color flow Doppler of MS. Note the aliasing flow across the MV in diastole and the flow convergence area, visible on the LA side of the valve. Note also the large LA.

Step 3: Spectral Doppler

• Diastolic gradients (Figure 2-22)

• The peak and mean gradients are best measured by CW Doppler, because the velocity is often too high for PW Doppler. Another reason to use CW is that it eliminates potential error in positioning the sample window: indeed, the narrowest point of a stenotic MV may not be at the valve leaflets. In some cases, the narrowest point may be in the subvalvular apparatus.

• The peak and mean diastolic gradients are typically elevated.

• A mean gradient greater than 10 to 12 mm Hg is consistent with severe MS.

Figure 2-22 Spectral Doppler in MS. Left, The peak and mean diastolic gradients are measured by tracing the CW Doppler envelope. Right, The PHT is calculated by placing the cursor at the peak of the CW Doppler; if the deceleration slope is nonlinear, use of the midportion of the velocity profile is preferred. The MVA is the constant 220 divided by the PHT in milliseconds.

Key Points

• Remember that mitral gradients are dependent on the cardiac output and loading conditions at the time of the examination.

• Pressure half time (see Figure 2-22)

• The pressure half-time (PHT) is defined as the time it takes for the diastolic pressure gradient across the MV to decrease by half (the pressure gradient, NOT the velocity).

• A smaller mitral orifice is associated with a greater PHT.

• Once the PHT is measured, the empirical formula: MVA = 220/PHT is used to calculate the mitral valve area (where MVA = mitral valve area).

Key Points

Pitfall: The measurement of PHT assumes that the rate of decrease in the transmitral gradient depends only on the size of the mitral orifice. However, any external factor that affects the upstream (LA) or downstream (LV) will invalidate the use of PHT:

• Severe aortic insufficiency causes LV pressures to rise in diastole, independently of mitral flow.

• An atrial septal defect (ASD) will cause LA pressure to drop, independently of mitral flow.

• Any acute change in LA or LV compliance may be seen in the immediate post-cardiopulmonary bypass period.

• Many patients with MS present with a large LA and atrial fibrillation. MV gradients and PHT depend on diastolic filling time and, in the presence of atrial fibrillation, may vary tremendously from beat to beat. An accurate measurement requires an average of multiple beats (ideally 5-10 beats).

• PISA (see the section on “Mitral Regurgitation” for additional details) (Figure 2-23)

• The same technique, described in the section on “Mitral Regurgitation,” applies to the evaluation of MS, except that the flow (in the ME four-chamber view) is away from the TEE transducer. Typically, as blood accelerates toward the MV orifice, the color changes from dark blue to lighter blue to yellow/red.

• Note that, owing to the shape of the MV (V-shaped pointing toward the LV), an angle correction must almost always be used because the PISA shell is usually restricted by the mitral leaflets.

• Continuity equation

• The continuity principle states that, unless there is an intracardiac shunt, the flow of blood is constant throughout the heart. What changes is the velocity of the blood, depending on the cross-sectional area of the chamber through which it flows. (By extension, the volume of blood that travels through the heart during one systole—the stroke volume—is the same throughout the heart.)

• We know that Flow = Velocity × Area.

• Therefore, V₁ × A₁ = V₂ × A₂.

• Similarly, Stroke volume = VTI × Area.

• Therefore, VTI₁ × A₁ = VTI₂ × A₂.

• If one calculates the flow in the LVOT or the pulmonary artery, assuming there is no major valvular regurgitation or intracardiac shunt, one can calculate the MVA using one of these two formulas.

Figure 2-23 Demonstration of the calculation of the MVA using the PISA method. (1) After identifying the flow convergence area, the radius of the PISA shell is measured. (2) The Nyquist limit is noted, in the direction of flow. (3) The peak velocity of the mitral flow is measured using CW. (4) Next, the angle of correction is estimated. Finally, the MVA is calculated using the same equation used for MR (discussed previously). In this example, r = 0.89 cm, Nyquist = 36 cm/s, V_max = 227 cm/s, angle of correction 150 degrees. Note that all the measurements are in cm.

Mitral Valve Endocarditis

• Echocardiographically, the presence of a vegetation is the hallmark finding in endocarditis and it confirms the diagnosis (Figure 2-24).

• Vegetations are accumulations of microorganisms, platelets, and fibrin, which attach to the MV.

• The echo density of fresh vegetations is that of soft tissue or thrombus (making the distinction difficult in certain cases). Older vegetations are often dense and calcified. Comparison with the surrounding tissues is important.

• Vegetations tend to be located on the upstream side of a valve. MV lesions usually occur on the LA side.

• They can be pedunculated (narrow base) or sessile (broad base). Unless completely sessile, most vegetations tend to move in an erratic fashion, independent of the movement of adjacent tissue.

• The leaflet edges can be destroyed by vegetations, leading to failure of coaptation and intravalvular regurgitation. Sometimes, the vegetation results in perforation and the MR jet is seen through the leaflet. Multiple mechanisms can coexist in the same valve.

Figure 2-24 MV endocarditis. This ME four-chamber view shows a large vegetation (arrow) attached to the posterior mitral leaflet.

Key Points

In the clinical context of a patient with a murmur and positive blood cultures, visualization of a vegetation by TEE is very specific for endocarditis. However, absence of a vegetation does not rule out the diagnosis of endocarditis. If there is strong clinical suspicion, the TEE examination should be repeated 7 to 10 days later.

Figure 2-25 Complications of mitral endocarditis: This TG long axis view of the MV shows a large posterior mitral annular abscess (marked by the arrows). Ab, abscess cavity.

Surgical Management of Mitral Regurgitation

The surgical management of MR is surgeon dependent. The current expert consensus is that MV repair is always the treatment of choice for mitral degenerative disease. In experienced hands, it is highly successful with low complication rates and good long-term results. For rheumatic valve disease, the success rate of mitral repair varies among surgeons, but it is still the treatment of choice if feasible. MV replacement is much more common in this patient population. Finally, the surgical management of functional MR is controversial, as described later.

Specifically:

Figure 2-26 Quadrangular posterior leaflet resection. This is one of the most commonly performed MV repair procedures. The prolapsed scallop is resected and the surrounding leaflets are detached from the annulus. The remaining valve segments are sewn together, with varying amounts of “sliding” of the leaflets along the mitral annulus. Then a supportive annuloplasty ring is inserted.

Modified from Verma S, Mesana TG. Mitral-valve repair for mitral-valve prolapse. N Engl J Med. 2009;361:40-48. With permission.

Mitral Repair for Mitral Regurgitation

Mitral Replacement (See Chapter 5)

Evaluation of Surrounding Structures

After any mitral procedure, one must carefully check the surrounding structures and the other cardiac valves. All valves are intimately related and a procedure involving one valve may cause disruption of another valve.